Yellowing polyester resin

Polyesterification. High molecular weight linear polyester resins, such as poly(ethylene terephthalate) (PET), poly(propylene terephthalate) (PPT), and poly(butylene terephthalate) (PBT), can be produced by either transesterification of dimethyl terephthalate (DMT) with an excess of the corresponding diol or by direct esterification of terephthalic acid (TPA). Tetraalkyl titanates, such as TYZOR TPT or —TYZOR TBT, have been found to be excellent catalysts for either of these reactions. However, in the case of PET, the residual titanate catalyst reacts with trace quantities of aldehydic impurities produced in the polymerization process to generate a yellow discoloration of the polymer (468,469). In the case of PPT and PBT, where the color of polymer is not as critical, organic titanates are the catalyst of choice because of their greater reactivity than antimony or tin (470). Numerous processing variations have been described in the literature to minimize formation of tetrahydrofuran in the PBT process (471—472). 

Dyes can be used to obtain transparent colours in polyester resins. Considerable care in their selection needs to be taken as most will quickly fade on the addition of catalyst to the liquid resin or on exposure of the cured resin outdoors. However, certain quinone-type aromatic-soluble dyes in the yellow-red range are extremely lightfast and transparent blues and greens can be satisfactorily produced using small quantities of the corresponding phthalocyanine pigments. 

Palatal . See Polyester resin, thermosetting Palatase. See Esterase-lipase Palatine fast yellow BLN. See Acid yellow 54 Palatinol 11P-E. See Diundecyl phthalate Palatinol A. See Diethyl phthalate Palatinol C Palatinol DBP. See Di butyl phthalate... 

The main producers of safflower oil are the USA, Mexico, India, Australia and Europe. It is a semi-drying oil which dries better than soybean oil. There is no yellowing in the dried film, even under conditions of extreme exposure. Safflower oil is used successfully in house paints, especially when blended with tung oU, linseed oil or perilla oil. Raw or bodied safflower oil is the best suited to the production of non-yellowing paints. Safflower oil can replace soybean oil in polyester resin. 

Chlorinated paraffin (chlorocosane) n. Any of a family of yellow to light amber liquids produced by chlorinating a paraffin oil, with uses as secondary plasticizers for vinyls, polystyrene, polymethyl methacrylate, and coumarone-indene resins. Chlorinated paraffins also impart flame resistance to polyolefins, polystyrene, PVC, natural rubber, and unsaturated polyester resins. 

Known also as Diphenyl Ketone. p-Benzoquinone -kwi- non (1,4-benzoquinone, chinone) A yellow crystalline compound used, along with many of its derivatives, as an inhibitor in unsaturated polyester resins to prevent premature gelation during storage. 

Polyester resins tend to yellow under the influence of sunlight, which is very intensive when styrene is used as a copolymerization component. Translucence is reduced by yellowing. 

Fiame-protected polyester resins tend to yellow more intensely than those not equipped with flame retardant. Self-extinguishing polyester resins containing organic haiogen derivatives are especially prone to yellowing [32],... 

Color/Transparency. Almost all amorphous engineering thermoplastics, except PC and some polyester carbonates, are inherently colored. Even polycarbonates have yellowness indexes (YI) (36) of 0.1 to 5.0. Colorless material is produced from these resins by compounding with complementary blue dyes which reduce transmission. Ha2e in amorphous resins is an indication of particulates. Ha2e reduces optical clarity and transmission. 

To improve the weatherabihty of epoxies, which normally chalk and yellow, epoxy—polyester alloys or hybrids are used. These powders with improved overbake resistance cure at temperatures as low as 130°C. They have film flexibility similar to epoxy resins, but their hardness is slightly decreased. Corrosion resistance is equivalent to epoxy powders in most cases, although solvent and alkali resistance is inferior. 

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