Study on long fiber–reinforced thermoplastic composites prepared by in situ solid‐state polycondensation

Long glass fiber–reinforced thermoplastic composites were prepared by a new process, in situ solid‐state polycondensation (INSITU SSP). In this process reinforcing continuous fibers were impregnated by the oligomer of PET melt, and then the impregnated continuous fibers were cut to a desired length (designated prepreg); finally, the prepreg was in situ polymerized in the solid state to form the high molecular weight matrix. SEM, FTIR spectra, short‐beam shear stress test, flexural strength test, impact strength test, and the intrinsic viscosity measurement were used to investigate the wetting and interfacial adhesion, the mechanical properties of the composite, and the molecular weight of matrix resin in the composite. The results showed that the molecular weight of PET in the matrix resin and mechanical properties could be adjusted by controlling the SSP time and that the high level of interfacial adhesion between reinforcing fibers and matrix resin could be achieved by this novel INSITU SSP process, which are attributed to the good wetting of reinforcing fibers with low molecular weight oligomer melt as the impregnation fluid, the in situ formation of chemical grafting of oligomer chains onto the reinforcing fiber surface, and the in situ formation of the high molecular weight PET chains in the interphase regions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3959–3965, 2004     

Short-fiber-reinforced styrene–butadiene rubber composites

Processing characteristics, anistropic swelling, and mechanical properties of short-jute-fiber-and short-glass-fiber-reinforced styrene–butadiene rubber (SBR) composites have been studied both in the presence and absence of carbon black. Tensile and tear fracture surfaces of the composites have been studied using scanning electron microscopy (SEM) in order to assess the failure criteria. The effects of bonding agent. carbon black, jute fiber, and glass fiber on the fracture mode of the composites have also been studied. It has been found that jute fiber offers good reinforcement to SBR as compared to glass fibers. The poor performance of glass fibers as reinforcing agent is found to be mainly due to fiber breakage and poor bonding between fiber and rubber. Tensile strength of the fiber–SBR composites increases with the increase in fiber loading in the absence of carbon black. However, in the presence of carbon black a minimum was observed in the variation of strength against fiber loading. SEM studies indicate that fracture mode depends not on the nature of the fiber but on the adhesion between the fiber and the matrix.     

Graded glass mat–reinforced polypropylene

In the impregnation process, when pressure is applied, the dry fiber preform is first compressed and then unloads as the matrix flows within the pores. It has been shown earlier that for glass mat–reinforced thermoplastic (GMT) materials, the time to provide complete infiltration of the matrix is significantly shorter than the unloading time of the reinforcement. This effect is exploited here to control the processing time in order to provide full infiltration but limited relaxation of the fiber bed, thereby producing a graded fiber content structure. Symmetric glass fiber/polypropylene (PP) composites were impregnated for different processing times to produce parts with a higher fiber content on the surface, decreasing towards the center. The elastic modulus in bending of the GMT parts was measured by a three‐point flexure test while the distribution of fibers in the matrix was quantified using optical microscopy combined with image analysis. The flexural modulus of GMT was found to decrease with the impregnation time, in good agreement with the prediction from infiltration and mechanics theory. Controlled processing could therefore be used to maximize the bending stiffness of GMT. POLYM. COMPOS., 26:361–369, 2005. © 2005 Society of Plastics Engineers.     

Microwave irradiation of nadic-end-capped polyimide resin (RP-46) and glass–graphite–RP-46 composites: cure and process studies

Microwave energy was investigated to cure nadic-end-capped polyimide precursors (RP-46 resin) using a Cober Electronics Model LBM 1.2A/7703 microwave oven at a frequency of 2.45 GHz. Both neat resin samples and glass cloth and hybrid glass cloth–graphite cloth–RP-46 resin composites were studied. For the resin studies, the effect of various parameters, such as power level, sample size, processing temperature, time, and graphite fiber absorber, were investigated. The variables investigated with the composite study were the power level, mold material, vacuum, and low pressure. The results showed that microwave energy was effective in curing both neat resin samples and composite specimens. The presence of a small quantity of absorber (chopped carbon fiber) accelerates the cure dramatically. Moreover, soapstone mold material was found to be an efficient absorber for glass and glass–graphite composite processing, causing an effective cure in less than 1 h. Glass and glass–graphite hybrid composites with flexural strengths of 372–588 MPa (54–85 ksi) and moduli of 28.7–31.7 GPa (4.2–4.6 Msi) have been fabricated. This is equivalent to 50 to 80% of the properties of composites fabricated by conventional means. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2391–2411, 1999     

玻纤/石墨/聚芳醚腈复合材料的制备与性能

以聚芳醚腈(PEN)为基体,采用双螺杆挤出机熔融共混制备了玻纤、石墨复合材料,重点研究了两种不同形貌的增强填料对PEN树脂的协同增强作用。测试了不同样品的拉伸、弯曲和冲击等力学性能,利用扫描电镜对拉伸断面进行形貌分析,并对样品进行了TGA测试和流变性能测试。结果表明,大量玻纤以棒状存在于PEN树脂当中,构成骨架结构,使得PEN树脂力学性能大幅度提高,石墨以片层形状存在于PEN树脂与玻纤之间,进一步增强了PEN树脂基体的连接作用,从而使得复合材料力学性能进一步提高;石墨在提高PEN树脂强度的同时能够提高PEN树脂的热稳定性;在相同频率下,PEN基复合材料的储能模量和耗能模量均随玻纤和石墨填料含量增加而提高,低含量的石墨填入对体系的模量和黏度影响较小。     

Effects of thermal history on mechanical behavior of PEEK and its short-fiber composites

The effect of crystallinity differences induced by mold wall temperature and annealing on mechanical behavior is evaluated for poly(etheretherketone) (PEEK) resin and its composites. The systems investigated were neat PEEK, glass fiber (GF) reinforced PEEK, and carbon fiber (CF) reinforced PEEK. Both composite systems were reinforced with 10, 20, and 30 wt% fiber. The degree of crystallinity (X_c) of PEEK was found to increase by processing at higher mold temperatures, by annealing, and by fiber length reductions, which appears to indicate the ability of short fibers to nucleate the crystallization of PEEK under favorable thermal conditions. Improvements in Young's modulus and strength together with ductility reductions are generally obtained as crystallinity increases in both neat PEEK and its composites. The contribution of crystallinity to mechanical behavior is significant only for neat PEEK and PEEK reinforced by 10% fiber. SEM micrographs reveal that this is due to a change in failure mode. When PEEK is reinforced by carbon fibers or by 20–30% glass fibers, a macroscopic brittle mode of failure is observed irrespective of matrix crystallinity, and mechanical behavior is principally determined by the nature and content of the reinforcing fibers.     

Effect of compaction treatment on laminated CFRP composites fabricated by vacuum‐assisted resin‐transfer molding

Carbon fiber‐reinforced polymer (CFRP) composites were fabricated using ordinary and compaction setups (OS and CS, respectively) in the vacuum‐assisted resin‐transfer molding (VARTM) process. The mechanical properties and acoustic emission (AE) spectra of the CFRP composites were compared among fabricated samples. The CFRP plates with sequences of [+30/−30]₆ were sectioned to make specimens for Mode I interlaminar fracture tests and three‐point bending tests. The difference between the material properties and AE characteristics of the OS and CS specimens were statistically compared using one‐way analysis of variance. The OS specimens had a thicker resin layer, a higher resin fraction, larger average fracture toughness, and AE energy corresponding to the Mode I fracture, whereas the CS specimens had more macro‐scale voids and higher bending strength. AE analysis showed that frequency bands in the interlaminar fracture tests corresponding to matrix‐related fracture were dominant for the OS specimens, whereas those corresponding to the mixed fracture mode of the fiber and matrix fracture were dominant for the CS specimens. In the bending tests, mixed fiber‐matrix fractures were dominant for the OS specimens, and fiber‐related fractures were dominant for the CS specimens. In conclusion, the compaction treatment diminished interlaminar fracture toughness, due to the enhanced formation of macro‐scale voids around the fiber bundles during the resin impregnation stage. However, the bending strength improved with an increased fiber volume fraction. POLYM. COMPOS., 38:217–226, 2017. © 2015 Society of Plastics Engineers     

Mechanical characterization and fractography of glass fiber/polyamide (PA6) composites

The mechanical properties of the glass fiber reinforced Polyamide (PA6) composites made by prepreg tapes and commingled yarns were studied by in‐plane compression, short‐beam shear, and flexural tests. The composites were fabricated with different fiber volume contents (prepregs—47%, 55%, 60%, and commingled—48%, 48%, 49%, respectively) by using vacuum consolidation technique. To evaluate laminate quality in terms of fiber wet‐out at filament level, homogeneity of fiber/matrix distribution, and matrix/fiber bonding standard microscopic methods like optical microscopy and scanning electron microscopy (SEM) were used. Both commingled and prepreg glass fiber/PA6 composites (with V_f ∼ 48%) give mechanical properties such as compression strength (530–570 MPa), inter‐laminar shear strength (70–80 MPa), and transverse strength (80–90 MPa). By increasing small percentage in the fiber content show significant rise in compression strength, slight decrease in the ILSS and transverse strengths, whereas semipreg give very poor properties with the slight increase in fiber content. Overall comparison of mechanical properties indicates commingled glass fiber/PA6 composite shows much better performance compared with prepregs due to uniform distribution of fiber and matrix, better melt‐impregnation while processing, perfect alignment of glass fibers in the composite. This study proves again that the presence of voids and poor interface bonding between matrix/fiber leads to decrease in the mechanical properties. Fractographic characterization of post‐failure surfaces reveals information about the cause and sequence of failure. POLYM. COMPOS., 36:834–853, 2015. © 2014 Society of Plastics Engineers     

玻纤增强PP热塑性片材的制备及力学性能研究

采用熔融浸渍法制备了玻璃纤维毡增强聚丙烯（PP）热塑性复合片材;通过在PP中加入复合改性PP改善了基体与增强纤维间的相容性;考察了相容剂、PP种类及玻纤毡种类对复合片材的影响。结果表明,相容剂的加入可使复合片材的拉伸强度提高29％、拉伸模量提高23％、弯曲强度提高42％、弯曲模量提高25％;高熔体质量流动速率PP可使片材的弯曲与冲击性能进一步改善。连续玻纤毡和长玻纤毡增强PP复合片材,前者综合力学性能良好,而后者则冲击强度较弱、弯曲性能加强。     

Structure–property relationships in glass‐reinforced polyamide,part 1: The effects of fiber content

We present the results of an extensive study of the performance of injection‐molded glass‐fiber reinforced polyamide 66 with glass content between 0 and 40% and based on two chopped glass products both sized with polyamide compatible sizing. Mechanical properties generally improved with increasing glass content, modulus linearly, strength with a maximum at 40–50% glass content, and impact showing an initial decrease from the resin value with a minimum at 4% glass content before increasing at higher glass contents. Residual fiber length decreased linearly with increasing glass content. Interfacial strength was found to be in the range of 30–36 MPa, and no significant differences in dry as molded performance was found between the 123D and 173X sizings. Conditioning these composites in either boiling water or water/glycol mixtures leads to a dramatic drop in both tensile modulus and tensile strength. This is most likely due to the high level of matrix plasticization. After conditioning, the 173X sized glass delivered a significantly higher level of tensile elongation at all fiber contents. Excellent agreement was obtained between the experimental data and the theoretical predictions of the rule of mixtures model for modulus and the Kelly‐Tyson model for strength over the range of fiber concentrations studied. POLYM. COMPOS. 27:552–562, 2006. © 2006 Society of Plastics Engineers     

吸水对连续玻璃纤维增强聚丙烯复合材料的力学性能影响的研究

采用连续玻璃纤维增强聚丙烯(PP)预浸布制备复合材料层压板,通过人工加速老化的方法,对不同铺层的连续玻璃纤维增强PP复合材料进行常温、60℃、80℃的海水浸泡实验,研究连续玻璃纤维增强PP复合材料的弯曲强度随老化时间、老化温度等因素的变化规律及性能退化趋势。研究表明,老化初期吸水趋势符合菲克扩散,老化程度与时间和温度成正比关系。对试样断裂部分拍摄扫描电子显微镜(SEM)图像,观察不同环境条件下样品老化情况,老化温度越高、时间越长,增强纤维与树脂基体界面腐蚀越严重。     

多孔微珠用于制备低密度BMC材料

采用多孔微珠为填料制备了不饱和聚酯低密度团状模塑料(BMC)。选取多孔微珠的粒径及掺量,短切玻璃纤维的长度及掺量为4因素,设计L16(44)正交试验,并结合示差扫描量热法(DSC)和扫描电镜(SEM)对复合体系的增强机理进行了研究。结果表明,制备轻质BMC材料的最佳条件为:多孔微珠的粒径<0.710 mm,掺量4%,短切玻纤长度6 mm,掺量30%,此时制得BMC材料密度为1.314 g/cm3,弯曲强度为81.50 MPa,满足国标GB/T 23641—2009对BMC弯曲强度的要求(≥80 MPa)。多孔微珠的蜂窝壁对树脂的固化起到了阻碍作用,固化时间延长,放热不完全,同时多孔微珠的填充使得树脂基体的应力分散不均,样品的表观密度和弯曲强度降低。     

长玻纤增强聚丙烯复合材料的制备及力学性能

使用熔融浸渍法制备了长玻璃纤维增强聚丙烯复合材料(LFTPP-G),研究了不同纤维含量、不同牵引速度及不同相容剂马来酸酐接枝聚丙烯(PP-g-MAH)添加量对复合材料力学性能的影响.结果表明,玻璃纤维在复合材料体系中起增强增韧作用,复合材料力学性能随纤维含量增加而升高;提高牵引速度可以提高生产效率,但复合材料的力学性能...     

Hot water resistance of glass‐fiber and glass‐bead reinforced thermoplastics

The hot water resistance of three kinds of short glass fiber or glass bead‐reinforced plastics [polyphenyleneether (PPE), polyphenylenesulfide (PPS), and polyoxymethylene (POM)] was studied by hot water immersion testing, tensile testing and water‐hammer fatigue testing. It was found that the degradation of the strength was observed only for the reinforced plastics under hot water immersion and that the change of the tensile strength was most drastic in glass fiber‐reinforced PPS (GFPPS). Scanning electron microscope (SEM) observations of the tensile fracture surface revealed that the change in tensile strength was attributable to the deterioration of the interface between the glass fiber and the matrix resin. The results of acoustic emission analysis also supported the conclusion that the change in strength was due to the deterioration of the interface. Although the change in the tensile strength of glass fiber‐reinforced PPE (GFPPE) was small compared with that of GFPPS, debonding between the glass fiber and the matrix resin and surface cracks was observed on the surface of the GFPPE specimens.     

GFRP填料塔的设计

以双酚A型不饱和聚酯，胶衣树脂为基体树脂，玻璃纤维表面毡，玻璃布，短玻璃纤维毡为增强材料，制备了玻璃纤维增强塑料（GFRP）填料塔。论述了基体树脂，增强材料的选择，GFRP塔的结构设计，强计计算和手糊成型，组装的工艺要求。应用结果表明，该GFRP填料完全可满足硫酸生产净化工艺的使用要求。     

The effect of hydroxyl‐terminated polybutadiene‐grafted carbon fiber on the impact performance of carbon fiber–epoxy resin composites

Carbon fiber (CF) containing 1.4 and 2.1 mmol/g of —COOH and —OH groups, respectively, was functionalized by using an excess of tolylene‐2,4‐diisocyanate. The NCO‐modified CF was submitted to a graft reaction with hydroxyl‐terminated polybutadiene (HTPB). The HTPB‐grafted carbon fiber was employed as reinforcing agent for epoxy resin‐based composites. The presence of the flexible HTPB at the interface between the fiber and the matrix resulted in a substantial improvement on impact strength. Additional improvement on toughness was achieved by using epoxy matrix containing dispersed phase of HTPB. The composite morphology was also studied by scanning electron microscopy. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1424–1431, 1999     

Ionomer. I. The effect of woven glass mat reinforcement on tensile properties

An investigation was conducted on ionomer polymer. The ionomer pellets were molded into a thin sheet before fabrication into composites. The reinforcing agent used was woven glass mat. Before fabrication, the woven glass mat was treated with the following: 1. silane coupling agent for 5 min and dried at room temperature; 2. silane coupling agent for 5 min and dried in the oven at 110°C for 15 min; 3. Ultraviolet radiation for 5 min; and 4. silane (oven dried + ultraviolet). The composites were fabricated at various pressure, time, and temperature. An ideal processing condition was established, i.e., pressure = 5 MPa, temperature = 180°C, and the impregnation time = 30 min. The void contents of the composites were estimated using the ignition method and the tensile properties were measured. The results revealed that good impregnation of the matrix ionomer into the reinforcing agent can be achieved at 180°C. This was confirmed by low void content as compared with other test temperatures. Further clarification was through the tensile properties, which were higher than those at lower temperatures (120 and 150°C). The effect of fiber orientation was checked, and both 0 and 90° had identical strengths and moduli irrespective of the various fiber treatments. Apart from the void contents, the degree of impregnation was also checked based on the tensile strengths in 45, 25, and 60° fiber orientations. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1395–1400, 2001     

FTIR and SEM analysis of polyester‐ and epoxy‐based composites manufactured by VARTM process

Polyester‐ and epoxy‐based composites containing glass and carbon fibers were manufactured using a vacuum‐assisted resin transfer molding (VARTM) process. Fourier transform infrared (FTIR) spectroscopy analyses were conducted to determine the interaction between fibers and matrix material. The results indicate that strong interaction was observed between carbon fiber and epoxy resin. However, weak interactions between remaining fiber‐matrix occur. Scanning electron microscopy (SEM) analysis was also performed to take some information about strength of interaction between fibers and matrix material. From SEM micrographs, it is concluded that the findings in SEM analysis support to that obtained in FTIR analysis. Another aim of the present work was to investigate the influence of matrix on composite properties. Hence, the strengths of composites having same reinforcement but different matrix systems in axial tension and transverse tension were compared. Short beam shear test has been conducted to characterize the interfacial strength in the composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Dynamic properties of thermoplastic butadiene–styrene (SBS) and oxidized short carbon fiber composite materials

In composites consisting of a thermoplastic butadiene–styrene (SBS) elastomer matrix reinforced with oxidized short carbon fiber, scanning electron microscopy (SEM) reveals the existence of matrix–fiber interactions, which are not detected when employing commercial carbon fiber. Interpretation of the dynamic properties and other parameters, such as equivalent interfacial thickness, and glass transition temperature, measured in terms of maximum damping temperature, as well as the apparent activation energy of the relaxation process, helps to explain the existence of such interactions. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1819–1826, 1998     

Optimizing fiber wetout for composites manufacturing

Decreased mechanical strength in a fiber reinforced plastic part can often be traced to poor or incomplete impregnation of the reinforcing fiber with the matrix. To properly understand the impregnation process in the design of new composites manufacturing machinery (specifically in unidirectional tape machines), or to optimize wetout in existing machine designs, the raw process materials and their relationship within the process environment must be examined. The critical factors are: resin viscosity vs. temperature; the work of adhesion between the fiber and resin; and the problem of forcing the resin to completely penetrate a fiber bundle. If these factors are known, nip rolls can be designed to meet a specific process envelope, or in the case of existing equipment, the existing process envelope for specific fiber/matrix combinations can be manipulated for maximum fiber wetout.