In many contexts undesired, odor and/or taste-producing substances appear owing to chemical degradation or transformation during production or compounding of materials. These substances can be of a highly varying chemical character. The occurrence of such degradation can constitute a health hazard or merely a source of irritation. Since the human being normally is most susceptible to odors and tastes, the substances need not appear in very high concentrations, but in most cases as low concentrations as 1 or a few ppm are sufficient to make a taste or odour evident. Until now, attempts were made to overcome or at least reduce such odour and taste problems in various ways, such as by degassing the material. Such a method is not only lengthy and expensive; it also results in but a moderate improvement in respect of odour and taste, respectively.
Zeolite (Aluminum Sillicate in molecular sieve form) when added at less than 0.5% in polymer before converting into end product eliminates undesired odor. From a general point of view, it is known to remove any undesired odour and/or taste by means of adsorbing substances, and as examples of such adsorbing substances, activated carbon, silica gel, activated aluminum oxide, diatomaceous earth and zeolites may be mentioned. Addition of aluminum hydroxide, clay, diatomaceous earth, kaolin, talc, betonies, activated carbon or activated carbon fiber for materials for packing foodstuffs to be heated in the packing will remove odor/taste. However, such additives have been found to be without any appreciable effect, except under special circumstances, in the case of undesired components in plastic materials lose their absorbing capacity when contacting water or water vapor.
It has been found that not all zeolites are active. Zeolite should be substantially hydrophobic (oleophilic) to be effective in the elimination of odour and taste. A measure of the hydrophobic properties is the water sorption of the zeolite, and this should suitably be less than 10 wt.-percent, preferably less than 6 wt.-percent, at 25° C. and 4.6 torr. The Si/Al molar ratio of the zeolite in the oxide units of its crystal lattice seems to affect the hydrophobic properties and should exceed 35 and preferably be between 200 and 500. The pore diameter of the zeolite, which according to the molecular size determines which compounds can be caught by the zeolite, should be at least 5.5 and preferably at least 6.2 Å. The zeolite, which generally is in the form of a powder, should have such a small particle size that it does not detrimentally affect the appearance of the plastic material or the other properties thereof. Thus, the zeolite should have an average particle size not exceeding about 10 �m, such as about 0.1-7 �m, preferably not exceeding about 5 �m.
Containers, such as bottles, of blow-moulded or moulded plastic, for packing foodstuffs, beverages or pharmaceutical preparations can also benefit from this usage of zeolite to eliminate odor and taste. Plastic fittings such as panels for use in buildings or cars can take the advantage of using zeolite to remove odor.