Reduction of whitening of polymer parts
This invention relates to a process for producing non-whitening molded articles of poly(trimethylene terephthalate) (PTT) with reduced whitening by treating the articles with heat.
1. A process comprising:
heat-treating a molded article of poly(trimethylene terephthalate) by exposing the molded article to heat for a time period between about 1 minute and 1 hour,
wherein the whiteness of the molded article, due to oligomer blooming, is decreased by at least 10 percent from the original value, based on L* values.
2. The process of claim 1 , wherein the poly(trimethylene terephthalate) contains about 70 mole % or more of repeat units derived from 1,3-propane diol and terephthalic acid and/or an equivalent thereof.
3. The process of claim 1 , wherein the molded article of poly(trimethylene terephthalate) is exposed to a temperature of between about 180 degrees C. and 225 degrees C., and the time periods are between about 2 minutes and 30 minutes.
4. The process of claim 1 , wherein the heat is provided by convection heating, radiant heating, conduction heating, or any combination thereof.
5. The process of claim 2 , wherein the poly(trimethylene terephthalate) contains up to 30 mole % of repeat units made from:
(i) diacids comprising isophthalic acid; 1,4-cyclohexane dicarboxylic acid; 2,6-naphthalene dicarboxylic acid; 1,3-cyclohexane dicarboxylic acid; succinic acid; glutaric acid; adipic acid; sebacic acid; 1,12-dodecane dioic acid; dimethyl, diethyl, or dipropyl ester derivatives of the diacids; or mixtures thereof; and
(ii) diols comprising ethylene glycol; 1,4-butane diol; 1,2-propanediol; diethylene glycol; triethylene glycol; 1,3-butane diol; 1,5-pentane diol; 1,6-hexane diol; 1,2-, 1,3- and 1,4-cyclohexane dimethanol; or the longer chain diols and polyols made by the reaction product of diols or polyols with alkylene oxides.
6. The process of claim 1 , wherein the poly(trimethylene terephthalate) comprises up to about 5 mole % of sulfonate compounds.
7. The process of claim 6 , wherein the sulfonate compounds comprise 5-lithium sulfoisophthalate, 5-sodium sulfoisophthalate, 5-potassium sulfoisophthalate, 4-sodium sulfo-2,6-naphthalenedicarboxylate, tetramethylphosphonium 3,5-dicarboxybenzene sulfonate, tetrabutylphosphonium 3,5-dicarboxybenzene sulfonate, tributyl-methyl phosphonium 3,5-dicarboxybenzene sulfonate, tetrabutylphosphonium 2,6-dicarboxynaphthalene-4-sulfonate, tetramethylphosphonium 2,6-dicarboxynapthalene-4-sulfonate, ammonium 3,5-dicarboxybenzene sulfonate, or ester derivatives thereof.
8. The process of claim 1 , wherein the poly(trimethylene terephthalate) is blended with up to about 30 wt % of other polymers, based on the total weight of the poly(trimethylene terephthalate) and the other polymers.
9. The process of claim 8 , wherein the other polymers comprises poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(ethylene) (PE), poly(styrene) (PS), nylon-6, or nylon-6,6.