Short glass fibre reinforcedpoly(butylene terephthalate) Part 2 –Effect of hygrothermal aging onmechanical properties

Abstract

The mechanical properties of injection moulded poly(butylene terephthalate) (PBT) containing various loadings of short glass fibres (SGF) have been investigated. Properties studied include tensile, flexural, and impact. Effect of hygrothermal aging on the mechanical properties was investigated by immersing the respective specimens in distilled water at 30, 60, and 90°C. All the materials tested showed poor retention in mechanical properties upon exposure to hygrothermal aging. The effect became particularly pronounced at an immersion temperature of 90°C. Fractographic inspection of the fracture surfaces revealed that both PBT and SGF–PBT composites embrittled owing to a hydrolitic degradation process. Hydrolysis not only suppressed the matrix ductility but also reduced the bonding quality between PBT and SGF. Poor interfacial bonding was indicated by the absence of polymer matrix adhering to the fibre surfaces. The decrease in the impact strength of hygrothermally aged SGF–PBT composites provided further evidence that hygrothermal aging at high temperature reduces the contribution of fibre related toughening mechanisms. The residual mechanical properties of both PBT and its composites were not fully recovered after redrying. The permanent damage to these materials was attributed to severe hydrolytic degradation of PBT.     

单向玻纤增强BMI复合材料的酸雨和温热老化行为

针对潮湿和酸雨多发地域的航空器用复合材料老化问题,模拟酸雨和温热(普通热水)环境,研究了单向玻璃纤维增强双马来酰亚胺树脂(BM I)复合材料(UGFRBC)吸水行为,通过红外光谱仪、力学测试装置、热力学分析装置分别表征了老化前后复合材料基体的结构、弯曲性能、层间剪切性能、动态粘弹性和玻璃化转变温度,分析了酸雨与温热环境下吸湿率对复合材料力学性能影响,建立了一种预测该复合材料酸雨和温热老化力学性能的经验公式。     

玻纤增强环氧树脂复合材料的酸雨循环老化性能与机理

针对潮湿和酸雨多发地域的航空器复合材料老化问题,模拟酸雨和湿热(普通热水)环境,研究了单向玻纤增强环氧树脂复合材料(UGFREC)在酸雨和湿热环境下的吸湿-干燥循环老化行为;分析了不同循环次数下的UGFREC的吸水动力学;采用力学测试装置、热力学分析装置和扫描电镜,分别表征酸雨和湿热循环老化前后UGFREC的弯曲性能、层间剪切性能、冲击强度、动态粘弹性、玻璃化转变温度和冲击破坏形貌;初步给出反映酸雨和湿热循环过程中基体树脂与纤维间的界面应力变化模型。     

Effects of poly(butylene adipate‐co‐terephthalate) and ultrafined wollastonite on the physical properties and crystallization of recycled poly(ethylene terephthalate)

Recycled poly(ethylene terephthalate) (rPET), obtained mainly from postconsumer bottles, was melt‐mixed with either poly(butylene adipate‐co‐terephthalate) (PBAT) or PBAT plus ultrafine wollastonite (～5 μm) at different weight ratios on a twin‐screw extruder and then injection‐molded. Among the five rPET/PBAT blends (10–50 wt% PBAT) evaluated, the 80/20 wt% rPET/PBAT blend exhibited the highest tensile strength and degree of crystallinity, a slight increase in the tensile strain, and a remarkable increase in the melt flow index, but a lower tensile modulus and thermal stability with respect to the neat rPET. This blend was subsequently filled with four loading levels of wollastonite (10–40 wt%), where the tensile properties (modulus, strain at break, and strength) and thermal stability of the blend were all improved by the addition of wollastonite in a dose‐dependent manner. Based on differential scanning calorimetry analysis, the crystallinity of rPET in the rPET/PBAT/wollastonite composites decreased in the presence of wollastonite, accompanied with a noticeable increase in the glass transition, cold crystallization, and crystallization temperatures, but only a slight change in the melting temperature was noted compared with those of the neat 80/20 wt% blend. Moreover, the addition of wollastonite at 30 wt% or higher showed a strong reduction in the melt dripping of the composites during combustion. J. VINYL ADDIT. TECHNOL., 23:106–116, 2017. © 2015 Society of Plastics Engineers     

Effects of hygrothermal aging on the thermomechanical properties of a carbon fiber reinforced epoxy sheet molding compound: An experimental research

Carbon fiber sheet molding compounds (C-SMCs) are discontinuous fiber reinforced composite materials. Among them, epoxy-based C-SMCs are becoming relevant materials due to their high thermomechanical performance and better formability than continuous fiber reinforced composites. The thermomechanical performance of epoxy resins and epoxy based continuous carbon fiber composites have shown to be influenced by hygrothermal aging. In this work, this influence is studied for an epoxy-based C-SMC. Epoxy-based C-SMC samples were hygrothermally aged by means of accelerated conditioning, exposing them to 65% relative humidity, and 80°C in a climatic chamber. The equilibrium moisture content, as well as the moisture diffusion coefficient has been determined. The thermomechanical properties of epoxy C-SMC have been analyzed by dynamic mechanical analysis, tensile, 3-point bending, and short beam tests in dry and aged samples. The results showed that epoxy C-SMC is affected by hygrothermal aging in the cases of moisture intake and its effects on T_g value, but interestingly, the hygrothermal aging did not generate any degradation effects in the mechanical response of epoxy C-SMC.     

Hygrothermal aging and fracture behavior of styrene‐acrylonitrile/acrylate based core–shell rubber toughened poly(butylene terephthalate)

A study of hygrothermal aging in terms of the kinetics of moisture absorption by poly(butylene terephthalate) (PBT) and styrene‐acrylonitrile/acrylate based core–shell rubber (CSR) toughened PBT (PBT‐CSR) was undertaken. The diffusion of water into the PBT compounds with various CSR contents was investigated by immersion of specimens in water at temperatures between 30 and 90°C. It was observed that the equilibrium moisture content and the diffusion coefficient of the PBT both increased with increasing CSR content. The fracture behaviors of the PBT and PBT‐CSR were investigated. The focus of investigation was on the effect of an internal parameter (rubber content) and external parameters (testing temperature, deformation rates, and hygrothermal aging) on the fracture behavior of these materials. The fracture response of the various materials was evaluated by the fracture toughness and energy measured on static‐loaded compact tension specimens. The tensile and fracture behavior of PBT and PBT‐CSR was affected by both the internal and external parameters. On its own the CSR impact modifier failed to improve the toughness of PBT at either high testing speed or subambient temperature (−40°C). Based on the dynamic mechanical analysis study, the CSR is believed to behave as a rigid particulate filler in the PBT that consequently reduces the ductility of the PBT. All the materials tested showed poor retention of the tensile and fracture properties upon exposure to hygrothermal aging at 90°C, and these properties could not be restored by subsequent drying. This was attributed to severe hydrolytic degradation of the PBT that caused permanent damage to the materials. The failure modes of PBT and PBT‐CSR were assessed by fractographic studies in a scanning electron microscope. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2470–2481, 1999     

EVAC/ADP/MPP复合材料的抗老化性能

在乙烯–乙酸乙烯共聚物(EVAC)/二乙基次膦酸铝(ADP)/三聚氰胺聚磷酸盐(MPP)复合材料中加入紫外线吸收剂UV–531和抗氧剂1010,并对其进行老化性能研究,主要研究了"双85"湿热老化以及紫外老化对其力学性能以及热稳定性的影响。研究结果表明,经过"双85"湿热老化后,EVAC/ADP/MPP复合材料的拉伸强度和断裂伸长率都呈现出先上升后下降的趋势。经过紫外老化试验的EVAC/ADP/MPP复合材料的拉伸强度和断裂伸长率却都呈现出不断下降的趋势。通过红外光谱研究发现,EVAC/ADP/MPP在"双85"湿热老化试验时老化降解在乙烯和乙酸乙烯链段同时进行,而在紫外老化试验中老化降解主要发生在乙烯链段;热失重以及差示扫描量热分析发现,经过长时间的湿热以及紫外老化试验之后EVAC/ADP/MPP复合材料的热稳定性变差、残炭量变少。     

玻璃纤维增强回收聚对苯二甲酸乙二醇酯复合材料的力学性能

用熔融共混制备了玻璃纤维（GF）增强的回收聚对苯二甲酸乙二醇酯（rPET）复合材料,研究了复合材料的力学性能并进一步利用Halpin-Tsai模型、Krenchel-COX模型和Kelly-Tyson模型探讨了GF的近程和远程结构与复合材料性能间的关系。结果表明,GF对rPET具有较为显著的增强、增韧效果。当玻璃纤维含量为30 %(质量分数,下同)时,复合材料的冲击强度、拉伸强度以及弯曲强度分别提高了245 %、113 %以及84 %;长径比和取向度是影响GF改性rPET复合材料性能的重要结构参数;Halpin-Tsai方程能够较好地描述rPET/GF复合材料中GF的有效长径比;而相比于Krenchel-COX方程,由Kelly-Tyson方程获得的GF的取向度更接近实验结果。     

rPET/POE/LDPE-g-AA复合材料的制备及性能

以回收聚对苯二甲酸乙二酯( rPET)为基体材料,乙烯-辛烯共聚物(POE)为增韧材料,丙烯酸接枝低密度聚乙烯( LDPE-g-AA)为增容剂,制备了rPET/POE/LDPE-g-AA复合材料.分析了POE、LDPE-g-AA对rPET 玻璃化转变温度、断面相结构、结晶性能、力学性能的影响.结果表明,加入POE...     

Kinetics of water absorption and hygrothermal aging rubber toughened poly(butylene terephthalate) with and without short glass fiber reinforcement

The objectives of this paper were to investigate the water absorption and hygrothermal aging behavior of rubber‐toughened poly(butylenes terephthalate) (RT‐PBT) with and without short glass fiber (SGF) reinforcement. The rubbers used in the study were AX8900 and EXL2314, both of which are acrylate‐based terpolymer. The effect of the hygrothermal aging on its fracture properties was also studied. The kinetics of the water absorption study were carried out on the injection‐molded samples of the RT‐PBTs and the SGF‐reinforced rubber‐toughened PBT (SGF‐RT‐PBT) at three immersion temperatures, 30, 60 and 90°C, for a total of 450 h. The study of the deterioration caused by the hygrothermal aging was conducted by investigating the fracture parameters and flexural properties of all the materials as both hygrothermally aged (HA) and redried state (RD). The modes of the failure of HA and RD samples were studied using the scanning electron microscopy (SEM) technique. It was found that all the samples conformed to Fickian behavior and the kinetics of absorption exhibited a strong dependency on the rubber types, presence of SGF, as well as the immersion temperature. Generally, SGF‐RT‐PBT showed a better resistance to hygrothermal aging than that of RT‐PBT and PBT, though a declining trend was observed in the fracture parameters, K_c and G_c. However, an opposite observation was exhibited in the flexural properties in some, but not all cases. Finally, the results obtained from SEM micrographs showed that permanent damage occurred in the materials and the hygrothermal aging had suppressed the plastic deformation ability of the PBT matrix and both types of impact modifiers where brittle failure was observed. Fiber pull‐out was apparently the failure mode of the SGF‐reinforced materials. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 506–516, 2004     

Acoustic emission characterization of damage in short hemp‐fiber‐reinforced polypropylene composites

This article aims at investigating the effects of hygrothermal aging on the damage mechanisms of short white Hemp Fiber Reinforced Polypropylene (HFRP) composites with various fiber contents (10, 20, 30, and 40 wt%). Injected molded specimens were subjected to hygrothermal aging with a relative humidity of 80% and two temperatures, 25 and 50°C. The water absorption and its effect on tensile properties of HFRP composites were investigated. The Acoustic Emission (AE) technique combined with scanning electron microscopy observations was used to identify microstructural damage events leading to overall failure of the HFRP composites. This identification according to hemp‐fiber content and hygrothermal aging was made with an unsupervised method based on a statistical multi‐variable analysis (k‐means algorithm). The AE results indicate that the quality of fiber‐matrix interface plays a major role in the damage process of HFRP composites, shown by the number of AE signals induced by the interface failure and their amplitude ranges. POLYM. COMPOS. 37:1101–1112, 2016. © 2014 Society of Plastics Engineers     

RTM制备玻璃纤维增强环氧树脂复合材料的力学性能分析

以环氧树脂为基体,短切玻璃纤维和玻璃纤维布为增强材料,通过RTM工艺制备了玻璃纤维增强环氧树脂(GF/EP)复合材料,并研究了RTM工艺制备玻璃纤维布增强环氧树脂(L-GF/EP)和短切玻璃纤维增强环氧树脂(S-GF/EP)复合材料的拉伸和弯曲性能,分析了开孔对两种复合材料拉伸性能的影响。结果表明:在拉伸过程中,开孔试样因孔边产生的应力集中,导致其拉伸强度与无孔试样相比下降了30%左右;玻纤铺层类型的不同对复合材料的力学性能具有显著影响;L-GF/EP复合材料内部结构完整,在载荷作用下,复合材料的弯曲断裂呈现一定的假塑性断裂模式,达到弯曲极限挠度值后,出现一定程度的回弹现象,其力学性能优于S-GF/EP复合材料。     

In situ microfibrillar‐reinforced composites of isotactic polypropylene/recycled poly(ethylene terephthalate) system and effect of compatibilizer

Recycled poly(ethylene terephthalate) from waste bottles (hereafter, rPET) was used as an reinforcing material for isotactic polypropylene (iPP) based on the concept of in situ microfibrillar‐reinforced composites (iMFCs). Microfibers of rPET were successfully generated during melt‐extrusion and subsequent drawing and preserved in the final injection‐molded specimens. The effects of draw ratio, initial size of ground rPET flakes, and rPET content on morphological appearance of the extrudates and the as‐formed rPET fibers and mechanical properties of the as‐prepared iMFCs were investigated. The results showed that diameters of the as‐formed rPET fibers decreased with increasing draw ratio, and the initial size of ground rPET flakes did not affect the final diameters of the as‐formed rPET fibers nor the mechanical properties of the as‐prepared iMFCs. Flexural modulus, tensile modulus, and tensile strength of iPP/rPET iMFCs were improved by the presence of rPET microfibers and further improvement could be achieved by the addition of maleic anhydride‐grafted iPP (PP‐g‐MA), which was used as the compatibilizer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1173–1181, 2006     

A comparison between the static and fatigue properties of glass‐fiber and carbon‐fiber reinforced polyetherimide composites after prolonged aging

The static and fatigue behavior of two fiber‐reinforced composites was characterized after samples were subjected to both natural and accelerated aging. The composites consisted of a thermoplastic matrix (PEI: polyetherimide) reinforced with glass or carbon fabric. Natural aging involved exposing samples to the elements over a period of two years, while accelerated aging was conducted in a saline solution during 200 days. Subsequently, static (tensile and interlaminar shear) and fatigue tests were carried out with the aim of determining the mechanical properties of the materials after exposure. A negligible decrease in the value of these properties was observed, while different behavior was detected depending on the type of aging of the material.     

相容剂对rPET/mLLDPE共混物性能的影响

以回收聚对苯二甲酸乙二醇酯(rPET)为基体材料,茂金属线型低密度聚乙烯(mLLDPE)为共混材料,马来酸酐接枝线型低密度聚乙烯(LLDPE-g-MAH)、丙烯酸酯复合接枝苯乙烯-丁二烯弹性体为相容剂,制备了rPET/mLLDPE共混物。采用DSC和SEM分析了相容剂对共混物结晶性能及断面结构的影响,并检测了共混物的力学性能。结果表明:mLLDPE的加入使得rPET/mLLDPE共混物的熔体结晶峰向右移动,结晶温度提高了29.03℃;相容剂的加入使得共混物中rPET的玻璃化转变温度向低温方向移动,rPET与mLLDPE相容性增强;含3%LLDPE-g-MAH的rPET/mLLDPE共混物中,MAH基团与rPET中的羟基发生接枝反应,相界面模糊,rPET与mLLDPE界面黏结力增强,与纯rPET相比,其断裂伸长率提高了93.73%,缺口冲击强度提高了54.6%。     

Durability of Glass-Fiber-Reinforced Cements with Different Alkali-Resistant Glass Fibers

The durability of glass-fiber-reinforced cement composites prepared with different commercial alkali-resistant glass fiber strands was studied to determine the effect of aging in different environments on the flexural behavior of the composites and on their microstructure. Considerable differences in degradation of mechanical properties could be observed in composites prepared with different glass fiber strands, and they could be correlated with the SEM observations: higher rates of degradation were obtained in composites in which hydration products grew more readily between the glass filaments. It is suggested that during the first year of aging in water at 207deg;C, this growth of hydration products is mainly responsible for the reduction in mechanical properties; chemical degradation of the glass does not play an important role, at least not at this earlier stage.     

新型扩容导线用玻纤／碳纤复合芯恒温热老化研究

玻纤／碳纤维复合芯热老化是影响新型电力输电导线服役寿命的关键因素。本研究对输电导线玻纤／碳纤复合芯进行了人工加速老化试验,重点研究了老化过程中复合芯质量和机械性能变化,并利用复合芯微观组成变化对老化机理进行了分析。人工加速老化试验结果表明,在160℃进行了6000h高温热老化试验后,复合芯的质量、弯曲强度和拉伸强度保持率分别为96．5％,90．5％与81．5％,新型导线用复合芯表现出优异的耐热老化行为;复合芯的热老化行为与小分子分解速率和氧气扩散反应速率相关,长期热氧老化会腐蚀树脂基体,在复合芯表面形成疏松的玻纤层,进而影响到复合芯的机械性能。     

Concentration effect of γ‐glycidoxypropyltrimethoxysilane on the mechanical properties of glass fiber–epoxy composites

In this study, glass fibers were modified using γ‐glycidoxypropyltrimethoxysilane of different concentrations to improve the interfacial adhesion at interfaces between fibers and matrix. Effects of γ‐glycidoxypropyltrimethoxysilane on mechanical properties and fracture behavior of glass fiber/epoxy composites were investigated experimentally. Mechanical properties of the composites have been investigated by tensile tests, short beam tests, and flexural tests. The short‐beam method was used to measure the interlaminar shear strength (ILSS) of laminates. The tensile and flexural properties of composites were characterized by tensile and three‐point bending tests, respectively. The fracture surfaces of the composites were observed with a scanning electron microscope. On comparing the results obtained for the different concentrations of silane solution, it was found that the 0.5% GPS silane treatment provided the best mechanical properties. The ILSS value of heat‐cleaned glass fiber reinforced composite is enhanced by ∼59% as a result of the glass fiber treatment with 0.5% γ‐GPS. Also, an improvement of about 37% in tensile strength, about 78% in flexural strength of the composite with the 0.5% γ‐GPS treatment of glass fibers was observed. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Physical aging in particulate-filled composites with an amorphous glassy matrix

Physical aging was studied on particulate -filled glassy network polymers by means of mechanical -dilatational, differential scanning calorimetry (DSC) and density measurements on specimens that were aged at room temperature. The composites aged for 0.5 day fractured in a brittle manner at a constant ultimate stress, which is close to the tensile strength of the unfilled material, regardless of the filler content and the presence of a coupling agent. This type of mechanical behavior is caused by the compressive residual stresses that are present due to curing and differential thermal shrinkage. As aging takes place, the compressive residual stresses are relieved; as a result the ultimate tensile strengths of the composites decrease. The 120 -day -old untreated glass bead containing composites exhibited dilatation and yield in mechanical -dilatational testing. This type of behavior is described as “having no adhesion” between the filler and the matrix. The 120 -day -old composites with coupling agent -treated glass beads fractured at a tensile stress which is equal to 1/1.6 the tensile strength of the unfilled material. These materials did not exhibit dilatation and yield in mechanical -dilatational testing. Density and DSC data indicate densification and enthalpy relaxation upon again and support the hypothesis presented for the observed change in the mechanical -dilatational behavior.     

Hygrothermal cycling effects on the durability of phenolic based composites

Work has been performed to investigate the thermal and mechanical properties of carbon fiber/phenolic resin composites as engineering materials for the aerospace industry. These materials are cost effective while displaying excellent temperature and fire resistance as well as good mechanical properties. All phenolic and epoxy composite specimens used here were prepared by resin transfer molding (RTM) to model a cost‐effective process. Hygrothermal cycling effects on the property changes of phenolic composites were evaluated through thermal, mechanical, and morphological tests. The fracture performance of a phenolic composite modified with a silicone‐based additive decreased after fewer hygrothermal cycles than unmodified phenolic and epoxy composites. Results from dynamic mechanical analysis (DMA) experiments showed that the modified phenolic composite was more significantly affected by the hygrothermal cycling than the unmodified phenolic composites. Fatigue tests showed that the phenolic composites that were not exposed to hygrothermal cycling had more resistance to fatigue cycles than the epoxy composites.