High viscosity thermoplastic

For the processing of thermoplastic polymeric nanocomposites, standard equipment for the preparation of high viscosity thermoplastic compounds can be used the co-rotating twin-screw extruder with its flexible processing unit which allows for controlled dispersing shear and elongational flow. In the case of low viscosity components for the production of thermoset compounds, common mixing and dispersion techniques can be used. 

Chapters 5,6,7 and 8 specifically address issues associated with high viscosity thermoplastic processing. Chapters 5 and 6 are based on the stamping operation usually encountered in metal forming. Chapter 5 features the composite sheet forming process for thermoplastic matrix composites, which was attractive as one could save initial investment by modifying metal stamping equipment. In this process, a thermoplastic prelaminate (a flat... 

Hot Melt, Field-Extruded Sealants. Several butyl raw material manufacturers and sealant producers have recently developed butyl tapes. These are premasticated, high viscosity thermoplastic compositions that are fed as talced ribbons into a polymeric sealant applicator (PSA). Within the PSA, the compound is heated and extruded into the joint opening to form a smooth joint that cools rapidly with excellent adhesion claimed, even to oily or otherwise poorly prepared surfaces. These hot-applied, post-formed butyl tapes have been successfully used to seal insulated glass units, automotive windshields (Fig. 4), curtain walls, concrete pipes, precast concrete structural joints, and as bedding compounds in combi-... 

An entirely new concept was iatroduced iato mbber technology with the idea of "castable" elastomers, ie, the use of Hquid, low molecular-weight polymers that could be linked together (chain-extended) and cross-linked iato mbbery networks. This was an appealing idea because it avoided the use of heavy machinery to masticate and mix a high viscosity mbber prior to mol ding and vulcanization. In this development three types of polymers have played a dominant role, ie, polyurethanes, polysulftdes, and thermoplastic elastomers. 

The first commercial grades were introduced by Phillips Petroleum in 1968 under the trade name Ryton. These were of two types, a thermoplastic branched polymer of very high viscosity which was processed by PTFE-type processes and an initially linear polymer which could be processed by compression moulding, including laminating with glass fibre, and which was subsequently oxidatively cross-linked. 

I.R, Kramer E.L. Strauss, Thermoplastic Ablation-Shield Material Having a High Viscosity... 

The thermoplastic-rich phase may be separated in the course of polymerization (Sec. 13.4.2) or can be incorporated as a dispersed powder in the initial formulation (Sec. 13.4.3). A strong drawback of the in situ-phase separation for processing purposes is the high viscosity of the initial solution which results from the much higher average molar mass of the TP compared with the liquid rubbers. Also, for the same reason, the critical concentration crit has a smaller value (phase inversion is observed at smaller concentrations of modifier). 

The calendering process is commonly used for shaping high melt viscosity thermoplastic sheets and is particularly suitable for polymers susceptible to thermal degradation or containing substantial amounts of solid additives. This is because the calender can convey large rates of melt with a small mechanical energy input (compared to an extruder). 

As a matter of fact, the viscosity is a very dominant property for the processing technology. A fluid polymer mass with a high viscosity requires high pressures to be transported in processing machines. How strongly the processability prevails, has already been discussed in 2.2.3 for some thermoplasts like PE, PP and ABS,... 

The first question to be discussed is the polymer miscibility which governs the blend morphology. The solubility parameters of BMIs is 12-135 (cal cm 3)0,5 vs. 11-12 (cal cm"3)0,5 for the high-performance thermoplastics [112]. We can expect an important non-miscibility however, the morphology will also depend on some other factors (conversion at the gel point, viscosity...) and as a result different types of morphologies were identified. 

Reaction 1 produces a linear polymer (a thermoplastic) that should be soluble in acetone, while reaction 2 produces crosslinked, insoluble polymer (a thermoset resin). The viscosity of the crosslinked polymer when hot should be noticeably higher than that of reaction 1. Although individual results will depend upon the purity of the starting materials and the heating rate, often the linear product is glassy and hard while the crosslinked one tends to be more brittle and porous. The latter results from the extremely high viscosity that develops as the crosslinked polymer increases in molecular weight. 

Soluble thermoplastic polymer additions (e.g., epoxy-nylon and epoxy-vinyl) provide very tough and somewhat flexible systems, but they are limited because of their high viscosity and high raw materials costs. Almost all these systems need to be handled at elevated temperatures or as solvent solutions. They require elevated temperature to achieve wetting and cure. 

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