Many inherent materials found in plastics are responsible for objectionable odours. They include amines, phenols, mercaptans, peroxides, styrene, aldehydes, ketones, alcohols and some plasticizers and fire retardants. Organic solvents used in plastics processing can also give off strong chemical smells.
First of all those additives that offer objectionable odour, should be replaced, if feasible, by those additives that offer no odour. For example, in PVC products, heat stabilizers like Lead or mixed metal containing barium and zinc can be easily replaced by octyl tin or zinc heat stabilizer. Traces of monomers can produce unpleasant odours in many polymers, particularly in PVC, polystyrene, polyvinyl acetate and acrylic esters. Selecting resins with a minimum of monomer residues can eliminate these odours.

Polymer formulations can be filled with small amounts of synthetic zeolites, such as molecular sieve powders based on metal aluminosilicates, to absorb unwanted odours within the materials. The additives do this by trapping the organic odour-producing molecules within their highly porous crystal structures. Molecular sieve absorbents have been successfully used in extruded polyolefin pipes, injection and extrusion blow-molded containers, barrier packaging materials, extrusion coatings and sealant polymers. Molecular sieve powders can also be incorporated into plastics as desiccants to remove the moisture that contributes to odours.

Antimicrobials are often added to plastics, not only to reduce odours, but also to retard surface growth, staining and embrittlement. The most common antimicrobials are 10,10'-oxybisphenoxarsine (OBPA), trichlorohydroxydiphenylether (Triclosan), n-octyl-isothiazolinone (OIT), 4,5-di-chloro-isothiazolinone (DCOIT), mercaptopyridine-n-oxide (pyrithione), and butyl-benzisothiazolinone (butyl-BIT). Organometallic compounds of tin and silver are also sometimes used as antimicrobials. They also help in reducing the odours.

Another way to rid plastics of unwanted smells is to expose them to external odor absorbing agents such as activated charcoal or high-surface-area silica. This may be done under a vacuum to speed up the process.

Rinsing plastics in specially formulated detergent solutions can also aid in odour removal. Typically these are aqueous, alkaline solutions containing surfactants, useful in eliminating odours from vinyl monomers, styrene, acrylates, acrylic monomers and unsaturated hydrocarbons.

The addition of pleasant-smelling fragrances to plastics does not eliminate odours, but it masks them, which is sufficient for many purposes. Commercial scents are available for such polymers as PE, PP and olefin thermoplastic elastomers. They are suitable for injection moulding, extrusion or blow moulding. Fragrances do not always last for the lifetime of the moulded article. Their longevity depends on the initial concentrations, volume to surface-area ratio, exposure to heat or humidity and whether the finished parts are packaged in air-tight barriers. Typical applications of fragrances include toys, household goods, cosmetic containers, consumer electronics, and lawn and garden equipment.

Odours are a constant problem with post-consumer plastics. Most plastics that are recycled, such as PE, PP, PS, PVC or PET, are subjected to a washing step with aqueous solutions to remove contaminants. But odours trapped inside the recycled resins may linger. Solvent extraction using organic solvents can help eliminate the compounds responsible for these odors. A recent development has been solvent extraction using supercritical carbon dioxide as the solvent. The technology, which has been demonstrated on HDPE and PET can remove odorous contaminants from plastic oil containers, pesticide containers and other post-consumer items. The advantage of the CO2 system is that it does not employ organic solvents, which present troublesome disposal problems.

The degassing units that are part of the extruders used to pelletize plastics recyclate are also effective in stripping away some of the more volatile compounds that produce unwanted odors.

Because odors are subjective phenomena, it is a challenge to develop a system for classifying and measuring them. The first step in identifying odours objectively is to use panels of human test subjects to detect and rate odours on the basis of how pleasant or unpleasant they are. Responses of these panels can then be co-related with measurements of volatiles in plastics made with standard instrumental analytical methods such as gas chromatography/mass spectroscopy (GC/MS). But these older instrumental systems require careful evaluation by experts to interpret correctly.

Newer plastics odour detection instruments, known as "electronic noses," rely on electronic gas sensor arrays and pattern recognition technology. To use them, technicians heat a sample to drive off the volatiles, which are conducted to the sensor arrays. The results are presented in a statistical pattern that is easily correlated with sampling results from human panelists. Depending on the desired level of detail, odours from the volatiles may be classified as pleasant, neutral or unpleasant, or reported as intensity and molecular concentrations.