Transitional Materials

Polyvinyl alcohol (PVOH, PVA, or PVAl) is a synthetic polymer which is colourless, odourless and water-soluble. It is used to package laundry detergent pods and to laminate safety glass. It is typically supplied as a powder, granules or pellets, and sometimes as a solution in water.

Often derived from fossil fuels, PVOH is water soluble and dissolvable, making it an extremely useful packaging design property for some oil-based liquids. Some studies show the material is a concern for persistence or accumulation in the marine environment. Whilst these studies have been rebutted by manufacturers, stating that the results were not in relation to water soluble PVOH, but for fibrous PVOH, we believe further end of life studies are required to determine its true benign biodegradability.

PVOH is known for its oxygen barrier and oil and grease barrier properties. Its solubility in water allows for use in agricultural and chemical applications, as well as for personal products including shampoo, conditioner, soap, body wash, hair bleach, lotions and concentrates that can be used as refills and home-mixed with water. Its odour barrier makes it suitable for cosmetics.

PVOH can be injection moulded, making it useful in pharmaceutical applications for human or animal ingestion as a non-animal-derived gelatine replacement

PVOH dissolves rather than biodegrades, leaving synthetic monomers behind. It is a vinyl polymer joined by only carbon to carbon linkages. The linkage is the same in typical plastics such as polyethylene, polypropylene, and polystyrene, and of water-soluble polymers such as polyacrylamide and polyacrylic acid.

It is a synthetic polymer manufactured from ethylene and acetic acid, usually derived from fossil fuels.

PVOH formulations comply with the European Standard CEN EN 13432 for biodegradation and compostability, however there are no studies to determine if PVOH’s end of life will comply with the EU definition on plastics in the future.

PVOH is one of the many plastics found in marine micro-litter and unidentified polyvinyls, closely resembling polyvinyl alcohol or polyvinylchloride, have been found in the stomachs of fish 10km below the ocean surface.

PVOH is claimed to be nontoxic, however it has been found to produce foam as it degrades. This prevents the recovery of oxygen in the water, which threatens organisms.

Poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) - PHBV - is a biocompatible polymer which is produced by a number of microorganisms.

It is produced naturally by bacteria through microbial fermentation, but it is known as a thermoplastic polyester. Most end-of-life studies to date have involved short fibres, particulates and nanofibers, with very little work on continuous long natural fibres. In other words, PHBV’s biodegradation behaviour needs more scientific attention. Nonetheless, PHBV is not formed from fossil fuel derivatives and is therefore one of the more favoured transitional materials.

PHBV is a co-polymer with superior mechanical properties to PHB and all PHA’s. PHBV is used in speciality packaging, orthopaedic devices and for the controlled release of drugs. It has great potential as a drug carrier due to its biocompatibility, bioabsorption and slow degradation rate compared to other biopolymers.

PHBV is a microbial biopolymer with biodegradable properties. It is a chemically modified material.

PHBV seemingly lacks mechanical strength, water absorption and diffusion, electrical and/or thermal properties, antimicrobial activity, wettability, biological properties, and porosity, among others, which limits its application.

When PHAs are produced by bacteria, they can contain high levels of endotoxins. This can limit their application as a biomaterial if this compound is not removed. PHBV with low levels of endotoxins can be produced, but its application is limited due to its limited mechanical properties.

Researchers are currently working to improve PHBV. Some studies suggest combining PHBV with other materials with different structures and properties, (e.g. other polymers, natural fibres and nanocellulose) can produce a range of composite biomaterials with increased potential applications. Other R&D is also focusing on finding new microbial strains capable of accumulating higher levels of PHBV, developing more efficient fermentative routes for manufacturing purpose, and lowering the costs of the polymer extraction process.

The high cost of PHBV is a barrier to its commercialisation and a more efficient production process to lower the costs is being examined.

PHBV’s biodegradability has been demonstrated in soil, water, and compost. Some studies detected no changes in molecular weight during the degradation and concluded that it occurred only on the surface of the polymer. However, the molecular weight did decrease and PHBV degraded faster at higher temperatures (40°C). PHBV reinforced with catalysts showed a moderate degradation rate of 9–15% after one week. These results support the idea that PHBV presents a level of biodegradability.

PHAs refer to an umbrella of materials (PHBV, PBHH, P4HB and P3HB) which are bio polyesters produced in nature by microorganisms. The bacterial fermentation of sugars or lipids is a good example. PHAs have been reported in aquatic environments. However, when comparative biodegradation of two types of aliphatic polyesters, PLA and PHA, were studied in soil environments, PHA broke down much faster. PHA is an interesting material because of its biological origins, but more research is needed on its impact when it accumulates in the environment.

PHA’s physical properties are often compared to polypropylene, which is used for food packaging and single use products. PHAs are often used commercially in low value, high production markets such as compostable bin liners.

PHA are polymers that are bio-derived and produced as homopolymers or copolymers. In general, PHAs are biodegradable, compostable thermoplastics. What makes them transitional materials is that they are thermoplastics – meaning they become a ‘plastic’ upon heating and cooling to harden.

PHA’s thermoplastic nature makes them ideal materials for standard manufacturing techniques including injection moulding, extrusion and blow moulding. However, their low thermal decomposition temperature (typically just above 180°C) means that careful processing is needed.

Research to improve the thermal and mechanical properties of PHAs is ongoing. By controlling the process, it is possible to minimise PHA’s thermal degradation when it is turned into pellets.

PHAs are soluble in halogenated solvents such as chloroform, dichloromethane or dichloroethane. However, studies have shown that PHA’s biodegradability depends on the microbial activity, moisture levels, temperature, pH and molecular weight. Within the correct environment, PHA’s can biodegrade within seven weeks.

Typically made from fermented corn starch, PLA is often heralded as the biomaterial poster child to replace petroleum-based plastics. Made from renewable resources such as corn starch or sugar cane, it is a natural polymer designed to substitute widely used petroleum-based plastics like PET (polyethylene terephthalate). In the packaging industry, PLA plastics are often used for plastic films and food containers.

In its favour, PLA is not derived from fossil-fuels, however PLA is a chemically modified material that has to be industrially composted at high temperatures at the end of its life. At present, collection systems, and composting facilities are few and far between around the world, meaning PLA products often end up in landfill regardless. More work is needed in this area.

PLA is made from renewable resources including corn, cassava, maize, sugarcane or sugar beet pulp. These crops can be grown, harvested and regrown. Because PLA is made by fermenting starch, it also has a very high bio content. All good points.

PLA is a polyester made by fermenting the plant sugars, which turn into lactic acid, and then into polylactic acid, or PLA. As a biopolymer it is one of the more cost effective to make and is the most popular biopolymer globally which means it is widely available at commercial scale.

Despite the raw material differences, PLA can be produced using the same equipment as petrochemical plastics which makes the PLA manufacturing processes relatively cost efficient. PLA is the second most produced bioplastic (after thermoplastic starch) and has similar characteristics to polypropylene (PP), polyethylene (PE), or polystyrene (PS), as well as being biodegradable.

PLA is the most widely used plastic filament material in 3D printing. Its low melting point, high strength, low thermal expansion, good layer adhesion, and high heat resistance when annealed make it an ideal material for this purpose.

Despite being made from natural materials, PLA is classed as plastic by the EU definition.

PLA is widely recognised as a compostable material, however it does not comply with the EU composting facility standards for biodegradation. Many composting sites have deemed PLA a contaminant, therefore other ways of breaking down the material are needed.

PLA requires vast amounts of feedstock and research is now trialling alternative ways to produce and manufacture the material.

Research shows PLA breaks down into CO2, H2O, residue and biomass in both anaerobic and aerobic biodegradation conditions. However, a full understanding of its impact on the natural environment is still incomplete and needs more work.

A partially fossil-fuel based, but semi biodegradable material, PBAT is often used instead of low-density polyethylene (LDPE) because it shares the same attributes needed for plastic bags and wraps, such as flexibility and resilience.

Because of its fossil fuel content, PBAT requires the extraction and manufacturing of petrochemicals, meaning it is not a desirable choice of material in the fight against the climate crisis.

PBAT resin is widely used for shopping bags, mulching films, paper coating labels, bin bags, cutlery, and medical clothing. It was developed as an alternative to PET, one of the most ubiquitous plastics used for plastic bottles worldwide. Most importantly, adding PBAT to another polymer which degrades means the blended copolymer will also degrade.

PBAT’s physical properties include wide melting point, low elasticity and high modulus and stiffness, but high flexibility and toughness. The flexibility and toughness of this polymer makes it ideal for blending with another biodegradable polymer that is strong and rigid for bottle production.

PBAT is a petroleum-based plastic (using purified terephthalic acid, PTA, butanediol, and adipic acid) that is designed to biodegrade.

Much of the demand for biodegradable mulch films is driven by the amount of residual film in farmland soil in Northwest China. This demand means opportunities for PBAT manufacturers, but manufacturers need more R&E to improve the mechanical strength in biodegradable mulch films to prevent rupture during various applications.

PBAT needs to be industrially composted which some see as a limiting factor because of the lack of composting infrastructure across the globe. As a result, PBAT will often end up contaminating the plastic recycling streams and act the same way as plastic in the environment. Furthermore, studies show that PBAT does not biodegrade in marine or freshwater environments, which is hazardous for the climate.

PBS is a semicrystalline polymer with similar properties to polypropylene. It is produced by the polycondensation of fossil fuels or bio-based succinic acid. When derived from a renewable, biological source the material is a desirable choice. Studies show PBS’s biodegradation process is shorter than other transitional materials and without major evidence for microplastics.

PBS’s melting point is 115◦C, which is lower than polylactic acid (PLA). It has also been listed as compostable-certified according to the Biodegradable Product Institute, and is available in direct food contact grades.

PBS’ qualities, including a highly transparent surface and rigid construction, mean that it can be used in a wide variety of applications from mulching films and compostable bags to non-woven sheets, textiles, catering goods, and foams. PBS is widely found in industries such as agriculture (vegetation nets), fishery, forestry and civil engineering.

Given the shorter time to melt and blend PBS with other materials, it could potentially offer shorter manufacturing times. PBS is also an easy material to process and handle. PBS is rigid but can be slightly brittle because it is produced from petroleum-based materials.

PBS can be synthesised in various ways such as the polycondensation of succinic acid (or dimethyl succinate) and 1,4-butanediol. The monomers can be obtained from fossil-based or renewable resources.

Since PBS is expensive, researchers have used other materials, including natural fibres, to substitute a percentage of PBS. Oil palm fibre and tapioca starch are also used as reinforcing materials to minimise the amount of PBS needed and lower the production costs.

The biodegradability and biodegradation rate of PCL–starch blend and PBS were investigated under both aerobic and anaerobic conditions. PCL–starch blend was easily degraded, with 88% biodegradability in 44 days under aerobic conditions, and showed a biodegradation rate of 0.07 day−1, whereas the biodegradability of PBS was only 31% in 80 days under the same conditions, with a biodegradation rate of 0.01 day−1.

TPS is a compostable, plastic-based material processed from a blend of thermoplastic starch (TPS), aliphatic polyesters (AP) and natural plasticisers.

It is generally reinforced using plasticisers and is therefore not plastic free. Although starch is a useful material for alternatives, TPS does not possess mechanical strength without the use of plasticisers. Therefore, it is not a preferred transitional material and more R&D is needed to improve its mechanical properties without plastic.

Starch is considered a renewable resource and a good alternative to synthetic materials because of its availability and easy production. Products manufactured with TPS tend to exhibit good oxygen barrier properties, biodegradability and compostability.

Generally, all materials processed by thermoplastic manufacturing methods do not comply with the EU Standard. TPS blends are recognised as plasticised nanocomposites. They are usually blended with other polymers, fillers and fibres. Both natural and synthetic polymers have been used, including cellulose, natural rubber, polyvinyl alcohol, acrylate copolymers, polyethylene and ethylene copolymers, polyesters, and polyurethanes.

Due to the starch, TPS is sensitive to water. This causes its properties to change when exposed to humidity. TPS’s mechanical strength is much lower than that of plastic.

Unfortunately, starch cannot be transformed into a thermoplastic material without plasticisers. Manufacturers are testing plasticiser alternatives with TPS and reinforcing TPS with fibres to develop a plastic-free polymer. However, most methods to chemically modify starch will prevent TPS from being recognised under the EU Standard.

Research has shown TPS breaks down in composting environments, and its mass is reduced within seven days. However, little research has been done on TPS’s impact on soil and aquatic environments.

PEF is a bio-based polymer produced with plant-based sugars. PEF has similar qualities to PET and is seen as the most feasible non-fossil alternative. PEF’s chemical resemblance to PET makes it an undesirable transitional material and studies show its biodegradation is also slow and maybe unattainable.

PEF is suitable for drinks packaging such as alcohol, juices, and milk, as well as carbonated drinks due to its gas barrier properties. PEF also outperforms PET on several qualities and is therefore a highly desirable material.

PEF is a polymer that can be produced by polycondensation and has a similar chemical structure and mechanical properties to PET.

PEF’s similar chemical structure to PET makes it difficult to break down completely. Although the material is seen as ‘compostable’ it requires industrial composting environments that may reject PEF as a feedstock.

PEF can be blended with other transitional materials to improve its mechanical properties, but while this may be effective for industrial use, more testing is needed to test PEF’s biodegradability.

PEF is not recognised as a biodegradable material. TPS and PLA have been shown to biodegrade at a better, more concise rate.

Polyvinyl alcohol (PVA) is a water soluble synthetic polymer that is biodegradable under aerobic and anaerobic conditions.

The environmental impact of ethylene derived from biodegraded PVA is widely unknown, however is it of some concern. Ethylene can be taken up by plants at high concentrations which means this is not a sound transitional material choice.

PVA is commonly used as a protective film for liquid laundry and dish detergents, eliminating the need for individual plastic sachets. It is also used as a finishing agent in the textile industry and as a thickening or coating agent for paints, glues, meat packaging, and pharmaceuticals in paper and food industries.

PVA is a water-soluble plastic. How it impacts the environment is still unclear.

Although it has good mechanical and thermal properties, it tends to have low degradation rates in some environments including the soil. PVA is also a relatively high-cost material.

To improve PVA’s biodegradability and reduce its cost, some manufacturers are blending it with starch. Glycerol is one of the most popular plasticisers to mix with PVA/ST blends due to their similar solubility parameters.

The environmental consequences of PVA is widely unknown, however research has shown that PVA poses threats to soil and is sequestered through agricultural applications.

Ethylene is a by-product of PVA degradation and is a hormone utilised by plants. While more research is needed, it is alarming that ethylene from PVA can be absorbed by plants at high concentrations.

Initial studies show that PVA can alter gas exchanges, such as carbon dioxide exchange, affecting aquatic ecosystems.

The chemical dehydration of ethanol can be used to produce Bio-PE. Bio-ethanol is produced from sugar cane using a fermentation process. The bio-ethylene monomer can then be used in traditional polyethylene polymerisation processes to make the various grades of PE (HDPE, LDPE, LLDPE).

Bio-PE is chemically modified and recognised as a thermoplastic. It is generally derived from petroleum feedstock and is therefore an undesirable option for a transitional material.

PE is one of the most widely used polymers in the world. It dominates milk, cosmetic and detergent packaging. From polymerization, different types of bio-PE could be obtained - biological, renewable resources and petroleum feedstock. The ethylene can be obtained from sugar cane, sugar beet, starch crops coming from maize, wheat or other grains and lignocellulosic materials.

The same machinery can be used for bio-PE as is used for PE, making it an economically feasible alternative.

The starting monomer used for the production of Bio-PE is ethylene, which is also the case for other polymers such as PVC and PS, and it is generally obtained from petroleum feedstock.

Bio-PE is not biodegradable. The prefix ‘bio’ relates only to the feedstock used to manufacture the material. As a result there is no difference in biodegradability between polyethylene and bio-polyethylene, however the latter is relatively carbon neutral, while the former is not.

Bio-PE can be produced from ethanol coming from bagasse. To improve the material’s mechanical properties, natural fillers have been tested including wood flour, cellulose powder and kenaf fibres.

Bio-PE, bio-PP, bio-PET, bio-PVC and nylon are not biodegradable. They require the same waste streams mechanisms as plastic and more research is needed to identify a more biological breakdown of the material.