Tensile properties, copolymers

The copolymer fiber shows a high degree of drawabiUty. The spun fibers of the copolymer were highly drawn over a wide range of conditions to produce fibers with tensile properties comparable to PPT fibers spun from Hquid crystalline dopes. There is a strong correlation between draw ratio and tenacity. Typical tenacity and tensile modulus values of 2.2 N/tex (25 gf/den) and 50 N/tex (570 gf/den), respectively, have been reported for Technora fiber (8). 

Copolymers of S-caprolactone and L-lactide are elastomeric when prepared from 25% S-caprolactone and 75% L-lactide, and rigid when prepared from 10% S-caprolactone and 90% L-lactide (47). Blends of poly-DL-lactide and polycaprolactone polymers are another way to achieve unique elastomeric properties. Copolymers of S-caprolactone and glycoHde have been evaluated in fiber form as potential absorbable sutures. Strong, flexible monofilaments have been produced which maintain 11—37% of initial tensile strength after two weeks in vivo (48). 

In the pulp and paper industry, anionic and cationic acrylamide polymers are used as chemical additives or processing aids. The positive effect is achieved due to a fuller retention of the filler (basically kaoline) in the paper pulp, so that the structure of the paper sheet surface layer improves. Copolymers of acrylamide with vi-nylamine not only attach better qualities to the surface layer of.paper, they also add to the tensile properties of paper in the wet state. Paper reinforcement with anionic polymers is due to the formation of complexes between the polymer additive and ions of Cr and Cu incorporated in the paper pulp. The direct effect of acrylamide polymers on strength increases and improved surface properties of paper sheets is accompanied by a fuller extraction of metallic ions (iron and cobalt, in addition to those mentioned above), which improves effluent water quality. 

In nonrigid ionomers, such as elastomers in which the Tg is situated below ambient temperature, even greater changes can be produced in tensile properties by increase of ion content. As one example, it has been found that in K-salts of a block copolymer, based on butyl acrylate and sulfonated polystyrene, both the tensile strength and the toughness show a dramatic increase as the ion content is raised to about 6 mol% [10]. Also, in Zn-salts of a butyl acrylate/acrylic acid polymer, the tensile strength as a function of the acrylic acid content was observed to rise from a low value of about 3 MPa for the acid copolymer to a maximum value of about 15 MPa for the ionomer having acrylic acid content of 5 wt% [II]. Other examples of the influence of ion content on mechanical properties of ionomers are cited in a recent review article [7],... 

Finer dispersion of silica improves the mechanical and dynamic mechanical properties of the resultant composites. Figure 3.11a and b compares the tensile properties of the acrylic copolymer and terpolymers in the uncross-hnked and cross-linked states, respectively. 

A star copolymer (SCP) of PCLA was synthesized by Younes and coworkers. This kind of SCP PCLA elastomer was also synthesized in two steps. First, the small molecular SCP was produced by ring-opening polymerization of s-caprolactone (s-CL) with glycerol as initiator and stannous 2-ethyUiexanoate as catalyst. Second, the living SCP was further reacted with different ratios of a cross-linking monomer, such as 2,2-bis(s-CL-4-yl)-propane (BCP) and s-CL. The SCP elastomers had very low glass transition temperature (—32°C). It was reported that the SCPs were soft and weak with physical properties similar to those of natural bioelastomers such as elastin. A logarithmic decrease in each tensile property with time was observed in this SCP PCLA. 

Blends of EMA copolymer and EPDM containing vinyl norborene as a third monomer were also investigated. Blending was carried out at 180°C at a rotor speed of 100 rpm. After the reaction, the blends were quenched on the cold rolls and were sheeted out. They were examined by IR spectra. The reduction of peak area related to unsaturation indicated a progressive loss of EPDM due to reaction with EMA. The extent of reaction depended on the utilization of unsaturation which is estimated to be 14% for EMA/EPDM at a 70 30 ratio and 53% at a 50 50 blend ratio. The tensile properties exhibit synergism as the EMA proportions change from 0% to 50%. 

More definitive evidence of enzymatic attack was obtained with 1 1 copolymers of e-caprolactone and 6-valerolactone crosslinked with varying amounts of a dilactone (98,99). The use of a 1 1 mixture of comonomers suppressed crystallization and, together with the crosslinks, resulted in a low-modulus elastomer. Under in vitro conditions, random hydrolytic chain cleavage, measured by the change in tensile properties, occurred throughout the bulk of the samples at a rate comparable to that experienced by the other polyesters no weight loss was observed. However, when these elastomers were implanted in rabbits, the bulk hydrolytic process was accompanied by very rapid surface erosion. Weight loss was continuous, confined to the... 

To circumvent any effect on tensile properties that might have concurred in the presence of the third monomer, hydroperoxide curing of E-P copolymer samples comparable in and... 

Even though the first report about the synthesis of crystallizable ABC triblock copolymers was published in 1978 for PS-fo-PB-fo-PCL copolymers [114], in that work only a preliminary study of the tensile properties was performed, without considering the crystallizability of the materials. It was only 20 years later, when the preparation of these materials was reconsidered and optimized, that triblock copolymers with relatively narrow molecular weight distributions were obtained [115], a requisite which is indispensable for the generation of well-defined morphologies. To illustrate the complexity and richness of semicrystalline ABC triblock copolymers, PS-fc-PB-fc-PCL triblock copolymers have been chosen. These copolymers have been prepared with a wide composition range (with PCL contents from 11 to 77%) and they have been compared with PS-fc-PCL and PB-fo-PCL diblock copolymers [29,98, 115-118]. 

Figure 6.4 Properties of PET-BB copolymers as a function of BB content (a) tensile properties (b) viscosity, r o ( ) and relaxation time (O) [42]. Reprinted with permission from Ma, H., Hibbs, H., Collard, D. M., Kumar, S. and Schi-raldi, D. A., Macromolecules, 35, 5123-5130 (2002). Copyright (2002) American Chemical Society...

Table 4. Tensile properties of the poly(CL-[7-DXO-[7-CL) ABA triblock copolymers (see Scheme 39) ...

Conversion of copolymers to fibers and pertinent tensile date. Copolymers I-III described in Table I were melt extruded, and the extrudates were oriented by drawing and then annealed. The tensile properties of the unannealed and annealed fibers are summarized in Table II and III, respectively. 

Copolymers I-III were extruded into monofilaments and the tensile properties after drawing and annealing are shorn in Tables II and III. The reported data indicate that copolymeric monofilaments can be made to have equivalent or higher tensile strength as con ared with those made from PDS. 

Using dlethylene glycol (DEG) as an initiator, a copolymer (IV) of PDO/glycolide at 90/10 by weight was preapred and its properties are compared with those of a 90/10 copolymer (II) made in the presence of l-dodecanol (Table IV). Although the tensile properties of IV are comparable those of II, the percent BSR of the latter is higher. This may be associated with a difference in the copolymeric... 

The effect of the microstructure of acrylic copolymer/terpolymer on the properties of silica-based nanocomposites prepared by the sol-gel technique using TEOS has been further studied by Patel et al. [144]. The composites demonstrate superior tensile strength and tensile modulus with increasing proportion of TEOS up to a certain level. At a particular TEOS concentration, the tensile properties improve with increasing hydrophilicity of the polymer matrix and acrylic acid modification. 

Table 6. Comparative tensile properties of block copolymer blended molecular composite fibers...

While the processing and characterization of the graft copolymers have not been sufficiently pursued to this point to establish the viability of the concept, these research efforts have demonstrated that rigid-rod polymer fusibility could be substantially modified through the introduction of flexible coil side chains. Unfortunately, in spite of the careful processing and the attainment of excellent consolidation as well as minimal phase separation, the tensile properties are less than expected. 

Figure 17 shows some tensile properties for fibres spun from a series of copolymers... 

Other Mechanical and Thermal Properties. Table IV shows that the tensile properties, the Shore D hardness, and the deflection temperature of a PVC graft copolymer alloy containing 13% of a VC/LD-PE (50-50) graft copolymer are only slightly lower than the corresponding properties of the pure PVC (Solvic 239). There is no difference between the heat stabilities of the PVC and of the alloy. 

The viscoelastic and ultimate tensile properties of Kraton 101 (SBS copolymer containing 30.5% polystyrene and with total molecular weight 76000) and of Ther-... 

Ethylene copolymers were compared with liquid plasticisers for use as additives to improve the flexibility of poly(vinyl chloride) (PVC) for electrical cable insulation applications. The PVCs were assessed by determining smoke generation, flammability, tensile properties and the low temperature brittle point. The ethylene copolymers gave similar peak heat release rates, but the peak smoke and the total smoke generation were lower. They also gave similar or increased strength, similar elongation and flexural modulus, and lower brittle point temperatures. 4 refs. 

TABLE 1. Comparison of tensile properties of bis(4-isocyanatocyclohexyl) methane-basedpolydimethylsiloxane-urea and polyether/polydimethylsiloxane-nrea segmented copolymers. 

The micromechanical deformation behavior of SAN copolymers and rubber-reinforced SAN copolymers have been examined in both compression [102] and in tension [103,104]. Both modes are important, as the geometry of the part in a given application and the nature of the deformation can create either stress state. However, the tensile mode is often viewed as more critical since these materials are more brittle in tension. The tensile properties also depend on temperature as illustrated in Figure 13.6 for a typical SAN copolymer [27]. This resin transforms from a brittle to ductile material under a tensile load between 40 and 60 C. 

Figure 21.6 Effect of composition and block size on tensile properties of styrene -butadiene - styrene triblock copolymers (1 kg/cm2 = 0.1 MPa)...

Orientation of styrene-based copolymers is usually carried out at temperatures just above T. BiaxiaUy oriented films and sheet are of particular interest. Such orientation increases tensile properties, flexibility, toughness, and shrinkability. PS produces particularly clear and sparkling film after being oriented biaxiaHy for envelope windows, decoration tapes, etc. Oriented films and sheet of styrene-based polymers are made by the bubble process and by the flat-sheet or tentering process. Eibers and films can be produced by uniaxial orientation (237) (see Eilmand SHEETING materials). 

Both siloxane-polyimide copolymers and BPADA-derived copolymers exhibited excellent solubility in a variety of dipolar aprotic solvents, including tetrahydrofuran, n-methylpyrrolidone, and dimethyl sulfoxide, as well as chlorinated hydrocarbons such as o-dichlorobenzene and methylene chloride. The polymers and copolymers were typical thermoplastics exhibiting little elongation at failure. The tensile properties are summarized in Table II. 

Films of the copolymer derived from DiSiAn and mPD were quite brittle and made tensile specimen fabrication diflScult. Copolymers containing BPADA were much less brittle, and the tensile properties of the Di-SiAn-BPADA-mPD-based copolymer showed a marked improvement over the DiSiAn-mPD polymer. As noted previously, the copolymers were much easier to prepare and, in general, were of higher molecular weight, which may have contributed to the improved physical properties of the copolymers. 

Table II. Tensile Properties of DiSiAn-Polyimide Polymers and Copolymers...

Thus, Hope and his coworkers concluded for the solid-state extrusion of linear poly-ethylenes that increasing the molecular wei t reduced both the maximum degree of deformation and the tensile properties of the jaoduct. Hie sother hand, increased the maximum degree of deformation. The degree of stiffness enhancement upon extrusion and the melting points of the products were reduced. 

---