Tensile modulus polyesters

Cord materials such as nylon, polyester, and steel wire conventionally used in tires are twisted and therefore exhibit a nonlinear stress—strain relationship. The cord is twisted to provide reduced bending stiffness and achieve high fatigue performance for cord—mbber composite stmcture. The detrimental effect of cord twist is reduced tensile strength. Analytical studies on the deformation of twisted cords and steel wire cables are available (22,56—59). The tensile modulus E of the twisted cord having diameter D and pitchp is expressed as follows (60) ... 

Comparison with Asbestos and Glass. Tables III, IV, V, and VI catalog the properties obtained when the two polystyrenes were reinforced with asbestos and glass. Table VII compares the reinforcing effects of the several fibers studied at 30 wt %. The data show that particular fibers improve particular properties. The tensile modulus and tensile strength are most improved by glass the heat deflection is most improved by asbestos, and the impact strength is most improved by polyester. 

Reinforcement of epoxy, polyester, and other resins for use in aerospace, marine, automotive and sports industries. We have previously mentioned the vibration damping capacity of Kevlar aramid fiber. Layers of woven Kevlar are used in skis for damping purposes and, of course, to reduce the weight. Kevlar is used as a protective sheath in fiber optic wave guides and to reinforce optical fiber cables because of its high tensile modulus and strength, and low electrical conductivity. 

A polyester first prepared by Jackson (3) (20 mol% modified p-hydroxybenzoic acid poly(phenyl-1,4-phenylene terephthalate)) was spun at 320°C and fibers were characterized "as-made". The dynamic tensile modulus as a function of DR is seen in Figure 4 and shows that very high values are obtained at even low DR-values. 

Table VI compares the key properties of these two types of thermotropic polymers category by category. The samples compared had the same melting ranges, but were very different in reduced viscosities and solubility characteristics. The data compared were those processed under the most favorable conditions. Interestingly enough, the as-spun fibers from the polyester-carbonate can be heat-treated more efficiently than those fibers (of same tenacity) spun from the polyester. Both of them gave fiber properties far superior to those of nylons and polyethylene terephthalate. These two classes of polymers also had comparative properties (such as tensile strength, tensile modulus, flex modulus, notched Izod impact strength) as plastics and their properties were far superior to most plastics without any reinforcement.

Figure 14. Tensile modulus, (b), and tensile strain to failure (c) with rubber content, for samples with an epoxy-to-polyester ratio of 1 2. Tensile properties were measured using ASTM D-638 on dog-bone-shaped samples at a speed of 0.2 in. I min.

The procedure to obtain nanocomposites based on unsaturated polyester resins leads to improvements in the order of 120% in the flexural modulus, 14% in flexural strength and 57% increase in tensile modulus with 4.7% of clay slurry content. Thermal stability augments and the gelation temperature increases to 45 °C, as compared to that of the resin (Fig. 31.6). It seems that adding water to the MMT allows better intercalation of polymer chains into the interlamellar space. Because clay is first suspended in water, this improves dispersion and distribution of the particles in the resin matrix. Longer gelation times lead to more uniform and mechanically stronger structures and to yield stresses (Fig. 31.7). Enhanced polymer-clay interactions are revealed by XPS in this case (Fig. 31.8). 

The formation of anisotropic thermorever-sible gels was observed with this polyester, for example, in 3-phenoxytoluene as the solvent. These mixtures also retained their anisotropy above the gel melting point at a concentration of 35% or more [29]. In highly aligned fibers spun from the nematic melt and post-drawn, a tensile modulus of 40-45 GPa and a tensile strength of up to 550-650 MPa was reached [28c]. 

The following values of the tensile modulus E and rigidity modulus G, expressed in gigapascals, were found for a random co-polyester fibre at two different temperatures E = 125, G = 1.1 and E = 62, G = 0.28. Assuming that equation (12.19) applies, calculate the value of Ej ax and the order parameter S for the fibre. 

Thermotropic polyesters are melt-spun from the nematic phase and orient easily in an elongational flow field (moderate drawdowns/forces are sufficient). In the fiber case, highly oriented fibers form easily with an initial modulus close to theory—typical values range from about 70 to 150 GPa. Ward [46] has shown that the tensile modulus may be described by an aggregate model, i.e., the modulus is a function of the inherent chain modulus, the molecular chain orientation, and the shear modulus (which described the stress transfer between chains). The tensile strength of LCP fibers follows the prediction of the lag-shear model [47]. Both the aggregate model and the lag shear model treat the LCP as though it... 

A composite material consists of 40% (l volume) continuous, uniaxially aligned, glass fibres in a matrix of thermoset polyester. A tensile stress of 100 MPa is to be applied parallel to the fibres. Predict the strains which will result. Take the tensile modulus and Poisson s ratio of glass to be 76 GPa and 0.22, and of thermoset polyester to be 3 GPa and 0.38, respectively. 

Figure 4.102 Tensile modulus vs. temperature of Mitsubishi Polyester Film Hostaphan PEI film [8].

Figure 4.153 Tensile modulus vs. temperature for DuPont Crastin PBT/ASA polyester alloy/blend resins.

The tensile moduli of unorientated and orientated polyethylene fiber are 1.67-4.18 and 117 GNm , respectively [20]. These values may seem quite high for thermoplastic materials, but the theoretical tensile modulus (334 GNm ) is much higher than these values [20]. The large difference is because the polymer chains are not fully aligned and extended. In contrast, the tensile modulus of aromatic polyester LCP fibers is 125-175 GNm. These values approach the theoretical value 188 GNm [20]. 

Neat polyester composite showed tensile strength around 41 MPa, Young s modulus around 9.68 GPa, and flexural strength around 61 MPa. After reinforcement with fiber, mechanical properties were enhanced and some of the important properties are explained below. Singh et al. [102] reported that sisal-polyester composites from nonwoven sisal mats with fiber content 50% by volume showed a tensile strength of 30 MPa and a tensile modulus of 1.15 GPa. The composites were manufactured by impregnation of the nonwoven sisal mats under compression molding for 2 hrs [9, 102]. 

Effect of fiber loading The loss in tensile properties of OPF-polyester composites upon degradation in soil was quantified by. Loss in tensile strength by 8%, 17% and 35% were observed, respectively after exposure of 3,6 and 12 months. Similarly tensile modulus, elongation at break and impact strength also reduced upon soil exposure. A loss of impact strength by 6%, 18% and 43% were observed, respectively after 3, 6 and 12 months. Similarly the tensile stress, tensile modulus and elongation at break decreased from 35.1 MPa, 3.29 GPa and 3.75%, 34.6 MPa, 2.32 MPa and 2.48%, respectively upon soil burial for 12 months [61]. 

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