How to reduce the pungent smell of plastics

Plastics are an important raw material in the packaging industry. Plastic processed products emit an unpleasant smell. To overcome this problem, plastic resin producers have long been working to reduce the emission level of these odors. Solutions include: replacing low-odor alternatives with unpleasant additives; reducing the amount of residual monomer in the plastic; adding a gas sorbent to the plastic and adding an antibacterial agent to prevent those that are produced by bacteria and fungi The unpleasant smell; in the process of recycling plastics, solvent extraction and venting can be used to reduce residual odor.

Many of the compounds in plastics have an unpleasant odor, including amines, phenols, mercaptans, peroxides, benzenes, aldehydes, ketones, as well as some plasticizers and flame retardants. Solvents used in plastic processing also release a strong chemical odor. The following measures can be taken to reduce the smell of plastic:

Change additive

The tertiary amines of the catalysts used in the production of polyurethane foams often give rise to strong odors. The solution to the problem is to find alternatives to these amines. One of the measures is to use a polyhydroxy compound which not only has a component of a polyurethane molecular chain but also has catalytic activity. Some polyols can even replace half of the tertiary amine catalyst, and the resulting product emits a much weaker odor.

Phenolic stabilizers used in PVC extrusion or calendering processes are also often replaced by low odor zinc stabilizers. Plant extract oils such as erucic acid and oleic acid are much less odorous than amine lubricants (for polyolefin and styrenic food packaging materials) made from animal extract oils.

Use a cleaner resin

In many plastics, especially in plastics such as polyvinyl chloride, styrene, polyethyl acetate and acrylates, residual trace amounts of monomers can produce unpleasant odors. Those odors can be eliminated by using a resin with a small amount of monomer remaining.

If you use the odorless resin itself, it also has a good effect. For example, DuPont has developed a new grade of acetal copolymer that emits a very low odor during the injection process.

Adding adsorbent

If a small amount of zeolite (an aluminosilicate adsorbent) is filled in the polymer, it can act to remove the odor of the material. Zeolites have a large number of crystalline voids that capture small molecules of odorous gases. Molecular adsorbents have been successfully applied to polyolefin extruded tubing, injection and extrusion blow molded containers, insulation packaging materials, extruded outer packaging materials and sealing polymers. Molecular adsorption powders can also be added as moisture absorbers to plastics to remove moisture, which can also contribute to the odor of plastic products.

Antibacterial agent

Adding an antibacterial agent to the plastic not only reduces the odor it emits, but also delays the aging, discoloration and embrittlement of the surface of the product. The most commonly used antibacterial agents are 10,10'-oxobiphenanthrene (OBPa), triclosan, isothiazolinone (OIT), pyrythione. Organometallic compounds containing tin and silver are sometimes also used as antibacterial agents. The antibacterial agent is widely used for the thermoplastic styrene elastomer TPO for food packaging, medical facilities, transparent food storage cabinets and the like.

Desorption method

Another method of deodorization is to place the plastic in an odor adsorbent such as activated carbon and high surface area silicate. The vacuum treatment environment can speed up the desorption process.

Treatment of plastic granules with a special detergent solution can also help to remove odors. Generally these detergents are aqueous or alkaline solutions containing surfactants. These detergents are effective for removing vinyl chloride monomers, styrene, acrylates, acrylic monomers, and unsaturated hydrocarbons.

Adding fragrance

Adding a fragrance to a plastic does not eliminate the unpleasant odor, but it can cover these odors, which in many cases is sufficient. The method can be applied to polyethylene, polypropylene and polyolefin thermoplastic elastomers by injection molding, extrusion or blow molding. The preservation time of the fragrance is not necessarily equal to the life of the molded part. The storage time depends on the degree of aggregation, the volume to surface area ratio, whether it is exposed to a heated or humid environment, and whether the molded part is subjected to strict air separation and other factors. . Fragrances are generally used in toys, household goods, cosmetic containers, household appliances and gardening equipment.

Recycling treatment

Waste plastics tend to produce unpleasant odors. Most recycled plastic packaging materials, such as HDPE, PP, PVC, and PET, are washed with aqueous solutions to remove contaminants. However, the odor adsorbed inside the plastic will still remain. Organic solvent extraction methods help to remove odor-causing compounds. The latest solvent extraction method also uses supercritical carbon dioxide as a solvent. This technology has been applied to HDPE and PET, which can be used to remove odorous contaminants from degreasing containers, pesticide containers and other waste devices. The benefit of carbon dioxide extracts is that they do not cause troublesome post-treatment problems with organic solvents.

The odor removal device is an integral part of the waste plastic pellet extruder and it is also effective in removing some of the highly volatile compounds that produce odors.

Plastic odour scale

Smell is a subjective subject that varies from person to person, so how to develop a system scale odor is very difficult. The first step in objectively confirming the smell is to let a group of people identify whether the smell they smell is pleasant or unpleasant. According to the identification of the identification team, standard instrumental analysis methods such as gas chromatography, solid state spectroscopy (GS/MS), etc. are used to determine the grade of plastic volatiles. But these older instrumental analysis systems require expert analysis and evaluation to arrive at the right conclusion.

The latest plastic odour detector is a device called the "electronic nose" that relies on electronic probe dot matrix and pattern recognition technology to work. The instrument operator heats the sample to direct the released volatiles into the probe array for detection. The results obtained are displayed in digital mode, which makes it easy to correlate with the conclusions of the discriminating group. Depending on the specific requirements, volatile odors can be classified as pleasant, neutral, unpleasant, or reported in terms of strength and molecular aggregation.

In the highly competitive plastic packaging market, irritating odors can hamper sales, while neutral or pleasing scent is welcomed by customers. The use of odor removal technology may increase the cost of the product in the short term, but in the long run there will be a good return.

Developing plasticizer replacements in food packaging materials is imminent

Food safety is inseparable from the packaging safety of food. Food packaging is known as a "special additive" for food. In current food packaging materials, plasticizers are often added to improve the performance of the packaging material in certain aspects. However, while improving the performance of the packaging material, the harm of the plasticizer to the human body cannot be ignored.

There are several plasticizers in food packaging materials:

Polyethylene terephthalate (PET). Refillable plastic containers made of PET polycondensate have very good resistance to CO2 penetration loss, and are especially suitable for packaging beverages, drinking water, edible oil and the like. However, PET is an organic pollutant that causes carcinogenicity and mutagenicity in humans. Its toxicity is mainly caused by chronic poisoning, and the damage often manifests itself after many years.

Phthalates (PaEs). PaEs, also known as phthalates, are used in large quantities as plastics, especially plasticizers and softeners for polyvinyl chloride (PVC), which account for about 80% of plasticizer consumption. PaEs are also commonly used as an additive to the foil on the inner wall of paper packaging. However, long-term exposure to PaEs can cause symptoms such as polyneuritis, dysesthesia, and paralysis, which have inhibitory and anesthetic effects on the central nervous system of the human body. According to reports, in 1995, there were 75 cases of collective food poisoning in PaEs in Xi'an, China. Poisoned lower extremity gastrocnemius muscle pain, lower limb weakness, limbs soft, bedridden, Achilles tendon reverse or disappear. One month after the onset of the disease, the limbs were involved, the muscles showed different degrees of muscle atrophy, the severe cases showed pyramidal tract disease, and the surrounding axonal cord was damaged. FDa reported that mammals ingesting high doses of PaEs have signs of liver cancer. The experiment also confirmed that PaEs may have teratogenic and poisoning effects on the development of chicken embryos. In addition, PaEs also have the characteristics of estrogen and the biological effects of anti-androgen, which will interfere with the normal endocrine function of animals and humans. Frequent exposure of these substances to men will reduce the amount of sperm and lead to sperm deformity.

Bisphenol a (BPa). BPa is an additive for epoxy resins and polycarbonate plastics. The plastic products are used for food and beverage packaging. Resin products are widely used in metal coatings, including edible oil packaging materials, food cans, caps and water supplies. Tube and so on. BPa may be more or less present in people's daily lives such as paper cups, plastic cups and metal cans. The harm of BPa to the human body is the secretion disorder in the human body. Low levels of BPa reduce sperm count, improve the incidence of hormone-related cancers such as breast cancer, testicular cancer, prostate cancer, and cause birth defects in the reproductive system (non-hereditary testicular cancer), as well as hormone-related diseases such as Girls wait in advance for puberty. Even at very low concentrations, BPa affects the proportion of males and females in pheasants, resulting in the snail's breeding. BPa has a proliferative effect on lymphocytes, and different doses of BPa can induce lymphocyte proliferation and thus have latent immunotoxicity.

Plasticizers in food packaging materials can contaminate food through packaging that comes into contact with food. Therefore, it is urgent to strengthen the research and development of plasticizer substitutes in food packaging materials.