Sandwich structured composite films with improved mechanical and thermal properties for industrial coating

Abstract

Polymeric materials are becoming increasingly adaptable for industrial coatings, and core-shell films have been developed using kaolinite particles and recycled rubber, which are characterized by high thermal stability and enhanced flexibility. Polypropylene was melted and extruded combined with styrene-ethylene-butylene-styrene (SEBS), ground tire rubber (GTR), and kaolinite, and then subjected to the calendaring process to manufacture laminated composites. Several characterizations of the composites, including morphological, mechanical properties, and thermal analysis, were conducted. Micromechanical models have been employed to predict the elastic modulus of composite films and laminates. The addition of 15 wt% kaolinite particles resulted in increases of 14% in elastic modulus, 19.37% in storage modulus, and improved thermal stability. The substitution of kaolinite with SEBS and GTR particles compensated for the strain at yield properties, showing a 29% balance. Overall, the laminates exhibited synergistic properties. Analytical models demonstrated close agreement with the experimental data, suggesting their usefulness as reliable tools for producing core-shell films based on recycled waste and kaolinite.

Keywords

Sandwich structured composite ground tire rubber calendaring process clay powder

Introduction

Today, sandwich-structured composite films are becoming more popular and effective in a wide range of applications due to their mechanical performance and very favorable strength/weight ratio, displacing materials that were once considered indispensable, notably steels and alloys.^1–3 The development of this type of material by industry and researchers aimed to improve their toughness by combining small proportions of particles of different natures (soft and rigid) within a polymer to achieve synergy.⁴ As a result, this interaction between the matrix, shell, and core confers desirable properties, such as thermal conductivity,^5,6 dielectric properties,^7,8 flame resistance, and shielding against electromagnetic interference.⁹

Several studies have been carried out to obtain high-performance core-shell composite materials by selecting appropriate particles to incorporate into polymer matrices to get the required properties. Gam et al.¹⁰ have attempted to understand the fracture behavior of core-shell-modified rubber and clay-based epoxy nanocomposites, which is crucial for the efficiency of the design. These studies highlighted phenomena observed in the Epoxy matrix composite reinforced with core-shell particles (CSP), such as crack deflections, transparent fractures, crack pins, crack bridging, and delamination.^1,11 Meanwhile, core-shell composites exhibit cavitation effects, shear bands, and multiple hardening mechanisms as they absorb energy.¹² However, their incompatibility leads to a simultaneous increase in viscosity and segregation of particles during the hardening process. To solve these problems, CSPs have been developed for hardening bulk polymers, using an elastomer as a core to ensure toughness, and a rigid shell to improve compatibility.¹³ SEBS is a triblock copolymer obtained by hydrogenation of styrene-butadiene-styrene (SBS). It has highly arranged polystyrene zones serving as hard blocks, and a region flexibly formed by the soft block ethylene-butylene, which is kept connected by the hard blocks.¹⁴ Its unique chemical structure gives it remarkable properties such as good toughness, high elasticity, low density, resistance to aging, non-toxic electrical insulation, as well as the ability to be processed in a similar way to plastics using various industrial processes such as extrusion, injection molding, and melt spinning.^15,16 The excellent performance of SEBS, in particular the high elasticity of the rubber and the plasticity of the thermoplastic, makes it a good choice for reinforcement in PP. In addition, its hard segment may be compatible with stiff molecular chains. For example, adding SEBS transformed the PP/SEBS system from a sea-island system into a two-phase continuous system, ultimately improving mechanical properties.¹⁷ Acting as a compatibilizer, the addition of SEBS to PS/LDPE blends enhanced the interfacial adhesion between the polymer phases, stabilized the morphology of the phase, and improved the viscosity of the blends. Therefore, SEBS can generally be blended directly with a variety of polymers to obtain a synergistic effect on the properties of both materials.

At present, interest worldwide is focused on the development of new advanced materials that offer a good balance between efficiency, cost-effectiveness, and environment-friendliness.¹⁸ This issue underlines the growing complexity of managing the waste associated with these materials, requiring innovative and sustainable solutions to minimize their environmental impact and ensure responsible management of these resources. One of the wastes of concern because of its environmental impact is end-of-life tires. This growth highlights the urgent need to develop effective management and treatment strategies for reducing its impact on the environment. The first traditional way of treating end-of-life tires is to landfill them. However, this approach entails significant risks for public health and the environment. Potential dangers include the possibility of unexpected fires, which are often difficult to control in these environments, as well as the risk of contamination of valuable resources of groundwater resources.¹⁹ Faced with these proven risks, governments and organizations have been pushed to establish specific regulations. These regulations aim to provide a strict framework for the collection, disposal, and recycling of scrap tires. The fundamental objective is to promote the adoption of safer methods from a health point of view, to reduce potential risks to public health, and to minimize harmful effects on the environment. However, recycling tires at the end of their life is difficult due to their composition. Their cross-linked structure makes them non-melting and insoluble, classifying them as thermoset materials. It is imperative to develop tire recycling methods that are both feasible technologically and cost-effective in terms of economics.²⁰ Among the various initiatives aimed at recycling rubber from ground tires (GTR), the action of mixing GTR with thermoplastic polymer stands out as the only method that makes GTR suitable for new applications while improving its properties.^21–24 For example, Mujal-Rosas et al.²⁴ studied the dielectric, thermal, and mechanical properties of PP/GTR composites. The results suggest that the addition of GTR to the PP matrix caused a drop in various mechanical properties of the composites, such as tensile strength and stiffness, due to the low mechanical strength and inherent flexibility of GTR. However, when the GTR particles are smaller than 200 µm, the composites showed improvements in their mechanical properties, highlighting the crucial impact of particle size when combining GTR with a thermoplastic polymer. In a similar study, Lima et al.²⁵ reported an enhancement in the viscosity, ductility, and impact strength of composites following the incorporation of a substantial amount of GTR into the matrix (PP). Although considerable research has been carried out into the characteristics and processability of GTR blends and materials composites, accurately assessing the performance of these systems represents a major challenge for manufacturers, particularly in terms of their practical suitability for processing. On the other hand, the interest in the integration of particles into various polymer matrices such as thermoplastics, elastomers, thermosets, and TPE has grown significantly, as illustrated by the multiplication of publications devoted to this subject.^26–32

These particulate fillers, such as clay incorporated into a polymer matrix, induce significant modifications within composites, influencing aspects including crystallinity, thermal stability, mechanical and rheological properties, and the degree of dispersion.³³ Among the various types of clay used to enhance polymer properties, kaolin is often preferred because of its characteristics and its wider availability on the market.³⁴ Kaolin, known for its environmentally friendly properties such as its natural abundance, non-toxicity, and biodegradability, is commonly used in sustainable applications. It is a clay mineral with a very precise chemical composition: AlSi₂O₅(OH)₄. The crystalline structure of kaolin consists of tetrahedral layers of SiO₄ and octahedral layers of Al (OH)₆, forming an alternating 1:1 type layered configuration.³⁵ With its remarkable stability and relatively small surface area, kaolin has a limited ion exchange capacity. When integrated into polymers, it has the property of improving tensile modulus while reducing gas permeability.³⁶ In addition, this inclusion enhances the heat resistance of polymers and helps to reduce their flammability.³⁷ The size and morphology of kaolinite particles are fundamental factors that influence several key aspects of the material, including its specific surface area, pore volume, viscosity, and plasticity.^38,39 These characteristics are crucial not only to ensure optimum reactivity with the polymer matrix but also to ensure homogeneous and efficient mixing during the processing stages. However, in one study, Albach et al.⁴⁰ reported that incorporating 5 to 15 wt% kaolinite reduced the strain at yield of the PP/Kaol composite, while interfacial incompatibility was also observed on the various microscopic images obtained by SEM.

Despite the abundance of literature on composite films and the numerous studies on filler-reinforced thermoplastic films, there is a notable lack of research on composite films that utilize hybrid organic or inorganic fillers, as well as on core-shell composites derived from these kinds of fillers. Sandwich-structured or core-shell composite films offer numerous advantages for industrial coatings, primarily due to their multi-layer design, which combines different fillers to enhance performance. These films provide improved mechanical strength, durability, and impact resistance, making them ideal for high-demand environments. Their superior barrier properties protect against moisture, chemicals, and gases, while also offering thermal insulation and UV protection.⁴¹ The customizable nature of sandwich films allows for the optimization of various properties like flexibility, hardness, and chemical resistance, making them versatile for different industrial applications.⁴¹ In this study, sandwich-structured composite films were prepared using various combinations, including pure polypropylene (PP) mixed with styrene-ethylene-butylene-styrene (SEBS) and ground tire rubber (GTR), along with kaolinite. SEBS was chosen for its excellent elasticity and impact resistance, enhancing the toughness of the composite films. GTR, on the other hand, was selected for its cost-effectiveness and ability to enhance the sustainability of materials by incorporating recycled content. Additionally, laminates were created by stacking these films to explore synergistic effects on properties. The mechanical properties of the films and laminates were assessed through tensile tests, while their thermal properties were studied using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Scanning electron microscopy (SEM) was employed to observe the morphology and interfaces of the composite and laminated films. To complement the experimental analysis, micromechanical models were utilized to predict the elastic modulus of the composite films and laminates. These models consider the characteristics of the constituent materials, their arrangement in the laminates, and the interactions between the layers. The objective of this study is to deepen our understanding of the interactions between the structure and properties of composite films and laminates, thereby opening new avenues for their application across various fields.

Materials and methods

Materials

The thermoplastic employed is a polypropylene (PP 506P) homopolymer provided by SABIC Industries Corporation (Riyadh, Saudi Arabia). This polymer required for yarn extrusion has a melt flow index (MFI) of 4.8 g/10 min (230°C and 2.16 kg, ASTM D1238), a density of 0.905 g/cm³ (ASTM D792), and a melting temperature of 160°C (ASTM D3418). Kraton G1650 E linear triblock copolymer of styrene-ethylene-butylene-styrene (SEBS) with a density of 0.910 g/cm³ was supplied by Songhan Plastic Technology Co., Ltd. Kaolinite particles, originating from central Morocco, present an average size of 90 µm following a sieving process and have a density of 2.24 g/cm³. Finally, rubber particles from the grinding of the tread of a used passenger tire were supplied kindly by startup PnuVall (Sale, Morocco). These particles had an average size of 250 µm and a density of 1.18 g/cm³ and were used without any modification.

Compounding

At the start of the experimental phase, a preliminary step was to purify the kaolinite in the laboratory. Once this stage was complete, the kaolinite was then subjected to a drying process in an oven preheated to a constant temperature of 90°C for 24 hours. This drying stage has been extended to eliminate and carefully remove all traces of moisture present in the kaolinite to guarantee optimum results. Next, the thermoplastic matrix was mixed with the ground tire rubber (GTR), styrene-diene, and kaolinite particles in the melt state using a counter-rotating twin-screw extruder (Thermo Scientific HAAKE PolyLab OS) with a ratio (L/D = 40). The three main masterbatches, namely PP/GTR (50/50), PP/SEBS (50/50), and PP/Kaolinite (60/40), were obtained independently. Two Haake feeders were used to ensure optimum treatment conditions, delivering a flow rate of 1 kg/h. This approach aims to avoid overloading, reduce the residence time of materials in the system as much as possible, and prevent degradation caused by undesirable thermal effects. The temperature profile of the four heating zones (4 mm die diameter) was maintained at a constant 190°C, while the screw speed was increased to 80 r/min. Once extruded, the products are immersed in a water bath to ensure effective cooling. They were then carefully air-dried before undergoing the granulation process using a Thermo Scientific granulator. Both compounds were placed in a convection oven for 24 hours at a temperature of 70°C to remove any residual moisture, given further treatment.

Preparation of films

Thermoplastic matrix (PP) was combined with various masterbatches, each at a content of 15 wt%. These mixtures were processed using contrarotating twin-screw extrusion (Thermo Scientific HAAKE PolyLab OS System) to produce the composite films. The four heating zones (die width of 25 mm) were kept at a fixed temperature of 190°C. At the same time, to increase production output, the speed of the screws has been set at 80 r/min. The diameter and width of the spinning roller were 110 and 200 mm. The take-off speed constant was operated at 5 m/min. The POST Extrusion equipment system was connected to a Thermo HAAKE C35P refrigerated bath, controlled by the Phoenix II device. The refrigerated bath, which has a capacity of 8 L, was set at a temperature of 90°C exclusively for the spinning rollers. The composite films obtained had thicknesses that ranged from 0.33 mm to 0.56 mm.

Film stacking

As a first step, the virgins (PP) and composite films were carefully cut to match the specific dimensions of the mold cavity, measuring 97 × 66 mm². The films were organized by stacking the composite films to form laminates. Then, these laminates were placed between two sheets of baking paper, perfectly matching the shape of the mold. Plates are manufactured by compression molding using hydraulic press equipment (CARVER, 393.4PR3B02, WABASH, IN, U.S.A). The process of molding was carried out at a temperature of 180°C. The samples were subjected to a pressure of 3 tons for 10 min and then cooled using a water circulation system. Specimens produced, as schematically shown in Figure 1 and the different formulations used to study the effect of each filler and additive were summarized in Table 1, were around 1.6 mm thick and were cut into various geometric shapes so that they could be submitted to a variety of characterizations, including morphological, mechanical, dynamic, thermal, and rheological analysis.

Figure 1.

Schematic presentation of sandwich-structured composite film processing.

Table 1.

Formulations of sandwich-structured composites.

	Layers
Designation of formulation	PP	PP/SEBS	PP/Kaolinite	PP/GTR
P/S/P	2	1	0	0
K/S/K	0	1	2	0
P/G/P	2	0	0	1
K/G/K	0	0	2	1

Characterization

Morphological properties

The morphological characteristics of the samples were determined using a scanning electron microscope (SEM, HIROX SH 4000M) operating at an accelerating voltage of 15 kV. After being cryo-fractured in liquid nitrogen, the various materials were coated with a layer of gold/palladium on their surfaces to enable them to be visualized at different levels of magnification.

Mechanical properties

The mechanical properties of composite films and laminates produced by compression molding were measured on a universal testing machine (H10 KT TINIUS) equipped with a 5 KN load cell. The tests were performed according to ISO 527 standard, on samples of rectangular geometry, with dimensions of 1.5 mm in thickness, 76 mm in length, and 10 mm in width, under temperature conditions (24°C ± 1) and at a speed displacement of 5 mm/min. This geometry was chosen to adapt to the format of films and laminates obtained by calendaring and compression while avoiding any damage caused through cutting or clamping, thus guaranteeing the reproducibility of mechanical tests. Measurements were recorded as displacement (∆l) and force (F) data, then converted to strain (ε) and stress (σ) values. Experimental data were gathered on the software Horizon and then transferred to Excel for treatment. The results obtained during these tests have enabled us to determine a certain parameter, in particular tensile strength (σ), Young’s Modulus (E), and strain at yield (ε). For each formulation, the test was replicated five times per sample, and the average value of these replicates was used as the reported result.

Theoretical models

Several authors have developed theoretical models based on micromechanical analysis, enabling mathematical calculations of the effective mechanical properties of composites, hybrid composites, and laminates. These models are influenced by several key parameters, including density, volume fraction, strength, modulus of elasticity of the constituents, dispersion state, and filler distribution, as well as treatment conditions. For the present study, the experimental elastic moduli of the materials were compared with various analytical models, namely the Voigt, Reuss, Hirsch, and Tsai-Pagano models.

Volume fractions

Two methods are commonly used to determine the mechanical properties of composites and laminates, namely the weight fraction-based approach and that obtained by volume fraction for the two phases (matrix and filler). In general, weight fraction is preferred to volume fraction in laboratories and industries because of the widespread use of composite treatment equipment that operates with a feed system gravimetric, offering higher efficiency than volumetric systems.⁴² However, theoretical models have been developed from the volume fraction of the different constituents. To remedy these different approaches, a relationship linking volume fraction to weight fraction for a composite material was established to match measured results with those obtained theoretically. This relationship is determined from equation (1):⁴³

V_{f} = \frac{W_{f} \cdot ρ_{m}}{ρ_{f} + W_{f} \cdot (ρ_{m} - ρ_{f})}

(1)

Where

V_{f}

W_{f}

ρ_{m}

, and

ρ_{f}

are filler volume fraction, filler weight fraction, matrix density, and filler density, respectively.

The film thicknesses were assimilated to the specific volume fractions for each laminate obtained after compression molding and then used in the analytical models. Equation (2) provides a precise description of the correlation between volume fraction and layer thickness.

1 $e_{1} V_{f 1}$

2 $e_{2} V_{f 2}$

3 $e_{3} V_{f 3}$

n $e_{n} V_{f n}$

V_{f_{i}} = \frac{e_{i}}{\sum_{j = 1}^{n} e_{j}}

(2)

Rule of mixture (RoM)

The rule of mixtures, which stems from micromechanical analysis, is founded on reducing assumptions according to which the constituents present in the blend undergo the same deformation or are subjected to the same stress.⁴⁴ Thus, this model has proven to be the most basic model for appropriately predicting the tensile strength, modulus of elasticity, and Poisson’s ratio of materials. RoM also comprises two main models, Voigt and Reuss, which are recognized as the superior and inferior limits of the effective elastic modulus of materials, composites, hybrid composites, and laminates. In our context, particular importance has been attached to the modulus of elasticity.

RoM parallel

Voigt’s model, sometimes called RoM parallel, assumes that the deformation undergone by both the charge (fiber or particle) and the matrix is constant and identical to the deformation on the macroscopic scale. Furthermore, it abstracts from the interaction between the particles and the matrix and supposes that the fibers are aligned unidirectionally. The effective modulus of elasticity of composite materials in the longitudinal direction is obtained by adding the modulus of elasticity of the matrix and filler, weighted by their volume fractions, respectively Equation (3).⁴⁵

E_{/ /} = E_{f} V_{f} + E_{m} V_{m}

(3)

Where

E_{/ /}

E_{f}

E_{m}

V_{f}

, and

V_{m}

are longitudinal modulus (Voigt model), matrix modulus, filler modulus, volume fractions of the filler, and matrix, respectively.

RoM series

The Reuss model, also known as RoM, postulates that the stresses applied to each component (matrix and filler) are constant and equal to the stress subjected on the macroscopic scale. It excludes the influence of particle-matrix interaction while considering unidirectional fiber orientation. The effective elastic modulus (Reuss model $)$ of composite materials in the transverse direction is given by the following equation (4):⁴⁶

E_{⏊} = \frac{E_{f} \cdot E_{m}}{V_{f} E_{m} + (1 - V_{f}) E_{f}}

(4)

Hirsch RoM

The Hirsch model combines the approaches of Voigt and Reuss to estimate the tensile modulus of composite materials. This model is based on elastic modulus extracted from RoM ( $E_{/ /}$ , and $E_{⏊}$ ) considering their respective volume fractions, and includes a constant empirical parameter α. The presence of this parameter in the model is intended to accurately represent the interfacial stress transfer between the filler (particles or fibers) and the matrix, as well as the orientation of the filler during modeling. Hirsch model calculates the modulus of elasticity of composite materials according to the following expression equation (5):

{\begin{cases} E_{C} = α E_{/ /} + (1 - α) E_{⏊} \\ E_{c} = α (V_{f} E_{f} + (1 - V_{f}) E_{m}) + (1 - α) \frac{E_{f} \cdot E_{m}}{V_{f} E_{m} + (1 - V_{f}) E_{f}} \end{cases}

(5)

Tsai-Pagano equation (TP)

The rules of mixtures and the semi-empirical Hirsch equation are models that have been developed to provide a harmonious prediction of the modulus of elasticity of a composite material. Nevertheless, these models have their limitations in that they do not consider the morphological characteristics of the filler in the matrix. It is well established that the morphological characteristics of the filler (whether fibers or particles) exert a significant influence on the mechanical performance of a composite, on the aspect ratio.⁴⁷ Therefore, the Tsai-Pagano equation (6) was introduced to estimate the modulus of elasticity of composites, considering this parameter. Furthermore, the Tsai-Pagano model assumes that the charge is uniformly distributed and dispersed with random orientation, leading to a value of α equal to 3/8⁴⁵:

E_{c} = \frac{3}{8} E_{/ /} + \frac{5}{8} E_{⏊}

(6)

Differential scanning calorimetry (DSC)

The behaviors of crystallization and melting of the specimens were registered on a Q100 from TA Instruments. To carry out the measurements, a quantity of about 3 to 10 mg of each sample was deposited in an aluminum pan. Samples were gradually heated from −30 to 200°C at a rate of 10°C/min in a nitrogen atmosphere. Then, they were cooled from 200 to −30°C at the same rate of 10°C/min. The thermal properties of the samples were analyzed using various measurement methods. The enthalpy of fusion ( $∆ H_{m}$ ) was calculated by integrating the area under the endothermic peak, the crystallization temperature $(T_{c})$ was determined by identifying the maximum exothermic peak, and the melting temperature $(T_{m})$ was obtained by measuring the maximum of the endothermic peak. The degree of crystallinity was determined using the following equation (7):⁷

X_{c} = \frac{{∆ H}_{m}}{(1 - α) {∆ H}_{m}^{0}} \times 100

(7)

Where α,

∆ H_{m}^{0}

, and

∆ H_{m}

are the weight fraction of the filler in the mixture, the enthalpy of melting of 100% crystalline PP (209 J/g),^48,49 and the enthalpy of melting of the sample, respectively.

In the case of laminates, the total fraction of the reinforcement is calculated from equation (8):

α = 1 - \frac{1}{e_{T}} \sum_{i = 1}^{n} e_{i} {w t}_{P P i}

(8)

Where

e_{T},

e_{i}, a n d {w t}_{P P i}

are the total thickness, the thickness of the

i^{t h}

layer, and the mass fraction of PP in the

i^{t h}

layer.

Dynamic mechanical analysis (DMA)

Dynamic mechanical properties of the samples were performed using the DMA Q800 rheometer from TA Instruments (USA), configured in DMA multi-frequency mode. At least two samples of each formulation, with a rectangular shape and dimensions of (35 mm × 12.50 mm × 1.6 mm), were submitted to a sinusoidal cycle using a clamp double cantilever. During this test, a strain of 0.002 mm/mm was applied to the samples at a frequency of 1.0 Hz. In addition, the specimens were heated from 26 to 80°C at a rate of 3°C/min in an air atmosphere. The resulting data, including parameters such as storage modulus (E′) and loss factor (tanδ), were recorded using software from TA Instruments and then transferred to Excel for further treatment.

Results and discussion

Morphological properties

Figure 2 provides an overview of SEM micrographs of kaolinite, GTR, composite films, and laminates. Kaolinite particles present a pseudo-hexagonal plate-like structure, with highly irregular contours and rough surfaces, as shown in Figure 2(a). In addition, kaolinite particles aggregate, forming clusters because of the cohesive tension generated by the intermolecular forces acting between them. The visual representation in Figure 2(b) illustrates the diversity of particles derived from recycled rubber. These particles reveal a wide range of irregular shapes, detailing asperities, protuberances, and even smooth angular surfaces, testifying to the multiple phases of the grinding process that they went through to reach their current form. The large diversity of particles making up recycled rubber poses a challenge when it comes to obtaining dimensions and homogeneous distribution. This inherent heterogeneity implies considerable variability in particle size, shape, and structure, making it difficult to control these characteristics precisely and consistently. SEM images of the fractured surfaces of the blends were also presented to accurately assess the state of dispersion of the particles, their compatibility with the matrix, and their adhesion interface. Figure 2(c) of blend PP/K, containing 15 wt% kaolinite, shows good dispersion of these particles within the continuous polypropylene (PP) matrix. Due to the differences at the surface between the thermoplastic matrix and the kaolinite particle, the interfacial interaction between the two components was limited, resulting in very poor compatibility. Furthermore, Figure 2(d) reveals that a recycled rubber content of 15 wt% provides homogeneous dispersion and satisfactory wettability within the matrix. Moreover, no signs of gaps, voids, or faults, as well as of GTR agglomerates, were observed, indicating an adequate selection of compound conditions (flow rates, temperature profile, screw speed, and screw configuration). Figure 2(e)–(h) shows micrographs taken at different levels of magnification using scanning electron microscopy (SEM) of laminates. These detailed images provide an in-depth understanding of how morphology evolves as a function of the stacking of composite films. Examining Figure 2(e), the continuous layers of PP film are superposed on the layers of SEBS. This superposition creates discontinuous contact zones, resulting in the formation of small voids and cavities between adjacent layers. This observation suggests poor adhesion or incompatibility between the phases of the different layers. Voids and cavities can affect the properties of the film, such as its mechanical strength and sealing performance. In contrast, the P/G/P laminate demonstrated no overlap between layers, due to the more pronounced surface texture and uniform distribution of the films, as seen in Figure 2(f). Another explanation is the increased interaction and greater specific surface area between PP films and PP/GTR composite films. Figure 2(g) and (h) presents SEM images of the K/S/K and K/G/K laminates, revealing decohesion or the presence of voids between composite films. This observation indicates poor adhesion or incompatibility between the different layers of the laminate. The gaps between the films show separation or partial detachment of the layers, which can compromise the structural integrity and performance of the laminate.

Figure 2.

SEM micrographs of (a) Kaolinite, (b) GTR, (c, d) PP/K and PP/GTR composite films, (e, f, g, h) laminates.

Mechanical properties

The mechanical properties of PP film, composite films, and laminates were assessed using the tensile test method. This technique involves the application of a uniaxial tensile force on the samples to obtain specific measurements such as elastic modulus, tensile strength, and strain at yield. The tensile strength of polypropylene film, composite films, and laminates is represented graphically in Figure 3(a). The results indicate a slight increase in tensile strength in the case of the PP/SEBS blend film, while a decrease in tensile strength was observed for all the other samples compared with the PP reference film. For example, adding 15 wt% of SEBS increased the tensile strength of the PP film from 31.31 to 32.71 MPa, revealing good adhesion with PP and favoring compatibility between the two polymers. The long chains of the elastomer triblock copolymer (SEBS) confer greater mobility, which seems to be responsible for the formation of a homogeneous material, inferring better interfacial adhesion with the thermoplastic matrix.⁵⁰ This homogeneity of the triblock copolymer in the mixture enabled a more gradual transfer stress, which in turn helped to slightly improve the tensile strength of the composite film (PP/SEBS). However, incorporating 15 wt% of kaolinite particles into the pure PP matrix decreased the tensile strength of the PP/K composite film by 18% (from 31.31 to 25.65 MPa). This reduction in tensile strength observed may result from poor intermolecular interaction between the hydrophilic kaolinite particles and the hydrophobic PP polymer, leading to deficient interfacial stress transfer. The bonds between the non-polar functional groups present in the polymer matrix and the polar charges in the kaolinite could alter the compatibility of the two materials, causing a drop in tensile strength.⁵¹ Furthermore, the presence of recycled rubber in the thermoplastic matrix led to a decrease in the tensile strength of the composite film, measured at 22.25 MPa, compared with 31.07 MPa for the pure PP film. This notable reduction in tensile strength can be explained by the presence of larger GTR particles, which act as stress concentration points due to their vulcanized elastomer phase. In addition, the low interfacial affinity between the ground tire powder and the PP matrix causes rapid crack propagation and accelerates fracture, resulting in reduced tensile strength. Fazli and Rodrigue⁵² also found that incorporating 35 wt% GTR into the rHDPE matrix resulted in a 33% decrease in tensile strength value (from 11.6 MPa to 7.7 MPa). This decrease was attributed to the larger size of the powder particles, as well as to an unfavorable interaction between the particles and the matrix. Despite careful stacking of the various layers, a decrease in the tensile strength of the laminates was reported. This drop in laminate tensile strength can be attributed to the presence of adhesion defects between the various layers, as well as to internal stresses generated during the stacking process. Nevertheless, the P/G/P laminate stood out as having the highest tensile strength, measured at 27.11 MPa.

Figure 3.

Tensile properties of PP film, composite films, and laminates: (a) tensile strength, (b) Young’s modulus, and (c) strain at yield.

Figure 3(b) shows Young’s modulus of composite films and laminates containing 15 wt% of GTR, SEBS, and kaolinite content. Looking at the graph below, we can see that incorporating 15 wt% kaolinite particles into the thermoplastic matrix led to a 13.38% increase in Young’s modulus of the composite film, making it pass from 1550 to 1757.44 MPa. An explanation that was possible for this could be the extremely rigid nature of kaolinite, generating a molecular movements restriction in polypropylene chains.³⁵ In contrast, Young’s modulus of the PP/SEBS and PP/GTR composite films was 1175.77 MPa and 1085.75 MPa, respectively. A downward trend of 24.14% and 30% in elastic modulus was found after the addition of 15 wt% kaolinite to the PP matrix. Several elements could contribute to this finding. Firstly, the intrinsic moduli of elasticity of the block copolymer of SEBR and GTR are lower than those of the thermoplastic polymer.⁵³ SEBS and GTR particles, which are soft, substitute the phase rigid polypropylene, providing PP/SEBS and PP/GTR composite films with a rubbery texture.⁵⁴ The fact that the GTR powder is cross-linked also has the effect of lowering the rigidity of the PP/GTR composite film. The results of tensile tests for laminated composites were obtained after superimposing the different layers. As can be seen, PP/K composite films with an average thickness of 0.56 mm, stacked separately at PP/GTR and PP/SEBS composite films, exhibited the highest moduli of elasticity, which were 1462.90 MPa and 1397.56 MPa, respectively. It is plausible that these results are attributable to the high layer thicknesses of PP/K composite films, as well as to the rigid structure of the kaolinite particles and the various existing interactions between layers that play a crucial role in the stacking process. This combination gives the laminate obtained after compression molding an improved tensile modulus. Nevertheless, PP films as outer layers have revealed reduced Young’s modulus, measuring 1280.2 MPa and 1346.49 MPa, respectively. Although the PP layers were stacked around the composite films, the presence of their rubbery phase, which gives them a certain flexibility, led to a drop in laminate stiffness.^55,⁵⁶

Figure 3(c) presents the strain at yield of PP film, composite films, and laminates with 15% content of particles GTR and kaolinite. As expected, the strain at yield of the PP/SEBS composite film increased from 11.34 mm/mm (PP film) to 14.63 mm/mm due to the purely elastic phase of the SEBS triblock copolymer. However, the introduction of 15 wt% kaolinite into the thermoplastic matrix resulted in a significant reduction in the strain at yield of the PP/K composite film. The value fell from 11.34 mm/mm (PP film) to 5.88 mm/mm, which represents a decrease of 48.14%. The higher the material’s modulus of elasticity, the less likely it is to stretch before breaking.⁵⁷ The presence of kaolinite particles in the polypropylene led to a reduction in the deformability of the composite film due to the formation of stress concentration caused by decohesion between the kaolinite and the thermoplastic polymer, which accelerated the rupture of the composite film (PP/K). In this case, the addition of GTR powder to the matrix also led to a decrease in the strain at yield of the PP/GTR composite film of 22.31% (from 11.34 to 8.81 mm/mm), respectively. This could be attributed to poor interfacial adhesion between the phases of polypropylene and GTR particles, leading to low-stress transfer.⁵⁸ Previous studies of melt blends comprising a thermoplastic polymer and GTR particles have reported inferior elongations at break than the matrix. Kiss et al.⁵⁹ reported that incorporating (from 10 to 30 wt%) of GTR into the polymer matrix (HDPE) caused a significant decrease, from 350 to 45%, due to the low affinity and incompatibility between the phases, which favored rapid propagation of the crack. Concerning laminates, it was found that the stacking of PP film layers with PP/SEBS composite films showed the greatest strain at yield, measured at 10.94 mm/mm. This observation can be explained by the low layer thickness, which influences elastic properties, and by the inherent flexibility of SEBS. On the other hand, laminates comprising layers of PP/K composite films stacked with those of PP/GTR and PP/SEBS revealed the lowest strains at yield. This behavior is ascribed to the rigid nature of kaolinite particles, which significantly influences their elastic properties.

Theoretical models

The objective of elaborating theoretical models was to solve the problems associated with laborious and onerous experiments. Moreover, these models offer the possibility of carrying out an in-depth evaluation of multiple assemblies of constituents to identify the one that ideally meets material design requirements. This approach enables precise optimization, taking into consideration morphological characteristics, mechanical and physical properties, as well as a selection of material criteria. In this process, particular attention was paid to the most frequently employed micromechanical models to determine which best concurred with the experimental data obtained after mechanical characterization of the specimens manufactured by compression molding.⁶⁰ The key parameters identified in this study for model calculations, specifically the effective moduli of elasticity, comprised volume fraction and intrinsic moduli of elasticity (matrix and fillers). In Figure 4, micromechanical models and experimental results of composite films are presented as a function of filler volume fractions (V_F), which are assumed to be randomly dispersed in the thermoplastic matrix (PP film). The volume fractions of fillers (kaolinite, GTR, and styrene-diene) were deduced from the empirical relationship between weight fraction (15 wt%) with densities of 6.7, 11.9, and 14.5%, respectively. The various volume fractions for a fixed weight fraction can be attributed to the different filler densities used during formulation. Thus, just as the density of a charge increases, its volume fraction decreases proportionally. The elastic modulus of kaolinite, GTR, and SEBS particles, estimated to predict the effective elastic moduli of PP/K, PP/GTR, and PP/SEBS composite films, were 7000 MPa, 270 MPa, and 270 MPa, respectively. As Figure 4(a) clearly shows, the elastic modulus of the analytical models increases continuously as the kaolinite volume fraction increases. This observation can be ascribed to the presence of kaolinite particles, which are intrinsically more rigid than polypropylene film. Furthermore, Figure 4(b) and (c) illustrate that increasing the volume fraction of GTR and SEBS particles leads to a decrease in the effective moduli of elasticity of the micromechanical models, as the particles have a more ductile phase than the PP film. It was also remarked that the measured results were within the range defined by the upper (Voigt model) and lower (Reuss model) bounds, thus confirming the reliability and precision of the results obtained. Moreover, the experimental results showed that the Tsai-Pagano model was the most consistent, offering the best concordance with the data.

Figure 4.

Elastic modulus of micromechanical models and experimental: (a) PP/Kaolinite composite film, (b) PP/GTR composite film, and (c) PP/SD composite film.

Table 2 presents experimental results and Voigt model predictions of laminate tensile moduli as a function of layer volume fraction. As mentioned above, the Tsai-Pagano model showed better agreement with experimental measurements of the elastic moduli of composite films. The values obtained were used to predict laminate elastic modules, which were then compared with experimental data to assess their consistency. The experimental data were remarkably close to the predicted values, demonstrating a high degree of concordance between the measured results and those obtained by the Voigt model. This highlights the fact that the stacking of the PP as well as the composite film layers is aligned unidirectionally and parallel, without any noticeable interactions between them. In sum, the results confirm that the Voigt model is an appropriate choice for micromechanical modeling, attesting to its validity and accuracy in predicting the elastic moduli of laminates.

Table 2.

Elastic modulus of Voigt models and experimental laminates.

Series	Layer	$V_{f}$ (%)	E (MPa)	$E_{V o i g t}$ (MPa)	$E_{Exp}$ (MPa)	Error (%)
P/G/P	PP PP-GTR PP	21.87 54.38 23.75	1550 1175.77 1550	1346.49	1335.14	0.84
K/G/K	PP-K PP-GTR PP-K	25 50.63 24.37	1757.44 1175.77 1757.44	1462.94	1438.09	1.69
P/S/P	PP PP-SD PP	21.87 54.38 23.75	1550 1085.75 1550	1297.54	1280.20	1.33
K/S/K	PP-K PP-SD PP-K	25 50.63 24.37	1757.44 1085.75 1757.44	1417.36	1397.56	1.39

Differential scanning calorimetry (DSC)

DSC analysis was employed to identify eventual modifications in the microstructure and crystallinity of the polymer matrix (PP Film) as well as hybrid laminates upon the addition of various fillers, such as SEBS, Kaolinite, and GTR. Data relating to the melting temperature (Tm), crystallinity temperature (Tc), enthalpy of fusion (

∆ H_{m})

and degree of crystallinity (%) of PP films, composite films, and hybrid laminates as a function of fillers are listed in Table 3. It was observed that T_m and T_c values decreased slightly when 15% of the SEBS and GTR content was added to the polypropylene film. This drop in melting temperature may be associated with a lower lamellar thickness, as the SEBS and GTR particles, which are amorphous, interfere with the crystalline structure of the polypropylene (PP) film.⁶¹ In addition, a decrease in the enthalpy of fusion was reported for both the PP/SEB blend film and the PP/GTR composite film. For example, the melting enthalpy of PP/SEBS and PP/GTR composite films decreased from 99.43 J/g (PP) to 74.27 and 73.59 J/g, following melt blending at a content of 15% of SEBS particles and GTR, respectively. The SEBS and GTR particles act as dilution agents, provoking a reduction in the nucleation density and the size of the PP crystals, which leads to a decrease in the melt enthalpy.^62,63 However, incorporating 15% kaolinite into the PP/K composite film had no significant influence on the melting temperature of the thermoplastic matrix. Kaolinite, which is a clay mineral, is generally used as a filler to enhance the mechanical and thermal properties of polymers, but it does not affect their melting temperature. Nevertheless, the incorporation of kaolinite into the polymer film led to an increase in the T_c. This is explained by the fact that the kaolinite particles act as confining agents for the polypropylene (PP), thus limiting the mobility of the polymer chains and favoring conditions propitious to the crystallization of the PP film at higher temperatures.^64,65 The zigzag surface of Kaolinite likely aligns well with the crystalline structure of polypropylene, facilitating improved crystal growth on kaolinite. Additionally, kaolinite acts as a nucleating agent, leading to the formation of a greater number of smaller crystals. Consequently, in the presence of kaolinite, the crystallinity (Xc) is enhanced, while the enthalpy of fusion (ΔHm) is reduced.⁶⁶ This mechanism induces an early start to the crystallization process at higher temperatures. A decrease in the melting enthalpy of the PP/K composite film was also signaled, demonstrating an enhancement in the thermal stability of the PP film with the incorporation of kaolinite particles.³⁵ Overall, the stacking of composite films caused a general decrease in the enthalpy of fusion while leading to an increase in both the crystallization temperature and the melting enthalpy for the laminates. The degree of crystallinity of PP film, blend film, as well as composite films, was calculated using equation (7), while that of laminates was calculated taking into consideration equations (7) and (8). According to the data in Tables 3 and it was observed that the degree of crystallinity of the PP/SEBS blend film and the PP/GTR composite film decreased following the incorporation of a soft amorphous phase in SEBS as well as in GTR. The inclusion of fillers in the PP matrix improves the ratio of organic matter that is more flexible and has a less ordered structure compared to PP chains, causing disorganization of PP polymer chains, and leading to the formation of a reduced-size crystalline phase.⁶¹ This disruption led to a decrease in the degree of crystallinity of the PP/SEBS and PP/GTR films. On the other hand, a substantial increase in the degree of crystallinity was found in the PP/K composite film compared with the pure polypropylene (PP) film. This could be because the kaolinite particles contribute to slowing down the growth of PP crystals. Moreover, its sheet structure, which is rigid and flat, acts as a nucleation agent in the polymer matrix, thus favoring their alignment and crystallization.⁶⁷ In the case of laminates, a considerable increase in the degree of crystallinity has been remarked. The arrangement of the films to produce a laminate has resulted in a confined configuration, where the polymer chains of the PP film are restricted to occupy a limited space. This confinement can induce increased alignment and enhanced crystallization of polymer chains, leading to a significant increase in crystallinity.

Table 3.

Melting and crystallization parameters of film PP, composite film, and laminate hybrids were calculated from DSC.

Series	T_m (°C)	T_C (°C)	ΔH_m (J/g)	X_C (%)
PP	161.95	116.49	97.34	46.57
PP/SEBS	158.27	115.67	74.27	41.80
PP/K	161.86	120.26	94.27	53.06
PP/GTR	158.56	114.34	73.59	41.42
P/S/P	160.70	116.04	104.7	58.93
K/S/K	161.18	117.68	84.68	58.84
P/G/P	160.62	116.89	98.42	55.40
K/G/K	160.84	117.55	99.84	56.20

Dynamic mechanical analysis (DMA)

DMA represents an analytical approach for assessing the viscoelastic behavior of materials, including polymers, films, and composites. It consists of measuring the response of the sample to dynamically variable strains or stresses applied to it. Thus, the results of this DMA test reveal the material’s viscoelastic parameters, which change as a function of temperature, frequency, or time. The main properties measured are storage modulus, loss modulus, and damping factors. The dynamic modulus (E′) or elastic response measures the material’s ability to store energy when subjected to stress or deformation and characterizes its stiffness. E′ is correlated with Young’s modulus, although it should be noted that they do not share a common identity.⁶⁸ In contrast, the dynamic loss modulus underlines the viscous part of the sample, illustrating its ability to dissipate energy resulting from various internal friction. The damping factor represents the ratio between the energy dissipated in the form of heat by the sample and the energy it can store elastically. During our work, particular attention was paid to the storage modulus and the damping factor, which evolve as a function of temperature at a constant frequency. Figure 5 shows the sample storage modulus as a function of temperature. The addition of kaolinite particles to the thermoplastic matrix has led to an improvement in the storage modulus of the PP/K. To illustrate, the storage modulus of PP film recorded a 19.37 % increase, from 1502 MPa to 1793 MPa, after the addition of 15 wt% kaolinite to the low-temperature mix. This observation is mainly linked to the inherent stiffness of the kaolinite in the matrix, which played an essential role in enhancing the stiffness of the PP/K composite film. However, a considerable decrease in the storage modulus was found after incorporating 15 wt% GTR and styrene-diene in the blend, with values reaching 912 MPa and 809.1 MPa, respectively. The decrease in elastic contribution is most likely caused by the presence of the elastomer surface of ground tire rubber particles and SEBS block copolymer, which is responsible for the significant drop in stiffness of PP/GTR and PP/SEBS composite films. Similarly, Moghaddamzadeh and Rodrigue⁶⁹ reported a substantial decrease in storage modulus in a recycled PE/polyester blend after incorporating GTR particles. This reduction was attributed either to the low Young’s modulus of GTR or to stress transfer from the thermoplastic matrix to the ground tire rubber powder. As the temperature rises, there is a sharp decrease in the elastic contributions of all systems, the reason for the softening of the PP film and the onset of the relaxation phase. Moreover, at elevated temperatures, the PP matrix’s molecular chains gain in mobility and flexibility, making it much easier for the chains to slip together.⁷⁰ The laminates (Figure 4(b)) were subjected to dynamic mechanical analysis, and the results showed that assembling PP/K composite film layers with PP/GTR composite film resulted in the highest storage modulus, measured at 1415 MPa. The improvement in storage modulus was ascribed to the inherent rigidity of kaolinite, combined with the substantial thicknesses of the PP/K and PP/GTR composite films. However, the laminate comprising the PP/SEBS composite film layers stacked with the PP film layers exhibited a relatively low storage modulus due to the ductile nature of styrene-diene, which results in a low elastic modulus.

Figure 5.

Storage modulus of PP films, composite films, and laminates.

The damping factors for all the samples are presented in Figure 6. Referring to Figure 6(a), raising the temperature increases the loss factor, both for the individual PP film and the composite films. This is attributed to the increase in dissipative energy and internal friction generated by each material in response to sinusoidal stress applied at varying temperatures.⁷¹ The experimental data also revealed that the PP/SEBS and PP/GTR composite films stood out as having the highest damping factors of all the samples tested, recording 0.052 and 0.048, respectively. An explanation for this observation could be the very low storage modules of the composite films, probably influenced by the ductile nature of the SEBS and GTR particles. Thermal stresses engender an increase in the movement of the long chains contained in the SEBS and GTR particles within the thermoplastic matrix. This mobility causes internal friction between the chains, resulting in a more efficient absorption capacity and more pronounced energy dissipation. On the other hand, incorporating kaolinite particles into the polymer matrix reduces the damping factor of the PP/K composite. The drop in the damping factor of the PP/K composite is ascribed to the rigid nature of the kaolinite, which leads to a significant increase in the storage modulus. The inherent rigidity of the particles restricts the molecular movement of the PP during the relaxation process, leading to a decrease in the composite’s ability to dissipate energy.⁷² We now turn to the experimental results for the loss factor of hybrid laminates, illustrated in Figure 6(b). A rise in the damping factor was found for all systems as the temperature increased, highlighting an increase in energy dissipation. Moreover, the P/S/P and P/G/P hybrid laminates had the highest damping factors, with values of 0.047 and 0.046, respectively. This observation could be attributed to the low thicknesses of the PP layers and the ductile nature (characterized by a low storage modulus) of the PP/SEBS and PP/GTR composite films, which gives these systems an increased ability to absorb energy. In contrast, the PP/K composite film, due to its inherent rigidity and substantial thickness, could limit the energy absorption capacity of hybrid laminates when stacked with composite films (PP/SEBS and PP/GTR).

Figure 6.

Damping Factor (tanδ) of PP film, composite films, and laminates.

Conclusion

Despite the benefits of using recycled tire rubber (GTR) for thermoplastic elastomer (TPE) production, research on polymer composite films and laminates using GTR, kaolinite, and triblock copolymers is limited. This study focuses on developing durable polymer composite films and laminates with materials such as SEBS particles, GTR, and kaolinite as fillers in a thermoplastic matrix. Several properties were characterized, including phase morphology, mechanical properties, thermal stability, and dynamics. SEM observations revealed that PP composite films with SEBS and GTR showed good homogeneity, while kaolinite dispersion faced interface adhesion issues. The laminates exhibited some decohesion, except for P/G/P, which showed consistent distribution. Adding 15 wt% kaolinite increased the elastic and storage moduli slightly, but reduced strain at yield, whereas SEBS addition improved strain at yield due to enhanced elasticity. The P/S/P and P/G/P laminates had balanced tensile properties, beneficial for consistent mechanical performance. The Tsai-Pagano model best correlated with the elastic moduli of composite films, while the Voigt model aligned well with laminate data. These findings suggest potential industrial applications, notably in electrical components and automotive parts.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Mohammed VI Polytechnic University supported this work.

ORCID iD

Marya Raji

Data Availability Statement

The datasets generated and analyzed during the current study are available from the corresponding author upon reasonable request. All characterization results, experimental protocols, and supplementary materials used to support the findings are included within the article.

References

Liu

Fan

. Improving the fracture toughness of epoxy with nanosilica-rubber core-shell nanoparticles. Compos Sci Technol 2016; 125: 132–140. DOI: 10.1016/j.compscitech.2016.01.009.

Tsang

Taylor

. Fracture and toughening mechanisms of silica- and core–shell rubber-toughened epoxy at ambient and low temperature. J Mater Sci 2019; 54(22): 13938–13958. DOI: 10.1007/s10853-019-03893-y.

Imanaka

Narita

Nakamura

, et al. Fracture properties of epoxy polymers modified with cross-linked and core–shell rubber particles. J Mater Sci 2021; 56(2): 1842–1854. DOI: 10.1007/s10853-020-05339-2.

Manjunatha

Jagannathan

Padmalatha

, et al. The fatigue and fracture behavior of micron-rubber and nano-silica particles modified epoxy polymer. Int J Nanosci 2012; 11: 1240002. DOI: 10.1142/S0219581X12400029.

Wang

Xie

Gou

, et al. Epoxy nanocomposites with high thermal conductivity and low loss factor: realize 3D thermal conductivity network at low content through core-shell structure and micro-nano technology. Polym Test 2020; 89(Sep): 106574. DOI: 10.1016/j.polymertesting.2020.106574.

Eksik

Bartolucci

Gupta

, et al. A novel approach to enhance the thermal conductivity of epoxy nanocomposites using graphene core-shell additives. Carbon N Y 2016; 101: 239–244. DOI: 10.1016/j.carbon.2016.01.095.

Wang

Zhou

Guo

, et al. Ultrahigh enhancement rate of the energy density of flexible polymer nanocomposites using core-shell BaTiO3@MgO structures as the filler. J Mater Chem A Mater 2020; 8(22): 11124–11132. DOI: 10.1039/d0ta03304a.

Rybak

. Functional polymer composite with core-shell ceramic filler: ii. rheology, thermal, mechanical, and dielectric properties. Polymers (Basel) 2021; 13(13): 2161. DOI: 10.3390/polym13132161.

Wang

P-J

Huan-Huan

, et al. Ultrahigh enhancement rate of the energy density of flexible polymer nanocomposites using core–shell BaTiO₃@MgO structures as the filler. J. Mater. Chem. A. 2020; 8: 11124–11132.

10.

Gam’

Miyamot02

Nishimura2

, et al. Fracture behavior of core-shell rubber-modified clay-E poxy nanocom posites. Polymer Engineering & Science. 2003; 10(43): 1635–1645.

11.

Keller

Chong

Taylor

, et al. Core-shell rubber nanoparticle reinforcement and processing of high toughness fast-curing epoxy composites. Compos Sci Technol 2017; 147: 78–88. DOI: 10.1016/j.compscitech.2017.05.002.

12.

Quan

Carolan

Rouge

, et al. Carbon nanotubes and core–shell rubber nanoparticles modified structural epoxy adhesives. J Mater Sci 2017; 52(8): 4493–4508. DOI: 10.1007/s10853-016-0695-9.

13.

Glaskova-Kuzmina

Stankevics

Tarasovs

, et al. Effect of core–shell rubber nanoparticles on the mechanical properties of epoxy and epoxy-based CFRP. Materials (Basel) 2022; 15(21): 7502. DOI: 10.3390/ma15217502.

14.

Crawford

Gupta

Trinh

, et al. Styrene-ethylene-butylene-styrene (SEBS) melt-blown fibers for oil spill remediation and oil barrier geotextiles. Polymer (Guildf) 2024; 298(Apr): 126942. DOI: 10.1016/j.polymer.2024.126942.

15.

Cai

Jiang

, et al. Experimental and computational investigation on performances of the thermoplastic elastomer SEBS/Poly(lactic acid) blends. Mater Today Commun 2023; 35(Jun): 105600. DOI: 10.1016/j.mtcomm.2023.105600.

16.

Kurusu

Demarquette

. Blending and morphology control to turn hydrophobic SEBS electrospun mats superhydrophilic. Langmuir 2015; 31(19): 5495–5503. DOI: 10.1021/acs.langmuir.5b00814.

17.

Chen

Fan

, et al. Great toughness reinforcement of isotactic polypropylene/elastomer blends with quasi-cocontinuous phase morphology by traces of β-nucleating agents and carbon nanotubes. Compos Sci Technol 2018; 167: 277–284. DOI: 10.1016/j.compscitech.2018.08.015.

18.

Huang

, et al. Hybrid composites from wheat straw, inorganic filler, and recycled polypropylene: morphology and mechanical and thermal expansion performance. Int J Polym Sci 2016; 2016: 1–12. DOI: 10.1155/2016/2520670.

19.

Sienkiewicz

Kucinska-Lipka

Janik

, et al. Progress in used tyres management in the European Union: a review. Waste Manag 2012; 32(10): 1742–1751. DOI: 10.1016/j.wasman.2012.05.010.

20.

Ramarad

Khalid

Ratnam

, et al. Waste tire rubber in polymer blends: a review on the evolution, properties and future. Elsevier Ltd., 2015. DOI: 10.1016/j.pmatsci.2015.02.004.

21.

Vázquez-Fletes Roberto

Wang

Youhong

, et al. “Effect of compatibilizer type on the properties of thermoplastic elastomers based on recycled polyethylene at high ground tire rubber content” International Polymer Processing, vol. 40, no. 2, 2025, pp. 133-146. https://doi.org/10.1515/ipp-2024-0110

22.

Fazli

Rodrigue

. Thermoplastic elastomer based on recycled HDPE/ground tire rubber interfacially modified with an elastomer: effect of mixing sequence and elastomer type/content. Polymer-Plastics Technology and Materials 2022; 61(9): 1021–1038. DOI: 10.1080/25740881.2022.2033770.

23.

Saeb

Wiśniewska

Susik

, et al.

GTR/Thermoplastics blends: how do interfacial interactions govern processing and physico-mechanical properties?

Materials (Basel) 2022; 15(3): 841. DOI: 10.3390/ma15030841.

24.

Mujal-Rosas

Marin-Genesca

Ballart-Prunell

. Dielectric properties of various polymers (PVC, EVA, HDPE, and PP) reinforced with ground tire rubber (GTR). Sci Eng Compos Mater 2015; 22(3): 231–243. DOI: 10.1515/secm-2013-0233.

25.

Lima

Magalhães da Silva

Oliveira

, et al. Rheological properties of ground tyre rubber based thermoplastic elastomeric blends. Polym Test 2015; 45: 58–67. DOI: 10.1016/j.polymertesting.2015.05.006.

26.

Dhanasekar

Baskar

Vishvanathperumal

. Cure characteristics, compression set, swelling behaviors, abrasion resistance and mechanical properties of nanoclay (Cloisite 15A, Cloisite 20A and Cloisite 30B) filler filled EPDM/NBR blend system. J Polym Res 2023; 30(10): 375. DOI: 10.1007/s10965-023-03759-7.

27.

Karger-Kocsis

. Thermoset rubber/layered silicate nanocomposites. Status and future trends. Polymer Engineering and Science 2004; 44: 1083–1093. DOI: 10.1002/pen.20101.

28.

Faucheu

Gauthier

Chazeau

, et al. Properties of polymer/clay interphase in nanoparticles synthesized through in-situ polymerization processes. Polymer (Guildf) 2010; 51(20): 4462–4471. DOI: 10.1016/j.polymer.2010.07.028.

29.

Hsiao

S-H

Liou

G-S

Chang

L-M

. Synthesis and properties of organosoluble polyimide/clay hybrids. Journal of Applied Polymer Science. 2001; 80: 2067–2072.

30.

Il Park

Park

Lim

, et al. The fabrication of syndiotactic polystyrene/organophilic clay nanocomposites and their properties. Polymer. 2001; 42(17): 7465–7475.

31.

Suh

Lim

Park

. The property and formation mechanism of unsaturated polyester-layered silicate nanocomposite depending on the fabrication methods. Polymer. 2000; 4124: 8557–8563.

32.

Zanetti

Camino

Reichert

, et al. Thermal Behaviour of Poly(propylene) Layered Silicate Nanocomposites. Macromol. Rapid Commun 2001; 22: 176-180. https://doi.org/10.1002/1521-3927(200102)22:3<176::AID-MARC176>3.0.CO;2-C

33.

Nekhlaoui

Abdelaoui

Raji

, et al. Assessment of thermo-mechanical, dye discoloration, and hygroscopic behavior of hybrid composites based on polypropylene/clay (illite)/TiO2. Int J Adv Manuf Technol 2021; 113(9–10): 2615–2628. DOI: 10.1007/s00170-021-06765-5.

34.

Yang

Yuan

, et al. Effect of reaction temperature on grafting of γ-aminopropyl triethoxysilane (APTES) onto kaolinite. Appl Clay Sci 2012; 62-63(63): 8–14. DOI: 10.1016/j.clay.2012.04.006.

35.

Raji

Qaiss

AEK

Bouhfid

. Effects of bleaching and functionalization of kaolinite on the mechanical and thermal properties of polyamide 6 nanocomposites. RSC Adv 2020; 10(9): 4916–4926. DOI: 10.1039/c9ra10579d.

36.

Bombazaro

Bernardin

. Improving plasticity of kaolins by high-energy milling for use in porcelain tile compositions. Open Ceramics 2022; 10(Jun): 100256. DOI: 10.1016/j.oceram.2022.100256.

37.

Nekhlaoui

Ebah

Boujmal

, et al. Impact of reinforcement characteristics on the morphology and performance of acrylonitrile butadiene styrene/polyamide 6 multimicro-/nanolayer composites. Polym Bull 2024; 82(5): 1551–1589. DOI: 10.1007/S00289-024-05580-8/FIGURES/10.

38.

Zhang

Pan

Yin

, et al. Influence of clay mineral content on mechanical properties and microfabric of tailings. Sci Rep 2022; 12(1): 10700. DOI: 10.1038/s41598-022-15063-3.

39.

Albach

Munaro

Santos

, et al. Thermal, mechanical, and water vapor barrier behavior of polypropylene composite containing modified kaolinite. J Appl Polym Sci 2018; 135(5): 45785. DOI: 10.1002/app.45785.

40.

Kim

Kang

, et al. Improved output performance of hybrid composite films with nitrogen-doped reduced graphene oxide. Ceram Int 2023; 49(2): 1615–1623. DOI: 10.1016/j.ceramint.2021.12.271.

41.

Peng

. The sandwich structure of a polyimide/PTFE composite film designed to achieve a low dielectric constant and excellent thermal performance at high frequency. ACS Appl Polym Mater 2024; 6: 4c02531. DOI: 10.1021/ACSAPM.4C02531/SUPPL_FILE/AP4C02531_SI_001.PDF.

42.

Raji

Essabir

ElAchaby

, et al. Morphology control of poly(lactic) acid/polypropylene blend composite by using silanized cellulose fibers extracted from coir fibers. Cellulose. 2022; 29: 6759–6782. https://doi.org/10.1007/s10570-022-04675-7

43.

Abobakr

Raji

Essabir

, et al. Enhancing oriented strand board performance using wheat straw for eco-friendly construction. Construction and Building Materials. 2024; 417: 135135. DOI: 10.1016/j.conbuildmat.2024.13513

44.

Flynn

Amiri

Ulven

. Hybridized carbon and flax fiber composites for tailored performance. Mater Des 2016; 102: 21–29. DOI: 10.1016/j.matdes.2016.03.164.

45.

Nekhlaoui

Essabir

Kunal

, et al. Comparative study for the talc and two kinds of moroccan clay as reinforcements in polypropylene-SEBS-g-MA matrix. Polym Compos 2015; 36(4): 675–684. DOI: 10.1002/pc.22986.

46.

Malha

Nekhlaoui

Essabir

, et al. Mechanical and thermal properties of compatibilized polypropylene reinforced by woven doum. J Appl Polym Sci 2013; 130(6): 4347–4356. DOI: 10.1002/app.39619.

47.

Serra

Tarrés

Chamorro

MÀ

, et al. Modeling the stiffness of coupled and uncoupled recycled cotton fibers reinforced polypropylene composites. Polymers (Basel) 2019; 11(10). DOI: 10.3390/polym11101725.

48.

Sever

Atagür

Tunçalp

, et al. The effect of pumice powder on mechanical and thermal properties of polypropylene. J Thermoplast Compos Mater 2019; 32(8): 1092–1106. DOI: 10.1177/0892705718785692.

49.

VCF

Kuang

Mulyadi

, et al. 3D printed cellulose nanocrystal composites through digital light processing. Cellulose. 2019; 26: 3973–3985. https://doi.org/10.1007/s10570-019-02353-9

50.

Formela

Korol

Saeb

. Interfacially modified LDPE/GTR composites with non-polar elastomers: from microstructure to macro-behavior. Polym Test 2015; 42: 89–98. DOI: 10.1016/j.polymertesting.2015.01.003.

51.

Zulfiqar

Sarwar

Rasheed

, et al. Influence of interlayer functionalization of kaolinite on property profile of copolymer nanocomposites. Appl Clay Sci 2015; 112-113(113): 25–31. DOI: 10.1016/j.clay.2015.04.010.

52.

Fazli

Rodrigue

. Effect of ground tire rubber (Gtr) particle size and content on the morphological and mechanical properties of recycled high-density polyethylene (rhdpe)/gtr blends. Recycling 2021; 6(3): 44. DOI: 10.3390/recycling6030044.

53.

Yang

Xiao

, et al. Effect of interfacial enhancing on morphology, mechanical, and rheological properties of polypropylene-ground tire rubber powder blends. J Appl Polym Sci 2017; 134(40). DOI: 10.1002/app.45354.

54.

Ebah

Bensalah

Nekhlaoui

, et al. Smart and flexible PVDF/SEBS membranes reinforced with pyrolytic carbon black nanoparticles from waste tires for enhanced wastewater remediation. Journal of Water Process Engineering 2025; 72: 107469. DOI: 10.1016/j.jwpe.2025.107469.

55.

Raji

Essassi

Essabir

, et al. Properties of nano-composites based on different clays and polyamide 6/acrylonitrile butadiene styrene blends. In: Bio-based Polymers and Nanocomposites: Preparation, Processing, Properties & Performance. Springer 2019: 107–128. DOI: 10.1007/978-3-030-05825-8_6.

56.

Raji

Essabir

Essassi

, et al. Morphological, thermal, mechanical, and rheological properties of high density polyethylene reinforced with Illite clay. Polym Compos 2018; 39(5): 1522–1533. DOI: 10.1002/pc.24096.

57.

Song

Zhang

Cao

, et al. Bicontinuous laminated structure design of polypropylene/reduced graphene oxide hybrid films for thermal management. Adv Compos Hybrid Mater 2022; 5(4): 2873–2883. DOI: 10.1007/s42114-022-00470-x.

58.

García

López

Balart

, et al. Composites based on sintering rice husk-waste tire rubber mixtures. Mater Des 2007; 28(7): 2234–2238. DOI: 10.1016/j.matdes.2006.06.001.

59.

Kiss

Simon

DÁ

Petrény

, et al. Ground tire rubber filled low-density polyethylene: the effect of particle size. Advanced Industrial and Engineering Polymer Research 2022; 5(1): 12–17. DOI: 10.1016/j.aiepr.2021.07.001.

60.

Kablan

Nazih

Bensalah

, et al. Synergistic reinforcement of HDPE biocomposites with kaolinite nanoparticles and alfa fiber: a path toward enhanced performance. J Compos Mater 2025; 59: 1793–1810. DOI: 10.1177/00219983251320153.

61.

Esmizadeh

Naderi

Bakhshandeh

, et al. Reactively compatibilized and dynamically vulcanized thermoplastic elastomers based on high-density polyethylene and reclaimed rubber. Polym Sci B 2017; 59(3): 362–371. DOI: 10.1134/S1560090417030046.

62.

Essabir

El Achaby

Hilali

, et al. Morphological, structural, thermal and tensile properties of high density polyethylene composites reinforced with treated argan nut shell particles. J Bionic Eng 2015; 12(1): 129–141. DOI: 10.1016/S1672-6529(14)60107-4.

63.

Majewska-Laks

Sykutera

Ościak

. Reuse of ground tire rubber (GTR) as a filler of TPE matrix. MATEC Web Conf 2021; 332: 01003. DOI: 10.1051/matecconf/202133201003.

64.

Ning

Yin

Luo

, et al. Crystallization behavior and mechanical properties of polypropylene/halloysite composites. Polymer (Guildf) 2007; 48(25): 7374–7384. DOI: 10.1016/j.polymer.2007.10.005.

65.

Albach

Vianna dos Santos

da Silveira Rampon

, et al. An evaluation of modified Kaolinite surface on the crystalline and mechanical behavior of polypropylene. Polym Test 2019; 75: 237–245. DOI: 10.1016/j.polymertesting.2018.12.012.

66.

Bensalah

Gueraoui

Essabir

, et al. Mechanical, thermal, and rheological properties of polypropylene hybrid composites based clay and graphite. J Compos Mater 2017; 51(25): 3563–3576. DOI: 10.1177/0021998317690597.

67.

Clarizia

Bernardo

. A review of the recent progress in the development of nanocomposites based on poly(ether-block-amide) copolymers as membranes for CO2 separation. polymer, 2022, 14, p. 10.

68.

Haris

Mohamad

Ilyas

, et al. Dynamic mechanical properties of natural fiber reinforced hybrid polymer composites: a review . Journal of Materials Research and Technology , 2022, 19, pp. 167–182.

69.

Moghaddamzadeh

Rodrigue

. Rheological characterization of polyethylene/polyester recycled tire fibers/ground tire rubber composites. J Appl Polym Sci 2018; 135(34): 46563. DOI: 10.1002/app.46563.

70.

Cristea

Ionita

Iftime

. Dynamic mechanical analysis investigations of pla-based renewable materials: how are they useful? MDPI AG, 2020. DOI: 10.3390/ma13225302.

71.

Luo

Cao

McDonald

. Interfacial improvements in a green biopolymer alloy of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and lignin via in situ reactive extrusion. ACS Sustainable Chem Eng 2016; 4(6): 3465–3476. DOI: 10.1021/acssuschemeng.6b00495.

72.

Karaduman

Sayeed

MMA

Onal

, et al. Viscoelastic properties of surface modified jute fiber/polypropylene nonwoven composites. Compos B Eng 2014; 67: 111–118. DOI: 10.1016/j.compositesb.2014.06.019.