Polyamides weathering

Where transparency is required, a range of polymers is available. Polystyrene is the least expensive but polymethylmethacrylate has an outstanding high light transmission combined with excellent weathering properties. Also to be considered are the polycarbonates, glass-clear polyamides, SAN, butadiene-styrene block copolymers, MBS polymers, plasticised PVC, ionomers and cellulose esters such as cellulose acetate. 

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... 

Figure 12.3 Examples of the weathering performance of (a) a stabilised HDPE nonwoven and (b) a polyamide/polyester nonwoven deliberately unstabilised against ultraviolet radiation. Both were exposed to artificial weathering using three different types of apparatus and to natural weathering in two locations. All results are plotted against radiant exposure (total ultraviolet light energy...

PVC, polyamides, unsaturated crosslinked polyesters, ABS, and wood . Di- and tri-benzotriazole photostabilizers, such as (874) and (875) are synthesized from 2-nitro-benzenediazonium salts and an excess of 1,3-dihydroxybenzene or 1,3,5-trihydroxybenzene <85Mi 40i-0l>. The dibenzotriazole derivatives (874b and 875b) can be used as polymerizable acrylic UV absorbers <84PB237>. A few or/Ao-urethane and -trimethylsilane substituted 2-phenylbenzotriazoles (876 and 877) show similar photostabilization activity . Weather resistance of low-density polyethylene is improved by the addition of a benzotriazole-type photostabilizer <90M140i-04>. 

Fig. 5. Effect of outdoor weathering on the strength of aluminum alloy/epoxy-polyamide joints (chromic-sulfuric acid-etch metal surface pretreat-ment)61 (Reprinted from Ref. 61, p. 194, by courtesy of Gordon and Breach...

FIGURE 15.11 Effect of outdoor weathering on the strength of aluminum joints bonded with epoxy-polyamide.30... 

The behavior of two other formulations, microcapsules and small plastic laminate flakes, containing tetradecenol formate, were compared in applictions to plots of mature corn at Beltsville, in August 1980. (8) The Z-9-tetradecen-1-ol formate (TDF) is a mating disruptant, rather than a true pheromone, of the Heliothis species of moths. It was selected in these experiments because reliable analytical methods were available (9) and its behavior was expected to be similar to that of the actual pheromones, whose chemical structures and properties are also similar. The two formulations were polyurea-polyamide microcapsules 5-microns in diameter supplied by ICI at Bracknell, Berkshire, England, and a small (3 mm side) plastic laminate formulation supplied by the Herculite Corporation of York, PA. The microcapsules were applied at 300 g of TDF per hectare and the flakes at 285 g/h. Both formulations were applied by air to mature corn 240-270 cm in height in clear, hot weather with a daily maximum temperature of 39°C. 

The binders used in these ambient-cured formulations are generally low molecular weight reactive epoxy resins. These are cured with either amine or amine adducts to give the best chemical resistance, or with polyamide to give better water resistance, weathering and recoating properties (Dow Chemical Company, undated a). 

Considerable data have been published on the deterioration of some specific properties of polyamides as a consequence of natural or artificial weathering but few papers have been concerned with mechanistic photochemistry of these polymers. The results of Sharkey and Mochel [101] on the photo-oxidation of amides have opened the way to a better understanding of the problem. These authors have suggested that the primary photochemical step in the photolysis of amides is the breaking of the CO—NH bond with the formation of two free radicals which preferentially abstract hydrogen atoms from the methylene groups adjacent to the nitrogen namely,... 

In contrast to polyamides in polystyrene phenolic antioxidants are not able to reduce the decrease in tensile strength during UV irradiation [141]. UVAs as well as HALS stabilizers are effective in polystyrene (PS). The best protection can be reached by using combinations of a UVA and a HALS. According to Gugumus [133,134] the synergism between UVA and HALS is distinct when the time until a AYI = 5 is taken as failure criterion (see Table 17.12). However, when as criterion the yellowness index after 1600 h in a Weather-Ometer is taken, the synergism between a UVA and a HALS is much smaller (see Fig. 17.14). 

These polyesters, [-0-(t)-C(CH3)2-(t)-C02-(t)-C0-]jj (Tg = 188°C, and HDT = 120-175°C), were introduced in 1974. The commercial resins include U-polymer , Ardel , Durel , and Arylon . Their advantages include transparency, good weatherability and high HDT. PAr has been blended with nearly all resins, including ABS, EPDM, lonomers, LCP, PA, PB, PBI, PBT, PC, PEI, PEK, PET, Phenoxy, PMB, PS, PPE, PPS, etc. Three types of PAr blends are of particular importance — those with polyesters, PEST, polyamides, PA, and with polyphenylenesulhde, PPS. A summary of PAr blends is provided in Table 1.76. 

Polyamides are also resistant to UV degradation, weathering, and ozone. Refer to Table 2.16 for the compatibility of PA with selected corrodents. A more detailed listing will be found in Reference [1]. 

Polyamides are resistant to sun, weather, and ozone. Many metals are coated with polyamide to provide protection from harsh weather. 

Fig. 4.20. Effect of outdoor weathering on joint strengths (Refs. 92, 93 Adhesive epoxy polyamide film. Adherends aluminium alloy. Pretreatment Chromic-sulphuric add etch. Cure temperature 175 C.

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... 

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. 

Besides polyolefins, the outdoor weathering performance of unstabilised polyformaldehyde, polystyrene, PVC and polyamides is also inadequate, and that of unstabilised polycarbonate, ABS and SAN is not good. 

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. 

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