Polyvinyl alcohol (PVOH, PVA, or PVAl) is a synthetic polymer which is both colourless, odourless and water-soluble. It was initially discovered in the early 1920's and since has been used in numerous applications from the lamination of safety glass to the packaging of laundry detergents. It is usually supplied as a powder, granules, or pellets, or sometimes as a solution in water.
Contents
1 History
2 Current Uses
3 Polymer Properties
4 Distinctive and Unique Properties
5 Processing of PVOH
6 Recyclability of PVOH
7 The Future Role of PVOH
9 Find a supplier of PVOH or another polymer
Author: D B EDWARDS
Discovered in 1924 by a Nobel Laureate, polyvinyl alcohol (PVOH) resin was developed and commercialized three decades later by Japanese chemical manufacturer, Kuraray. It first gained notoriety in 1989 when PVOH film was used to package pesticides in unit-dose, water-soluble pouches that protected farmers from accidental chemical exposure. This concept then revolutionized the cleaning industry, where single-use laundry and dishwasher detergent packets and tablets offered consumers significantly improved convenience, safety and sustainability.
PVOH is safe and environmentally friendly. Beyond the popular laundry and detergent packets, it is used in many household, medical, personal care and industrial applications, including food packaging, textile yarns, paper products, unit- dose pharmaceuticals, water treatment chemicals, “artificial tears” used to treat dry eyes, contact lens lubricants, transfer printing, agrochemicals, embroidery and dust abatement.
Food-grade versions of the film are used to deliver pre-measured quantities of rice, pasta, cocoa seasoning and nutritional supplements. For example, in the US market, the material is being used to create packets that contain doses of whey protein powder, favoured by fitness enthusiasts for building lean muscle mass. The pre-measured packets make it easier and more convenient to simply drop the protein into a shaker bottle with water or milk, mix and drink. This ensures the correct amount of protein is used with no waste or mess.
Other grades of PVOH film are used in manufacturing processes, such as mould release film in the production of solid surface countertops and reinforced composites
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The use of PVOH is governed by its polymer properties:
Depending on the grade and environmental humidity conditions, PVOH contains water at 3-10%. Therefore, it can be used to hold products with water content in the same range without dissolving or creating holes in the film packaging. Shelf life and storage conditions are taken into account as part of the film selection and compatibility testing process. Pool and spa water treatment chemicals, for example, are tested to simulate storage in an outdoor garage for up to two years.
PVOH film has many distinctive and useful properties. It exhibits excellent tensile strength and elongation. It has one of the best oxygen barriers known to science, making it ideal for preventing food spoilage. It also provides a superior barrier to oil grease and solvents, which can damage, adhere to or bleed-through other substrates.
Typical PVOH properties are:
However, most impressive are its biodegradable credentials. PVOH in solution simply breaks down into carbon dioxide and water when consumed by any of the 55 acclimated organisms found in municipal wastewater treatment or activated sludge. In most water-soluble applications, such as laundry unit-dose, PVOH film is readily or inherently biodegradable as measured by OECD 301B criteria.
PVOH is currently used in recycling paper and cardboard and is added to the slurry to enhance the process. Because of its solubility, it does not contaminate recycling streams for other materials as it evacuates in the rinse process.
Vinyl alcohol-based thermoplastics are injection mouldable and extrudable while retaining water solubility and biodegradability. The uses and potential of being able to injection mould PVOH are again governed by PVOHs many unique properties.
The dissipative, nontoxic and water-soluble properties of PVOH, for example, allow PVOH to be used for the manufacture of pharmaceutical capsules. This provides an alternative to gelatine capsules that can have issues relating to static during manufacture. It also provides improved controlled release of active ingredients and a capsule that cannot be easily altered, offering greater protection to malicious tampering.
The innovation in recent moulding processes opens up the possibilities for complex, multi- treatments and staged release capsules. Such uses are possible, because unlike more conventional polymers, PVOH is suitable for human ingestion in food and ingestion by the Federal Drug Association. The veterinary industry also uses PVOH technology to develop fast-acting, anti-worming treatments where novel single-use delivery systems are used.
The unique mouldable and extrudable properties of PVOH could, for example, be used for novel controlled release of aroma therapy formulations. This could be achieved via the wall thickness of the moulding, which could be designed to dissolve over a set time, releasing the active ingredient of the treatment.
The potential of utilising moulded parts made from PVOH is in its infancy and limited only by ones imagination. For instance, the biodegradable properties of PVOH could provide a more environmentally responsible alternative to plastic and board shotgun cartridges and wads, which would provide a more environmentally responsible solution. In this scenario, the discarded case and wad could simply be allowed to biodegrade naturally.
Since PVOH is both mouldable and extrudable it is possible to imagine combining injection moulded components with thermoformed cavities, creating endless possibilities in the medical and pharmaceutical industry.
PVOH has an affinity with other plastic materials. As such, it can be thermoformed with other thermoformable polymers, allowing segregation in a recycling process. The material can replace other barrier polymers to enhance the overall biodegradability of composite packaging. PVOH also combines well with paper and corrugated packages to provide an internal vapour barrier or to dissipate static electricity. Water-soluble labels made from PVOH can be attached as labels to other plastic bottles and be simply washed off at the end of the bottle’s life. The labels are also biodegradable in municipal wastewater.
Water-soluble PVOH manufacturing is complex and requires considerable investment and technical expertise to produce resins that demonstrate the desired characteristics. However, in the last five years, there have been a substantial increase in new patent applications for PVOH resins and films.
Some of these patents describe combining PVOH with biodegradable materials, such as moulded pulp, to provide barrier packaging that is completely biodegradable. Others focus on harnessing PVOHs unique thermoforming characteristics to combine with other plastic materials, creating a multifunctional package that facilitates the recycling process.
The packaging industry is a significant user of plastic polymers with an annual spend of around £970 billion. Historically, it has been extremely resistant to change. Most recently, however, public attention and pressure to tackle global packaging pollution levels, from materials such as single-use plastics, has pushed brand owners to look for innovative materials, delivery systems and commercial models.
Like most traditional polymers, PVOH is fossil-based, but there are bio-based synthesis routes available, as well as options to combine it with complementary materials. With an engineering resin price that is often two times that of commodity packaging materials, consumers have shown a willingness, in some instances, to pay a premium for more sustainable products. This is a prime area for research and development, where more time can be spent evaluating the exciting potential of PVOH.
The current trends in sustainability and plastic pollution and the new advances in polymer synthesis make this an ideal time for us to reconsider this versatile material.
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