Processing, thermoplastics alloys

Keywords Dynamic vulcanization Polymer blends and alloys Reactive processing Thermoplastic elastomers Thermoplastic vulcanizates... 

Alcryn . [DuPont DuPont UK] Halo-genated ethylene inteipolymer alloy melt processable thermoplastic elastomer for seals, gaskets, weatherstripping, coated fabrics, sheet goods, belt-... 

BFGoodrich Specialty Chemicals produces a family of thermoplastic alloys that are inherently conductive. Alloys with 15% of the active conductive polymer differ little in surface resistivity from alloys with 25% active polymer. Further, the conductive polymer content remains relatively constant through processes such as injection molding, extrusion, and thermoforming, unlike resins containing conductive fillers. In contrast to chemical antistats, the conductive polymers are active at all humidity levels, do not lose their potency over time, and add no ionic contaminants to the surrounding atmosphere. 

Thermoplastic alloy of styrene maleic anhydride copolymer and polybutylene terephthalate. Has improved dimensional stability and tensile strength. Processed by injection molding. Also called SMA PBT Alloy. 

Dynamically vulcanized, elastomeric thermoplastic alloys or TPVs display properties as good as or even better than the block copolymers, viz., a high degree of rubber elasticity yet good melt processability. The main advantages of the thermoplastic vulcanizate elastomer blends over the uncured thermoplastic/elasto-mer blends are... 

Improving mechanical properties such as toughness usually serve as the main reasons for the development of novel thermoplastic alloys and blends [4]. Other reasons for blending two or more polymers together include (i) to improve the polymer s processability, especially for the high-temperature polyaromatic thermoplastics (ii) to enhance the physical and mechanical properties of the blend, making them more desirable than those of the individual polymers in the blend and (iii) to meet the market force (cost dilution). Most products succeed because of a beneficial combination or balance of properties rather than because of any single characteristic. In addition, a material must have a favorable benefit-to-cost relation if it is to be selected over other materials for a particular application. One key technical issue is whether the blend will exhibit additive properties, or not. In many cases properties are well below additive, while in others they may be above additivity. The property relationships exhibited by blends depend critically on the correct control of their phase behavior [3]. 

The combination of starch with a water soluble polymer such as PVOH and/or polyalkylene glycols has been widely considered since 1970 [157]. Recently, the system, thermoplastic starch/PVOH has been studied mainly for producing starch-based loose fillers as a substitute for expanded PS [158-164], As an example, Lacourse and Altieri developed a technology based on hydroxy propylated high amylose starch containing small amounts of PVOH for improving foam resiliency and density [158-162]. In this case loose fill was produced directly by a twin-screw extruder. Recently more advanced processes and alloys have been developed which have resulted in foams with lower foam densities (8-6 kg/m ) and better performance [165-167]. Other applications of modified starch/PVOH can be in the sector of sheet extrusion/thermoforming. 

Precrosslinked particles with low crosslink density exhibit elastic properties and ean be applied for toughening thermoplastics or thermosets. The size of the elastic domains in blends consisting of elastic particles and a polymer matrix can be adjusted precisely, provided that the particles are dispersible. Via functional groups, microparticles can be covalently attaehed to a (thermoset) matrix. The grafting of polymer shells onto elastic microparticles improves the compatibility with the polymer matrix to be modified [3]. Thus, after processing of the polymer alloy discrete elastic particles can be observed as disperse phase in a continuous thermoplastic matrix. 

The dynamic cross-linking process is used to produce thermoplastic elastomers from mixtures of crystallizable polyolefins and various rubbers. Variations of basically the same method are employed to produce novel, stable polymer alloys by performing chemical reactions during extrusion of such mixtures. In that case, the cunent industrial term is reactive extrusion. Such processes are used, for example, to improve processability of LLDPE s into tubular film (by introducing long chain branches during extrusion with low levels of peroxides) or to... 

The polyaromatic mesophase (PA-MP) is a nematic, discotic, chemotropic liquid crystal. Owing to its high density (about 1.5 gcm ), its high carbon yield of about 90 %, and its thermoplasticity, it is unique as a precursor of structure carbons. An important application is the manufacture of high modulus (HM) and ultra-high modulus (UHM) carbon fibers [1]. By alloying with silicon, physical and chemical properties of the materials, such as strength, hardness and oxidation resistance, can be improved. These modified carbons were available by chemical vapor deposition (CVD) processes only up to now. The preparation by liquid phase pyrolysis is novel, economic, and thus opens a completely new field of applications. 

Shah, S.D. Kakarala, S. Schneider, J.E. Thermoplastic Polymer Alloy Compositions and In-line Compounding Process for Direct Sheet Extrusion of Sheets Prepared from the Thermoplastic Polymer Alloy Compositions U.S. Patent No. 6,153,680, Nov 28, 2000. 

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