Thermoplastic Content Research Articles

Analytical fracture toughness model for multiphase epoxy matrices modified by thermoplastic and carbon nanotube/thermoplastic

The introduction of a toughener is considered one of the most effective approaches to address the brittleness of epoxy resins. This paper introduces an analytical model for investigating the Mode-I fracture toughness of modified epoxy resins by including a phase-separating thermoplastic (TP) polymer, polyetherimide (PEI), and the combination of PEI and carbon nanotubes (CNTs). The fracture energy contributions from different toughening mechanisms, identified by the fractographical studies of the modified epoxy resins, were calculated, in which the energy contribution from TP deformation was obtained by molecular dynamics model simulation. The developed fracture toughness model showed satisfactory agreement with the experimental data. In the TP/epoxy binary system, the increase in TP content from 5 to 20 wt% resulted in a rise in the contribution of TP deformation (crack bridging) leading to a commensurate increase in fracture toughness from 33% to 70%. This transformation established TP deformation as the dominant mechanism for crack energy dissipation. In the CNT/TP/epoxy ternary system, from the model, the observed synergy in toughness was attributed to the improved dispersion of nanotubes. The developed analytical model may be used to formulate multiphase toughened resin matrices for optimal fracture toughness.

The PLA content influence selected properties of wood-based composites

The PLA content influence selected properties of wood-based composites. The aim of the research was to find how the lower (25%) and higher (50%) PLA content affects the selected properties of the obtained WPC samples. The result of the strength tests (compressive strength) shows, that the increasing content of PLA, increases the compressive strength value. The ash content value determining mineral saturation, decreasing with increasing PLA content but there is no significant difference. The moisture content was carried for wood sampleby drying the material and was figured by differences in the material weight mass. Raw material samples was compacted inside the chamber to form the composites by using high temperature (230°C) and strength not higher than 600 N. Optical analyzed was performed for analyzing the structure of the prepared sample, and comparing that structure before and after strength test. It can be concluded, that increasing thermoplastic content in biocomposites causes better strength, and it has not significant bad impact on the environment.

Effect of PC/ABS blend in thermoplastic modification of DGEBA matrix for CF/EP composite in aerospace applications

Thermoplastic blend effect in modifying DGEBA matrix is found to be effective in improving the mechanical as well as the micro-crack resistance properties of the prepared composites. The thermoplastic content is selected to be 1.5 wt% of DGEBA resin for modification via melt mixing. The modified epoxy along with 2x2 twill weave carbon fiber was used to develop specimens for testing via vacuum assisted resin transfer molding (VARTM). The blend effect of poly(acrylonitrile-butadienestyrene) (ABS) in polycarbonate (PC) shows enhancement in impact resistance (maximum 20% increase) of DGEBA based carbon fiber (CF) composites compared to the unmodified system under room conditions. The SEM images reveal high levels of heterogeneity for the modified system with lesser levels of deeper cracks and delamination, making it more stable under room conditions. The laser scanning optical profilometry reveals minimal micro-cracks formed on the modified system under 150x magnification, making it more effective for aerospace applications.

The role of poly (ethylene-co-methacrylic acid) (EMAA) on cure kinetics and thermomechanical properties of epoxy

The addition of thermoplastic to thermosetting matrix systems has been proposed as a successful strategy to produce polymers with self-healing ability. Curing mechanism of diglycidyl ether of bisphenol A/triethylene-tetramine epoxy system modified with poly(ethylene-co-methacrylic acid) (EMAA) thermoplastic healing agent was investigated in this work. The effects of thermoplastic content, particle size and dispersion on thermomechanical properties were studied. Specimens were produced with 5 wt. %, 10 wt. % and 15 wt.% EMAA with particle sizes ≤ 125 μm or ≤ 425 μm. The addition of thermoplastic produced a reduction in E’ of about 27% for samples with particles ≤ 125 μm and about 45% for samples with particles ≤ 425 μm. Samples with particle size ≤ 125 μm showed a reduction in Tg of up to 37 °C as compared to neat epoxy. In the case of samples with particle size ≤ 425 μm, no direct correlation between Tg and mass fraction of added EMAA is found. Thus, particle size played an important role on thermomechanical properties and cure kinetics of epoxy. The greater the interfacial area, the greater was the change in final properties as compared to the unmodified material. It was also observed that the mass fraction and particle size can interfere in the curing reactions, where results suggest deceleration when smaller particles (≤ 125 μm) are added in larger fractions and acceleration with increasing mass fraction of larger particles (≤ 425 μm). All experimental reactions could be fit to the autocatalytic Sourour and Kamal model with good agreement; the model was able to predict the effects of thermoplastic addition in different particle sizes and mass fractions.

MXene-functionalised 3D-printed electrodes for electrochemical capacitors

3D printing is a manufacturing technique that can be used to produce electrochemical capacitors with customised shapes and minimal material waste. However, the range of carbon-additive filaments currently commercially available is limited, resulting in 3D-printed electrodes with a poor capacitive performance due to their high thermoplastic content. Herein, a novel approach is presented for enhancing the electrochemical properties of 3D-printed electrodes, based on electrochemical activation of the electrodes followed by MXene functionalisation. Archetypal MXene, Ti3C2, has been used to modify the 3D-printed electrode surface; it has been demonstrated that it enhances the capacitance of the electrodes almost three-fold. These findings show a new route towards enhancing the performance of 3D-printed electrochemical capacitors and pave the way for further developments leading to other electrochemical applications.

Reactive Compatibilization of Multi-Hydroxy Functional Compound Based on Polyoxymethylene/Thermoplastic Polyether Elastomer Blends

Polyoxymethylene/thermoplastic polyether elastomer composites were prepared by using the chain extender based on styrene, methyl methacrylate and glycidyl methacrylate copolymer as the reaction compatibilizer. The composites were fabricated by melt extrusion, and the content of thermoplastic polyether elastomer varied from 0 to 25 phr, while the amount of the chain extender was 0.2, 0.4, and finally 0.6 phr at thermoplastic polyether elastomer content 15 phr. The reactive compatibilization and the properties of the blends were studied. It was found that the viscosity of the blends increased gradually, and the notch impact strength did not change significantly after the addition of chain extender, but the tensile modulus increased significantly.

Phase morphology and mechanical properties of polyetherimide modified epoxy resins: A comparative study

This paper presents a detailed study of the relationship between phase morphology and fracture toughness of two types of thermoplastic modified epoxy resins, a tetrafunctional and a bifunctional type. The reaction-induced phase separation of the thermoplastic (TP) during curing leads to distinct morphologies, depending on the modifier content and the functionality of the matrix. This, in turn, impacts the fracture toughness of modified epoxy resins. A transition from a particulate to a co-continuous morphology is observed at sufficiently high TP content (20 wt%) in both epoxy systems. Thermoplastic phases exhibit a significant level of plastic deformation during crack propagation followed by tearing or debonding, depending on the composition. This, in addition to the formation of shear bands in the matrix, is the most dominant energy dissipation mechanism. Higher viscosity and cross-link density of the tetrafunctional epoxy result in the formation of uniformly distributed submicron-sized thermoplastic particles, where the limited diffusion growth of thermoplastic phase, following the onset of phase separation, is further restricted.

Co-woven carbon and nylon fibres for manufacturing thermoplastic composite plaques

Thermoplastic composites are in high demand and continually growing in use due to their inherent properties. Commingled fibre is one of the recent solutions developed for thermoplastic composites, but has not yet ready for weaving. An alternative to commingling approach, co-weaving of reinforcing and thermoplastic fibres is investigated in this study. In this work, the carbon and nylon fibres were woven separately through the warp and weft directions, respectively. A 5-multilayer 3D weave architecture was designed to produce the co-woven fabrics. By varying the weft filling or pick density, a set of woven fabrics of different thermoplastic content was obtained. The hot press was used to consolidate the composite plaques. Samples of the thermoplastic composites were physically characterised through density, fibre volume fraction and void content and then optically investigated. The composite samples were also mechanically tested to determine the interlaminar shear strength via the short beam bending test. The result proves that co-weaving method for thermoplastic composites is a feasible approach as the composite shows a low void content of approximately 1.14 percent. Comparing the four co-woven composites tested in this study it is found that the maximum achievable strength (ILSS) is ~ 41.36MPa in the case of lowest matrix (PA66) and the highest fibre (CF) contents, i.e. 13PA/7CF.

Trifunctional Epoxy Resin Composites Modified by Soluble Electrospun Veils: Effect on the Viscoelastic and Morphological Properties.

Electrospun veils from copolyethersulfones (coPES) were prepared as soluble interlaminar veils for carbon fiber/epoxy composites. Neat, resin samples were impregnated into coPES veils with unmodified resin, while dry carbon fabrics were covered with electrospun veils and then infused with the unmodified epoxy resin to prepare reinforced laminates. The thermoplastic content varied from 10 wt% to 20 wt%. TGAP epoxy monomer showed improved and fast dissolution for all the temperatures tested. The unreinforced samples were cured first at 180 °C for 2 h and then were post-cured at 220 °C for 3 h. These sample showed a high dependence on the curing cycle. Carbon reinforced samples showed significant differences compared to the neat resin samples in terms of both viscoelastic and morphological properties.

Influence of Soluble Electrospun Co‐Polyethersulfone Veils on Dynamic Mechanical and Morphological Properties of Epoxy Composites: Effect of Polymer Molar Mass

AbstractElectrospun veils from copolyethersulfones (coPES) with a number‐average molar mass (Mn) of 9000 g/mol (coPES9k) and 20,000 g/mol (coPES20k) were prepared as soluble interlaminar veils for carbon fiber/epoxy composites. Dry carbon fabrics were covered with electrospun veils and then infused with an unmodified epoxy resin to prepare reinforced laminates. CoPES powder was predissolved in the unmodified epoxy to obtain an epoxy/coPES blend used for preimpregnation of laminates which were compared to the laminates obtained with resin infusion. The thermoplastic content varied from 10wt% to 20wt% for coPES9k and from 5wt% to 10wt% for coPES20k. Unreinforced samples with no carbon fabrics were also studied. The coPES9k veils showed full solubility and homogeneous morphology when added to the epoxy resin. Unreinforced samples, modified by coPES9k veils, showed only minor morphological differences compared to epoxy/coPES blends obtained from coPES9k powder predissolution. The glass transition temperatures for these samples displayed differences less than 10°C. Carbon‐reinforced samples obtained using the same route showed larger differences. The coPES20k veils showed undissolved fibers and inhomogeneous morphologies when blended with an epoxy in the unreinforced samples.

Thermal Properties of Linear Low Density Polyethylene/Thermoplastic Starch/Banana Fiber Composites

The effect of thermoplastic starch (TPS) and banana fiber contents on thermal characteristics of linear low-density polyethylene (LLDPE) matrix were investigated. The measurements from differential scanning calorimetric (DSC) and thermogravimetric analysis (TGA), proved the effectiveness of TPS and banana fiber in improving the blend degradation. On the other hand the LLDPE/TPS/banana fiber composites showed better thermal stability than the LLDPE/TPS blend, which is reflected to the LLDPE chains movement restriction. The incorporation of banana fiber into the LLDPE/TPS blends was found to interfere with the chains movement and resulting in more thermally stable and improving the blends stiffness.

Effect of Blends Ratio on Mechanical and Morphological Properties of LDPE/Thermoplastic Soya Spent Powder Blends

This study investigates the properties of blends made from low density polyethylene (LDPE) with various levels of thermoplastic soya spent powder (SSP). The thermoplastic TPSSP content was varied from 5 to 20wt % whereas epoxidised natural rubber with 50 mol % (ENR 50) act as compatibilizer to improve the interfacial adhesion between low density polyethylene and thermoplastic TPSSP. The effect of the addition of ENR 50 on the LDPE/thermoplastic TPSSP was measured by using tensile test and thermal behaviour. The tensile strength and elongation at break (Eb) decreased with increasing TPSSP content. However, the addition of ENR 50 resulted in the increment of tensile strength and Eb LDPE/TPSSP blends.

Effect of Higher Thermoplastic Starch Content on TPS/LDPE Plastics

The TPS/LDPE starch plastic was prepared in the presence of the compatibilizer after the preparation of thermoplastic starch (TPS). The effect of starch content to properties of TPS/LDPE was studied by DSC, TG, electronic tensile machine and SEM. The results showed that the system had a good compatibility between TPS and LDPE, and the thermal properties were improved because of the forming of chemical bonds. When the TPS content is more than 58.54%, the tensile strength and elongation at break decreased dramatically, the main reason is the transformation of the continuous phase and the dispersed phase.

Thermo‐reversible healing in a crosslinked polymer network containing covalent and thermo‐reversible bonds

AbstractThe self‐healing behavior of a modified ureido‐amide based thermoplastic hybrid elastomer was investigated by increasing the concentration of non‐reversible (covalent) bonds compared to reversible (hydrogen) bonds. A crosslinked polymer network was synthesized using varying amounts of diglycidylether of bisphenol A and reacting with the ureido‐amide thermoplastic. Increasing epoxy content produced a more rigid and thermally stable hybrid network, which in turn decreased overall thermo‐reversible or healing behavior. Fracture toughness recoveries varied from 25% for the system containing the greatest number of covalent bonds to well over 200% for systems containing higher thermoplastic content. Substantial levels of healing, about 62% recovery, were still achieved despite the crosslinked network having a Tg above room temperature, 31°C as measured by differential scanning calorimetry (DSC). Dynamic mechanical thermal analysis was used to monitor thermo‐reversible behavior of the elastic moduli and thus probe molecular mobility within the glassy state. The extent and rate of recovery of the elastic modulus was dominated by the extent of thermal activation above the glass transition temperature. Fourier transform infrared spectroscopic and DSC studies confirmed that reacting the thermoplastic with an epoxy resin produced a covalently bonded crosslinked network and the epoxide groups were completely consumed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

In situ polymerization of polyester-based hybrid systems for the preparation of clay nanocomposites

Polystyrene and poly(methyl methacrylate/styrene) were prepared by in situ polymerization in the presence of Cloisite 20A, and were then used to synthesize unsaturated polyester-based thermoplastic/thermoset hybrids with improved properties. This approach allows for an increased degree of dispersion and delamination of the silicate layers as well as the presence of thermoplastic chains within the thermoset resin, which improve the physical properties of the system. During curing, methyl methacrylate promotes the conversion of styrene inside the clay galleries and also in the thermoplastic-rich phase. X-ray diffraction and transmission electron microscopy (TEM) revealed a fine intercalated/exfoliated structure in the nanocomposites. Fracture tests showed that a combination of clay and thermoplastic resulted in a synergistic improvement of the fracture toughness of the nanocomposite while stiffness was maintained at the level of the unmodified polyester. The hybrid systems exhibited spherical domains of thermoplastic-rich phase dispersed in the thermoset matrix. The clay was present only in the thermoplastic-rich phase with a portion congregated at the interface between the thermoset and thermoplastic domains. Interestingly, morphological studies showed that the clay layers surrounded microgels of thermoset contained within the thermoplastic domains. Such microgels of thermoset are thought to be fewer and smaller in the hybrid systems without clay, leading to smaller and more compliant dispersed phase domains at the same thermoplastic content and reduced fracture toughness.

Comparisons of microcellular polylactic acid parts injection molded with supercritical nitrogen and expandable thermoplastic microspheres: Surface roughness, tensile properties, and morphology

Microcellular injection molding is capable of fabricating light weight, dimensionally stable plastic parts while using less material and energy. Two kinds of blowing agents, namely, supercritical nitrogen and expandable thermoplastic microspheres, were employed to produce foamed polylactic acid parts. The surface characteristics were evaluated with a 2D surface roughness analyzer and a 3D white-light interferometer surface profiler. Through surface roughness comparisons, injection molded ASTM tensile test bars with expandable thermoplastic microspheres exhibited better surface quality than their supercritical nitrogen counterparts. The tensile properties of injection molded polylactic acid tensile bars with nitrogen and expandable thermoplastic microspheres at various weight concentrations were investigated. The results showed that the polylactic acid/nitrogen parts possessed a better Young’s modulus and tensile strength. The microstructure on the fractured cross-sectional surfaces was characterized using a scanning electron microscope. As reflected by the testing results, the cell microstructure—such as cell size and cell density, and multi-layered structure with a foamed core sandwiched by skin layers—played an important role in the surface quality and mechanical properties. In addition, while an appropriate expandable thermoplastic microsphere content had a positive effect on the cell microstructure and weight reduction, too high of a concentration of expandable thermoplastic microsphere adversely affected the tensile properties and surface roughness of the microcellular polylactic acid tensile test bars.

Chlorosulfonated polyethylene–polypropylene thermoplastic vulcanizate: Mechanical, morphological, thermal, and rheological properties

AbstractDifferent thermoplastic vulcanizate (TPV) blends were prepared from elastomeric chlorosulfonated polyethylene (CSM) and thermoplastic polypropylene (PP) by employing dynamic vulcanization technique. The mechanical properties of such blends were compared in respect of their stress at 25% modulus (25%M), ultimate tensile strength (UTS), percent elongation at break, and hardness to those of pure CSM. The mechanical analysis showed substantial improvement in stress at 25%M, UTS, and hardness values with the incorporation of 15–40 parts of thermoplastic contents (PP) (per hundred parts of blend). The two‐phase morphologies were clearly observed by scanning electron microscopy studies. The thermal properties were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC studies showed a decreasing trend in glass transition temperature (Tg) and TGA studies indicated the increase in thermal stability of all TPV blends with respect to the elastomeric CSM. Rheological studies showed that there is an increasing trend in shear melt viscosity of TPV blends with the increase in PP amount as the higher content of isotactic PP used in the present case increases the melt viscosity. The TPVs obtained after the rheotron studies displayed identical shear stress/strain pattern when further subjected to the same study. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Micro-crack behavior of carbon fiber reinforced thermoplastic modified epoxy composites for cryogenic applications

Three different types of thermoplastics, poly(ether imide) (PEI), polycarbonate (PC), and poly(butylene terephthalate) (PBT) were used to modify epoxy for cryogenic applications. Carbon fiber reinforced thermoplastic modified epoxy composites were also prepared through vacuum-assisted resin transfer molding (RTM). Dynamic mechanical analysis (DMA) shows that the storage moduli of PEI, PC, and PBT modified epoxies are 30%, 21%, and 17% higher than that of the neat epoxy respectively. The impact strength of the modified epoxies at cryogenic temperature increases with increasing thermoplastic content up to 1.5wt.% and then decreases for further loading (2.0wt.%). The coefficient of thermal expansion (CTE) values of the PBT, PEI, and PC modified epoxies also decreased by 17.76%, 25.42%, and 30.15%, respectively, as compared with that of the neat epoxy. Optical microscopy image analysis suggests that the presence of PEI and PC in the carbon fiber reinforced epoxy composites can prevent the formation of micro-cracks. Therefore, both the PEI and PC were very effective in preventing micro-crack formation in the composites during thermal cycles at cryogenic condition due to their low CTE values and high impact strength.

Effect of Cure Conditions on the Generated Morphology and Viscoelastic Properties of a Poly(acrylonitrile–butadiene–styrene) Modified Epoxy–Amine System

The curing behavior, phase morphology, and dynamic mechanical characteristics of an epoxy system based on the diglycidyl ether of bisphenol A (DGEBA) and 4,4′-diaminodiphenylsulfone (DDS), modified with different amounts of poly(acrylonitrile–butadiene–styrene) (ABS), were investigated by employing differential scanning calorimetry (DSC), field-emission scanning electron microscopy (FESEM), and dynamic mechanical thermal analysis (DMTA). The effects of different curing conditions on the generated morphologies and viscoelastic properties were evaluated. The amounts of ABS in the epoxy blends were 3.6, 6.9, 10, and 12.9 wt %. The rate of the curing reaction decreased with increasing thermoplastic content and with decreasing curing temperature. Morphological analysis revealed a phase-separated morphology for the blend systems. The storage modulus (E′), loss modulus (E″), and tan δ values of the systems were measured as functions of temperature and are discussed based on the morphological behavior of the epoxy blends with different amount of ABS.

Damage healing ability of a shape-memory-polymer-based particulate composite with small thermoplastic contents

The purpose of this study is to investigate the potential of a shape-memory-polymer (SMP)-based particulate composite to heal structural-length scale damage with small thermoplastic additive contents through a close-then-heal (CTH) self-healing scheme that was introduced in a previous study (Li and Uppu 2010 Comput. Sci. Technol. 70 1419–27). The idea is to achieve reasonable healing efficiencies with minimal sacrifice in structural load capacity. By first closing cracks, the gap between two crack surfaces is narrowed and a lesser amount of thermoplastic particles is required to achieve healing. The particulate composite was fabricated by dispersing copolyester thermoplastic particles in a shape memory polymer matrix. It is found that, for small thermoplastic contents of less than 10%, the CTH scheme followed in this study heals structural-length scale damage in the SMP particulate composite to a meaningful extent and with less sacrifice of structural capacity.