Thermoplastic Particles Research Articles

Synergistic enhancement of fracture toughness in multiphase epoxy matrices modified by thermoplastic and carbon nanotubes

Herein, we report the development of multiphase epoxy-based nanocomposite blends with enhanced fracture toughness and controlled microstructure. The blends are based on bifunctional and tetrafunctional epoxy resins, suitable for a wide range of applications particularly as matrices for advanced high temperature fibre reinforced composites with glass transition temperatures exceeding 200° Celsius. The multiphase blends comprise nanoscale (carbon nanotubes) and microscale (phase separating thermoplastic) inclusions which together form unique multiscale morphologies capable of dissipating crack energy through different energy absorption mechanisms. This work provides, for the first time, an in-depth investigation of the interactions between the nano- and micro-scale toughness modifiers which under appropriate conditions lead to a synergistic enhancement in the fracture toughness of the resin. A secondary agglomeration of carbon nanotubes during curing was shown to be suppressed by the phase separating thermoplastic particles, leading to a well dispersed state, justifying the synergistic increase in fracture toughness of the resulting blends. The molecular architecture of the epoxy matrix, in particular, the number of epoxide functional groups, was shown to be of significant importance in determining the final microstructure of the modified blends following curing reaction.

Development and Practical Application of Low-Temperature Sintering Nano Ag for Semiconductor IC Bonding

In recent years, lead-free has been promoted by the RoHS Directive which bans the use of lead in electronic devices, and nano Ag die attach pastes has attracted attentions. Nano Ag particles show high electrical and thermal conductivity, but generally require Au or Ag plating on the surface of the substrate. Therefore, demands for Cu substrate without the plating are also increasing to reduce costs. This paper deals with the fundamental study on nano Ag pastes newly developed with a unique approach. The technology provides a low-temperature sintering capability without pressure during cure process. In addition, resin reinforcing technology and lowering modulus technology have been developed to improve the mechanical properties. By adding epoxy resins, the porous area is filled with the resin and the sintered structure is reinforced. Additionally, the reliability can be more improved by thermoplastic resin particles. To meet the demand for the applications without Ag or Au plating, nano Ag pastes for bare Cu substrate have newly been developed. By using several types of Cu substrates without plating, surface analysis and bonding properties of the pastes were investigated in this study.

Effect of the characteristics of nylon microparticles on Mode-I interlaminar fracture toughness of carbon-fibre/epoxy composites

Interleaving a laminated composite with thermoplastic particles is known as an effective method to improve the interlaminar fracture toughness. In this work, to provide useful insight into what particle characteristics are the most critical to the toughening effect, the interlaminar fracture behaviours of carbon fibre/epoxy composites interleaved with different types of nylon 6 and 12 particles were investigated in the same range of particle areal weights.The results showed the particle size affects the toughness only when the particle–matrix interfacial bonding is well established, which is related to the curing temperature relative to the melting temperature of the particle. High interfacial bonding strength allowed the particles to be plastically deformed while bridging the crack, and smaller particles were more effective due to the increased density of particle bridging. It was also found that both the particle size and shape affect thickening of the interlayer, which can cause a knockdown of in-plane laminate properties due to the reduced fibre volume fraction.

Flexible thermoplastic starch films functionalized with copper particles for packaging of food products

Biodegradable films based on thermoplastic corn starch (TPS) and copper particles with antimicrobial capacity were developed. Copper nanoparticles (Cu) and silica coated copper microparticles (Si-Cu) in the range of 0.25 to 5% were used. Composite films were obtained by melt-mixing and subsequent thermo-compression. Particles distribution within TPS matrix and the presence of some pores and cracks, induced by Si-Cu particles, was evaluated by SEM. The presence of both fillers gave composite films a brown pigmentation and decreased their transparency; these effects were more pronounced at higher particles concentrations. Regarding mechanical properties, copper particles at 1 and 5% acted as reinforcing agents increasing the maximum tensile strength but their presence lead to a decrease in elongation at break, affecting films ductility. Composites inhibited the growth of Gram+ and Gram- bacteria, demonstrating their antimicrobial capacity. Copper effectively migrated to a simulant of aqueous foods and naked particles concentration in the simulant medium resulted higher than the minimum inhibitory concentration for bacteria. The characteristics and properties of developed composite films make them an interesting material for food primary packaging, mainly for meat fresh products.

Effect of low melting temperature polyamide fiber-interlaced carbon fiber braid fabric on the mechanical performance and fracture toughness of CFRP laminates

Fracture toughness and epoxy matrix brittleness have been main issues in carbon/epoxy composites. Various studies have been reported to improve the fracture toughness and brittleness of the carbon/epoxy composites. Although conventional method such as toughened epoxy matrix dissolving method, interleaving with a thermoplastic interlayer method, incorporating with a thermoplastic particles method improve the fracture toughness and brittleness of the carbon/epoxy composites, there have been no significant improvement. Therefore, in this study, due to improve the fracture toughness and brittleness of the carbon/epoxy composites, applied the carbon fiber/low melting temperature polyamide fiber co-braid fabric. In addition, the toughened effect of carbon fiber co-braid fabric with low melting temperature polyamide fiber and high melting temperature polyamide fiber were investigated. The carbon/epoxy composites manufactured by carbon fiber/low melting temperature polyamide fiber co-braid fabric, the fracture toughness significantly improved about 293% compared to the pristine specimens.

Cure-dependent microstructures and their effect on elastic properties of interlayer toughened thermoset composites

To shorten the cure cycle for thermoset prepreg composites, we can either increase the heating rate or the curing temperature. However, this raises the question whether modifying the cure cycle affects the laminate microstructure and physical and mechanical properties. Current state-of-the-art aerospace prepreg composites incorporate thermoplastic particles into the interlayer to increase delamination and impact resistance, which creates a more complicated composition and laminate microstructure. This research investigates the effect of curing conditions on the microstructure and elastic properties of an interlayer toughened prepreg system, Toray's T800SC/3900-2B. Laminates were processed to the same degree of cure using cure cycles with different heating rates. Optical microscopy showed that microstructural characteristics such as the interlayer thickness, particle shape, particle volume fraction and inter-particle distance are dependent on curing conditions. It was found that the glass transition temperature of the toughening particle, the resin viscosity and the elastic deformation of the fibre bed are important for the cure-dependent microstructural evolution at the pre-gelation stage. The out-of-plane lamina shear modulus (G13) dependence on temperature of fully cured laminates was measured with Dynamic Mechanical Analysis (DMA). The lamina G13 decreases with increasing cure cycle heating rate at 150–200 °C, where toughening particles are rubbery and the matrix is glassy. A micromechanical model demonstrates that the reduction of lamina G13 at higher heating rates results from a decrease in the interlayer shear modulus. Interlayer microstructural features such as particle volume fraction, particle aspect ratio and inter-particle contact contribute to the cure path dependence of the interlayer shear modulus. This study provides insight into the fundamental processing behavior of interlayer toughened prepregs and the influence on elastic properties.

Robust waterproof and self-adaptive breathable membrane with heat retention property for intelligent protective cloth

Wearable materials with properties of personal thermal management and self-adaptive breathability have attracted increasing attention due to urgent demand for energy and resources sustainable development. Particularly, ideal garment for utilizing in cold weather should be equipped with multifunctional properties, for instance, warmth, waterproofness, self-adaptive breathability, and self-cleanness. This study reported an all-around intelligent hybrid membrane based on synthesizing thermal-humid-sensitive thermoplastic polyurethane (THSPU) and blending silica aerogel particles (SAs) through a facile method. The obtained hybrid membrane exhibited robust waterproofness and self-adaptive breathability with varying humidity and temperature as well as warmth retention property. At a constant temperature of 25 ℃, by increasing relative water vapor partial pressure from 10% to 70%, water vapor transmission (WVT) increased from 140 g/m2·24h to 4400 g/m2·24h. At cool environment (5 ℃), WVT retains a low value of 1000g/m2·24h while WVT shows a significant increase to 4200 g/m2·24h at room temperature of 25 ℃. Besides, it is firstly revealed that the hybrid THSPUs membrane possesses robust hydrostatic pressure of 17,800 mmH2O and integrated mechanical strength of 35 MPa for broken strength, 750% for broken elongation. Moreover, the obtained hybrid membrane and its laminate textile exhibit heat retention property than commercial product (Gore-Tex). It is believed that the hybrid THSPUs membrane is an effective and scalable product for personal thermal management, smart wearable application.

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.

Study on cohesion and adhesion of high-viscosity modified asphalt

High-viscosity modified asphalt (T-HVA) specifically used for drainage/permeable asphalt pavement was prepared by composite modification of matrix asphalt using a thermoplastic elastomer (TPE) and SBS particles. The performance of the high-viscosity modified asphalt (T-HVA) was characterized by conventional tests, and compared with the performance of 70# asphalt, SBS modified asphalt and engineering high-viscosity asphalt. The results show that all the indicators of the modified asphalt are better than that of the matrix asphalt, and the dynamic viscosity of the T-HVA is greater than one million Pa.s, which is much higher than that of the engineering high-viscosity asphalt and SBS modified asphalt. The segregation test shows that the compatibility and stability of T-HVA asphalt are better than others. Cohesion test shows that the cohesion of the modified asphalt is obviously better than that of the matrix asphalt at different temperatures, and the higher the temperature, the better the cohesion, and the cohesion of the T-HVA before and after aging is relatively stable. The result of the peeling rate measured by ultraviolet spectrophotometry shows that: the peeling rate of the T-HVA is the smallest, i.e., the adhesion is the best, and is consistent with the dynamic viscosity, i.e., the greater the dynamic viscosity, the better the adhesion. Based on the comprehensive analysis of various indicators. The results of Performance Grade (PG) grading test show that T-HVA has good high and low temperature performance. The modified materials with good dispersion in asphalt and the TPE particles as high elastic interlocking units are uniformly distributed in the network structure; The T-HVA has relatively strong aggregate adhesion and cohesiveness, exhibits good high temperature stability and low temperature flexibility, and is suitable for drainage/permeable asphalt pavement.

Effect of Inter-laminar Toughened Layers on Process-induced Strain and Deformation of L-shaped Composites

L-shaped composites are fundamental parts of complex-shaped structures and it is well-known that shape distortion (i.e., spring-in deformation) arises after curing due to the orthotropic nature of composites. This residual deformation significantly increases the manufacturing costs, attracting significant attention to the mechanisms of spring-in deformation. Recently developed aerospace-grade composites include inter-laminar toughened layers composed of thermosetting resin and thermoplastic particles to enhance inter-laminar fracture toughness and improve impact resistance. Even though inter-laminar toughened layers can affect process-induced strain and deformation, their effects have not yet been studied in detail. Therefore, fiber-optic-based internal strain measurements were performed and residual deformation of L-shaped parts with inter-laminar toughened layers was investigated in this study. The through-thickness cure shrinkage strain at the corner part was relaxed and the spring-in angle decreased by holding the parts at the cure temperature, indicating that the viscoelasticity of the thermoplastic particles is important. Viscoelastic finite element analysis supported this finding and indicated that the effect of the toughened layers on the residual deformation should be considered to optimize curing processes.

Effect of inter-laminar toughened layers on process-induced strain and deformation of L-shaped composites

L-shaped composites are fundamental parts of complex-shaped structures, and it is well-known that shape distortion (i.e., spring-in deformation) arises after curing due to the orthotropic nature of composites. This residual deformation increases the manufacturing costs, attracting significant attention to the mechanisms of spring-in deformation. Meanwhile recent aerospace-grade composites include inter-laminar toughened layers composed of thermosetting resin and thermoplastic particles to enhance the inter-laminar fracture toughness and to improve the impact resistance. Even though the inter-laminar resin layers can affect the process-induced strain and deformation, their effects have not yet been studied in detail. Therefore, this current study performed fiber-optic-based internal strain measurement and evaluated the residual deformation of L-shaped parts with inter-laminar resin layers. Through-thickness cure shrinkage strain at the corner part was relaxed and the spring-in angle decreased by holding the parts at the cure temperature, indicating that viscoelasticity of the thermoplastic particles is important. Viscoelastic finite element analysis supported this finding and indicated that the effect of inter-laminar toughened layers on the residual deformation should be considered to optimize curing processes.

Heat transfer simulation of the cure of thermoplastic particle interleaf carbon fibre epoxy prepregs

Thermochemical properties are needed to develop process models and define suitable cure cycles to convert thermosetting polymers into rigid glassy materials. Uncertainty surrounding the suitability of thermal analysis techniques and semi-empirical models developed for conventional composite materials has been raised for the new class of particle interleaf materials. This paper describes kinetics, conductivity, heat capacity and glass transition temperature measurements of HexPly® M21 particle interleaf material. Thermal models describing conventional, non-particle epoxy systems were fit to the data and validated through a thick-section cure. Results from curing experiments agree with heat transfer simulation predictions, indicating that established thermal analysis techniques and models can describe polymerisation and evolving material properties during processing of a material representing the class of interleaf toughened systems. A sensitivity study showed time savings up to about 20%, and associated energy-efficiency-productivity benefits can be achieved by using cure simulation for particle interleaf materials.

Experiments and modeling of single plastic particle conversion in suspension

Conversion of single high density polyethylene (PE) particles has been studied by experiments and modeling. The experiments were carried out in a single particle combustor for five different shapes and masses of particles at temperature conditions of 900 and 1100°C. Each experiment was recorded using a camera. For selected experiments, the center and surface temperatures of the particles were measured using a thermocouple and an IR camera, respectively. During each experiment, the polyethylene particles went through melting, deformation, and decomposition. After the start of decomposition, the surface temperature became almost constant within the range of 480–550°C. The total conversion times of polyethylene particles were mainly influenced by the reactor temperature and particle mass, and the effect of particle shape was less significant. A non–isothermal 1D model was established and validated against the experiments as well as literature data. Furthermore, a simplified isothermal model appropriate for CFD applications was developed, in order to model the combustion of plastic particles in cement calciners. By comparing predictions with the isothermal and the non–isothermal models under typical calciner conditions, it is shown that the accuracy in prediction of the total conversion times of thermoplastic particles is within ± 30%, for particles lighter than 1000 mg.

Thermal and mechanical properties of wood‐plastic composites filled with multiwalled carbon nanotubes

ABSTRACTWood plastic composites (WPCs) are a new generation of green composites which can come mostly from recycled materials. This study focuses on the thermal conductivity and mechanical properties of WPCs filled multiwalled carbon nanotubes (MWCNTs). The thermal conductivity increases with increasing amount of MWCNTs and decreases with increasing temperature. By comparing the temperature changes of specimens during heating and cooling processes, WPCs with higher MWCNTs contents presents higher average temperature when heated until equilibrium temperature. From differential scanning calorimeter test, the melting temperatures of MWNTs reinforced WPCs change slightly, but the crystallinity is reduced with the increasing amount of MWCNTs. Based on a series of laboratory experiments carried out to investigate the mechanical performance, it can be concluded that the addition of the MWCNTs decreases the mechanical properties of WPCs due to the decohesion between thermoplastic matrix and MWCNTs particles under stress. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46308.

Solar bricks for lunar construction

A novel brick manufacturing technique is described, whereby natural mineral soil and added thermoplastic polymer particles are mixed, heated, and allowed to cool, to enable polymeric bonding of the soil grains. Experimental results indicate that the gradation of the soil plays a significant role on the compression strength of the manufactured bricks. This is because gradation controls fabric in highly compacted granular soils. A fabric that features pore filling by progressively smaller grains results in an increased likelihood of added polymer localization at intergranular contacts and therefore high strength. A conventional convection oven and a solar oven were used independently to implement the heat treatment; the comparison reveals the potential use of the latter for low energy cost brick construction in remote locations and nontraditional environments such as the Moon.

Dissipating mechanical mechanisms and their link to morphology in polyamide toughened carbon-epoxy UD laminates

Toughened carbon/epoxy laminates include thermoplastic particles. Depending of the curing cycle, the morphology of the thermoplastic phases can differ. This strongly impacts the degradation scenario of the composite. In the present paper, such reinforced laminates are evaluated. Different morphologies are studied. Classical experiments are used to evaluate the impact of the morphology on the damage and plasticity evolution laws at the scale of the ply. Some elements to model the toughening mechanism at the inter-ply scale are given and limitations are discussed.

Effect of confinement level and local heating on healing efficiency of self-healing particulate composites

Abstract Shape memory polymer based self-healing materials are a special class of materials that have been the subject of much research over the past decade and many impactful discoveries have been made thus far. In a previous study (Compos. Sci. Technol. 2010; 70: 1419–1427) it was shown that in order for efficient healing, confinement during healing is essential. It was also shown that use of a two-step close-then-heal (CTH) method during healing of damaged shape memory particulate composites provided molecular scale healing. The present study further investigates the influence of confinement levels and local heating on the healing efficiencies of a polystyrene based shape memory polymer with 6% by volume of thermoplastic particle additives (copolyester as solid healing agent). The healing process was conducted by locally heating fractured cylindrical specimens at three levels of lateral (radial) confinements and axial constraints, and varying heating times. It is found that, lateral confinement levels, axial constraints, and heating times all control the healing efficiency. Almost complete strength recovery is obtained with 100% lateral confinement, 12 MPa axial constraint stress, and 60 min of heating time.

Cure path dependency of mode I fracture toughness in thermoplastic particle interleaf toughened prepreg laminates

The effect of cure cycle on fracture behaviour of a commercial thermoplastic particle interleaved prepreg system was investigated. Laminates were manufactured at 700kPa in an autoclave using eight different thermal cycles that included both raising the cure temperature above the standard 180°C cure cycle and incorporating an intermediate dwell stage between 150 and 170°C prior to reaching the 180°C cure temperature. Double cantilever beam tests were conducted on specimens from the cured laminates. The stick–slip crack behaviour, observed in samples manufactured using the standard cure cycle, changed to stable crack growth when processing deviated by 10°C. The mode I fracture toughness values were reduced by 11–22% when incorporating an intermediate dwell stage before the final cure temperature. Scanning electron microscopy inspection of the fracture surfaces showed differences between samples made by standard cure cycles and those made using process deviations.

Healing-on-demand composites based on polymer artificial muscle

In this study, a new polymer artificial muscle based healing-on-demand composite was prepared and characterized. The composite consists of polymer artificial muscle made of commercial fishing line, thermoset host, and thermoplastic particle. Three-point bending damage to the beam sample can be healed even at a constrained boundary condition upon local heating, undergoing a close-then-heal procedure. The fractured beams were heated locally by a heat gun for 10 min. The healing efficiency was investigated at both free boundary condition and fixed boundary condition. The fast contraction of artificial muscle brings the fractured surfaces in spatial proximity; simultaneously, the melting thermoplastic agent fills the crack via capillary action and bonds the two fracture surfaces. With 60% prestrain of the reinforcing polymer artificial muscles (8% volume fraction), over 60% of healing efficiency was achieved at free boundary condition and 54% at fixed boundary condition after repeated damage-healing events. Due to its low cost, high healing efficiency, good compatibility, and excellent flexibility, we envision that the polymer artificial muscle will be a new device in designing next generation healing-on-demand polymer composite.

A multiscale theory of self-crack-healing with solid healing agent assisted by shape memory effect

Solid healing agents, such as thermoplastic particles, have been widely used in molecular healing of thermosetting polymers, including conventional thermosetting polymers such as epoxy and thermosetting shape memory polymers (SMPs) such as polystyrene. Despite extensive experimental developments in this field, there is an urgent need for healing theories with the ability to correlate molecular level healing events to the bulk scale recovered material properties. A multiscale healing constitutive theory is developed in this manuscript for self-crack-healing composites with embedded solid healing agents. It is assumed that the matrix is made of SMP; and the model accounts for several microscopic healing processes including: (a) rearrangement of free crack surfaces, (b) surface approaching due to shape memory effect, (c) wetting the free surfaces by the molten solid healing agent, (d) diffusion of the solid healing agent, which has been molten upon heating, into the crack surfaces, and (e) randomization. The Continuum Damage Healing Mechanics (CDHM) is utilized to bridge the microscopic and bulk scales. The healing parameters correlate the microscopic level descriptions of the healing to the recovery of bulk material properties. The model is then introduced into the ABAQUS, through user-defined coding, and it is shown that it correlates well with the experimental observations. The developed physically consistent multiscale theory provides material designers with the ability to optimize their self-healing systems via computer aided simulations.