Thermoplastic melt blending process

Certain thermoplastic polyimides possess excellent resistances to high temperatures and chemicals, with Tgs ranging from 217 to 371 °C. Certain polyimides also exhibit excellent toughness and dielectric properties. The melt blending process of polyimides with other thermoplastic polymers is difficult due to polyimides high Tg, high melt viscosities, and incompatibility. A solution process is used, therefore, to achieve a semi-interpenetrating polyimide network... 

Multiblock Copolymers. Replacement of conventional vulcanized mbber is the main appHcation for the polar polyurethane, polyester, and polyamide block copolymers. Like styrenic block copolymers, they can be molded or extmded using equipment designed for processing thermoplastics. Melt temperatures during processing are between 175 and 225°C, and predrying is requited scrap is reusable. They are mostiy used as essentially pure materials, although some work on blends with various thermoplastics such as plasticized and unplasticized PVC and also ABS and polycarbonate (14,18,67—69) has been reported. Plasticizers intended for use with PVC have also been blended with polyester block copolymers (67). 

Other properties of thermoplastics as well. Owing to the relatively low-melt viscosity of thermotropic LCPs, often a small amount of LCP decreases the blend viscosity significantly and renders the matrix thermoplastics easier to process [9-211. 

Blends. There has been considerable research in recent years on polymer blends that contain an LCP. This subject was recently reviewed by Dutta et al. (67). The addition of an LCP to another thermoplastic melt effectively lowers the melt viscosity and improves processability. In addition, if the flow field contains an extensional stress component, the LCP dispersed phase is extended into a fibrous morphology and oriented in the flow direction. This microstructure can be retained in the solidified blend to provide self-reinforcement. 

Several liquid cryatalline polymers were melt blended with an amorphous (Ultem) and two semicrystalline (PEEK and PPS) engineering thermoplastics in a single screw extruder. Flat film was processed with different degrees of stretch imparted while the film was being cooled. In the case of Vectra, which was thought to be ideally suited to be blended with PPS based on thermal and rheological... 

Other effective plasticizers for starch for imparting melt processibility include a variety of low molecular weight compounds, such as glycerol and diethylene glycol, and also polymers such as poly(ethylene-co-vinyl alcohol) [55]. Furthermore, starch plasticized in that manner can be melt blended with minor amounts of hydrophobic thermoplastics, such as polyethylene and poly( methyl methacrylate), to obtain biodisintegratable molded articles with good mechanical properties. 

Two important types of elastomeric polyolefin blends are reactor-made iPP/ EPR blends and postreactor blend iPP/EPDM. The latter is called thermoplastic vulcanizates (TPVs), produced by dynamic vulcanization of blends containing a thermoplastic and an elastomer. To make iPP/EPDM TPV, the two polymers PP and EPDM are mixed with curatives, such as peroxides, phenolic resins, or sulfur with accelerators, and dynamically cured in an extmder resulting in a blend consisting of micrometer-sized elastomer particles dispersed in the PP matrix (20-24). Paraffinic oils are added in the melt mixing process for viscosity control and cost. In iPP/ EPDM TPV, the crystalline iPP resin is normally the minor phase. Recently, polyolefin plastomers have been added to the class of elastomeric polyolefin blends. Polyolefin plastomers are ultralow molecular weight linear low density polyethylenes (ULMW-LLDPE). Nonelastomeric polyolefin blends are blends of polyolefins with mostly nonpolyolefin (other thermoplastic) matrices as mentioned earlier. 

The problem of PP/EPR functionalization is important from a practical standpoint because starting blends are a widely available commercial product EPR is added to PP to increase impact strength and low temperature resistance (53). Functionalized PP/EPR blends have been used as modifiers of impact strength and rheological behavior of engineering thermoplastics melts (54). From the scientific viewpoint, the functionalization of PP/EPR blends attracts attention of researchers, similarly to PP/PE blends, because of the differences in the course of secondary reactions in certain POs that accompany grafting and because of the process selectivity. 

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