Mechanical and thermal expansion properties of glass fibers reinforced PEEK composites at cryogenic temperatures

Polyetheretherketone (PEEK) has been widely used as matrix material for high performance composites. In this work, 30% chopped glass fibers reinforced PEEK composites were prepared by injection molding, and then the tensile, flexural and impact properties were tested at different temperatures. The modulus, strength and specific elongation of glass fibers reinforced PEEK at room temperature, 77 K and 20 K have been compared. And the fracture morphologies of different samples were investigated by scanning electron microscopy (SEM). The results showed a dependence of mechanical properties of glass fibers reinforced PEEK composites on temperature. The coefficient of thermal expansion of unfilled PEEK and glass fibers reinforced PEEK were also investigated from 77 K to room temperature. The results indicated that the thermal expansion coefficient (CTE) of PEEK matrix was nearly a constant in this temperature region, and it can be significantly decreased by adding glass fibers.     

聚醚醚酮及其复合材料的摩擦学研究进展

评述了聚醚醚酮（PEEK）及其复合材料的摩擦磨损性能，在滑动过程中形成的摩擦转移膜以及磨屑的研究，总结了聚合物基复合材料摩擦学研究的一般方法及规律，介绍了关于用PEEK复合材料制造的轴承，齿轮等进行的摩擦学研究，以及等离子体表面处理和颗粒增强对PEEK及其复合材料摩擦学性能的影响。     

PEEK composites reinforced with zirconia nanofiller

The present investigation deals with the preparation and characterization of nanocomposites of polyether ether ketone (PEEK) containing nanosized zirconia filler up to 3 wt.% loading. It has been observed that presence of zirconia filler dispersed in polymer matrix enhances various basic and functional properties (e.g., mechanical properties, thermal stability & other physico-mechanical properties). The SEM studies reveal that the dispersion of zirconia nanofiller is uniform throughout the polymer matrix. The thermal stability of the nanocomposites has been studied by TGA. Thermal analysis of the composites shows an increase in the thermal stability with increase of nanofiller content. This may be attributed to strong interaction between polymer chains and filler particles. DMA studies show the significant improvement in storage modulus of the nanocomposites because of better interaction of zirconia particles in PEEK matrix.     

Influence of BaTiO<Subscript>3</Subscript> on damping and dielectric properties of filled polyurethane/unsaturated polyester resin interpenetrating polymer networks

A series of BaTiO₃ fiber and nanopowder unfilled and filled interpenetrating polymer networks (IPNs) composed of polyurethane (PU) and unsaturated polyester resin (UP) are prepared by simultaneous polymerization process. The effect of PU/UP component ratios, the types and amounts of BaTiO₃ filled, the polarization treatment to filled IPNs, on the damping properties are investigated by dynamic mechanical thermal analyzer (DMTA). The morphology and microstructures of unfilled and filled IPNs are examined by transmission electron microscope (TEM). The dielectric loss and dielectric constant at different temperatures are studied by AC impedance analyzer. Moreover, the relationship between damping and dielectric properties is discussed in terms of dielectric constant and dielectric loss measured. The results show that the PU/UP component ratios in IPNs, the types of filler, and the amount of nanopowder added all affect the damping behaviors and degree of phase separation of unfilled and filled IPNs. Through polarization treatment, the filled IPNs exhibit synergistic action in systems caused by elastomeric damping mechanism, interfacial frictional damping mechanism and piezoelectric damping mechanisms. The maximum value of E″ of filled IPNs with 70% BaTiO₃ increase above 100 MPa and the temperature ranges of tan δ > 0.3 is higher than 100°C compared with unfilled IPNs. Moreover, the maximum value of E″ and the temperature ranges of tan δ > 0.3 increases dramatically after polarizing process. The dielectric properties and its relation with damping properties studies reveal that the temperature ranges exhibit excellent consistency of maximum dielectric loss and dielectric constant with damping loss factor.     

Influence of carbon nanotube-polymeric compatibilizer masterbatches on morphological, thermal, mechanical, and tribological properties of polyethylene

Study was made of the effect of multiwall carbon nanotubes (MWCNTs) and polymeric compatibilizer on thermal, mechanical, and tribological properties of high density polyethylene (HDPE). The composites were prepared by melt mixing in two steps. Carbon nanotubes (CNTs) were melt mixed with maleic anhydride grafted polyethylene (PEgMA) as polymeric compatibilizer to produce a PEgMA-CNT masterbatch containing 20 wt% of CNTs. The masterbatch was then added to HDPE to prepare HDPE nanocomposites with CNT content of 2 or 6 wt%. The unmodified and modified (hydroxyl or amine groups) CNTs had similar effects on the properties of HDPE-PEgMA indicating that only non-covalent interactions were achieved between CNTs and matrix. According to SEM studies, single nanotubes and CNT agglomerates (size up to 1 μm) were present in all nanocomposites regardless of content or modification of CNTs. Addition of CNTs to HDPE-PEgMA increased decomposition temperature, but only slight changes were observed in crystallization temperature, crystallinity, melting temperature, and coefficient of linear thermal expansion (CLTE). Young’s modulus and tensile strength of matrix clearly increased, while elongation at break decreased. Measured values of Young’s moduli of HDPE-PEgMA-CNT composites were between the values of Young’s moduli for longitudinal (E₁₁) and transverse (E₂₂) direction predicted by Mori-Tanaka and Halpin-Tsai composite theories. Addition of CNTs to HDPE-PEgMA did not change the tribological properties of the matrix. Because of its higher crystallinity, PEgMA possessed significantly different properties from HDPE matrix: better mechanical properties, lower friction and wear, and lower CLTE in normal direction. Interestingly, the mechanical and tribological properties and CLTEs of HDPE-PEgMA-CNT composites lie between those of PEgMA and HDPE.     

Effect of aluminum nitride on thermomechanical properties of high performance PEEK

High performance polymer matrix composites based on poly(ether–ether–ketone) (PEEK) as matrix and aluminum nitride particle (AlN_p) as filler were prepared. The effect of AlN_p on the storage modulus, loss modulus, mechanical loss factor, and glass transition were investigated. The AlN_p reinforcement is more pronounced above glass transition temperature (T_g). Composite containing 70 wt.% AlN_p exhibit about 100% increase in storage modulus at 50 °C and about 500% increase at 250 °C, and 19 °C increase in glass transition temperature as compared to pure PEEK. Peak height of tan δ for composites was decreased to one sixth of the pure PEEK. It is probably due to improved crystallinity of PEEK and strong interaction between the AlN_p and PEEK matrix. SEM reveals excellent distribution of AlN_p in PEEK matrix and good interaction between AlN_p and PEEK matrix.     

Woven hybrid biocomposites: Dynamic mechanical and thermal properties

The dynamic mechanical and thermal analysis of oil palm empty fruit bunch (EFB)/woven jute fibre (J_w) reinforced epoxy hybrid composites were carried out. The storage modulus (E′) was found to decrease with temperature in all cases, and hybrid composites had showed better values of E′ at glass transition temperature (T_g) compared to EFB and epoxy. Loss modulus showed shifts in the T_g of the polymer matrix with the addition of fibre as reinforcing phase, which indicate that fibre plays an important role in case of T_g. The Tan δ peak height was minimum for jute composites and maximum for epoxy matrix. Complex modulus variations and phase behaviour of the hybrid composites was studied by Cole-Cole analysis. Thermal analysis result indicates an increase in thermal stability of EFB composite with the incorporation of woven jute fibres. Hybridization of EFB composite with J_w fibres enhanced the dynamic mechanical and thermal properties.     

Tribological properties of surface modified nano-alumina/epoxy composites

Nano-sized Al₂O₃ particles grafted with polystyrene or polyarcrylamide were employed as fillers for fabricating epoxy based composites. Curing habit, mechanical properties and tribological performance revealed by sliding wear tests of the composites were investigated. The experimental results indicated that the nanoparticles accelerate curing of epoxy, increase composites' impact strength and decrease wear rate and frictional coefficient of the composites. The surface modification by means of grafting polymerization can further enhance the properties improvement of epoxy due to the increased filler/matrix interfacial interaction. Compared to frictional coefficient, wear rate of epoxy can be decreased more remarkably by the addition of nano-alumina when rubbing against steel. The wear mode changes from severe peeling off of unfilled epoxy to mild micro-ploughing in the case of nano-alumina filled composites.     

Surface oxidation of carbon fibre on tribological properties of PEEK composites

Abstract

In this work, ozone modification method and air oxidation were used for the surface treatment of polyacrylonitrile (PAN) based carbon fibre. The surface characteristics of carbon fibres were characterised by X-ray photoelectron spectroscopy. The interfacial properties of carbon fibre reinforced PEEK (CF/PEEK) composites were investigated by means of the single fibre pull-out tests. As a result, it was found that IFSS values of the composites with ozone treated carbon fibre are increased by 60% compared with that without treatment. X-ray photoelectron spectroscopy results show that ozone treatment increases the amount of carboxyl groups on carbon fibre surface, thus the interfacial adhesion between carbon fibre and PEEK matrix is effectively promoted. The effect of surface treatment of carbon fibres on the tribological properties of CF/PEEK composites was comparatively investigated. Experimental results revealed that surface treatment can effectively improve the interfacial adhesion between carbon fibre and PEEK matrix. Thus the wear resistance was significantly improved.     

Study on mechanical properties of nano-Fe3O4 reinforced nitrile butadiene rubber

In this study, we used nano-Fe₃O₄ particles as modified filler to prepare NBR/nano-Fe₃O₄ composites. With adding different mass fraction of nano-Fe₃O₄, mechanical properties such as tensile strength, modulus at 300% elongation, shore A hardness, surface microstructure, magnetic character and tribological properties such as friction and wear performance of the NBR/nano-Fe₃O₄ composites were investigated. The anti-wear and friction-reducing properties were also discussed. The results indicated that there was little change on mechanical properties, but the tribological properties were greatly improved, which laid both theoretical and applied foundation for the design of high-performance lubricating composites used for sealing.     

Influence of CaCO3 Whisker Content on Mechanical and Tribological Properties of Polyetheretherketone Composites

The mechanical and tribological properties of polyetheretherketone (PEEK) composites filled with CaCO3 whisker in various content of 0-45% (wt pct) were investigated. The composite specimens were prepared by compression molding. Tribological testing of composites in dry wear mode against carbon steel ring was carried out on a MM200 block-on-ring apparatus. Data on neat PEEK were also included for comparison. It was observed that inclusion of CaCO3 whisker affected the most mechanical properties and the friction and wear in a beneficial way. With an increase in CaCO3 whisker content, friction coefficient continuously decreased but the trends in wear performance varied. The specific wear rate showed minima as 1.28×10-6 mm3/Nm for 15% CaCO3 whisker inclusion followed by a slow increase for further CaCO3 whisker addition. In terms of friction applications, when the tribological and mechanical properties are combined, the optimal content of CaCO3 whisker in the filled PEEK should be recommended as 15% to 20%. Fairly good correlations are observed in friction coefficient vs bending modulus and wear rate vs bending strength, confirming that the bending properties prove to be the most important tribology controlling parameters in the present work.     

Recycling effects on microstructure and mechanical behaviour of PEEK short carbon-fibre composites

The effect of recycling on microstructure and mechanical properties has been evaluated for injection-moulded poly-ether-ether-ketone (PEEK) composites reinforced with 10% and 30% short carbon fibres. Microstructure characterization was carried out by determining fibre length distributions, PEEK molecular weight, and by SEM observations of fracture surfaces before and after processing. These studies reveal degradation of fibres and matrix during recycling. Tensile Youngs modulus and strength, as well as impact strength reductions are presented for recycled composites.     

On the impact performance of carbon fibre laminates with epoxy and PEEK matrices

A study was made of the mechanical properties and impact performance of carbon fibre/PEEK (0,90), ($\text{±45}$) and ($\text{±45,0}$) laminates and comparisons were made with similar carbon fibre/epoxy laminatesFibre dominated properties such as plain tensile strength were similar to those of epoxy laminates with similar fibres and volume fractions. Because of the increased toughness of PEEK there was less extensive matrix cracking, even though there was fibre debonding, and this gave increased transverse and shear cracking strains, increased shear strengths but decreased notched tensile strengths. The lower modulus and yield stress of PEEK caused lower compressive strengths, but PEEK absorbed little moisture and at 120°C moisture had little effect on mechanical properties.Dropweight impact produced less extensive damage in carbon fibre/PEEK laminates. Residual tensile strengths were similar but, because of the less extensive damage and greater delamination fracture energy, the residual compressive strengths were significantly greater with a PEEK matrix.Microscopic examination showed less matrix cracking and more fibre buckling in the carbon fibre/PEEK and this is discussed in relation to mechanical properties.     

Study on the synergistic effect of carbon fiber and graphite and nanoparticle on the friction and wear behavior of polyimide composites

In this paper, the effect of short carbon fiber (SCF), graphite (Gr) and nano-Si₃N₄ on the friction and wear behavior of polyimide (PI) composites were studied using a block-on-ring arrangement. Experimental results revealed that single incorporation of SCF and Gr can improve the friction-reducing and anti-wear abilities of the PI composites significantly. However, nano-Si₃N₄ deteriorated the wear resistance of the PI composite drastically as single filler. A synergistic effect was found for the combination of nano-Si₃N₄ and SCF and Gr, which lead to the best tribological properties. It also can be found that the filled PI composites exhibited better tribological properties under higher PV product (the product of load and sliding speed). Moreover, the filled PI composites showed better tribological properties under oil lubrication and worse tribological properties under water lubrication compared with that under dry sliding condition.     

Influence of the microstructure on the mechanical and tribological behavior of TiC/a-C nanocomposite coatings

The performance of protective thin films is clearly influenced by their microstructure. The objective of this work is to study the influence of the structure of TiC/a-C nanocomposite coatings with a-C contents ranging from ~ 0% to 100% on their mechanical and tribological properties measured by ultramicroindentation and pin-on-disks tests at ambient air, respectively. The microstructure evolves from a polycrystalline columnar structure consisting of TiC crystals to an amorphous and dense TiC/a-C nanocomposite structure when the amount of a-C is increased. The former samples show high hardness, moderate friction and high wear rates, while the latter ones show a decrease in hardness but an improvement in tribological performance. No apparent direct correlation is found between hardness and wear rate, which is controlled by the friction coefficient. These results are compared to the literature and explained according to the different film microstructures and chemical bonding nature. The film stress has also been measured at the macro and micro levels by the curvature and Williamson-Hall methods respectively. Other mechanical properties of the coating such as resilience and toughness were evaluated by estimating the H³/E?² and H/E? ratios and the percentage of elastic work (W_e). None of these parameters showed a tendency that could explain the observed tribological results, indicating that for self-lubricant nanocomposite systems this correlation is not so simple and that the assembly of different factors must be taken into account.     

Influence of adsorbed moisture on the properties of cyanate ester/BaTiO3 composites

The effect of moisture adsorbed on BaTiO₃ on the properties of cyanate ester (CE)/BaTiO₃ dielectric composites is examined using undried and dried BaTiO₃ particles. The influence of moisture on the dielectric constant, thermal stability, dynamic mechanical properties, flexural behavior and micro morphology of the composites is investigated. Dielectric constant (ε) and dielectric loss (tan δ) of composites with the dried BaTiO₃ are both higher than composites manufactured with undried filler at the same frequency. The dielectric properties of the dried system are stable over a broader temperature range than the undried composites. Adsorbed moisture causes the initial decomposition temperature and the maximum degradation temperature of the composite to decrease by 27 °C and 15 °C, respectively. By removing the moisture from BaTiO₃, the CE/BaTiO₃ composite exhibits a lower modulus (E′), higher strength, higher flexural elongation and a dramatically increased glass transition temperature (T_g).     

Effects of aluminium nitride inclusions on thermal and electrical properties of epoxy and polypropylene: An experimental investigation

Thermal and dielectric properties of polymers reinforced with micro-sized aluminium nitride (AlN) particles have been studied. A set of epoxy–AlN composites, with filler content ranging from 0 to 25 vol% is prepared by hand lay-up technique. With similar filler loading, polypropylene -AlN composites are fabricated by compression molding technique. Density (ρ_c), effective thermal conductivity (k_eff), glass transition temperature (T_g), coefficient of thermal expansion (CTE) and dielectric constant (ε_c) of these composites are measured experimentally. The various experimental data were interpreted using appropriate theoretical models. Incorporation of AlN in both the resin increases the k_eff and T_g whereas CTE of composite decreases favourably. The dielectric constant of the composite also found to get modified with filler content. With improved thermal and modified dielectric characteristics, these AlN filled polymer composites can possibly be used for microelectronics applications.     

Influence of processing conditions on bending property of continuous carbon fiber reinforced PEEK composites

The purpose of this study is to achieve an optimum fabrication condition for the continuous carbon fiber reinforced PEEK matrix composites based on a micro-braiding fabrication method. The composite plates were fabricated at three processing temperatures (380, 410 and 440 °C) and three holding times (20, 40 and 60 min), respectively, with a total number of nine different fabrication conditions, and their bending properties were investigated in terms of thermal and fracture characterizations. As a result, the bending performance of the fabricated composites was significantly affected at the 440 °C temperature. Although no significant change in the bending performance was seen at the 380 and 410 °C with all the holding times, the thermal and fracture characterizations implied a degradation of the PEEK matrix property during the fabrication process. In order to avoid the matrix degradation and the decrease of mechanical properties, a lower fabrication temperature with a shorter holding time should be recommended for the carbon/PEEK composites fabricated by the micro-braiding method.     

The effect of thermal ageing on carbon fibre-reinforced polyetheretherketone (PEEK)

The static and dynamic mechanical properties of carbon fibre-reinforced PEEK (APC-2) laminates subjected to long-term thermal ageing and cycling treatments have been studied using three-point bend flexure tests. Results are discussed with respect to morphological changes and degradation analysis. S/N curves were modelled using fatigue modulus degradation data. Ageing laminates at high temperatures, for long time periods, between the glass transition temperature, T _g, and the melting temperature, T _m, caused a significant reduction in mechanical properties. However, for short ageing periods, a crystal-perfection process occurs which enhanced the low stress level fatigue resistance of both laminate geometries.     

Consolidation Process of PEEK/Carbon Composite for Aerospace Applications

Processing of PEEK/carbon composites into an aerospace structural part like the space arm can be very complex and necessitates repetition of the consolidation process in order to obtain a void free structure. The objective of the present work was to evaluate the effect of successive consolidations on the PEEK/carbon composite properties in order to determine optimum consolidation conditions.It is well known that the properties of the PEEK matrix in PEEK/carbon fiber composite are dependent on the processing conditions. Since each of the successive consolidations is done at a temperature of 400°C for a period of 60 minutes, it can be predicted that after a few cycles of consolidation, such thermal treatment can lead to matrix modifications. The results of the present study indicate that successive consolidations lead to modifications of the crystallization behavior of the PEEK matrix in the composite; alteration of the mechanism of nucleation of the PEEK matrix as well as the global rate of crystallization and a reduction in the recrystallizable material was observed. Modifications in the crystallization behavior of the PEEK matrix probably result from alteration of the chemical structure of the PEEK matrix when the composite is submitted to long treatment at high temperature. In particular, under oxidizing conditions, in air for example, chain scission followed by crosslinking reactions was proposed as the mechanism responsible for the matrix evolution.The evaluation of the tensile properties and the short beam shear strength of the consolidated samples also suggests that successive consolidations can affect the mechanical behavior of the PEEK/carbon composites. The mechanical characterization indicates that up to a certain level, the evolution of the PEEK structure during the consolidation process can be beneficial in terms of tensile and interfacial performance since crosslinks are strengthening structure.