Polyamides weathering tests

Weathering tests, 245 Wholly aromatic liquid crystalline polyesters, degradation of, 38 Wholly aromatic polyamides, 136-137, 139 synthesis of, 184-189 Wholly aromatic polyesters, 25-26, 32 copolymerization and, 35 synthesis of, 71-72... 

Since the effect of temperature varies with type of polymer aud its formulations, temperatures different than those encountered in end-use environments can distort the stability rankings of materials in addition to causing unrealistic aging behavior. For example, it was shown [141] that change in air temperature from 30 to 60°C in an artilicial weathering test changed the rank order of the stabilities of polyamide, polypropylene, and polyester yam based on reduction... 

Combinations of zinc dust (particle diameter 12-20 xm) and extrafine zinc dust (particle diameter 3-6 p,m) yield optimal corrosion resistance. Small amounts of aluminum paste or powder, added to obtain a more silvery appearance, will however decrease corrosion resistance—as found in comparative weathering tests by Van Eijnsbergen (personal communication). Generally, nonsaponifiable binders, such as vinyl copolymers, chlorinated mbber, methacrylic resins, and epoxy resins, are used. For welding zinc-rich primers, epoxy-polyamide binders are widely used. They allow a wider range of sealers and top coatings. 

The effect of fillers in adhesives might be considered as another general effect which may have similar responses for a variety of surface conditions. Bodnar and Wegman(96) have shown the superior resistance to natural weathering of filled polyamide-epoxy adhesive/aluminum joints as compared to the corresponding joints made with nonfilled Epon 828/Versamid 140 combinations. Minford<97) has obtained similar results comparing filled and unfilled Epon 815/Versamid 125 combinations in a variety of accelerated lab tests. Minford ) has also noted durability differences between different fillers in certain exposures. For example, aluminum-powder-filled polyamide/epoxies tested superior in four-year exposures to marine conditions. 

Two types of paint systems were used for experiments. First system used was zinc phosphate primer (50 % Zn as compound) with micaceous iron oxide (MIO) as intermediate coat followed by polyurethane (PU) as top coat denoted as ZP. Other system used was zinc rich primer (80 % Zn as dust) with MIO as intermediate coat and PU as top coat denoted as ZR. This system is costlier with respect to ZP and considered for laboratory evaluations purpose only. ZP is designed with respect to places where test panels are deployed for exposure based on manufacturers catalogues and standards [4]. These systems possess good resistance from water permeability, weathering, abrasion and good adhesion to maintain a proper barrier to the environment. The drying mechanism of the systems is the reaction between epoxy resin and polyamide. The details of each paint system used comprising primer, intermediate and top coats with the respective layer of film thickness are shown in Table 2.2. 

Table 1.20 shows the influence of acid rain on various materials. Under strictly artificial weathering conditions, only polycarbonate and unstabilized polyamide 6 clearly exhibit graying. The other specimens show no visible changes. Acid rain (in the ADF test) leads to obvious changes in all materials. There are recognizable differences in the order resulting from acid concentration, especially between ABS and PBT specimens. ABS appears to react particularly sensitively to acid concentration, whereas PBT reacts to extended UV radiation. 

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