Plastic pallets often have the smell of plastic, which has a certain impact on food packaging. Generally speaking, there are the following methods to reduce the smell of plastic:
1. Use purer resin. In many plastics, especially in plastics such as polyvinyl chloride, styrene, polyethylene acetate, and acrylate, residual trace monomers can cause unpleasant odors. Those odors can be eliminated with resins with very little monomer residue. If the resin itself is odorless, it also has a good effect. For example, DuPont has developed a new grade of acetal copolymer that releases very little odor during injection processing.
2. Change the additives. Some additives tend to bring odors to plastics, such as the catalyst tertiary amines used in the production of polyurethane foam, which often brings strong odors. The solution to the problem is to find alternatives to these amines. One of the measures is to use polyhydroxy compounds, which not only have components of the polyurethane molecular chain but also have catalytic activity. Some polyols can even replace half of the tertiary amine catalyst, resulting in a much less odorous product. Phenolic stabilizers used in PVC extrusion or calendering are also often replaced by low-odor zinc stabilizers. Vegetable-derived oils such as erucic acid and oleic acid are much less odorous than amine-based lubricants made from animal-derived oils (used in polyolefin and styrenic food packaging materials).
3. Add adsorbent. If a small amount of zeolite (an aluminosilicate adsorbent) is filled in the polymer, it can play a role in removing the odor of the material. Zeolites have a large number of crystalline voids that trap small gaseous molecules that have odors. Molecular adsorbents have been successfully used in polyolefin vertical extruded pipes, injection and extrusion blow molded containers, barrier packaging materials, extruded overwrap materials, and sealing polymers. Molecular adsorption powders can also be added to plastics as moisture absorbents to remove water vapor, which also contributes to the odor of plastic products.
4. the use of antibacterial agents. Adding antibacterial agents to plastics can not only reduce the odor it emits, but also delay the surface aging, discoloration, and brittleness of the product. The most commonly used antibacterial agents are 10,10'-oxobisphenoxarsenic (OBPA), trioxyhydroxydiphenyl ether (Triclosan), isothiazolone (OIT), and pyridinethione (Pyrithione). Organometallic compounds containing tin and silver are also sometimes used as antimicrobial agents. Antibacterial agents are widely used in thermoplastic styrene elastomers, TPO, etc., and can be used in food packaging, medical facilities, transparent food storage cabinets, etc.
5. Use the desorption method. Placing plastics in odor adsorbents such as activated carbon and high-surface-area silicates desorbs odors through desorption. The vacuum treatment environment can speed up this desorption process.
Treating plastic pellets with a special detergent solution can also help remove odors. Generally these cleaners area unit binary compound or alkaline solutions containing surfactants. These cleaners will effectively take away vinyl chloride monomers, styrene, acrylates, acrylic monomers, and unsaturated hydrocarbons.
6. Add fragrance. Adding fragrance to plastic won't get rid of bad odors, but it can mask them. The method can be applied to polyethylene, polypropylene, and polyolefin vertical thermoplastic elastomers, and the processing methods include injection molding, extrusion, or blow molding. The retention time of the fragrance is not necessarily equal to the life of the molded part, and its retention time depends on the degree of aggregation, the volume surface area ratio, whether it is exposed to heat or humidity, and whether the molded part is tightly sealed against air and other factors.
7. Organic solvent extraction. Waste plastics tend to have unpleasant odors. Most recycled plastic packaging, such as HDPE, PP, PVC, and PET, is washed with an aqueous solution to remove contaminants. However, the odor absorbed inside the plastic will still linger. Organic solvent extraction methods help remove odor-causing compounds. A newer solvent extraction method also uses supercritical carbon dioxide as the solvent. This technology has been applied to HDPE and PET, and it can remove odorous contaminants from oil containers, pesticide containers, and other waste devices. The advantage of carbon dioxide extractants is that they do not bring the troublesome post-processing problems of organic solvents.