Rubber Toughening Research Articles

Mouldable Conductive Plastic with Optimised Mechanical Properties.

This paper investigates making an injection mouldable conductive plastic formulation that aims for conductivity into the electromagnetic interference (EMI) shielding range, with good mechanical properties (i.e., stiffness, strength, and impact resistance). While conductivity in the range (electrostatic charge dissipation) and EMI shielding have been attained by incorporating conductive fillers such as carbon black, metals powders, and new materials, such as carbon nanotubes (CNTs), this often occurs with a drop in tensile strength, elongation-to-break resistance, and impact resistance. It is most often the case that the incorporation of high modulus fillers leads to an increase in modulus but a drop in strength and impact resistance. In this work, we have used short carbon fibres as the conductive filler and selected a 50/50 PBT/rPET (recycled PET) for the plastic matrix. Carbon fibres are cheaper than CNTs and graphenes. The PBT/rPET has low melt viscosity and crystallises sufficiently fast during injection moulding. To improve impact resistance, a styrene-ethylene-butadiene-styrene (SEBS) rubber toughening agent was added to the plastic. The PBT/rPET had very low-impact resistance and the SEBS provided rubber toughening to it; however, the rubber caused a drop in the tensile modulus and strength. The short carbon fibre restored the modulus and strength, which reached higher value than the PBT/rPET while providing the conductivity. Scanning electron microscope pictures showed quite good bonding of the current filler (CF) to the PBT/rPET. An injection mouldable conductive plastic with high conductivity and raised modulus, strength, and impact resistance could be made.

Brittle–Ductile Transitions of Rubber Toughened Polypropylene Blends: A Review

Brittle–Ductile Transitions of Rubber Toughened Polypropylene Blends: A Review

Modifications of Poly(lactic Acid) with Blends and Plasticization for Tenacity and Toughness Improvement

This review focuses on the modification of the inherent brittleness of biodegradable poly(lactic acid) (PLA) to increase its toughness, as well as recent advances in this field. The most often utilized toughening methods are melt blending, plasticization, and rubber toughening. The process of selecting a toughening scheme is still difficult, although it directly affects the blend's mechanical properties. There has been a lot of development, but there is still a long way to go before we get easily processable, totally bio-based, 100% biodegradable PLA. The blends of PLA with other polymers, such as plasticizers or rubber, are often incompatible with one another, which causes the blend's individual components to behave in a manner consistent with phase separation. Polymer blending has been shown to be particularly effective in attaining high-impact strength. This review addresses the recent progress in improving the toughened PLA to gain properties necessary for the material's future engineering applications. As 3D and 4D printing becomes more accessible, PLA characteristics may be modified and treated utilizing more sophisticated production techniques.

Processing‐Properties Correlation for a Rubber Toughened Wood Plastic Composite

AbstractIssues of environmental sustainability attract more and more attention to polymeric systems that can be considered environmentally friendly. A class of materials that meets the demand for a lower environmental impact are Wood Polymer Composites, or WPCs. These are thermoplastic polymers compounded with wood fibers or flour, usually coming from industrial or agricultural waste. With these materials, the greatest benefit is obtained by increasing the wood content, thus reducing the percentage of polymeric matrix. On the other hand, two of the main drawbacks coming from an increase in the wood content are brittleness and a significant reduction in processability. In this work, concentration will be on reducing brittleness by adding different amounts of a toughening agent (i.e., a thermoplastic elastomer) and on finding the optimal combination between processing conditions and elastomer content. This target will be obtained by comparing the tensile properties of all composites that are produced with different extrusion conditions with their apparent density.

In Service Performance of Toughened PHBV/TPU Blends Obtained by Reactive Extrusion for Injected Parts.

Moving toward a more sustainable production model based on a circular economy, biopolymers are considered as one of the most promising alternatives to reduce the dependence on oil-based plastics. Polyhydroxybutyrate-co-valerate (PHBV), a bacterial biopolyester from the polyhydroxialkanoates (PHAs) family, seems to be an attractive candidate to replace commodities in many applications such as rigid packaging, among others, due to its excellent overall physicochemical and mechanical properties. However, it presents a relatively poor thermal stability, low toughness and ductility, thus limiting its applicability with respect to other polymers such as polypropylene (PP). To improve the performance of PHBV, reactive blending with an elastomer seems to be a proper cost-effective strategy that would lead to increased ductility and toughness by rubber toughening mechanisms. Hence, the objective of this work was the development and characterization of toughness-improved blends of PHBV with thermoplastic polyurethane (TPU) using hexamethylene diisocyanate (HMDI) as a reactive extrusion agent. To better understand the role of the elastomer and the compatibilizer, the morphological, rheological, thermal, and mechanical behavior of the blends were investigated. To explore the in-service performance of the blends, mechanical and long-term creep characterization were conducted at three different temperatures (−20, 23, 50 °C). Furthermore, the biodegradability in composting conditions has also been tested. The results showed that HMDI proved its efficiency as a compatibilizer in this system, reducing the average particle size of the TPU disperse phase and enhancing the adhesion between the PHBV matrix and TPU elastomer. Although the sole incorporation of the TPU leads to slight improvements in toughness, the compatibilizer plays a key role in improving the overall performance of the blends, leading to a clear improvement in toughness and long-term behavior.

Effect of silanised reinforcements on thermal, wear, visco-elastic and fatigue behaviour of stitched E-glass fibre-reinforced epoxy hybrid composite

Carboxyl-terminated butadiene acrylonitrile liquid rubber toughened silicon carbide and stitched E-glass fibre-reinforced epoxy composite has been fabricated and tested for their relative effect on thermal, wear, visco-elastic and fatigue behaviour. The main objective of this present work is to explicate the importance of rubber toughening on high brittle polymer matrix and the need for secondary strengthening to improve properties. The reinforcements were surface-treated using an amine-functional coupling agent for better adhesion and uniform dispersion on matrix. The composites were made using hand layup method and post cured at 120 °C. The addition of micro rubber into epoxy resin improved the fatigue and visco-elastic properties with a marginal decrement in thermal stability and wear resistance behaviour whereas the addition of silicon carbide significantly improved the properties. A highest fatigue life cycle of 12,941 and storage modulus of 7.8 GPa was observed for composite contains 1 and 10 vol% of silicon carbide and micro rubber, respectively. The initial thermal stability of composite, which contains 2 and 10 vol% of reinforcement measures 348 °C and the lowest coefficient of friction of 0.36 and specific wear rate of 0.028 mm3/Nm. The Scanning electron microscope images illustrate uniform dispersion and improved adhesion of silane surface-modified reinforcements in epoxy matrix. These high toughness polymer composites could be used in high load-bearing engineering applications wherever possible.

Chip formation mechanism during orthogonal cutting of rubber microparticles and silica nanoparticles modified epoxy polymers

The addition of well-dispersed nanoparticles can significantly increase the mechanical properties and toughness of epoxy polymers. In this study, an epoxy resin was modified by addition of silica nanoparticles, (CTBN) rubber microparticles and a combination of both. An in-situ orthogonal cutting rig combined with high magnification and high-speed imaging system was used to determine the effects on the chip formation mechanism and machining induced damage to the material. This study indicates that chip formation in silica-modified epoxy is governed by a fracture process with large cracks both at the machined surface level and subsurface within the chip formation zone. The presence of rubber enables larger plastic deformation within the epoxy-modified polymer as the toughening mechanism of the rubber deflects the generated cracks within the primary deformation zone. The magnitude of machining induced damage was found to be lower for rubber microparticles and was correlated with a rubber toughening mechanism observed during cutting. The higher magnitude of machining induced damage of silica-modified epoxy was linked to the material’s poor resistance to crack initiation and growth. These findings of the effect of rubber microparticles and silica nanoparticles on chip formation process will give engineers a greater ability to create a trade-off between filler properties vs material properties vs machining induced damage during Design for Manufacturing (DFM) stages of a product design.

Experimental investigation of the dynamic fracture of a class of RT-PMMAs under impact loading

The present work aims to investigate experimentally the crack arrest capability and dynamic fracture mechanisms under impact loading of three commercial, rubber-toughened (RT) PMMA grades differing by their rubber nano-particle concentration and resulting Charpy impact toughness. For that purpose, Kalthoff and Winkler (KW)-like impact tests were performed using gas launcher considering impact velocities ranging between 20 and 100 m/s. A high-speed camera was used to record the projectile/specimen interaction and the progressive failure of the specimen. The fracture surfaces of the fragments were observed using a scanning electron microscope (SEM). It is seen that the higher the impact velocity the larger the number of fragments. On the other hand, it is shown that increasing the rubber nano-particle concentration favors the crack arrest capability under impact loading by promoting inelastic deformation, reducing the crack propagation velocity, limiting crack multi-branching, and reducing the number of fragments.

Examining an Alternative Molecular Mechanism To Toughen Glassy Polymers

Contrasting the conventional rubber-toughening mechanism, we show that the new PMMA-based rubber-toughened nanocomposite (PMMA-rt/nc) achieves the desired rubber toughening through molecular-level ...

Blends of tri-block copolymers and addition curing resins: Influence of block copolymer-resin compatibility on toughness and matrix properties on toughenability

In any sort of rubber toughening of thermosets, there are two principal influences on toughness: Morphology of the elastomer particulate phase and toughenability of the matrix resin. These two factors are difficult to separate experimentally. A new approach is presented which is based on large numbers of data. By analysing property-property-relationships an attempt is made to identify generalizable rules. A tri-block copolymer (PCL-PDMSi-PCL) is analysed in detail: By varying the molecular weights of the compatible and incompatible blocks in two different epoxy resins the influence of morphology on toughness is studied. Linear (Tg and rubbery plateau modulus) and non-linear (yield stress and post-yield behaviour) matrix properties are examined for a larger number of resin/curing agent combinations toughened with three different toughening agents in order to elucidate which matrix property controls toughenability. The same resin/curing agent array was used to study the influence of matrix polarity on morphology and properties for one PCL-PDMSi-PCL tri-block-copolymer.

Synergistic Mechanisms Underlie the Peroxide and Coagent Improvement of Natural-Rubber-Toughened Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Mechanical Performance.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a promising bio-based and biodegradable thermoplastic with restricted industrial applications due to its brittleness and poor processability. Natural rubber (NR) has been used as a toughening agent, but further physical improvements are desired. In this study, rubber toughening efficiency was significantly improved through the synergistic use of a trifunctional acrylic coagent and an organic peroxide during reactive extrusion of PHBV and NR. The rheological, crystallization, thermal, morphological, and mechanical properties of PHBV/NR blends with 15% rubber loading were characterized. The peroxide and coagent synergistically crosslinked the rubber phase and grafted PHBV onto rubber backbones, leading to enhanced rubber modulus and cohesive strength as well as improved PHBV–rubber compatibility and blend homogeneity. Simultaneously, the peroxide–coagent treatment decreased PHBV crystallinity and crystal size and depressed peroxy-radical-caused PHBV degradation. The new PHBV/NR blends had a broader processing window, 75% better toughness (based on the notched impact strength data), and 100% better ductility (based on the tensile elongation data) than pristine PHBV. This new rubber-toughened PHBV material has balanced mechanical performance comparable to that of conventional thermoplastics and is suitable for a wide range of plastic applications.

Effect of core–shell rubber toughening on mechanical, thermal, and morphological properties of poly(lactic acid)/multiwalled carbon nanotubes nanocomposites

ABSTRACTThe effect of core–shell rubber (CSR) toughening on mechanical and thermal properties of poly(lactic acid)/multiwalled carbon nanotubes (PLA/CNT) nanocomposites were investigated. The nanocomposites were prepared by direct melt blending method in a counter‐rotating twin‐screw extruder. The contents of CSR were varied between 5 and 20 wt % while the content of CNT was kept at 5 phr. The extruded samples were injection molded into the desired test specimens for mechanical and thermal properties analysis. The impact strength of PLA/CNT increased with increasing CSR content with concomitant decrease in tensile strength and modulus. Interestingly, the flexural strength increased at low CSR content before decreasing at 15 and 20% content. Differential scanning calorimetry analysis on the second heating cycle shows no crystallinity content for PLA/CNT and all CSR toughened PLA/CNT nanocomposites, while thermogravimetric analysis shows lower thermal degradation of all CSR toughened PLA/CNT as compared to PLA/CNT nanocomposite. This study reveals significant correlation between CSR loading with the mechanical and thermal properties of the nanocomposites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2019,136, 47756.

Rubber Toughening of Polylactic Acid (PLA) with Poly(butylene adipate-co-terephthalate) (PBAT): Mechanical Properties, Fracture Mechanics and Analysis of Ductile-to-Brittle Behavior while Varying Temperature and Test Speed

The present work fits into the stream of study and analysis of biobased and/or biodegradable materials, considering the need to improve their properties from a technological point of view to allow their wider use in final products. In this paper a blend of an extrusion grade poly(lactic acid) (PLA) and a percentage of a particular type of high molecular weight poly(butylene adipate-co-terephathalate) (PBAT) was investigated. The blend was such that the PBAT resulted in a dispersed phase in the PLA matrix. Tensile properties, Charpy impact strength, energy absorbed by the sample during three-point bending tests, melt flow index, fracture behavior and morphology were determined to characterize PLA/PBAT blends with the aim of correlating the composition to processability and final properties. Furthermore, analytical models were applied to check if variations of the mechanical properties with an increase of the rubber content were in agreement with existing predictive theories. To evaluate the fracture behavior, starting from the Load Separation Criterion, “material key curves” of the materials, a support for a comparative study (macroscopic scale) of the plastic deformational mechanisms involved in the fracture process was achieved.The influence of the deformation rate and the temperature on the toughness of the PLA/PBAT was investigated. In particular, the ductile-to-brittle transition temperature, at a fixed test speed was estimated and a theoretical model, which is useful to predict the absorbed energy by varying the deformation rate, was proposed. This last model was validated by comparing the resulting analytical equation with the experimental data obtained through three-point bending and impact tests at different velocities.

Toughening poly(lactic acid) with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers

This study describes the toughening of poly(lactic acid) (PLA) through blending it with poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymers (EPE, Pluronic®) at loadings less than 10 wt%. The miscibility of EPE copolymers in PLA was examined by thermal, morphological, and rheological analysis. Copolymers with low molecular weight and low poly(propylene oxide) (PPO) content were more miscible with PLA but less efficient as a toughening agent. In contrast, copolymers with high PPO content and high molecular weight formed droplets in the PLA and significantly increased the ductility of PLA at 5 wt% loading. More importantly, it was found that the toughening mechanism in those toughened PLA/EPE blends is similar to “rubber toughening of brittle plastics” rather than plasticization. Since the refractive indices of PLA and EPE are nearly matched, the blends were transparent. For the first time, the rheological properties of PLA/EPE blends are studied. Both the miscible and immiscible blends exhibited lower viscosity than neat PLA on account of different mechanisms. The low viscosity of the miscible blends resulted from the plasticization effect of the molecularly dissolved EPEs while the low viscosity of the immiscible blends resulted from the lubrication effect of the phase-separated EPE liquids. This lubrication effect also led to low adhesion on metal surfaces.

Cavitation-crazing transition in rubber toughening of poly(lactic acid)-cellulose nanocrystal composites

In this work, the mechanism behind rubber toughening of poly(lactic acid)/cellulose nanocrystal-g-rubber-g-poly(d-lactide) (CNC-rDx-PDLA) composites was elucidated through systematic study of the effects of rubber segment content (length) in CNC-rDx-PDLA nanofillers and the nanofiller concentrations on the deformation behavior of the nanocomposites. It was shown that with an increase of rubber segment length and rubber filler concentration, the elongation at break of the resulting composites increased. Moreover, a dramatic increase in elongation at break (from 20% to 200%) was observed when the rubber segment content (length) in the CNC-rDx-PDLA nanofillers was increased from 52 to 68%. Cavitation mechanism was found dominant when the rubber segment content in the nanofillers was 52% and below, whereas, stable crazes were formed and followed by fibrillation when the rubber segment content in the nanofillers was increased to 68%, which was evident by small angle X-ray scattering (SAXS) study and scanning electron microscopy (SEM) analysis. The existence of a transition from cavitation to crazing in the composite systems could be attributed to a more mobile rubber phase because of longer rubber chain length. Our study suggests that the effective toughening mechanism for thermoplastics such as PLA is crazing induced plastic deformation.

Structure and properties of NR- and XNBR-toughened polypropylene produced with latex by melt compounding

Binary blends composed of polypropylene (PP) and natural rubber (NR) or carboxylated acrylonitrile butadiene rubber (XNBR) were produced in batch-type melt compounding process. The rubbers used as toughening agents were introduced into PP in up to 20 wt% in their dry and latex forms. Structure-property relationships of the blends were studied. Both NR and XNBR were homogenously dispersed in the PP matrix: XNBR in microscale, NR in the submicronic scale. Fracture toughness and energy, determined on notched Charpy specimens, were improved by rubber toughening, however, at the cost of stiffness and strength, determined in tensile tests. NR toughened blends were superior to blends containing XNBR with respect to impact resistance. The introduction of rubbers in latex form resulted in slightly better mechanical performance compared to addition in dry form.

Effects of glass fiber reinforcement and thermoplastic elastomer blending on the mechanical performance of polylactide

Abstract The purpose of this study was to investigate how optimum mechanical properties (strength-modulus-toughness) of inherently very brittle polylactide (PLA) could be obtained by reinforcing with E-glass fibers (GF) and blending with thermoplastic polyurethane elastomer (TPU). Composites and blends were compounded by twin-screw extruder melt mixing, while specimens were shaped by injection molding. SEM analyses revealed that 15 wt% GF and 10 wt% TPU domains, alone and together, could be uniformly distributed in the PLA matrix leading to significant improvements in properties. Mechanical tests indicated that use of TPU blending alone resulted in enormous increases in the ductility and fracture toughness values, while GF reinforcements led to significant increases in strength and elastic modulus values. When GF and TPU were added together, it was observed that crack deflection, debonding and fiber pull-out toughening mechanisms of GF reinforcements were as effective as the rubber toughening mechanism of TPU blending.

Characterization of PP/TPV/MMT Ternary Nanocomposites Produced by Injection Molding

SummaryOne of the most valued and required features of new polymers are a high level of stiffness combined with good toughness. In this way, it seems useful to combine nanoclay reinforcement with rubber toughening to balance end use performance. In this work, the feasibility of producing this kind of nanocomposites by direct injection molding is evaluated. The performance of actual injected pieces of polypropylene (PP) compounded with thermoplastic vulcanizate (TPV) and organoclay (MMT) is analyzed and compared. Ternary composite presents low warpage and so better final quality. Morphology developed in actual pieces is influenced both by processing and by MMT presence, this morphology giving place to alternative deformation mechanisms and crack arrest. Also, a good impact resistance compared with neat PP is observed. Weld lines are diluted and they do not act as stress concentrators, this being of mechanical and aesthetical interest. The use of PP/TPV/MMT seems to be promising for injected moldings.

The role of surface modified TiO2 nanoparticles on the mechanical and thermal properties of CTBN toughened epoxy nanocomposite

The primary objective of this study was to investigate the role of surface modified TiO2 nanoparticles on the mechanical and thermal properties of rubber toughened epoxy nanocomposite. TiO2 nanoparticles were surface modified using 11-aminoundecyltriethoxysilane (TiO2-AUTES) and n-octyltriethoxysilane (TiO2-OTES) and the successful functionalization of nanoparticles was established by performing FTIR, contact angle, and TGA measurements. The graft density of silane groups on TiO2 nanoparticles was established to be 13.7 % for TiO2-AUTES and 11.4 % for TiO2-OTES. Functionalized TiO2 (fTiO2) was mixed with carboxyl-terminated butadiene (CTBN) toughened epoxy by ultrasonication followed by the addition of curing agent, and the overall mixture was blended with planetary shear mixer. The loss in the modulus of epoxy due to addition of rubber toughener was offset by the addition of nanoparticles. One of the significant findings of the work was the observed trend in the fracture energy of the samples: fTiO2 filled CTBN toughened epoxy >TiO2 filled CTBN toughened epoxy >TiO2 filled epoxy >CTBN toughened epoxy >epoxy resin. The findings of our work show promise for use of TiO2 nanoparticles in conjunction with CTBN toughener as fillers for improving the toughness of epoxy resin without comprising the tensile strength of advanced structural materials.

Determination of the size of the Representative Volume Element (RVE) for the simulation of heterogeneous polymers at finite strains

The definition of the size of the Representative Volume Element (RVE) is extremely important for the mechanics and physics of heterogeneous materials since it should statistically represent the micro-structure of the material. In the present contribution, a methodology based on statistical analysis and numerical experiments is proposed to determine the size of the RVE for heterogeneous amorphous polymers subjected to finite deformations. The approach is applied to Rubber Toughened Polystyrene (RT-PS) composed by a two phase random micro-structure. Different micro-structural samples with two different percentages of rubbery particles, namely 10% and 15%, inside the micro-structure are studied. Periodic boundary conditions (PBC) are enforced to the RVE due to their fast convergence to the theoretical/effective solution when the RVE size increases. The Finite Element Method (FEM) is used in combination with mathematical homogenization to obtain the macro-stress. Two criteria are proposed for the RVE size determination. The proposed statistical-numerical approach is general and easy to use, when compared to the previously proposed approaches, and covers other criteria available in the literature.