Water absorption characteristics of aluminised E-glass fibre reinforced unsaturated polyester composites

Novel aluminised E-glass fibre reinforced unsaturated polyester composites, originally formulated for enhanced thermal and electrical shielding properties were evaluated in terms of their water absorption. One of the major obstacles delaying the acceptance of novel composites in engineering applications is the degradation of the polymer matrix material by moisture, which effects the physical and mechanical performance over time. The objective of this study was to characterise and quantify the degree of water absorption of novel aluminised E-glass reinforced unsaturated polyester composites. Aluminised E-glass composites were compared alongside their unmetallised E-glass counterparts. Two sets of temperature were used for this study. Results show that aluminised E-glass significantly reduces the saturation point compared to unmetallised E-glass. The differences between aluminised and unmetallised are correlated to fibre coatings. At elevated temperatures the aluminised E-glass sample is unstable and exhibits significantly higher water absorption indicating that a new failure mechanism is occurring.     

Effect of water absorption on the mechanical properties of hemp fibre reinforced unsaturated polyester composites

Hemp fibre reinforced unsaturated polyester composites (HFRUPE) were subjected to water immersion tests in order to study the effects of water absorption on the mechanical properties. HFRUPE composites specimens containing 0, 0.10, 0.15, 0.21 and 0.26 fibre volume fraction were prepared. Water absorption tests were conducted by immersing specimens in a de-ionised water bath at 25 °C and 100 °C for different time durations. The tensile and flexural properties of water immersed specimens subjected to both aging conditions were evaluated and compared alongside dry composite specimens. The percentage of moisture uptake increased as the fibre volume fraction increased due to the high cellulose content. The tensile and flexural properties of HFRUPE specimens were found to decrease with increase in percentage moisture uptake. Moisture induced degradation of composite samples was significant at elevated temperature. The water absorption pattern of these composites at room temperature was found to follow Fickian behaviour, whereas at elevated temperatures it exhibited non-Fickian.     

Flexural properties of hemp fibre reinforced polylactide and unsaturated polyester composites

In this work, flexural strength and flexural modulus of chemically treated random short and aligned long hemp fibre reinforced polylactide and unsaturated polyester composites were investigated over a range of fibre content (0-50 wt%). Flexural strength of the composites was found to decrease with increased fibre content; however, flexural modulus increased with increased fibre content. The reason for this decrease in flexural strength was found to be due to fibre defects (i.e. kinks) which could induce stress concentration points in the composites during flexural test, accordingly flexural strength decreased. Alkali and silane fibre treatments were found to improve flexural strength and flexural modulus which could be due to enhanced fibre/matrix adhesion.     

The moisture absorption of glass fibre reinforced vinylester and polyester composites

The water absorption characteristics of unidirectional glass reinforced vinylester and polyester laminates in distilled water and in 95% relative humidity at 25°C, 50°C, 60°C and 70°C were investigated. The results show that the calculated values and the experimental data agree reasonably well, but deviation occurred at higher temperatures.     

The low velocity impact response of non-woven hemp fibre reinforced unsaturated polyester composites

Hemp fibre reinforced unsaturated polyester composites (HFRUPE) were subjected to low velocity impact tests in order to study the effects of non-woven hemp fibre reinforcement on their impact properties. HFRUPE composites specimens containing 0, 0.06, 0.10, 0.15, 0.21 and 0.26 fibre volume fractions (V_f) were prepared and their impact response compared with samples containing an equivalent fibre volume fraction of chopped strand mat E-glass fibre reinforcement. Post-impact damage was assessed using scanning electron microscopy (SEM). A significant improvement in load bearing capability and impact energy absorption was found following the introduction hemp fibre as reinforcement. The results indicate a clear correlation between fibre volume fractions, stiffness of the composite laminate, impact load and total absorbed energy. Unreinforced unsaturated polyester control specimens exhibited brittle fracture behaviour with a lower peak load, lower impact energy and less time to fail than hemp reinforced unsaturated polyester composites. The impact test results show that the total energy absorbed by 0.21 fibre volume fraction (four layers) of hemp reinforced specimens is comparable to the energy absorbed by the equivalent fibre volume fraction of chopped strand mat E-glass fibre reinforced unsaturated polyester composite specimens.     

Fibre reinforced organic rectorite/unsaturated polyester composites

Three series of glass fibre (F) reinforced unsaturated polyester (UP)/organic rectorite (OREC) (F/UP/OREC) composites were manufactured by selecting two types of fibres, different gelation time of UP matrix and different content of OREC. The morphologies of F/UP/OREC composites were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The dispersion of OREC in the cured UP matrix was investigated using transmission electron microscopy (TEM). The mechanical properties of UP/OREC and F/UP/OREC composites were evaluated. Additionally, the hot–wet resistance and alkali resistance of UP/OREC and F/UP/OREC composites were investigated. The mechanical properties and the resistance to hot–wet and alkali of UP composites can be improved by adding appropriate OREC without reference to the gelation time of UP matrix or the type of F. The maximum mechanical properties of UP composites can be obtained by adding 2 wt% OREC due to the high stiffness and uniform dispersion of OREC.     

Fracture characterisation of short bamboo fibre reinforced polyester composites

In the study, fracture behaviour of short bamboo fibre reinforced polyester composites is investigated. The matrix is reinforced with fibres ranging from 10 to 50, 30 to 50 and 30 to 60 vol.% at increments of 10 vol.% for bamboo fibres at 4, 7 and 10 mm lengths respectively. The results reveal that at 4 mm of fibre length, the increment in fibre content deteriorates the fracture toughness. As for 7 and 10 mm fibre lengths, positive effect of fibre reinforcement is observed. The optimum fibre content is found to be at 40 vol.% for 7 mm fibre and 50 vol.% for 10 mm fibre. The highest fracture toughness is achieved at 10 mm/50 vol.% fibre reinforced composite, with 340% of improvement compared to neat polyester. Fractured surfaces investigated through the Scanning Electron Microscopy (SEM) describing different failure mechanisms are also reported.     

Mechanical property evaluation of sisal–jute–glass fiber reinforced polyester composites

The composite materials are replacing the traditional materials, because of its superior properties such as high tensile strength, low thermal expansion, high strength to weight ratio. The developments of new materials are on the anvil and are growing day by day. Natural fiber composites such as sisal and jute polymer composites became more attractive due to their high specific strength, lightweight and biodegradability. Mixing of natural fiber with Glass-Fiber Reinforced Polymers (GFRPs) are finding increased applications. In this study, sisal–jute–glass fiber reinforced polyester composites is developed and their mechanical properties such as tensile strength, flexural strength and impact strength are evaluated. The interfacial properties, internal cracks and internal structure of the fractured surfaces are evaluated by using Scanning Electron Microscope (SEM). The results indicated that the incorporation of sisal–jute fiber with GFRP can improve the properties and used as a alternate material for glass fiber reinforced polymer composites.     

Dynamic properties of pultruded natural fibre reinforced composites using Split Hopkinson Pressure Bar technique

The paper presents results on dynamic mechanical properties of jute, and kenaf fibre reinforced composites at various strain rates using compression Split Hopkinson Pressure Bar technique. The stress–strain curves for both pultruded natural fibre reinforced composites at strain rates of nearly 1400 s⁻¹ are illustrated and then compared with statically determines stress–strain curve (1.0 × 10⁻³ s⁻¹). Results show that the strain rate does affect the value of dynamic compressive properties of both pultruded natural fibre composites. Higher dynamic compression modulus and 2.5% flow stress were recorded for higher strain rates as compared to lower strain rate over the range of strain rates investigated. Under dynamic loading, jute fibre reinforced composites recorded the highest value of dynamic response in terms of compression modulus, 2.5% flow stress and compressive strength than that of kenaf fibre reinforced composites. In addition, kenaf fibre reinforced composites is more severely damaged as compared to jute fibre reinforced composites for all tested strain rate.     

Low-velocity impact response of non-woven hemp fibre reinforced unsaturated polyester composites: Influence of impactor geometry and impact velocity

In this study, the influence of varying impactor geometries on the impact damage characteristics of hemp fibre reinforced unsaturated polyester composites were subjected to a low-velocity impact loading using an instrumented falling weight impact test setup. The three varying tup geometries: hemispherical, 30° and 90°, at four different impact velocity levels: 2.52 m/s, 2.71 m/s, 2.89 m/s and 2.97 m/s were assessed. The experimental results to investigate the influence of impactor geometry suggest that HFRUP composites were able to withstand higher loads when tested with hemispherical impactor and also absorbed more energy than that for 90° and 30° shaped tup geometry. The post impact damage patterns and failure mechanisms of impacted samples were further characterised by ultrasonic (UT) inspection. Impact induced damage characterised by scanning electron microscope (SEM) suggests that damage induced by the impact included a typical failure mechanisms showing matrix cracking, fibre breakage and fibre pullout. As the impact velocity increases the damage to back face of the laminate increased for laminates tested with a hemispherical impactor while it decreased to certain extent for laminates tested with 90° and 30° impactor geometries.     

Mechanical behaviour of carbon and glass hybrid fibre reinforced polyester composites

Mechanical behaviour of carbon fibre/glass mat/polyester resin hybrid composites of sandwich construction is studied through tension, flexure, impact and post-impact tension tests. Tensile and flexural strength, modulus and failure strain values are compared to the calculated values. Total impact fracture energy and residual (after impact) tensile strength values of hybrid composites are analysed with regard to corresponding values of carbon/polyester composites. Failure of tested coupons was analysed by visual inspection and observation by scanning electron microscopy.     

天然细菌纤维素增强不饱和聚酯树脂复合材料的制备及性能

将天然纤维-细菌纤维素（BC）作为增强材料加入不饱和聚酯树脂（UPR）基体中,采用RTM工艺制备BC/UPR复合材料,并对其力学性能、吸湿性能进行了研究。通过紫外辐照方法探讨了BC/UPR复合材料的降解性能。研究结果表明:通过对细菌纤维素的表面改性,在亲水性的天然纤维和疏水性的高聚物基体之间形成了化学键结合,提高了BC/UPR复合材料的力学性能;BC纤维体积分数的增加也有助于提高力学性能, 当纤维体积分数为20%时,该复合材料拉伸强度最高可达152.9MPa; BC/UPR复合材料的吸湿过程符合Fick定律,吸湿可导致力学性能下降; BC/UPR复合材料吸收光能后,表面含氧官能团数量增加,发生一定程度的光降解。      

Effect of water absorption on dimensional stability and impact energy of jute fibre reinforced polypropylene

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

An experimental study of water absorption in polyester composites reinforced with macambira natural fiber

The use of raw materials from renewable sources, such as vegetable fibers, for example, has been the subject of several studies and researches. One major disadvantage in the use of vegetable fibers in polymer composites is their hydrophilic nature which provides weak interfacial adhesion in polymer‐fiber composites. Due to its importance, the purpose of this paper is to present an experimental study of water absorption in unsaturated polyester composites reinforced with macambira natural fiber. The studied samples have weight composition 30% macambira fiber and 70% unsaturated polyester, with dimensions of 20×20×3 mm³ and 20×20×6 mm³. Tests for water absorption were performed by immersing the samples in a bath of distilled water at 25, 50 and 70°C, and water uptake was measured gravimetrically along the process. Results of the micrographs (SEM), moisture content and area / volume relationships of the composites are shown and analyzed.     

改性亚麻布/不饱和聚酯复合材料的吸湿及力学性能

采用阳离子表面活性剂十八烷基三甲基溴化铵（STAB）对亚麻布进行了水相改性,并采用压片法进一步制备了亚麻布质量分数为28wt%的亚麻布/不饱和聚酯（UPE）复合材料。经过STAB改性后,亚麻布的吸湿率降低了30.3%,显著提高了其疏水性;改性亚麻布（TL1）/UPE复合材料的平衡吸湿率比未改性的亚麻布（UL）/UPE复合材料降低了26%;UL/UPE的水分子在复合材料中的扩散系数D值为1.11×10^-2 mm²/h,而TL1/UPE的D值仅为0.63×10^-2 mm²/h,说明水分子在UL/UPE中的扩散速度大于其在TL1/UPE中的速度;TL1/UPE复合材料的冲击强度比UPE提高了2.4倍,极大地改善了UPE的脆性。热稳定性测试显示TL1/UPE复合材料的热稳定性能满足应用要求。研究结果表明,对亚麻布进行STAB改性可有效改善复合材料的吸湿性,同时提高天然纤维与基体间的界面结合力及复合材料的力学性能,可用于制备得到综合性能优异的、有应用前景的亚麻布增强UPE天然纤维环保复合材料。     

Influence of silane coupling agents on interlaminar fracture in glass fibre fabric reinforced unsaturated polyester laminates

The relationship between the adhesive properties of the interphase of glass fibre/resin and the resultant composite Mode I delamination fracture toughness in glass fibre fabric laminate (GFFL) was studied. The Mode I interlaminar fracture toughness of GFFL was obtained by using a double cantilever beam (DCB) specimen. The delamination resistance of GFFLs which have two silane coupling agents and three concentration finishes is discussed on the basis of interlaminar fracture toughness. The crack propagation behaviour of DCB testing was mainly divided into stable and unstable manners. The fracture toughness and the crack propagation behaviour were dependent on the types and concentration of silane coupling agents.     

Interfacial effects in glass fibre composites as a function of unsaturated polyester resin composition

The tensile strengths of polyester laminates have been examined with respect to E-glass fibre–unsaturated polyester resin (UPR) interfacial properties. The tensile strengths of the polyester laminates were determined as a measure of interfacial bond strength. In accordance with the principles of Factorial Design several compositions of UPRs were prepared varying three factors: the saturated to unsaturated acid ratio, the branched to linear ether glycol ratio and the amount of styrene. The influence of UPR composition on the tensile strength of polyester laminates is owing to the effects on flexibility of the cured UPR. The compositions with lower degrees of unsaturation and with higher amount of linear ether glycol increase the flexibility of UPRs, improve adhesion with E-glass fibre and consequently increase the tensile strength of the polyester laminates.