Polyethylene pigments

Nelson, K.H., Cathcart, W.M. 1984. Transmission of light through pigmented polyethylene milk bottles. J. Food Prot. 47, 346-348. 

Absorbers especially 2-hydroxy-4-alkoxy benzophenones Pigments, such as carbon black, also can serve as UV stabilizers. Pheonhc antioxidants, hindered amines, and metal salts are effective in pigmented polyethylene. 

Fig. 26.9 Effect of natural aging on elongation of pigmented polyethylene...

To determine whether this phenomenon is associated solely with the increase in conductivity, we investigated a pigmented polyethylene system. This system does not become conductive at a critical volume concentration. The aim was to determine whether in these circumstances as well there would be a phase transition comparable with that found in the systems filled with carbon black. And indeed Irgalith yellow BAWP dispersed in a polyethylene matrix also displays a stagnation of density on the same scale as is found with carbon black in a variety of polymer matrices (Fig. 19.27). 

EFFECT OF INTERFACE MODHICATION ON THE PHOTO-STABILITY OF PIGMENTED POLYETHYLENE FILMS... 

Rigid Applications. The use of the lead stabilizers is very limited in the United States but, they are stiU used in several rigid PVC appHcations in Europe and Asia. The highest use of lead stabilizers in rigid PVC is for pipe and conduit appHcations. Tribasic lead sulfate is the primary heat stabilizer with lead stearates included to provide lubrication. The lead products are typically fully formulated, usually including lubricants and pigments for pipe extmsion appHcations. These lead one-packs, when used at about 1.8—2.5 phr, provide all of the stabilizer and lubrication needed to process the polymer. A lead one-pack contains tribasic lead sulfate, dibasic lead stearate calcium stearate, polyethylene wax, paraffin wax, ester wax, and pigments. 

Available Forms. Phthalocyanines are available as powders, in paste, or Hquid forms. They can be dispersed in various media suitable for aqueous, nonaqueous, or multipurpose systems, eg, polyethylene, polyamide, or nitrocellulose. Inert materials like clay, barium sulfate, calcium carbonates, or aluminum hydrate are the most common soHd extenders. Predispersed concentrates of the pigments, like flushes, are interesting for manufacturers of paints and inks (156), who do not own grinding or dispersing equipment. Pigment—water pastes, ie, presscakes, containing 50—75% weight of water, are also available. 

Functional derivatives of polyethylene, particularly poly(vinyl alcohol) and poly(acryLic acid) and derivatives, have received attention because of their water-solubility and disposal iato the aqueous environment. Poly(vinyl alcohol) is used ia a wide variety of appHcations, including textiles, paper, plastic films, etc, and poly(acryLic acid) is widely used ia detergents as a builder, a super-absorbent for diapers and feminine hygiene products, for water treatment, ia thickeners, as pigment dispersant, etc (see Vinyl polymers, vinyl alcohol polymers). 

Functional polyethylene waxes provide both the physical properties obtained by the high molecular weight polyethylene wax and the chemical properties of an oxidised product, or one derived from a fatty alcohol or acid. The functional groups improve adhesion to polar substrates, compatibHity with polar materials, and dispersibHity into water. Uses include additives for inks and coatings, pigment dispersions, plastics, cosmetics, toners, and adhesives. 

Siding. The resin most used for siding is poly(vinyl chloride) homopolymer, compounded with modifiers, stabilizers, and pigments. Modifiers are most often acryhc esters, followed by chlorinated polyethylene or ethylene—vinyl acetate, used at 6—8 phr (parts per hundred resin). The modifier increases the impact strength of the rigid PVC. 

Monoazo Pigments. In combination with other groups, the a2o linkage, —N=N—, imparts color to many dyes and pigments (see Azo Dyes). The simplest of these, ie, the Hansa yellows, toluidine reds, and naphthol reds, do not have the lightfastness and heat stabiUty required for plastics. Permanent YeUow FGL and Permanent Red 2B are stable enough for vinyls, polyethylene, polypropylene, and ceUulosics (11). Permanent Red 2B is available as the calcium, barium, or manganese salt. 

DlsaZO Pigments. The diaiylide yeUows and oranges also known as benzidines are derivatives of benzidine coupled to two moles of substituted acetoacetanilide. Benzidine Yellows AAMX, AAOT, AAOA, and HR (PY 13, 14, 17, and 83) ate examples (Fig. 1). Yellows AAMX and AAOT are used in flexible vinyls. AAOA also colors polyethylene and polypropylene. These three differ only slightly in shade. Benzidine YeUow HR is redder. 

These pigments are recommended for most plastic systems because of their excellent stabiUty to chemicals, bleeding, and light. They are widely used in vinyls, polyethylene, polypropylene, and ceUulosic plastics. The Colourindex classes are Hsted as PR 123, 149, 179, and 190. 

In general the selection of pigments for polypropylene follows the same considerations as for polyethylene. Because of the higher processing temperatures and the lesser resistance to oxidation, selection does, however, require rather more care. 

Other factors which can affect impact behaviour are fabrication defects such as internal voids, inclusions and additives such as pigments, all of which can cause stress concentrations within the material. In addition, internal welds caused by the fusion of partially cooled melt fronts usually turn out to be areas of weakness. The environment may also affect impact behaviour. Plastics exposed to sunlight and weathering for prolonged periods tend to become embrittled due to degradation. Alternatively if the plastic is in the vicinity of a fluid which attacks it, then the crack initiation energy may be reduced. Some plastics are affected by very simple fluids e.g. domestic heating oils act as plasticisers for polyethylene. The effect which water can have on the impact behaviour of nylon is also spectacular as illustrated in Fig. 2.80. 

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