General-purpose resins molecular weight

Epoxy resins. The reaction of Bisphenol A and epichlorohydrin gives a low molecular weight linear polymer. This polymer further reacts with an amine-curing agent, R-NH2, to give a general-purpose thermoset. See Figure 24-2.) Now that s not as complicated as it sounds. First of all, you d think... 

Table I lists typical properties of a baker s dozen of these resins, produced by typical direct preparations, without extensive purification. Overall, the viscosities of these resins were quite low, particularly by comparison to the well known general purpose epoxy resins based on the diglycidyl ether of bisphenol A (DGEBA). The more shielded higher alkylsubstituted hydantoin rings favored lower viscosities. Some anomalies in these viscosities presumably reflected either a tendency of certain resins to crystallize, or the presence of some species of higher molecular weight, formed by reaction of the glycidyl group with a second hydantoin ring.

Figure 9.113 Shore D hardness vs. temperature for Daikin Industries Neoflon M-300H— general purpose and M-400H— higher molecular weight, increased toughness PCTFE resins [13].

Because of their relatively low molecular weight, solution PVC/VA resins are formulated with plasticizer levels of 0-25 phr. These are useful not only in improving flexibility but also in minimizing solvent retention in the coating. Most commonly, general purpose phthalate plasticizers (DOP, DINP) are used. For increased flexibility, linear phthalates are used, and for least volatility, DIDP, DTDP, and trimellitates. Phosphate plasticizers are used in flame-retardant applications, and polymeric polyesters where resistance to migration or extraction is required. 

Plasticizers may also be further subdivided into primary and secondary types. Primary plasticizers are those used as the sole plasticizer or as the major component of the plasticizer system. Secondary plasticizers are typically blended with primary plasticizers to improve certain performance properties such as reduced flammability and improved processing, or simply to lower cost. Acmally, there are some overlaps in these definitions, since some secondary plasticizers, can function as primary plasticizers when used at relatively low levels. An example is di-2-ethylhexyl adipate (DOA). DOA is often used as the sole or primary plasticizer in PVC meat wrap, typically at 30 parts per 100 of resin (phr). But it also functions as a secondary plasticizer when added at the 10 percent level to a general purpose plasticizer, for example to improve the low-temperature flexibility or flex rating of a PVC shoe sole. Other examples would include the use of a primary plasticizer, such the higher-molecular-weight phthalate diisodecyl phthalate (DIDP) for use as a minor component in blends with polymeric plasticizers to help improve processability or to lower costs. 

Prior to melt processing, PLA requires sufficient drying to prevent hydrolysis, which can reduce the mechanical properties of the PLA article due to reduced molecular weight. NatureWorks LLC, one of the main suppliers of PLA, recommends drying PLA to a maximum of 250 ppm moisture before extmsion. In terms of extrusion equipment, PLA resins can be processed using a conventional extmder with a general purpose screw of 24 to 30 L/D or typical PET extruder with... 

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