Improved mechanical and rheological properties of recycled polyethylene by acrylic acid-assisted melt grafting of glycidyl methacrylate

Abstract

The use of glycidyl methacrylate (GMA) and acrylic acid (AAc) as grafting monomers to improve the mechanical properties, particularly tensile strength, of recycled polyethylene (R-PE) is reported in this study. The AAc monomer was implemented to improve the stability of radical chains which could undergo GMA grafting. When the content of GMA and AAc was 1.2% and 0.6%, respectively, the tensile strength increased from 17.26 to 29.3 MPa, the elongation at break increased from 107% to 647%, and the melt index decreased from 3.42 to 0.97 g/10 min. The sensitivity of the dynamic behaviour of R-PE-g-(AAc-co-GMA) to temperature was also reduced relative to R-PE. Differential scanning calorimetry (DSC) results showed that the melting temperature was increased and the crystallisation temperature of R-PE-g-(AAc-co-GMA) was reduced. The fracture morphology of the samples was also shown by scanning electron microscope (SEM) observations to transition from brittle fracture to ductile fracture upon undergoing the grafting process.

Keywords

Recycled polyethylene glycidyl methacrylate acrylic acid melt grafting

Introduction

Polyolefins are attractive materials due to their light weight, transparency, moisture impermeability, aesthetics, chemical stability, toughness, and corrosion resistance, allowing them to replace metals, ceramics, and natural products in many fields [1-5]. However, an enormous amount of polyolefin waste is generated each year [6]. The recycling of modified polyethylene waste, in particular, has remained a difficult problem and significant area of research [7]. The modification of polyolefins is mainly divided into mechanically mixing [8-10] and chemical grafting. As is known, the compatibility is poor between high-density polyethylene and low-density polyethylene. It is not improved by mechanically mixing simply. Liu et al. studied the mechanical properties of blends have been improved by adding elastomers to polyolefins, the study has shown that mechanically mixed recycled polyethylene and polypropylene blends with subsequent elastomers addition display improved mechanical properties, but the amount of elastomer is very large, resulting in appearing a morphology of clear phase separation [11, 12]. For another method, free-radical melt grafting of polyolefins has also been studied [13-18]. Many studies use maleic anhydride (MAH), silane, glycidyl methacrylate (GMA) and styrene (St) as grafting monomer because of the strong reactivity of the group of them. However, the reactivity of GMA monomers is low in the melt grafting reaction, with a tendency to homopolymerisation, the compatibility of the blends is not improved significantly. Cartier [19] used GMA and St grafted polyethylene improved the mechanical properties of polyethylene. Owing to the complexity of recycled polyethylene components, the use of GMA and AAc grafted recycled polyethylene has rarely been reported. Here we use AAc to assist GMA grafting to recycled polyethylene, which improves the miscibility of recycled polyethylene.

In this study, in order to improve the mechanical properties of recycled polyethylene, recycled polyethylene was grafted with bicomponent monomers GMA and acrylic acid in order to improve the interaction intensity of recycled polyethylene chains. It undergoes multifunctional reactions with carboxyl, hydroxyl groups in the blends, producing improved mechanical properties and rheological properties of the polyethylene blends [20-22]. The complex grafting reactions that increase the interaction between recycled PE chains, improving the mechanical properties of R-PE blends.

Experimental

Materials

The examined materials were commercial products of recycled low-density polyethylene (R-LDPE), recycled low viscosity high density polyethylene (R-HDPE1), and recycled high viscosity high density polyethylene (R-HDPE2). Three types of polyethylene (PE) with different viscosities were chosen for the matrix phase. Recycled polyethylene materials (R-LDPE, R-HDPE1 and R-HDPE2), were derived from recycled plastic films (widely sourced with universally poor mechanical properties), recycled inexpensive beverage bottles (also exhibiting poor mechanical properties) and recycled machine oil bottles, which have higher standards and are correspondingly more expensive, respectively. These materials were supplied by Hubei Fangyuan Green Recycled Technology Co., LTD. GMA was purchased from Shanghai Macklin Biochemical Co., LTD, Shanghai, China. Acrylic acid was purchased from Guoyao Chemical Reagent Co., LTD, Shanghai, China. Dicumyl peroxide was purchased from Yuhe Chemical Product Co., LTD, Zhengzhou, China. Antioxidant (1010) was purchased from Dongguan Bao Sheng Plastic Co., LTD, Guangdong, China. Liquid paraffin was purchased from Wuhan Mingrui Prosperity Materials Co., Ltd, Hubei, China.

All polyethylene blends studied in this work were R-LDPE/R-HDPE1/R-HDPE2 (60:20:20) blends. The recycled polyethylene blends described above were represented by R-PE [20]. The recycled materials were characterised by chemical and physical methods according to standard procedures in order to determine molecular parameters, type and concentration of impurities, and mechanical properties. The composition and source of the examined materials are summarised in Table 1.

Table 1

Basic properties of materials.

Materials	Composition	Technical	Producer
R-LDPE	LDPE, [inorganic filler] < 3‰	MFI = 4.325 g.10 min⁻¹ (190°C, 5 kg)	Hubei Fangyuan Green Recycled Technology co., LTD
R-HDPE1	HDPE, [inorganic filler, Color Master] < 3‰	MFI = 2.895 g.10 min⁻¹ (190°C, 5 kg)	Hubei Fangyuan Green Recycled Technology co., LTD
R-HDPE2	HDPE, [inorganic filler, Color Master] < 1‰	MFI = 0.341 g.10 min⁻¹ (190°C, 5 kg)	Hubei Fangyuan Green Recycled Technology co., LTD

Preparation of samples

R-PE blends were prepared with R-HDPE1/R-HDPE2/R-LDPE content of 60/20/20 wt%. The content of dicumyl peroxide, antioxidant and liquid paraffin were 0.1, 0.15 and 0.15 wt%. Eight samples of R-PE/GMA/AAc blends were prepared with the GMA/AAc content of 0/0, 1.8/0, 0/1.8, 0.3/1.5,0.6/1.2,0.9/0.9,1.2/0.6 and 1.5/0.3 wt%, denoted R-PE, R-PE-g-GMA_1.8, R-PE-g-AAc_1.8, R-PE-g-(GMA_0.3-co-AAc_1.5), R-PE-g-(GMA_0.6-co-AAc_1.2), R-PE-g-(GMA_0.9-co-AAc_0.9), R-PE-g-(GMA_1.2-co-AAc_0.6) and R-PE-g-(GMA_0.3-co-AAc_1.5), respectively. The melt grafting experiments were carried out primarily in a torque rheometer. The mixer platform of the torque rheometer was used in the chamber. The mixed particles samples were processed and mixed with a high-speed mixer. First, particle samples were dry-blended for 1 h before being charged into the mixing chamber. Then the dry-blended particles were added to the preheated mixing chamber with stirring over 5 min. After a fixed time, 50 g of mixed particles were removed from the chamber for sampling and AAc and GMA particles were added in succession to form the complete blends. Finally, the blends were deposited in the torque rheometer. All samples are Single extrusion. The torque rheometer temperature was set at 180°C, the screw rotating speed was set at 30 r min⁻¹ and mixing time was set to 15 min to prepare all the samples in this work.

Mechanical properties

Dumbbell-shaped splines were formed with a thickness of 1 mm, length of 75 mm, and a width of 4 mm in the studied region. The tensile strength of samples was tested according to the GB/T1040. 2–2006 standard using an electronic tensile tester (GMT4000, GTS systems co., LTD, China). Tests were conducted at an extension rate of 100.0 mm/min at 25°C.

Fourier transform infrared spectroscopy (FTIR)

A sample of the grafted product (1 g) was dissolved in xylene (45 mL) in a three-necked flask, refluxed at 140°C for 1 h, and slowly poured into an acetone/xylene solvent mixture (6:/1 V/V), stirred for 1 h after filtering, washed with acetone, dried at 80°C for 12 h, then vacuum dried at 65°C for 12 h. The grafted R-PE was hot-pressed with a Teflon plate at a pressure of 2 MPa, a temperature of 180°C and a pressing time of 3 min. The obtained flakes were analysed with a Fourier transform infrared spectrometer (Vertex 70, Bruker, Germany).

Dynamic rheological behaviour

The rheological behaviour of samples was studied with a rheometer (TDHR-2, Ta Instruments Waters LLc, America) under N₂ atmosphere. The rheometer was used in parallel-plate oscillatory mode to perform rheological tests of the melt. The change in rheological properties with frequency was observed with a dynamic frequency sweep test performed in the range of 0.01–100 Hz at 180°C with a predetermined strain amplitude of 0.1%. Three different temperatures (180, 200, and 220°C) were selected for performing dynamic frequency sweep tests.

The morphology of samples

The specimens were cooled in liquid nitrogen for 15 min then cryo-fractured and coated with platinum. The fracture surface morphology of the blends was investigated by scanning electron microscopy (SEM, S-4800, Hitachi Limited Co., Japan) with the accelerating voltage of 15 kV.

Melt and crystallisation behaviour of samples

The crystallisation behaviour of samples was studied with a dynamic scanning calorimeter (DSC8000, Perkin Elmer, America) in N₂ atmosphere. The test is divided into three stages, heating, cooling, and reheating; the first temperature ramp was to eliminate the thermal histories of the samples. The heating and cooling rates were set to 20°C min⁻¹ and the scanning range was 25–180°C. Heat (enthalpy) of fusion (ΔH_m) was evaluated from the second heating ramps. The degree of crystallinity (X_c) was calculated using the relation: (1) where ΔH_m is the heat of fusion of the test sample, ΔH⁰m (289J/g) is the heat of fusion for 100% crystalline PE [23].

Results and discussion

Table 2 shows the mechanical properties of R-PE, R-PE-g-AAc, as well as R-PE-g-GMA and R-PE-g-(AAc-co-GMA). R-PE tensile strength is only 17.26 MPa, the elongation at break is 107%, and the melt index is as high as 3.42 g/10 min. The melt index and tensile strength of R-PE-g-AAc was reduced significantly, likely due to AAc self-polymerisation. With increasing of GMA concentration, the mechanical properties of R-PE-g-(AAc-co-GMA) first improved and then remained consistent; the properties were best when the concentrations of GMA and AAc were 1.2% and 0.6%, respectively, producing a tensile strength of 29.3 MPa. This is an improvement of nearly 70%, with elongation at break increased by 547%, and the melt index decreased to 0.97 g/10 min. Improvement in elastic modulus and strain at break for the R-PE-g-(AAc_0.3-co-GMA_1.5) sample is probably due to the optimised GMA/AAc ratio of 1.2/0.6, at which the degree of homopolymerisation of GMA as well as crosslinking of polyethylene were effectively inhibited, leading to a desired grafted polymer with long chain branches. Besides, due to the introduction of polar groups to the grafted polymer, the interaction among recycled polyethylene molecular chains was enhanced, increasing the compatibility between the matrix resins. In general, the mechanical properties of drainage pipes require tensile strengths above 20 MPa, elongation at break above 350%, and melt index below 1.5 g/10 min (according to CJ/T358-2010, only for sewer pipes for trenchless installation). Thus, the modifications explored here allow pipe material requirements to be achieved. The AAc monomer, which has higher reactivity than GMA, is believed to react with the free radical chain of polyethylene to form stable R-PE-AAc free radicals, and then the R-PE-AAc free radicals reacted with GMA monomer to form R-PE-g-(AAc-co-GMA). Since the stability of the R-PE-AAc group is higher than that of the PE radical, the GMA has sufficient time to react with the R-PE-AAc free radical; the addition of AAc effectively inhibits the crosslinking of PE, promoting the GMA grafting process. When the content of GMA is more than 1.2%, the mechanical properties maintain a stable level; this may be due to a balance between grafting and depolymerisation being reached at this concentration. Based on the above study, it is found that the mechanical properties of R-PE-g-(AAc-co-GMA) are the best when the content of GMA and AAc is 1.2% and 0.6%, respectively. As a result, the optimal formula GMA_1.8, AAc_1.8 and GMA_1.2 /AAc_0.6 was selected for further study.

Table 2

Mechanical properties of samples.

Sample	Tensile strength (MPa)	Elongation (%)	Tensile Modulus (MPa)	MFI (g/10 min)
R-PE	17.26	107	253	3.42
R-PE-g-GMA_1.8	19.53	275	297	2.31
R-PE-g-AAc_1.8	13.67	122	236	0.7
R-PE-g-(AAc_1.5-co-GMA_0.3)	21.60	371	339	2.12
R-PE-g-(AAc_1.2-co-GMA_0.6)	24.41	465	376	1.75
R-PE-g-(AAc_0.9-co-GMA_0.9)	27.08	554	371	1.28
R-PE-g-(AAc_0.6-co-GMA_1.2)	29.30	647	398	0.97
R-PE-g-(AAc_0.3-co-GMA_1.5)	28.87	606	393	1.02

Fourier transform infrared spectroscopy was used to analyse the presence of functional groups in the materials under study. The FTIR transmittance curves of R-PE and R-PE-g-(AAc_0.6-co-GMA_1.2) are compared in Figure 1. R-PE displayed an absorption band at 1368and 1466 cm⁻¹, which was assigned to the characteristic absorption of R-PE skeleton, which is chosen as the internal reference. In the case of R-PE-g-(AAc_0.6-co-GMA_1.2), a new absorption band at 1730 cm⁻¹ was observed and assigned to the absorption of the carbonyl groups (-C=O) of GMA [23]. The absence of the AAc carboxyl peak in the figure is due to the small amount of AAc that participated in the reaction. Through the comparison between R-PE and R-PE-g-(AAc_0.6-co-GMA_1.2) infrared absorption, the clear peak at 1730 cm⁻¹ of AAc assisted GMA grafted R-PE provided sufficient evidence of the presence of GMA in the sample. The absorption band peaked at 1630 cm⁻¹ was attributed to the stretching vibration of C=C on benzene rings due to the small amount of polystyrene in the recycled polyethylene.

Figure 1

FTIR of RPE and RPE-g-(AAc_0.6-co-GMA_1.2).

Figure 2(a) shows the damping behaviour where tan δ is plotted as a function of frequency for R-PE, R-PE-g-AAc_1.8, R-PE-g-GMA_1.8 and R-PE-g-(AAc_0.6-co-GMA_1.2). As shown in the figure, the tan δ of samples decreased with increasing frequency. The value of tan δ of R-PE-g-(AAc_0.6-co-GMA_1.2) was less than 1 and the slope of R-PE-g-(GMA_1.2-co-AAc_0.6) was nearly zero [24]. This was attributed to a change in viscoelasticity; The internal energy consumption of the flexible molecular chain was less than that of the rigid molecular chain and the viscoelasticity and strength of the material was improved. Figure 2(b) shows storage modulus (G′) with loss modulus (G″) for R-PE, R-PE-g-AAc_1.8, R-PE-g-GMA_1.8 and R-PE-g-(AAc_0.6-co-GMA_1.2). The crossover frequency was determined to characterise the transformation of the material from liquid to the solid behaviour. The crossover frequencies of R-PE, R-PE-g-AAc_1.8, R-PE-g-GMA_1.8 and R-PE-g-(AAc_0.6-co-GMA_1.2) were about 6, 4.7, 2.2 and 1.7 Hz, respectively. It was observed that the crossover frequencies were reduced when adding modifiers; increasing the transformation from liquid-like to solid-like for the polymers. The AAc-assisted grafting of GMA onto R-PE inhibited the depolymerisation of the PGMA branch chain of polyethylene.

Figure 2

Plots of (a) tan δ (b) storage and loss moduli as a function of frequency for R-PE, R-PE-g-AAc_1.8, R-PE-g-GMA_1.8 and R-PE-g-(AAc_0.6-co-GMA_1.2).

Figure 3 shows the effect of temperature on viscosity of R-PE, R-PE-g-AAc_1.8, R-PE-g-GMA_1.8, and R-PE-g-(GMA_1.2-co-AAc_0.6). Complex viscosity was used to characterise the resistance factors associated with melt liquid properties. The complex viscosity of polyethylene decreased with increasing temperature. For R-PE, the complex viscosity changed significantly with temperature in the low-frequency zone and was not changed in the high-frequency zone. In contrast, the complex viscosity varied significantly with temperature across the entire frequency range for R-PE-g-GMA_1.8 and R-PE-g-AAc_1.8. However, the complex viscosity had no significant change with temperature for R-PE-g-(AAc_0.6-co-GMA_1.2). This may be because the strength of R-PE-g-(AAc_0.6-co-GMA_1.2) was enhanced due to the addition of AAc; with a higher degree of chain entanglement, the complex viscosity was increased and higher energies were needed to overcome the forces between the polyethylene chains in this temperature range. It can be seen in Figure 4 that the temperature sensitivity of R-PE-g-(AAc_0.6-co-GMA_1.2) was not strong, indicating that it has a wider processing range and is conducive to the processing of modified polyethylene. First, the complex viscosity of R-PE-g-(AAc_0.6-co-GMA_1.2) samples at high or low frequencies was almost one order of magnitude higher than that of other samples, indicating that molecular chain entanglement of in R-PE-g-(AAc_0.6-co-GMA_1.2) samples was tighter and the compatibility is better. Second, the shear-thinning behaviour of R-PE-g-(AAc_0.6-co-GMA_1.2) was most obvious, indicating that GMA and AAc were grafted onto recycled polyethylene and long chain branches were formed [25].

Figure 3

The curve of complex viscosity as a function of frequency at different temperatures (180–220°C) for R-PE, R-PE-g-AAc_1.8, R-PE-g-GMA_1.8 and R-PE-g-(AAc_0.6-co-GMA_1.2).

Figure 4

The curves of the (a) melting and (b) crystallinity for R-PE, R-PE-g-AAc_1.8, R-PE-g-GMA_1.8 and R-PE-g-(AAc_0.6-co-GMA_1.2).

The curves of the melting (a) and R-PE crystallinity (b) of the R-PE, R-PE-AAc_1.8, R-PE-g-GMA_1.8 and R-PE-g-(AAc_0.6-co-GMA_1.2) are displayed in Figure 4. As shown in Figure 4(a), the addition of AAc and GMA to R-PE resulted in melting peak shifts of varying degrees. The melting temperature of R-PE is 133.2°C, when the content of GMA and AAc were 1.2% and 0.6%, respectively, the melting temperature of R-PE-g-(AAc_0.6-co-GMA_1.2) increased to 139.6°C, with a decreased crystallisation temperature of about 114°C. With the addition of GMA and AAc alone, the melting temperature increased by only about 2°C and. This maybe due to the fact that the monomers homopolymerised. Moreover, R-PE-g-GMA is unstable; PGMA chains on polyethylene are easily depolymerised to form GMA monomer radicals at higher temperatures and the depolymerised monomer radicals are difficult to re-bond at higher temperatures. In contrast, R-PE-g-(AAc-co-GMA) is not easily depolymerised, increasing the main chain or branch length and decreasing regularity decreased, producing a decreased capacity for crystallisation. As seen in Figure 4(a), the peak areas of the three grafted polyethylenes vary greatly compared to that of intact recycled polyethylene, indicating that grafting had a remarkable effect on the crystallinity of polyethylene. On the other hand, the polypropylene content is small and the melting peak area of polypropylene did not change much (Figure 4), indicating that grafting has little influence on the crystallinity of the polypropylene. Thus, only the crystallinity of polyethylene in the recycled material was taken into consideration and calculated.

Figure 5 shows the morphology of R-PE, R-PE-g-AAc_1.8, as well as R-PE-g-GMA_1.8 and R-PE-g-(AAc_0.6-co-GMA_1.2). SEM observations show that R-PE had a smooth broken surface, homogeneous deformation is observed during crack propagation. The damage initiation on the surface is mostly due to the simultaneous influence of tearing and shear fracture. evidence of a weaker fracture toughness (Figure 5(a,e)); As seen in Figure 5(b,f), R-PE-g-AAc_1.8 exhibited a sliced layer structure morphology which is related to the strong reactivity of AAc. The AAc monomers connected to two polyethylene chains rapidly, resulting in the formation of the cross-linked structure of polyethylene, leading to relatively hard grafted chains. This is not a significant improvement to morphology from bare R-PE. The fracture behaviour of R-PE-g-GMA_1.8 and R-PE-g-(AAc_0.6-co-GMA_1.2) showed relatively rough fracture and filament-like structure can be seen in Figure 5(c,g), the R-PE-g-(AAc_0.6-co-GMA_1.2) fracture surface is observed to be very rough and accompanied with extensive tearing zones which has been formed at final deformation stages. Furthermore, the quantity of these structures in Figure 5(d,h) is more than that observed in Figure 5(c,g), therefore, R-PE-g-GMA_1.8 had smooth broken surface with some rigid characteristics, while R-PE-g-(AAc_0.6-co-GMA_1.2) showed enhanced toughness characteristics [26]. R-PE-g-(AAc_0.6-co-GMA_1.2) had better mechanical properties and breaking elongation than the other materials due to the enhanced degree of the molecular chain entanglements.

Figure 5

SEM micrographs of fracture surfaces of R-PE (a, e), R-PE-g-AAc_1.8 (b, f), R-PE-g-GMA_1.8 (c, g) and R-PE-g-(AAc_0.6-co-GMA_1.2) (d, h).

The mechanism of AAc assisted GMA grafting on polyethylene is presented in Figure 6. R-PE generated long chain free radicals under the initiation of dicumyl peroxide. Upon addition of GMA, Owing to the low reactivity of GMA monomers with macromolecules, it tends to self-polymerise. So it underwent homopolymerisation to form unstable PGMA branches on the polyethylene chain in Route 1. When both AAc and GMA were added to R-PE at the same time during the reaction process, the AAc reacted with R-PE preferentially to form R-PE-g-AAc with free radicals due to the higher reactivity of AAc, and then the GMA reacted with R-PE-g-AAc with free radicals to form R-PE-g-(AAc-co-GMA) in Route 2, this method can improve the grafting rate of GMA and avoid the side effects of grafting. Of course, the polyethylene chain in the presence of initiator will also inevitably occur crosslinking to a certain extent in Route 3. Therefore, in order to obtain products with high GMA grafting rate, GMA and AAc were used as co-monomers to graft polyethylene to enhance the interaction between three different polyethylene molecular chains and improve the mechanical properties of recycled polyethylene.

Figure 6

Mechanism of AAc assisted GMA grafting on R-PE.

Conclusion

In this work, grafting polymers R-PE-g-AAc, R-PE-g-GMA, and R-PE-g-(AAc-co-GMA) were prepared by a torque rheometer to improve the mechanical properties and compatibility of recycled polyethylene. The mechanical behaviour, morphology and rheological properties, and chemical analysis of the grafted polymers were studied. GMA/AAc was successfully grafted onto recycled polyethylene as indicated by IR spectroscopy. With the addition of GMA and AAc at 1.2/0.6 ratio, the tensile strength of the resulting graft polymer was improved by approximately 70%, while the elongation at break approximately 5 times. Further, the melt index decreased to 0.97 g/10 min, a characteristic of the material to be sufficient for the production of high-quality pipes. The crossover frequency of R-PE-g-(AAc-co-GMA) decreased due to the increased degree of chain entanglements of the grafted polymers. The highest complex viscosity was seen from R-PE-g-(GMA_1.2-co-AAc_0.6) and did not change with frequency, indicating good compatibility. SEM imaging revealed a transition from a brittle to tough material with grafting modification and R-PE-g-(GMA_1.2-co-AAc_0.6) showed superior mechanical performance than the un-grafted recycled polyethylene.

Footnotes

Disclosure statement

No potential conflict of interest was reported by the authors.

References

Colangelo

, Cioffi

, Liguori

, Recycled polyolefins waste as aggregates for lightweight concrete. Compos B. 2016;106:234–241. doi: 10.1016/j.compositesb.2016.09.041

Verdolotti

, Iucolano

, Capasso

, Recycling and recovery of PE-PP-PET-based fiber polymeric wastes as aggregate replacement in lightweight mortar: evaluation of environmental friendly application. Environ Prog. 2014;33:1445–1451.

Anouar

, Guinot

, Ruiz

, Purification of post-consumer polyolefins via supercritical CO 2 extraction for the recycling in food contact applications. J Supercrit Fluids. 2015;98:25–32. doi: 10.1016/j.supflu.2014.12.022

Fel

, Khrouz

, Massardier

, Comparative study of gamma-irradiated PP and PE polyolefins part 2: properties of PP/PE blends obtained by reactive processing with radicals obtained by high shear or gamma-irradiation. Polym. 2016;82:217–227. doi: 10.1016/j.polymer.2015.10.070

Chung

TCM.

Functional polyolefins for energy applications. Macromol. 2013;46:6671–6698. doi: 10.1021/ma401244t

Koitabashi

, Sameshima-Yamashita

, Koike

, Biodegradable plastic-degrading activity of various species of Paraphoma. J Oleo Sci. 2016;65:621–627. doi: 10.5650/jos.ess16067

Padhan

, Sreeram

Enhancement of storage stability and rheological properties of polyethylene (PE) modified asphalt using cross linking and reactive polymer based additives. Constr Build Mater. 2018;188:772–780. doi: 10.1016/j.conbuildmat.2018.08.155

Park

, Lim

, Nho

YC.

Radiation-induced grafting with one-step process of waste polyurethane onto high-density polyethylene. Mat Plast. 2017;54:18–21.

Ghioca

, Spurcaciu

, Iancu

, Composite of waste polypropylene by styrene-isoprene block-copolymers blending. Mat Plast. 2015;52:281.

10.

Ghioca

, Iancu

, Spurcaciu

, Modification of waste polypropylene by styrene-isoprene block-copolymers. Mat Plast. 2013;50:32.

11.

Liu

, Zhang

, Fu

Synthesis of polyethylene/poly (ethylene-co-propylene) in-reactor alloys by periodic switching polymerization process: effects of switching frequency on polymer structure and properties. Macromol Res. 2017;25:534–541. doi: 10.1007/s13233-017-5084-y

12.

Moad

The synthesis of polyolefin graft copolymers by reactive extrusion. Prog Polym Sci. 1999;24:81–142. doi: 10.1016/S0079-6700(98)00017-3

13.

Jahani

, Valavi

, Ziaee

Reactive melt modification of polyethylene by ethyl acrylate/acrylic acid copolymers: rheology, morphology and thermal behavior. Iran Polym J. 2015;24:449–458. doi: 10.1007/s13726-015-0336-1

14.

, Stevanovic

, Rodrigue

Unmodified and esterified Kraft lignin-filled polyethylene composites: compatibilization by free-radical grafting. J Appl Polym Sci. 2015;132:1–8.

15.

Shao

, Qin

, Guo

Melt grafting copolymerization of glycidyl methacrylate onto acrylonitrile-butadiene-styrene (ABS) terpolymer. Sci Eng Compos Mater. 2015;22:391–398. doi: 10.1515/secm-2013-0121

16.

Medjdoub

, Melia

, Magali

Viscoelastic, thermal and environmental characteristics of poly (lactic acid), linear low-density polyethylene and low-density polyethylene ternary blends and composites. J Adhes Sci Technol. 2017;31:787–805. doi: 10.1080/01694243.2016.1232547

17.

Wongpanit

, Khanthsri

, Puengboonsri

Effects of acrylic acid-grafted HDPE in HDPE-based binder on properties after injection and debinding in metal injection molding. Mater Chem Phys. 2014;147:238–246. doi: 10.1016/j.matchemphys.2014.04.035

18.

Pracella

, Pazzagli

, Galeski

Reactive compatibilization and properties of recycled poly (ethylene terephthalate)/polyethylene blends. Polym Bull. 2002;48:67–74. doi: 10.1007/s00289-002-0001-7

19.

Cartier

, Hu

GH.

Styrene-assisted free radical grafting of glycidyl methacrylate onto polyethylene in the melt. J Polym Sci Pol Chem. 1998;36:2763–2774. doi: 10.1002/(SICI)1099-0518(19981115)36:15<2763::AID-POLA13>3.0.CO;2-Y

20.

Saki

TA.

Reactive melt blending of low-density polyethylene with poly (acrylic acid). Arab J Chem. 2015;8:191–199. doi: 10.1016/j.arabjc.2011.05.021

21.

Zou

, Li

, Long

SJ.

Effect of compatibiliser on rheological behaviour of straw fibre/low density polyethylene composites. Plast Rubber Compos. 2015;44:238–244. doi: 10.1179/1743289815Y.0000000022

22.

Kord

, Ravanfar

, Ayrilmis

Influence of organically modified nanoclay on thermal and combustion properties of bagasse reinforced HDPE nanocomposites. J Polym Environ. 2017;25:1198–1207. doi: 10.1007/s10924-016-0897-x

23.

Nesic

, Popovic

, Rabasovic

, Thermal diffusivity of high-density polyethylene samples of different crystallinity evaluated by indirect transmission photoacoustics. Int J Thermophys. 2018;39:24–28. doi: 10.1007/s10765-017-2345-0

24.

Nasef

, Abbasi

, Ting

TM.

New CO2 adsorbent containing aminated poly (glycidyl methacrylate) grafted onto irradiated PE-PP nonwoven sheet. Radiat Phys Chem. 2014;103:72–74. doi: 10.1016/j.radphyschem.2014.05.031

25.

Rinawa

, Maiti

, Sonnier

Dynamic rheological studies and applicability of time–temperature superposition principle for PA12/SEBS-g-MA blends. Polym Bull. 2015;12:3305–3324. doi: 10.1007/s00289-015-1467-4

26.

, Xu

, Long

, Improved compatibility in recycled-PE/LDPE using glycidyl methacrylate, acrylic acid grafted mPE. Polym Test. 2018;69:508–513. doi: 10.1016/j.polymertesting.2018.06.008