Self-reinforced Polymer Composites Research Articles

Self-Reinforced Composite Materials: Frictional Analysis and Its Implications for Prosthetic Socket Design.

Friction and wear characteristics play a critical role in the functionality and durability of prosthetic sockets, which are essential components in lower-limb prostheses. Traditionally, these sockets are manufactured from bulk polymers or composite materials reinforced with advanced carbon, glass, and Kevlar fibres. However, issues of accessibility, affordability, and sustainability remain, particularly in less-resourced regions. This study investigates the potential of self-reinforced polymer composites (SRPCs), including poly-lactic acid (PLA), polyethylene terephthalate (PET), glass fibre (GF), and carbon fibre (CF), as sustainable alternatives for socket manufacturing. The tribological behaviour of these self-reinforced polymers (SrPs) was evaluated through experimental friction tests, comparing their performance to commonly used materials like high-density polyethylene (HDPE) and polypropylene (PP). Under varying loads and rotational speeds, HDPE and PP exhibited lower coefficients of friction (COF) compared to SrPLA, SrPET, SrGF, and SrCF. SrPLA recorded the highest average COF of 0.45 at 5 N and 240 rpm, while SrPET demonstrated the lowest COF of 0.15 under the same conditions. Microscopic analysis revealed significant variations in wear depth, with SrPLA showing the most profound wear, followed by SrCF, SrGF, and SrPET. In all cases, debris from the reinforcement adhered to the steel ball surface, influencing the COF. While these findings are based on friction tests against steel, they provide valuable insights into the durability and wear resistance of SRPCs, a crucial consideration for socket applications. This study highlights the importance of tribological analysis for optimising prosthetic socket design, contributing to enhanced functionality and comfort for amputees. Further research, including friction testing with skin-contact scenarios, is necessary to fully understand the implications of these materials in real-world prosthetic applications.

Fabric Insert Injection Molding for the Preparation of Ultra-High Molecular Weight Polyethylene/High-Density Polyethylene Two-Component Self-Reinforced Composites.

The fabric insert injection molding approach can be applied to produce easily recyclable self-reinforced polymer composites (SrCs) whose reinforcement and matrix are from the same polymer. However, the mechanical properties of the SrCs are usually limited due to the poor impregnation of the inserted fabric. In this work, the ultra-high molecular weight polyethylene (UHMWPE) fabrics were used as the insert, and the high-density polyethylene (HDPE) melt was injected to fill the mold cavity and impregnate the fabrics. The UHMWPE/HDPE two-component SrCs were prepared. The large difference of melting temperatures between UHMWPE and HDPE can establish a wide processing temperature window, and thus the impregnation of the fabric can be improved by increasing temperature. The tensile strength and modulus of the UHMWPE/HDPE SrCs were up to 148 and 1132 MPa, respectively. The peel strength could be up to 35.2 N/cm. The influences of four main injection molding parameters, including the injection temperature, injection pressure/packing pressure, injection velocity, and packing time, were investigated. The temperature, pressure, viscosity, and density of the matrix in the mold cavity were calculated by the numerical simulation to indicate the impregnation process during the fabric insert injection molding process.

Self-reinforced composites based on polypropylene fiber and graphene nano-platelets/polypropylene film

Self-reinforced polymer composites (SrPCs) have many advantages such as light weight, easy recyclability, improved bonding, and low cost. However, the enhancement of mechanical properties of SrPCs is generally restricted by the composite structure and the narrow processing temperature window. The combination of graphene and self-reinforcing mechanism is a potential method to realize a significant improvement in the mechanical properties of polymer composites. It is necessary to study the self-reinforcing mechanism on adjusting the orientation of graphene, so as to reduce the amount of graphene and improve the mechanical properties. This paper presents SrPCs that combine polypropylene (PP) fibers and graphene nano-platelets (GnPs)/PP composite films through film stacking. The unidirectionally arranged PP fibers form narrow channels which facilitate the orientation of GnPs during the impregnation process. The prepared GnPs/PP SrPCs were characterized in comparison with neat PP. At a very low GnPs content of only 0.019 wt%, the tensile strength and modulus of PP were increased by 152% and 186%, respectively, and the interfacial adhesion force of PP SrPCs was improved by 280%. Numerical simulation was successfully conducted to evaluate the processing temperature and the mechanism of graphene orientation in the film stacking process. It proved that the GnPs were highly oriented over the region of unidirectional fibers by the flow field. This new technical method can be potentially used in the industrial manufacturing of economical graphene/polymer nanocomposites with superior mechanical properties.

Microbond multiple fiber pull-out test to evaluate interface properties of UHMWPE/LDPE self-reinforced polymer composites

Interfacial properties of composite materials play an important role in overall efficiency and reliability of these materials in structural applications. The objective of this study is to develop a multiple fiber microbond pull-out test to determine the interfacial properties of self-reinforced polymer composites (SRPC) and compare it with single fiber multiple fiber pull-out tests. SRPC possess better interfacial adhesion due to their similarity in chemical structure. The system used in this study is LDPE sheet reinforced with plain weave ultra-high molecular weight polyethylene (LDPE/ UHMWPE). The optimal operating temperature was estimated with DSC and TGA analysis. The micromechanical and meso-mechanical approaches were compared to validate the results. A fractographic study was performed to correlate lamina and meso-mechanical properties found in this study. It was observed that the multiple fiber pullout test explained in this study is on par with or better than the other conventional methods to evaluate interface properties.

Investigation of mass distribution between core and face sheet on bending energy absorption of self-reinforced PP sandwich beams

Self-reinforced polymer composites (SRCs) are thermoplastic composites. The matrix and reinforcement belong to the same family of polymers that makes SRCs fully recyclable compared to multi-component traditional fiber-reinforced epoxy matrix-based composites. There have been several studies on fabrication methods and material properties of flat SRCs laminates. Still, it is quite challenging to implement these methods for large scale automatic production of SRCs based sandwich structures. We fabricated self-reinforced polypropylene (SrPP) sandwich beams (SrPPSBs) through an ex-situ consolidation based fabrication method that can be potentially applied for high volume cost-effective production of SRCs structures. Three-point bending tests were performed on SrPPSB with non-symmetric mass distribution between core and face sheet (FS) to investigate the effects of mass distribution on their flexural properties and energy absorption capacity. As the sandwich beams' deflection is a complex phenomenon due to many material and geometrical parameters, a finite element model was developed to predict the deflection behavior and energy absorption capacity. The FEA results showed good agreement with experimental data.

Effect of core corrugation angle on static compression of self-reinforced PP sandwich panels and bending energy absorption of sandwich beams

The structural weight of an electric vehicle and its material’s recyclability are the important parameters to optimize the overall cost as well as the mileage of a vehicle. Self-reinforced polymer composites (SRCs) can be potentially used for these applications because of their 100% recyclability as compared with multicomponent traditional epoxy matrix based fibre reinforced composites. In case of SRCs the fibres and matrix are synthesized from same family of polymers. An optimization study is required based on integration of material and structural parameters to reduced overall weight of the vehicles while keeping the strength up to the safety mark. We fabricated self-reinforced polypropylene (SrPP) sandwich structures through an ex-situ consolidation based fabrication method. An FEA based study was conducted to optimize the effect of core corrugation angle of sandwiched structures on out of plane compressive strength and flexural strength of SrPP sandwiched beams. The finite element study was preferred in order to save the experimental cost. Beams with 60° core corrugation angle have optimal flexural properties. The sandwiched panels with 45° corrugated core exhibited optimal stiffness while maximum energy absorption capacity was shown with 60° corrugated core sandwiched structures.

The incorporation of graphene to enhance mechanical properties of polypropylene self-reinforced polymer composites

Lightweight, easy recyclability and improved bonding can be achieved by self-reinforced polymer composites (SPC). However, the mechanical properties of SPC are usually limited. This paper describes the incorporation of graphene platelets (GNP) into polypropylene (PP) to produce PP/GNP SPC. PP/GNP fibers were firstly prepared by melt compounding and spinning, and then PP/GNP SPC were produced by film stacking. The thermal, mechanical, and morphological properties of the produced samples were characterized via DSC, WAXD, tensile test, peeling test, optical microscopy, and SEM. The combination of film stacking technology of SPC and nanotechnology of graphene enhanced the mechanical properties significantly. The tensile strength, tensile modulus, and interfacial strength of PP SPC with only 0.062 wt% GNP were increased by 117, 116, and 116%, respectively. The reinforcement is attributed to the high intrinsic mechanical properties of GNP and the self-reinforced mechanism. The spinning promotes the alignment of GNP, and the compaction process induces the in-plane orientation of GNP. In addition, a small number of GNP do not increase the cost significantly.

Analysis of Self-Reinforced Mechanism of Over-Molding Polypropylene Parts

Abstract On the premise that the overall structure and composition of the parts remain unchanged, the over-molding of self-reinforced polymer composites parts (OM-SRCs parts) prepared in this paper...

A comparative investigation of interfacial adhesion behaviour of polyamide based self-reinforced polymer composites by single fibre and multiple fibre pull-out tests

Interfacial adhesion of composite materials plays an important role in their mechanical properties and performance. In the present investigation, analysis of the interfacial properties of self-reinforced polyamide composites by using microbond multiple fibre pull-out test is emphasised. Microbond specimens prepared through thermal processing are tested for their interfacial properties by multiple fibre bundle pull-out tests and compared with that of traditional single fibre pull-out test specimens. Multiple fibre pull-out addresses the volume fraction as well as eliminates the possibility of fibre breakage before matrix shear. Higher scatter in the data in the samples is addressed in the present studies. FTIR and Fractographic studies are carried out for deep understanding of the post pull-out interfacial adhesion.

Failure mechanisms in unidirectional self-reinforced biobased composites based on high stiffness PLA fibres

Biobased self-reinforced polymer composites using polylactic acid (PLA) were developed. To create PLA based self-reinforced composites (SR-PLA) with improved properties, first high stiffness PLA fibres with high melting temperature were produced by optimising the melt spinning process parameters. Unidirectional SR-PLA composites with enhanced stiffness were obtained, comparable to the commercially available self-reinforced polypropylene composites. The failure strain of the composites was several times higher than the failure strain of the compact PLA. An increased strength, compared to the compact PLA, was obtained but the increase was less pronounced. To understand the behaviour of unidirectional self-reinforced PLA composites, in-situ tensile tests were performed inside the chamber of an Environmental Scanning Electron Microscope. The damage initiation and evolution under tension was monitored. It was found that the primary limiting strength factor is the high brittleness of the compact (matrix) PLA.

Polylactide-based self-reinforced composites biodegradation: Individual and combined influence of temperature, water and compost

Self-reinforced polymer composites (SRCs) are proposed as a suitable alternative for composite development, based in the combination of a polymeric matrix and a polymeric fibre made of the same polymer. SRCs based in polylactide (PLA) could be fully biodegradable and their valorisation routes could presumably be assimilated to those for neat PLA. In this sense, the aim of this study was to develop new self-reinforced PLA-based composites and ascertain their biodegradability. For this purpose, PLA-based SRCs were obtained through a thermo-compression procedure and their biodegradability corroborated under standard conditions (ISO 20200). Moreover, a deep study of the effect of the different factors involved in the biodegradation of the composites such as the temperature, the water and the compost medium was considered relevant to delimitate the long-term properties and valorisation routes for these materials. The macroscopic and microscopic appearance as well as the thermo-oxidative stability, the thermal properties and the molar mass were evaluated. Although degradation was perceived due to the effect of temperature, the synergistic combination of water and temperature ‒and compost‒ was found to play a key role in the biodegradation of these materials. Overall, these SRCs can be considered as promising candidates, since their end-of-life management options can be guaranteed under standardised composting conditions.

Self-reinforced biobased composites based on high stiffness PLA yarns

In self-reinforced polymer composites (SRPC) the same polymer material forms both the reinforcing fibre and the matrix phase. The current project aims to develop a biobased alternative for these composites using polylactic acid (PLA). Both the development of the reinforcing fibres, the modelling and production of the composites are being studied. The stiffness of the PLA filaments could be increased to 9 GPa by optimising processing parameters during extrusion. After consolidation to composites, promising results are obtained showing that the stiffness of the PLA SRPC can match the requirements of currently used commercial self-reinforced polypropylene composites (ca 4GPa).

Dynamic compression response of self-reinforced polypropylene composite structures fabricated through ex-situ consolidation process

In case of Self-reinforced polymer composites (SRCs) the fibres and matrix belong to the same family of polymers that can ensure 100% recyclability as compared to traditional fibre reinforced epoxy matrix based composites. Most of the SRCs were studied only on material bases not structural bases, although some structures were fabricated but most of their fabrication methods can hardly be applied for mass production. We fabricated self-reinforced polypropylene (SrPP) structures by ex-situ consolidation process that can be potentially applied for mass production. Instead of conventional stamping process that involves complex formability phenomenon; a mould was designed to fabricate corrugated core from the pre-consolidated SrPP sheets and then face sheets were joined by same family of polymer adhesives to achieve maximum recyclability. Optimal bending temperature was investigated to maintain proper fibre matrix contents of corrugated SrPP sheets. Interface between core and face sheet (FS) was enhanced through phenomenon of mechanical lock by creating various abrasion levels. Dynamic strengthening effect and collapse behaviour of structures during out of plane dynamic compression tests was investigated and compared with theoretical predictions.

Development of PLA hybrid yarns for biobased self-reinforced polymer composites

Lightweight materials are a necessity in various industries. Lightweight design is in the key interest of the mobility sector, e.g. the automotive and aerospace industry. This trend applies also for the consumer industries, e.g. sporting goods. In addition, the worldwide demand for replacing fossil-based materials has led to a significant growth of bioplastics. Due to their low mechanical performance and durability, their use is still limited. Therefore, it is necessary to develop biobased, sustainable polymeric materials with high stiffness, high impact and high durability without impairing recyclability at a similar price level of non-biobased solutions. Biobased self-reinforced polymer composites offer these unique properties.

Development of Bio-Based Self-Reinforced PLA Composites

Self-reinforced polymer composites (SRPCs) are receiving increasing attention by the industry for lightweight applications. The polymers used for SRPCs today are derived from fossil resources. However, due to a limitation of resources, interest is growing regarding the use of new alternatives for petrol based polymers in form of bio-based ones. SRPCs combine high stiffness, high impact and high durability with impairing recyclability. In SRPCs the same polymer is used for the reinforcing and matrix phases. SRPCs can be manufactured by commingling reinforcing and matrix fibres with different melting temperatures. The use of commingled yarns allows the combination of a large variety of fibres and therefore a wide range of material properties.

Multivariable dependency of thermal shrinkage in highly aligned polypropylene tapes for self-reinforced polymer composites

Self-reinforced composites offer a unique combination of properties such as high specific strength, high impact resistance, and recyclability by incorporating highly aligned fibers within a random matrix of the same polymer. However, high temperatures will shrink the system to recover randomness in the aligned segments, compromising the composite thermal stability during processing as self-reinforced tapes are consolidated into the final composite through heating and pressure. Hence, the dynamic nonlinear multivariable (i.e., time, temperature, stress) shrinkage exhibited by self-reinforced polypropylene (SRPP) tapes was measured and modeled at the maximum shrinkage limit achieved in the proximity of the composite processing temperature [∼140 to160°C]. At high stress (∼7.5MPa) the thermal shrinkage of the SRPP tapes was reduced and a parallel creep mechanism was activated. The modeling, and prediction of the main factors governing the thermal shrinkage expand and diversify the dynamic design window for new SRPP composites.

Calorimetric Investigations of Oriented Polypropylene Tapes and Self‐Reinforced Composites

SummaryDifferential scanning calorimetry (DSC) is a commonly applied method of determining various physical properties of thermoplastic polymers. Analyzing DSC melting and crystallization curves it is possible to verify whether the macromolecules orientation occurs in fibers, films and self‐reinforced polymer composites (SRC). This paper presents the comparison of the results of calorimetric investigations of polypropylene (PP) single polymer composites (SRC) with the investigations of constrained PP tape samples additionally annealed before the measurement. The program of thermal treatment resembled temperature changes in the mold during SRC production by hot compaction method. The results confirmed a substantial influence of compression molding pressure on the melting process of oriented PP reinforcement used in the production of single polymer composites.

A constitutive model for self-reinforced ductile polymer composites

Self-reinforced polymer composites are gaining increasing interest due to their higher ductility compared to traditional glass and carbon fibre composites. Here we consider a class of PET composites comprising woven PET fibres in a PET matrix. While there is a significant literature on the development of these materials and their mechanical properties, little progress has been reported on constitutive models for these composites. Here we report the development of an anisotropic visco-plastic constitutive model for PET composites that captures the measured anisotropy, tension/compression asymmetry and ductility. This model is implemented in a commercial finite element package and shown to capture the measured response of PET composite plates and beams in different orientations to a high degree of accuracy.

Failure of compression molded all-polyolefin composites studied by acoustic emission

This paper is aimed at studying the failure behavior of polyolefin-based self-reinforced polymer composites (SRPCs) via acoustic emission (AE). Three matrix materials (ethylene octene copolymer (EOC), polypropylene-based ther- moplastic elastomer (ePP), random polypropylene copolymer (rPP), and three kinds of reinforcing structures of PP homopolymer (unidirectional (UD), cross-ply (CP) and woven fabric (WF)) were used. SRPCs were produced by compres- sion molding using the film-stacking method. The composites were characterized by mechanical tests combined with in situ assessment of the burst-type AE events. The results showed that rPP matrix and UD reinforcement produced the greatest reinforcement, with a tensile strength more than six times as high as that of the matrix and a Young's modulus nearly dou- bled compared to the neat matrix. The number of the detected AE events increased with increasing Young's modulus of the applied matrices being associated with reduced sound damping. The AE amplitude distributions shows that failure of the SRPC structure produces AE signals in a broad amplitude range, but the highest detected amplitude range can be clearly linked to fiber fractures.

Self-reinforced poly(ethylene terephthalate) composites by hot consolidation of Bi-component PET yarns

Self-reinforced polymer composites or all-polymer composites have been developed to replace traditional glass-fibre-reinforced plastics (GFRP) with good lightweight, mechanical and interfacial properties and enhanced recyclability. Poly(ethylene terephthalate) (PET) is one of the most attractive polymers to be used in these fully recyclable all-polymer composites, in terms of cost and properties. In this work, unidirectional all-PET composites were prepared from skin–core structured bi-component PET multifilament yarns by a combined process of filament winding and hot-pressing. During hot-pressing, the thermoplastic copolyester skin or sheath layers were selectively melted to weld high-strength polyester cores together creating an all-PET composite. Physical properties of the resulting composites including thickness, density and void content were reported. The effect of processing parameters, i.e. consolidation temperature and pressure on mechanical properties and morphology was investigated in order to balance good interfacial adhesion with residual tensile properties of the composite.