Biopolymers

Novel biomaterials become ever more important in the field of injection moulding. After many years of research and development, this group of materials achieves ever more commercial success. Especially such aspects as the pricing pressure of conventional polymers, the conservation of depletable resources, the protection of the environment and climate protection, or the ever more draconic requirements regarding disposal or recycling will set the course in favour of eco-products in future. Here, ever more mass-produced items will take hold based on special applications.

Biomaterials are materials gained from biodegradable polymers that are fully or substantially based on agricultural raw materials or wood. Here, typical elements include starch, sugar, vegetable oils or cellulose as well as specific biomolecules such as lignin or rubber. The share of these basic raw materials in the material is no less than twenty percent (20%). By now, many biomaterials have reached a high level of engineering or commercial maturity. This is supplemented by special and sometimes unique properties in terms of appearance, look and feel or biodegradability.

The generic term of ”biopolymer“ can be basically divided in three different categories. Decisive criteria are the various source materials and the biodegradability of plastics. Here, a differentiation is made between:

• Biopolymers made from renewable raw materials, and being biodegradable,
• Biopolymers made from renewable raw materials, and not being biodegradable, and
• Biopolymers made from fossil fuels, and being biodegradable.

Each of these categories, in turn, can be divided into several classes. The most interesting and thus most important category is that of biodegradable plastics made from renewable resources. Because they are carbon-neutral and compostable, the products of this group are the veritable "organic plastics or bioplastics", and can be classified as follows:

• Biopolymers from renewable resources, biodegradable, of micro-organic origin:
  - Polylactic acid (PLA) -> extrusion,
  - Polyhydroxy alkanoates (PHB) -> injection moulding, and
  - Polyhydroxy fatty acids (PHF) -> injection moulding;

• Biopolymers from renewable resources, biodegradable, of plant origin:
  - Derivates from starch -> extrusion and injection moulding,
  - Cellulose blend (CA) -> injection moulding, and
  - Lignin basis -> injection moulding;

• Biopolymers from renewable resources, biodegradable, of animal origin:
  - Chitin and chitosan -> dry moulding process;

• Biopolymers, biodegradable, of fossil origin:
  - Polyester -> extrusion, and
  - Ethanol (PVA)

• Conservation of depletable petrochemical resources,
• Renewable resources are carbon-neutral,
• Reduction of the amount of waste produced, biodegradable,
• Reduction of the amount of toxic or allergenic intermediate products produced,
• Biopolymers may be combined with natural fibres, and
• Properties can be adjusted (noise, surface or similar).

However, in most cases it is not quite as easy as that to process these special raw materials on conventional injection moulding machines. A large number of products are compounds of the most varied shapes and variants. For these reasons, the injection moulding system should be adjusted accordingly, especially in terms of the plasticating unit.

• To guarantee appropriate feeding or conveying behaviours,
• To provide adjusted and gentle plastification through customized worm design,
• To use coated systems for reasons of abrasion and chemical resistance,
• To use high injection rates or pressures,
• To provide adequate venting: some materials tend to degas (temperature profile, improved venting, venting programme, press forming or similar), and
• To use appropriate know-how in the field of tool engineering.

At present, some five hundred thousand (500,000) tonnes of novel biomaterials are processed every year. However, the overall production volume is much higher than that, and biomaterials are introduced in ever more sectors such as the automotive sector, the packaging industry or the consumer goods industry, and many more:

• Automotive engineering (e.g. housings or casings, fairing supports, sun visors),
• Packaging industry (e.g. bio-caps, knives and forks, cups or mugs, bowls),
• Construction industry (e.g. patio railings, tools, switchboards),
• Furniture industry (e.g. chairs, tables, shelves, cupboards),
• Consumer goods industry (e.g. enclosures, connectors, musical instruments),
• Gardening and landscaping (e.g. planting pots, bottom dishes, urns),
• Sporting goods (e.g. canoe manufacture, golf sticks, sneakers), and
• Textile industry (e.g. buttons, clips, straps).