Resins semicrystalline polymer

The effect of orientation on permeability is dependent on the morphological nature of the barrier resin. Semicrystalline polymers, VDC copolymer, and aromatic nylon MXD-6... 

Polyethylene (PE) is a genetic name for a large family of semicrystalline polymers used mostiy as commodity plastics. PE resins are linear polymers with ethylene molecules as the main building block they are produced either in radical polymerization reactions at high pressures or in catalytic polymerization reactions. Most PE molecules contain branches in thek chains. In very general terms, PE stmcture can be represented by the following formula ... 

Semicrystalline polymers, 20 351, 352, 588 toughness of, 20 354 Semicrystalline resins, 19 537 Semicrystalline thermoplastics, melting temperature of, 19 538t Semiefficient (semi-EV) sulfur... 

PVDF is among the few semicrystalline polymers that exhibit thermodynamic compatibility with other polymers,80 in particular with acrylic or methacrylic resins.81 The morphology, properties, and performance of these blends depend on the structure and composition of the additive polymer, as well as on the particular PVDF resin. These aspects have been studied and are reported in some detail in Reference 82. For example, polyethyl acrylate is miscible with polyvinylidene fluoride, but polyisopropyl acrylate and homologues are not. Strong dipolar interactions are important to achieve miscibility with PVDF, as suggested by the observation that polyvinyl fluoride is incompatible with polyvinylidene fluoride.83... 

The coalescence of polymers is driven by the work of surface tension, which counteracts the viscous dissipation associated with the molecular diffusion within the coalescing domain. This phenomenon is often referred to in the literature as polymer sintering. In the rotational molding process, coalescence occurs at temperatures above that of the material melting point when dealing with semicrystalline polymers, or above the glass transition temperature for amorphous resins. The first analytical model describing the coalescence process was proposed by Frenkel ... 

Composition (type of polymeric components). The base polymer (which is to be modified) may be an amorphous polymer [e.g., polystyrene (PS), styrene-acrylonitrile copolymer, polycarbonate, or poly(vinyl chloride)], a semicrystalline polymer [e.g., polyamide (PA) or polypropylene (PP)], or a thermoset resin (e.g., epoxy resin). The modifier may be a rubber-like elastomer (e.g., polybutadiene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, or ethylene-propylene-diene copolymer), a core-shell modifier, or another polymer. Even smaller amounts of a compatibilizer, such as a copolymer, are sometimes added as a third component to control the morphology. 

The effect of orientation on oxygen permeability of the medium and high barrier resins is seen to be dependent upon the morphological nature of the barrier resin prior to orientation. A plot of the oxygen transmission rates as a function of the overall draw ratio (figure 3) illustrates this clearly. While the semicrystalline polymers, VDC copolymer, and aromatic nylon MXD-6, show little change in the permeability with moderate amounts of orientation in the solid state, orientation of the amorphous polymers SELAR PA 3426 and XHTA-50A causes reduction in the permeability by 5-30% in both resins, depending upon the overall level of orientation. 

The results here suggest that amorphous polymers are more readily orientable than semicrystalline polymers. The difficulty in orientability of semi-crystalline resins can be attributed to the fact that crystallinity is fully developed in the films prior to the orientation step.. In commercial practice, therefore, these polymers are rapidly quenched to permit orientation while still in the amorphous state. 

Abrasion resistance is usually measured by the Taber Test procedure described by ASTM D1044. Abrasion resistance of unfilled semicrystalline polymers is linked to the degree of crystallinity that is itself related to the molecular stmcture and weight of the resin and its processing. Table 3.54 includes the results of testing two types of perfluoroalkoxy polymers, PFA and MFA, and ECTFE. Notice the large difference between wear index (weight loss by abrasion in 1000 cycles) of ECTFE which is a partially... 

Incorporation of semicrystalline polymer into an amorphous resin to improve solvent and chemical resistance (e.g., in blends of PC with PEST). 

Polypropylene is a white, semicrystalline polymer. The resins are generally solid and used according to their melt index, which in the case of polypropylene is more commonly called the melt flow rate (MFR). Polymers with MFRs ranging from less than 1 to more than 35 are commercially produced. Most fibers are produced from resins having MFR between 3 and 35. 

Another miscible semicrystalline polymer/amorphous polymer blend SMP is a polyethylene oxide (PEO)/novolac-type phenolic resin blend [24]. The blend was found to be completely miscible in the amorphous phase when the phenolic content is up to 30 wt%, and the crystalline melting temperature (T,f) of the PEO phase working as a transition temperature can be tuned. 

OlWan Wang, H.-H., Chen, J.-C. Toughening of epoxy resin by functional-terminated polyurethanes and/or semicrystalline polymer powders. J. Appl. Polym. Sci. 82 (2001) 2903-2912. 

Plastics can be divided according to their character into amorphous and crystalline. Crystallization is never complete and the so-called crystalline polymers are virtually semicrystalline ones. Examples of amorphous plastics are polystyrene, acrylonitrile-butadiene—styrene copolymers, styrene—acrylonitrile copolymers, polymethylmethacrylate, poly(vinyl chloride), cellulose acetates, phenylene oxide-based resins, polycarbonates, etc. Amorphous polymers are characterized by their glass transition temperature, semicrystalline polymers by both melting and glass transition temperatures. 

As demonstrated before, the shifting involves three shift factors, one horizontal, usually expressed as a-j- = bi-rio(T)/rio(To), where b-j- = PoTo/pT is the first vertical shift factor that originates in the thermal expansion of the system (p is density). The subscript o indicates the reference conditions, defined by the selected reference temperature To, usually taken in the middle of the explored T-range. For homopolymer melts as well as for amorphous resins, the two shift factors, a and bj, are sufficient. However, for semicrystalline polymers the second vertical factor Vj has been found necessary - it accounts for variation of... 

Today, very few unmodified resins are being used. Some polymers require less modification than others. For example, the semicrystalline polymers that aheady have a two-phase structure may need modification less urgently. By contrast, the amorphous resins, such as PVC, PS, PPE, or polycarbonate of bisphenol A (PC), are brittle and require blending more frequently. The advantages of blending fall into two categories. 

In reality, the morphology of a polycrystalline thermoplastic consists of spherulites that holds for common polymer types (e.g. PP, PE, PA6, PA6,6, and polyether-ether ketone (PEEK) crystalhzed under common conditions). Some semicrystalline polymers and moderately filled composites of the above resins may exhibit lamellar crystalline morphology without any spherulitic order. As a result of random orientation of individual crystallites in spheruhtes and the manner of their connectivity, the elastic modulus of about 10 GPa has been extrapolated for a hypothetical ideal polycrystalhne PE containing no amorphous phase from the dependence of the elastic modulus of PE on the degree of crystallinity. Presence of amorphous phase reducing the content of crystalhne phase results in a further reduction of the overall elastic modulus of the semicrystalline polymers compared with ideal monocrystals (109). 

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