Making plastic that melts away

Materials World magazine
,
1 Jul 2019

Founder and CEO of Edwards Innovations, David Edwards, makes a case for extending the use of polyvinyl alcohol to produce plastics that dissolve in water.

The majority of plastics provide valuable, cost-effective solutions that support our way of life, but we cannot deny they also contribute to the complex global issue of pollution. There are numerous ways of addressing the issues associated with plastics and one seemingly impossible solution is to ensure that no plastic is left behind at the end of its useful life.

Having worked in the packaging and materials industry for more than four decades, I believe it is time to revisit a concept and a chemistry I began experimenting with 25 years ago – producing packaging that disappears after use through the unique trait of water solubility.

Biodegradable materials and, more specifically, a water-soluble polymer called polyvinyl alcohol (PVOH), can break down quickly into carbon dioxide and water. This material is already accepted by regulatory authorities for food, medical and pharmaceutical applications, as well as by bureaus of land management for direct application to soil.

Outside of its prevalent use in the laundry and fabric care industry, however, water-soluble PVOH is not widely known. In my lectures and consulting practice, I am often surprised by how few of my fellow packaging engineers and designers have worked with PVOH. Current trends in sustainability and new advances in polymer synthesis make this an ideal time for us to reconsider this versatile material.

An innovative history

Discovered in 1924 by a German Nobel Laureate, then developed and commercialised in 1950 by Japanese chemical manufacturer Kuraray, it gained notoriety in 1989 when PVOH film was used to protect farmers from accidental exposure to pesticides. Using PVOH it was possible to pack a measured dose of hazardous chemicals inside a bag which, due to its water-soluble properties, could be simply dropped into a spray tank. The bag rapidly dissolved, releasing the contents safely and precisely with no concerning byproducts to worry about. It was convenient, provided a precise dose of the formulation, elevated user safety, and eliminated the disposal of contaminated packaging waste.

During the 1980s, a major agricultural chemical manufacturer packaged a crop protection product in a blow-moulded bottle, which after being rinsed three times could be left to biodegrade on a farmer’s compost pile. Like many good ideas that were ahead of their time, the moulded PVOH jugs were eventually abandoned in favour of less costly commodity plastic packaging that needed to be recycled or incinerated following careful container management practices.

It was not until the 1990s that we saw the fabric care industry take on the soluble unit dose concept for the economical and convenient dispensing of detergents. It proved exceedingly popular with consumers and the market for this type of packaging in water-soluble film has grown substantially over the years since. Today, PVOH can be found in many homes for the unit dosing of laundry and dishwashing detergents, and cleaning products for refillable bottles.

Unique properties

PVOH film has many highly useful properties. It exhibits excellent tensile strength and elongation, has one of the best oxygen barriers known to science, making it ideal for preventing food spoilage, and provides a superior barrier to oil, grease and solvents, which can damage, adhere to or bleed-through other plastics.

Typical PVOH film properties are:

  • Tensile strength at break of 30–100MPa
  • Elongation at break of 100–600%
  • Oxygen transmission (38µ, 0%RH) of 0.2–5cm3/day/m2/bar

However, most impressive are its biodegradable credentials. PVOH in solution simply breaks down into carbon dioxide and water when consumed by any of 55 acclimated organisms found in municipal wastewater treatment or activated sludge. In most water-soluble applications, such as a laundry unit dose, PVOH film is readily or inherently biodegradable as measured by OECD 301B test criteria.

PVOH is currently used in the recycling of 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. Most importantly, it does not leave behind dangerous microplastics.

A multitude of uses

The properties of water-soluble PVOH, including being safe and environmentally friendly, make the potential of this polymer virtually limitless for applications where moisture exposure can be controlled until point of use. This is substantiated by the yearly increase in patent activity for PVOH applications.

Beyond the familiar detergent pods, PVOH is used for many domestic purposes including medical and personal care applications, food packaging, textile yarns, paper products, unit-dose pharmaceuticals, artificial tears used to treat dry eyes and even contact lens lubricant.

Depending on the grade and environmental humidity conditions, PVOH film contains water at three–10%. Therefore, it is can be used to contain products with water content in the same range without dissolving or creating holes in the packaging. Shelf-life and storage considerations 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.

Food-grade versions of water-soluble film can be used to package pre-measured quantities of rice, pasta, cocoa, seasoning and nutritional supplements. It is also kosher, halal and vegan certified.

Credit: David Edwards

In the US market, the material is being used by four different brands to create packets that contain doses of whey protein powder, favoured by gym goers and 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, mix and serve. It eliminates the frustration of digging for buried scoops or cleaning up messy spills.

Other grades of the film are used in manufacturing processes such as a mold-release film in the production of solid surface countertops.

The diverse uses of PVOH are often governed by the polymer’s properties, for instance, it is:

  • An excellent gas and oxygen barrier, making it effective for food packaging, bags, liners or unit doses
  • Inherently static dissipative, which is important when making barrier bags for electronics sensitive to electrostatic discharge
  • A barrier to oils, grease and solvents, which are typically destructive to other plastic materials
  • Soluble in water for unit dosing of agricultural chemicals, swimming pool and spa chemicals, detergents, personal care items such as shampoo and lotion, ready-to-use or concentrates for refills, and pre-measured foods or supplements that are mixed or cooked in water
  • Modifiable for controlled solubility, for hospital laundry bags containing contaminated materials that dissolve at a set temperature in a washing machine
  • Printable and require no corona treatment
  • An odour and perfume barrier for cosmetic unit dosing
  • Injection and blow mouldable for pharmaceutical capsules for human or animal ingestion, and
  • Biodegradable to support products such as paper making, adhesives, coatings or water-soluble labels.

Making more of PVOH

Water-soluble PVOH manufacturing is complex and requires considerable investment and know-how to produce the resins that demonstrate the desired characteristics. In the last five years, there has been a substantial increase in new patent applications for PVOH resins and films in packaging applications.

Some of these patents, for example, describe the combining of PVOH with biodegradable materials such as moulded pulp, to provide barrier packaging that is completely biodegradable. Or harnessing PVOH’s unique thermoforming characteristics to combine with other plastic materials, creating a multi-functional package that facilitates the recycling process.

The packaging industry is worth around £970bln and can be quite resistant to radical change and innovation. In the last few years, however, public attention on and pressure to tackle global plastic pollution levels has pushed brand owners to look for innovative new 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 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 and drawing out the potential of PVOH.

There has never been a more exciting time to adopt water-soluble PVOH and take early advantage of the opportunities it presents.