Materials Science Research International, Vol.2, No.2, pp. 87-92 (1996) General paper MECHANICAL AND THERMAL PROPERTIES OF INJECTION MOLDED LONG GLASS FIBER REINFORCED RUBBER TOUGHENED POLYAMIDE 6 COMPOSITE S.H. LIN*, C.C.M. MA*, H.F. MENG* and L.H. PERNG** * Instituteof ChemicalEngineering National TsingHua University ** Ta Hwa College of Technologyand Commerce Hsin-Chu, Taiwan, R.O.C. 30043 Abstract: Long glass fiber reinforced Nylon 6/Amine Terminated Butadiene Acrylonitrile (ATBN) block copolymer pellets were prepared by a pultrusion process. Optical microscope (OM) and scanning electron microscope (SEM) showed that the fiber dispersion and fiber-matrix bonding in the injection molded long glass fiber reinforced Nylon 6/ATBN block copolymer pellets are better than that from the conventional melt pelletized process. The fiber length distribution in the molded samples was calculated by image analyzer. The static tensile strength, tensile modulus, flexural strength, flexural modulus, notched Izod impact and heat deflection temperature (HDT) of injection molded long glass fiber reinforced Nylon 6/ATBN composites are superior to those of the short fiber reinforced Nylon 6 composites. Moreover, the effect of acrylonitride content on the degradation temperature of injection molded long glass fiber reinforced Nylon 6/ATBN composites was studied. Key words: Injection molded composites, Long glass fiber, Nylon 6/ATBN block copolymer, Pultrusion 1 INTRODUCTION polymer blends [12] and copolymerization. In this study, the polar acrylonitrile in amine-terminated butadiene The resins used in the pultrusion process have been acrylonitrile (ATBN) copolymer is used to provide considered almost exclusively with thermoset resins, sufficient solubility of the propagation polymers in ƒÃ- such as vinyl ester, epoxy and unsaturated polyester. caprolactam and to improve the homogeneity of the However, thermoplastic composites possess several reaction system. advantages such as high degree of processing freedom, For a conventional pultrusion process, fiber rovings fast production rate, high toughness, reusability of scrap pass through the resin tank to impregnate the resin and being free from solvent pollution problem. Hence, before entering the die. A special impregnation there has been an increasing interest in the research and procedure was designed to eliminate the restriction of application of thermoplastic pultrusion in recent years [1- pot life in the resin tank. The reactive species were 4]. However, there are some difficulties in thermoplastic mixed on-line just before enter the impregnation pultrusion. One of the major problems is the poor fiber chamber [7]. Since there is no resin dipping problem, the wettability with resin owing to the very high viscosity of viscosity was kept as low as possible to obtain a better the thermoplastic resins. Considerable researches [1-6] fiber wet-out. A mathematical model with a kinetic have been devoted to reduce this problem. In situ expression and a heat transfer equation had been polymerization offered one approach to achieve good developed to simulate the pultrusion of glass fiber fiber wet out by directly converting prepolymer to reinforced Nylon 6/ATBN composites. It was found that polymer in the pultrusion process [7-10]. the theoretically predicted data of temperature profile Polyamide 6 (Nylon 6) is one of the engineering and extent of reaction along the pultrusion length were plastics with several unique properties, such as high in good agreement with experimental results [8]. thermal stability, good mechanical properties, good Recent development of long fiber reinforced abrasion and oil resistance. However, the impact composites has been attracted by the composite industry strength of Nylon 6 decreased at low temperature or in pursuit of the longer fiber length and better property. with low moisture content [11]. Generally, rubber- The static mechanical properties of long fiber reinforced modified Nylon 6 may be fabricated by means of composites are better than those of short fiber reinforced Received December 27, 1995 87 S.H. LIN, C.C.M. MA, H.F. MENG and L.H. PERNG composites [13-16]. However, the poor fiber wet-out will TMI43-1 impact tester from Testing Machine Inc., affect the properties of injection molded long fiber U.S.A. The heat deflection temperature (HDT) was reinforced composites. The aim of this study is to measured under 0.455MPa loading, a Model CS-107-C, develop pultrusion process for fabricating long glass from the Atlas Equipment Corp., U.S.A. was used. The fiber reinforced Nylon 6/ATBN block copolymer morphology was analyzed by SEM and OM. pellets. In this research, long glass fiber reinforced Nylon 6/ 3 RESULTS AND DISCUSSION ATBN block copolymer pellets were prepared. The fiber length, mechanical properties, thermal properties and The cross section surface of pultruded long glass fiber morphology of the injection molded short glass fiber reinforced Nylon 6/ATBN block copolymer pellet was reinforced Nylon 6 (SF) and long glass fiber reinforced investigated by an optical microscope as shown in Fig. 1. Nylon 6/ATBN copolymer composites (LF) were The long glass fiber reinforced Nylon 6, 6 thermoplastic compared and discussed. composites made by hot melt method was shown in Fig. 2. From Figs. 1 and 2, it was observed that the fiber 2 EXPERIMENT bundles of pultruded long glass fiber reinforced Nylon 6/ATBN block copolymer pellets were distributed better 2.1 Materials compared to the conventionally extruded long glass fiber The materials used in this study were described reinforced Nylon 6, 6 composite pellets. The poor fiber elsewhere [8]. Therephthaloyl biscaprolactam (TBC) was distribution by hot melt method may be attributed to the higher viscosity of thermoplastic resin. prepared from terephthaloyl dichloride and ƒÃ- caprolactam. The initiator, ƒÃ-caprolactam magnesium bromide (MgBr-CPL) was synthesized from ethyl magnesium bromide and ƒÃ-caprolactam, the former being dissolved in diethyl ether and added gradually into an excess of molten ƒÃ-caprolactam with stirring under nitrogen atmosphere at 80•Ž. The optimum processing conditions for preparing the long glass fiber reinforced Nylon 6/ATBN block copolymer pellets prepared were (a) Nylon 6/ATBN block copolymer containing 15wt% ATBN, (b) 0.75mole% (MgBr-CPL), (c) molding temperature 180-200•Ž, (d) pulling rate 25-50cm/min, and (e) pellets contain 70wt% glass fiber. The 10mm long glass fiber reinforced Nylon 6, 6 pellet made by hot melt method was supplied by the Imperial Chemical Fig. 1. The OM photograph of the cross section of long Industry Co. (I.C.I.), U.K. The short glass fiber glass fiber reinforced Nylon 6/ATBN block copolymer reinforced Nylon 6 pellets were supplied by the Han pellet fabricated by pultrusion method. Hung Co., Taiwan. 2.2 Apparatus The pultrusion machine that consists of a pultrusion die was self-designed and has been described elsewhere [7]. Injection molded long glass fiber (LF) reinforced Nylon 6/ATBN copolymer composites, diluted by pure Nylon 6 resin, with various glass fiber contents were made by ARBURG 6 oz injection molded machine. Fiber degradation during the injection molding was found by the measurement of the fiber length distribution in the molded samples with an Olympus image analyzer, Japan. Tensile and flexural properties were measured following the specifications of ASTM D-683 and D-790, respectively. The universal material testing machine used was a Testometric 500, U.K. The notched Izod Fig. 2. The OM photograph of the cross section of long impact strength under dry condition was measured glass fiber reinforced Nylon 6, 6 pellet made by following the specifications of ASTM D-256 with a conventional hot melt method. 88 LONG FIBER REINFORCED POLYAMIDE 6 COMPOSITES The shear force in extrusion and injection process bonding between fiber and matrix. may cause the degradation of fiber length seriously in The "Rule of Mixtures" is one of the simplest the fiber reinforced composites. Tables 1 and 2 show the expressions which has been employed to correlate the fiber distribution and the average fiber length of short relationship between tensile strength and fiber volume fiber (SF) and long fiber (LF) at various fiber contents, for short fiber reinforced composites [17]: respectively. They revealed that the fiber length of injection molded LF composite was two times as long as σc=η σf'Vf+σ'mVm, (1) that of SF at the same fiber contents. Owing to friction where between the fibers during injection molding, the fiber σ=tensile strength, length decreased with the increase of the fiber contents. V=volume fraction, ATBN is the soft segment in the copolymer, and its C=composite, mechanical strength, stiffness and heat stability are f=fiber, lower than those of the hard segment Nylon 6 in the m=matrix, Nylon 6/ATBN. The content of ATBN is a little in σ'=stress at composite breaking strain, injection molded LF composite, but approving the η=fiber orientation factor, Table 1. Fiber length distribution of short glass fiber η=1, in the aligned fiber direction, reinforced Nylon 6 composite with various glass fiber η=1/2 for planar, cross-plied fiber, and contents after injection molding. η=1/3 for fiber random in 2 directions. If the fiber length is not continuous and has a distribution, then a modified rule of mixture has been presented by Kelly and Tyson [18]: where ƒÑ is the fiber/matrix interface strength and d is a diameter of fiber. McNally, et al. [19] proposed a modified Eq. (3) by addition of an orientation factor, D, to take into account the contribution of fiber orientation. Table 2. Fiber length distributionof long glass fiber reinforcedNylon 6/ATBN block copolymer composite with variousglass fiber contents after injection molding. where D is an empirical fitting factor. The length and width are much larger than the thickness of injection molded specimen, and the fiber orientation is random in two directions. Consequently, the value of D is equal to the ƒÅ of 0.333 in Eq.