Polyolefins exposure

Oxidation by flame treatment for polyolefins exposure to a flame of methane, propane or butane and oxygen in excess for a very short time (less than 0.2 seconds) to create oxidation and reactive sites such as hydroxyl, carbonyl, carboxyl... Particularly used for polyethylene and polypropylene. 

Fig. 2. Schematic of the RISTON dry film photoresist process, (a) Removal of polyolefin separator sheet and laminate resist to clean surface, using special laminator (b) exposure to uv source using positive or negative phototool (positive to plate negative for print-and-etch) (c) removal of the protective Mylar, which is readily removed by hand and (d) development using a special processor (3).

A WBL can also be formed within the silicone phase but near the surface and caused by insufficiently crosslinked adhesive. This may result from an interference of the cure chemistry by species on the surface of substrate. An example where incompatibility between the substrate and the cure system can exist is the moisture cure condensation system. Acetic acid is released during the cure, and for substrates like concrete, the acid may form water-soluble salts at the interface. These salts create a weak boundary layer that will induce failure on exposure to rain. The CDT of polyolefins illustrates the direct effect of surface pretreatment and subsequent formation of a WBL by degradation of the polymer surface [72,73]. 

Oridation. This is caused by contact with oxidising acids, exposure to u-v, prolonged application of excessive heat, or exposure to weathering. It results in a deterioration of mechanical properties (embrittlement and possibly stress cracking), increase in power factor, and loss of clarity. It affects most thermoplastics to varying degrees, in particular polyolefins, PVC, nylons, and cellulose derivatives. 

Flame treatment is predominantly used with articles of relatively thick section, such as blow moulded bottles, although it has been applied to polyolefin films as well. The most important variables in the process are the air-gas ratio and their rate of flow, the nature of the gas, the separation between burner and surface, and the exposure time. 

P.O.34 is rarely used in polyolefins. In such media, it only withstands exposure to 200°C, and its opaque colorations show insufficient lightfastness. P.O.34 tends to bloom, especially in extrusion products made of low molecular weight LDPE types. The pigment is, however, recommended for a variety of other media. These range from aromatic polyurethane foams to cast resins of unsaturated polyester, in which the pigment slightly delays the hardening process. 

P.R.170 is not always heat stable enough to allow application in polyolefins. In HDPE systems formulated at 1/3 SD, the pigment tolerates exposure to 220 to 240°C for one minute. Its tinctorial strength, on the other hand, is excellent. P.R.170 is also occasionally used in polypropylene and polyacrylonitrile spin dyeing in the latter medium, it satisfies the specifications of the clothing and home textiles industries. Besides, P.R.170 lends color to viscose rayon and viscose cellulose it is used for the mass coloration of semisynthetic fibers made of cellulose last but not least, it colors yarns, fibers, and films made of secondary acetate. 

P.Br.23 shows excellent heat stability in polyolefins. 1/3 SD samples containing 1 % TiOz, as well as transparent colorations at 1/3 SD in HDPE are stable to exposure to 300°C for 5 minutes. In injection molding, P.Br.23 considerably affects the shrinkage of the plastic at 220°C, an effect which diminishes with increasing temperature (Sec. 1.8.3.2). 

In terms of heat stability, 1/3 SD polyolefin systems containing P.V.23 withstand exposure to 280°C. In lighter tints, this value is appreciably lower 1/25 SD... 

Asahi Chemical Industry carried out an exploratory investigation to determine the requirements for cellulose based separators for lithium-ion batteries. In an attempt to obtain an acceptable balance of lithium-ion conductivity, mechanical strength, and resistance to pinhole formation, they fabricated a composite separator (39—85 /cellulosic fibers (diameter 0.5—5.0 /pore diameter 10—200 nm) film. The fibers can reduce the possibility of separator meltdown under exposure to heat generated by overcharging or internal short-circuiting. The resistance of these films was equal to or lower than the conventional polyolefin-based microporous separators. The long-term cycling performance was also very comparable. 

PBS (Figure 30) is an alternating copolymer of sulfur dioxide and 1-butene. It undergoes efficient main chain scission upon exposure to electron beam radiation to produce, as major scission products, sulfur dioxide and the olefin monomer. Exposure results first in scission of the main chain carbon-sulfur bond, followed by depolymerization of the radical (and cationic) fragments to an extent that is temperature dependent and results in evolution of the volatile monomers species. The mechanism of the radiochemical degradation of polyolefin sulfones has been the subject of detailed studies by O Donnell et. al. (.41). 

Common to these photopolymer products was the use of coinitiators, such as 2-MBO, diacrylate and triacrylate monomers, binders, and other additives as required. In general, the film products were coated on a polyester support and a polyolefin sheet laminated to the coated material, to permit exposure of the films in an oxygen-free environment, as was required to obviate the chain-stopping effect of peroxide formation. 

An increase in carbonyl content (2,14, 20, 25, 30, 32) has been used by some investigators to determine the stability of polyolefins. Instability was related to the relative increase in carbonyl content. In this study, the relative carbonyl content of the nine commercial polymers was measured in 25-mil plaques after 0, 100, 200, 300, and 400 hours exposures... 

Dibromanthrone red, PR 168, Cl No. 59300 is a bright, yellow-shade red with excellent fastness properties with no tendency to fade on prolonged outdoor exposure at all depths of shade. However, the pigment tends to bloom in flexible PVC and polyolefins and cannot be recommended for such polymer systems. 

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