Characterisation of thermoplastic matrix composites using variable frequency microwave

Abstract

In most industrial microwave processing operations, the frequency of the microwave energy launched into the waveguide or cavity containing the sample is fixed. This brings with it inherent heating uniformity problems. This paper describes a new technique for microwave processing, known as variable frequency microwave (VFM) processing, which alleviates the problems brought about by fixed frequency microwave processing. In VFM processing, microwave energy over a range of frequencies is transmitted into the cavity in a short time, e.g. 20 μs. It is therefore necessary to determine the best frequency range for processing a material. The best range frequency for microwave processing of five different thermoplastic matrix composites using the VFM facilities has been determined. The optimum frequency band for microwave processing of these five materials was in the range 8–12 GHz. This data enables bonding of the materials using microwave energy under the most favourable conditions.     

New GMT material suitable for various polymers and high glass fibre content

Abstract

As a kind of long fibre reinforced thermoplastic, a new glass mat thermoplastic (GMT)-like material is introduced. It is designed to be suitable for various polymers and high glass fibre (GF) content, which might be a promising attempt to overcome the limit of conventional GMT material (PP matrix and maximum 40 wt-% GF). The concept is based on a multi-layered hybrid structure consisting of several thin GF sub-layers and polymer films having an inherently high viscosity. They are then needle-matted all together. The capability of higher GF content was derived from the porosity changes under pressure and the cross-sectional view after impregnation. It was finally confirmed by measurement of flexural properties up to 70 wt-% of GF content in PP grade. Moreover, PA6 grade was investigated to show the other capability of multi-layered hybrid mat for various polymers.     

Effect of the various coupling agents on the mechanical and physical properties of thermoplastic‐bagasse fiber composites

Various types of bonding agents have been tried with blends of bagasse fibers and some thermoplastics such as low‐density polyethylene (LDPE), high‐density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), and polyvinyl chloride (PVC). These bonding agents are, namely, pentaerythritol tetracrylate (PETA), 1,6 hexandiol diacrylate (HDA), and dicumyl peroxide (DCP). In addition, a traditional coupling agents 3‐aminopropyltrimethoxy silane (AMPS) and di‐aminopropyltrimetoxy silane (DAMPS) were included for comparison. Electron beam (EB) irradiation is applied only for LDPE and HDPE at 40 and 10 kGy, respectively, before mixing with bagasse fibers. The data obtained reveal that incorporation of bonding agents remarkably increases the mechanical properties for all samples under investigation; the maximum improvement is observed in LDPE followed by HDPE, PP, PS, and PVC composites. Also, the physical properties enhanced but not at the same degree as mechanical properties. Among the tested bonding agents, it was found that PETA, DCP followed by DAMPS have highest efficiency in LDPE, whereas in case of HDPE, EB radiation was higher than PETA followed by DCP. PETA was superior in case of PS composites. Furthermore, PETA and HDA experienced higher efficiency than DAMPS and AMPS in case of PP and PVC composites. Comparison between the properties of thermoplastic composites and medium density fiberboard (MDF) reveals that most of the properties of thermoplastics composites are better than MDF. However, modulus of rupture of MDF was found to be slightly higher than thermoplastics except for PVC composite. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Thermal and ablative properties of binary carbon nanotube and nanodiamond reinforced carbon fibre epoxy matrix composites

The thermal and ablative properties of carbon nanotube (CNT) and nanodiamond (ND) reinforced carbon fibre epoxy matrix composites were investigated by simulating shear forces and high temperatures using oxyacetylene torch apparatus. Three types of composite specimens—(i) carbon fibre epoxy matrix composite (CF/Epoxy), (ii) carbon fibre epoxy matrix composite containing 0.1 wt-% CNTs and 0.1 wt-% NDs, and (iii) carbon fibre epoxy matrix composite containing 0.2 wt-% CNTs and 0.2 wt-% NDs—were explored. The ablative response of composites was studied through pre- and post-burnt SEM analysis and further related with thermogravimetric analysis, weight loss profile and thermal conductivity measurements. The novel nanofiller composites showed marked improvement in their thermal and ablative properties. A 22% and 30% increase in thermal conductivity was observed for composites containing 0.1 wt-% CNTs/0.1 wt-% NDs and 0.2 wt-% CNTs/0.2 wt-% NDs respectively. These nanofillers also improved the thermal stability of thermosetting epoxy matrix, and an increase of 13% and 20% was recorded in the erosion rate of composites containing 0.1 wt-% CNTs/0.1 wt-% NDs and 0.2 wt-% CNTs/0.2 wt-% NDs respectively. This improvement is due to the increased char yield produced by the increase in the loading of nanofillers, i.e. CNTs and NDs. Insulation index and insulation to density performance have also been improved due to increased thermal conductivity and char yield.     

Short PET and PA fibre composites based on LDPE and HDPE matrices. Morphology-behaviour relationship

The effect of unmodified and azide-modified short poly(ethylene terephthalate) (PET) and polyamide 66 (PA) fibres on the mechanical properties of thermoplastic composites based on low density (LDPE) and high density polyethylene (HDPE) matrices was investigated. The results have shown that both organic fibres are suitable reinforcements for LDPE and HDPE matrices. The weakest the matrix the strongest is the reinforcing effect of the fibres, so, the reinforcing effect of the fibres is more sensible in the LDPE matrix. p-(Azidosulfonyl)benzoyl azide is an adequate coupling agent for both fibres, especially for PET fibres. A better adhesion at the fibre/matrix interface of the composites has been observed by scanning electron microscopy, mainly in the PET-filled LDPE.     

Synthetic fibers and thermoplastic short‐fiber‐reinforced polymers: Properties and characterization

Among the synthetic fibers, glass fibers (GF) are most widely used in thermoplastic short‐fiber‐reinforced polymers (SFRP), as they offer good strength and stiffness, impact resistance, chemical resistance, and thermal stability at a low price. Carbon fibers (CF) are applied instead of GF, when highest stiffness is required. Other types of synthetic fibers like aramid (AF), basalt (BF), polyacrylonitrile (PAN‐F), polyethylene terephthalate (PET‐F), or polypropylene fibers (PP‐F) are rarely used in SFRP, although they offer some advantages compared with GF. The aim of this article is, to give an overview of various fiber types with regard to their mechanical properties, densities, and prices as well as the performance of their thermoplastic composites. The mechanical properties are presented as Ashby plots of tensile strength versus tensile modulus, both in absolute and specific (absolute value divided by density) values. This overview also focuses on modification of fiber/matrix interaction, as interfacial adhesion has a huge impact on composite performance. A summary of established methods for characterization of fibers, polymers, and composites completes this article. POLYM. COMPOS., 35:227–236, 2014. © 2013 Society of Plastics Engineers     

Extrudate swell and texture of PS,LDPE, ABS,PVC melts and their blends in extrusion capillary flow using a magnetic die

The extrudate swell behavior and extrudate texture of various thermoplastic melts, namely, polystyrene (PS), low‐density polyethylene (LDPE), acrylonitrile‐butadiene styrene (ABS) copolymer, poly(vinyl chloride) (PVC), and their blends, were examined weith a magnetic die system in a constant‐shear‐rate capillary rheometer at a shear rate range 5–28 s^?1 and a temperature range 170–230 °C. The extrudate swell results obtained from the magnetic die were then compared with those produced by a nonmagnetic die. The results showed that the extrudate swell increased with shear rate, but decreased with temperature. In a pure polymer system, up to 25% increase in the extrudate swell was observed with the application of the magnetic field to the PS melt, and the effect decreased in the order ABS > LDPE > PVC. The extrudate swell changes were associated with the changes in rheological properties of the melts. The extrudate textures of the ABS and PVC melts were improved by the magnetic field. In PS/LDPE or PS/ABS blend, it was found that the magnetic die resulted in higher values of the extrudate swell than the nonmagnetic die for all blends, the magnetic effect being less as the LDPE or ABS content was increased. For PS/LDPE system, the extrudate swell of the PS melt did not change much with addition of 20% LDPE, but slightly decreased at the LDPE loading of 40%. At higher LDPE loadings, the extrudate swell increased towards the value of the pure LDPE melt. For PS/ABS system, the extrudate swell ratio progressively decreased with increasing ABS content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 509–517, 2002     

Effect of alkali‐resistant glass fiber on polypropylene/polystyrene blends: Modeling and characterization

Alkali‐resistant glass fiber (GF) reinforced polypropylene (PP)/polystyrene (PS) blends were prepared by melt mixing in a Thermo Haake Rheochord mixer. Variation in thermal and mechanical properties with the addition of glass fibers into the polypropylene/polystyrene blends was investigated. The characterization of PP/PS/GF composites was done by dynamic mechanical analysis (DMA), thermogravimetric analysis, scanning electron microscope, and transmission electron microscope. The experimentally observed tensile properties of glass fiber reinforced PP/PS blends were compared with various published models. It was found that the experimental results agree well with Hui‐ Shia and series models. DMA tests revealed an increase in storage modulus with fiber loading confirms the greater degree of stress transfer from the matrix to the fiber. TEM micrographs reveal that the glass fibers are located at the interface between the blend components. POLYM. COMPOS., 37:398–406, 2016. © 2014 Society of Plastics Engineers     

Reinforcement effect of poly (methyl methacrylate)-<Emphasis Type="Italic">g</Emphasis>-cellulose nanofibers on LDPE/thermoplastic starch composites: preparation and characterization

The effect of cellulose nanofibers (CNFs) and poly [methyl methacrylate (MMA)]-grafted cellulose nanofibers (CNF-g-PMMA) on mechanical properties and degradability of a 75/25 low density polyethylene/thermoplastic starch (LDPE/TPS) blend was investigated. Graft copolymerization on CNFs was performed in an aqueous suspension by free radical polymerization using MMA as an acrylic monomer. In addition, a LDPE/TPS blend was reinforced by different amounts of CNFs (1–5 wt%) and CNF-g-PMMA (1–7 wt%) using a twin-screw extruder. A 61% grafting of PMMA on the surface of CNFs was demonstrated by gravimetric analysis. Moreover, after modification the X-ray photoelectron spectroscopy analysis showed a 20% increase of carbon atoms on the surface of CNFs and a 22.6% decrease in the oxygen content of its surface. The mechanical properties of the CNFs-modified composites were significantly improved compared to the unmodified nanocomposites. The highest tensile strength and Young’s modulus were obtained for the composites reinforced by 3 and 7 wt% CNF-g-PMMA, respectively. The degradability of cellulose nanocomposites was studied by water absorption and soil burial tests. Surface modification of CNFs lowered water absorption, and soil burial test of the LDPE/TPS blend showed improvement in biodegradability by addition of CNF-g-PMMA.     

Highly efficient preparation of multi-angle continuous carbon fibre reinforced hydroxyapatite composites by electrostatic splitting method

An electrostatic splitting device was self-designed and manufactured for highly efficient preparation of multi-angle continuous carbon fibre (CF)-reinforced ceramic-based composites and was used to prepare multi-angle continuous CF and nano-hydroxyapatite (nHA)-coated CF reinforced HA composites with improved CF dispersion and content. The compressive strength of sintered [0°/90°] CF reinforced hydroxyapatite (CF/HA) composites is more than two and a half times that of hydroxyapatite and is superior to that of cortical bone (26.42–110.7%). Compared with hydroxyapatite, fracture toughness of [0°/0°], [0°/90°] and [? 45°/+ 45°] CF/HA composites increase by 28.83%, 66.32% and 115.95%, respectively. The strength and fracture toughness (30.2 MPa·m^1/2) of [? 45°/+ 45°] CF/HA bioceramics display synchronously improving. Micromechanical property and crack propagation process of the composites were simulated in depth. Based on optimised dispersion and arrangement of CF, the introduction of nHA coating enhances the mechanical properties of nHA-coated CF reinforced HA composites because nHA coating can block the generation and propagation of cracks.     

Influence of temperature,molecular weight,and polydispersity of polystyrene on interfacial tension between low‐density polyethylene and polystyrene

In this work, the influence of temperature, molecular weight, and polydispersity of polystyrene on interfacial tension between low‐density polyethylene (LDPE) and polystyrene (PS) was evaluated using the pendant drop method. It was shown that interfacial tension between LDPE and PS decreases with increasing temperature for all LDPE–PS pairs studied. The temperature coefficient (∂γ/∂T) (where λ is interfacial tension and T is temperature) was higher for lower molecular weight and larger polydispersity of PS. The interfacial tension between LDPE and PS at a temperature of 202°C increased when the molecular weight of polystyrene was varied from 13,000 to 30,000. When the molecular weight of PS was further increased, the interfacial tension was shown to level off. The effect of polydispersity on interfacial tension between PS and LDPE, at a temperature of 202°C, was studied using PS with a constant‐number average molecular weight and varying polydispersity. The interfacial tension was shown to decrease with increasing polydispersity. However, the influence of polydispersity was lower for PS of higher molecular weight. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2423–2431, 1999     

Application of phase dispersion–crosslinking synergism on recycling commingled plastic wastes

A tetra‐component blend, consisting of low‐density polyethylene (LDPE), polyvinyl chloride (PVC), polypropylene (PP), and polystyrene (PS), was studied as a model system of commingled plastic wastes (LDPE/PVC/PP/PS, mass ratio: 70/10/10/10). Effects of chlorinated polyethylene (CPE), ethylene–propylene–diene monomer (EPDM), styrene–butadiene–styrene (SBS), and their mixture (CPE/EPDM/SBS, mass ratio: 2/2/2) on the mechanical properties and morphology of the system were investigated. With addition of several elastomers and their mixture, the tensile strength of the blends decreased slightly, although both the elongation at break and the impact strength increased. Among these elastomers, EPDM exhibited the most significant impact modification effect for the tetra‐component blends. SBS and the mixture have a good phase‐dispersion effect for the tetra‐component blend. By adding a crosslinking agent [dicumyl peroxide (DCP)], the mechanical properties of the tetra‐component blends also increased. When either SBS or the mixture was added to the blend together with DCP, the probability that the crosslinking agent (DCP) would be at the interface improved because of the phase‐dispersion effect of SBS. Therefore, more co‐crosslinked products will form between LDPE and other components. Accordingly, remarkable improvement of the interfacial adhesion and hence the mechanical properties of the tetra‐component blends occurred. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2947–2952, 2001     

Structural,thermal and dielectric properties of AlN–SiC composites fabricated by plasma activated sintering

Highly dense AlN–SiC composites with various SiC additions (0–50?wt-%) were fabricated at 1800°C by plasma activated sintering. The effect of SiC addition on structural, thermal and dielectric properties as well as microwave absorbing performance of the composites was investigated. The thermal conductivity decreases with increasing SiC addition, from 68.7 W (m?K)^?1 for 0?wt-% SiC to 19.38?W (m?K)^?1 for 50?wt-% SiC. On the contrary, the permittivity and dielectric loss increase gradually, from 7.6–8.5 to 22–26.7 and from 0.02–0.1 to 0.2–0.53, respectively. AlN–SiC composite with better thermal and dielectric properties in 30?wt-% SiC, whose thermal conductivity and dielectric loss are found to be 24.88?W (m?K)^?1 and 0.15–0.74, respectively. Furthermore, the composite exhibits microwave absorbing performance with the minimum reflection loss (RL) of ?16.5 dB at 15.5 GHz and the frequency range of 2.6 GHz for RL below ?10 dB (90% absorption).     

Studies on recyclable composites: nylon fibre reinforced high density polyethylene composites

Abstract

A commercial grade of high density polyethylene (HDPE) matrix reinforced with nylon fibre up to 30 wt-% of HDPE was studied as a potential candidate for recyclable composites. These composite materials show improvement in mechanical properties such as tensile strength and flexural strength. Modification using styrene maleic anhydride – grafted HDPE significantly improved the mechanical and thermal properties. The HDPE/nylon composites/blends obtained by recycling of the composites also show good mechanical properties.     

Effect of electron-beam radiation on thermoplastic composites

Abstract

The effect of electron beam (EB) radiation on carbon fibre reinforced (CF) thermoplastic (PBT, PPS, PA) composites was investigated. To clarify whether crosslinking could take place without or only with the presence of a crosslinking agent, special attention was paid to the incorporation of this agent into polymer sheets with a carbon fibre content of 50% by volume. The thermal and mechanical properties of the materials before and after exposure under different irradiation doses were evaluated. For materials based on PBT, PPS and PA46, no significant changes in properties after irradiation could be observed. However, CF/PA66 exhibited some changes in the presence of a crosslinking agent after irradiation, which could be related to an irradiation-induced crosslinking reaction. The effect of irradiation on the flexural properties was insignificant but an improvement in the creep behaviour was observed. Non-reinforced PA66 plates were also manufactured and a gel content measurement indicated that crosslinking was successfully induced. Additional studies allowed the changes in the polymer due to this crosslink to be quantified.     

Recycling of poly(ethylene terephthalate) as polymer‐polymer composites

Microfibrillar reinforced composites (MFC) comprising an isotropic matrix from a lower melting polymer reinforced by microfibrils of a higher melting polymer were manufactured under industrially relevant conditions and processed via injection molding. Low density polyethylene (LDPE) (matrix) and recycled poly(ethylene terephthalate) (PET) (reinforcing material) from bottles were melt blended (in 30/70 and 50/50 PET/LDPE wt ratio) and extruded, followed by continuous drawing, pelletizing and injection molding of dogbone samples. Samples of each stage of MFC manufacturing and processing were characterized by means of scanning electron microscopy (SEM), wide‐angle X‐ray scattering (WAXS), dynamic mechanical thermal analysis (DMTA), and mechanical testing. SEM and WAXS showed that the extruded blend is isotropic but becomes highly oriented after drawing, being converted into a polymer‐polymer composite upon injection molding at temperatures below the melting temperature of PET. This MFC is characterized by an isotropic LDPE matrix reinforced by randomly distributed PET microfibrils, as concluded from the WAXS patterns and SEM observations. The MFC dogbone samples show impressive mechanical properties—the elastic modulus is about 10 times higher than that of LDPE and about three times higher than reinforced LDPE with glass spheres, approaching the modulus of LDPE reinforced with 30 wt% short‐glass fibers (GF). The tensile strength is at least two times higher than that of LDPE or of reinforced LDPE with glass spheres, approaching that of reinforced LDPE with 30 wt% GF. The impact strength of LDPE increases by 50% after reinforcement with PET. It is concluded that: (i) the MFC approach can be applied in industrially relevant conditions using various blend partners, and (ii) the MFC concept represents an attractive alternative for recycling of PET as well as other polymers.     

Compatibilizing Effect of SEBS for Electrical Properties of LDPE/PS Blends

Summary: In the previous study, we observed compatibilizing effects of low density polyethylene (LDPE)/polystyrene (PS) with polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene (SEBS), a triblock copolymer. Blends consisting of 70 wt.‐% LDPE and 30 wt.‐% PS were prepared with a SEBS concentration of up to 10 wt.‐%. This study examined the electrical properties such as the electrical breakdown, water tree length, permittivity and tan δ in the blends. The possibility of using these blends as insulating material substitutes for LDPE was investigated. The electrical breakdown strength reached a maximum of 66.67 kV/mm, which is superior to 50.27 kV/mm of the LDPE used as electrical insulators for cables. In addition, the water tree length decreased with increasing SEBS concentration. The water tree lengths of the blends containing SEBS were shorter than that of the LDPE. The permittivity of the blends was 2.28–2.48 F/m, and decreased with increasing SEBS concentration with the exception of S‐0. Tan δ of the blends increased smoothly with increasing SEBS content.

Breakdown strength , water tree length, permittivity and tan δ of the LDPE/PS/SEBS blends and raw materials.     

Synthesis of glass fiber‐multiwall carbon nanotube hybrid structures for high‐performance conductive composites

The conductive polyamide 66 (PA66)/carbon nanotube (CNT) composites reinforced with glass fiber‐multiwall CNT (GF‐MWCNT) hybrids were prepared by melt mixing. Electrostactic adsorption was utilized for the deposition of MWCNTs on the surfaces of glass fibers (GFs) to construct hybrid reinforcement with high‐electrical conductivity. The fabricated PA66/CNT composites reinforced with GF‐MWCNT hybrids showed enhanced electrical conductivity and mechanical properties as compared to those of PA66/CNT or PA66/GF/CNT composites. A significant reduction in percolation threshold was found for PA66/GF‐MWCNT/CNT composite (only 0.70 vol%). The morphological investigation demonstrated that MWCNT coating on the surfaces of the GFs improved load transfer between the GFs and the matrix. The presence of MWCNTs in the matrix‐rich interfacial regions enhanced the tensile modulus of the composite by about 10% than that of PA66/GF/CNT composite at the same CNT loading, which shows a promising route to build up high‐performance conductive composites. POLYM. COMPOS. 34:1313–1320, 2013. © 2013 Society of Plastics Engineers     

气相沉积CF改性PS的选择性激光烧结

由于普通碳纤维(CF)对聚苯乙烯(PS)烧结件弯曲强度的改善有限,在前期理论及实验基础上,对CF材料做气相沉积处理,制备PS/CF复合材料,再进行选择性激光烧结(SLS)实验,验证其增强效果;然后,改变经气相沉积法处理的CF与PS的配比,分析CF含量对制件强度及精度的影响;最后结合扫描电子显微镜(SEM)观察烧结件断面内部结构并进行分析。结果表明,经气相沉积处理的CF含量为10%时复合材料的弯曲强度较高,达10.17 MPa,比纯PS制件提高约76.3%。微观形貌SEM显示,随着CF含量的增加,孔隙量增加,从而导致SLS烧结件的强度降低。     

The effect of the architecture and concentration of styrene–butadiene compatibilizers on the morphology of polystyrene/low‐density polyethylene blends

The effect of styrene–butadiene block copolymers (SB) with varying number of blocks and length of styrene blocks on the morphology, rheology, and impact strength of 4/1 polystyrene/low‐density polyethylene (PS/LDPE) blends was studied. The scanning and transmission electron microscopy and X‐ray scattering were used for determination of the size of LDPE particles and the localization and structure of SB copolymers in blends. It is shown that the dependence of the LDPE particle size on the amount of added SB and localization of SB copolymers in blends is predominantly controlled by the length of their styrene blocks. It follows from thermodynamic considerations that the reason is the difference in composition asymmetry between SB with short and long styrene blocks. Coalescence of particles of SB having short styrene blocks at the surface of LDPE droplets and movement of SB with long styrene blocks to the PS–LDPE interface were observed during annealing of PS/LDPE/SB blends. Pronounced migration of SB copolymer during annealing shows that their localizations in blends in steady state on long steady mixing and at thermodynamic equilibrium are different. The values of tensile impact strength of PS/LDPE/SB blends correlate well with the size of LDPE particles and the amount of SB at the interface. Viscosity of PS/LDPE/SB depends on molecular structure of SB copolymers by a manner different from that of tensile impact strength. The results of this study and literature data lead to the conclusion that the compatibilization efficiency of SB copolymers for a certain polystyrene‐polyolefin pair is a function of not only molecular parameters of SB but also of the polystyrene/polyolefin ratio, the amount of SB in a blend, and mixing and processing conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2803–2816, 2006