Renewable raw materials and plastics made of renewable raw materials

Under the aspect of sustainability, the plastics industry – like all other industries – is called on to conserve classic fossil resources and make increasing use of renewables – but only to the extent that they grow again naturally and that there is no possibility of competing with food production. On the other hand, the plastics industry must also make its contribution to protecting Nature and the environment, which means saving energy in production processes and handling waste materials responsibly. The high molecular weight and biodegradability of renewable raw materials provide particularly good conditions for this: biopolymers behave CO2-neutrally, not only as regards biological degradation but also in terms of thermal recycling of the waste materials and energy production.

In this respect, renewable raw materials are gaining increasing importance as feedstocks for plastics and as components in their production. Natural fibre composites are one example. A particular challenge here is to ensure not only ecological sustainability but also economic sustainability. This will necessitate further research to constantly improve product quality/functionality compared with conventional fossil-based materials and thus to increase production volumes. A further challenge is to cope with the inconsistent quality of renewable raw materials.

The most important raw materials are the two biopolymers*, starch and cellulose, as well as sugar (saccharose). The list also includes casein, chitin and chitosan, collagen (gelatine) and other proteins as well as natural resins and waxes, vegetable oils (linseed oil) and animal fats. Secondary products include polylactide (PLA) and copolymers as well as polyhydroxybutyric acid/polyhydroxybutyrolactone (PHB) and other polyhydroxycarboxylic acids/polyhxdroxyalkanoates, which are produced from sugar or starch by fermentation to form lactic acid via dilactide, and subsequent polymerisation into PLA or from bacteria as storage materials (PHB). Classic biopolymers based on cellulose are the cellulose esters. Secondary products also include diols and dicarboxylic acids from biopolymers, which can be reacted with the relevant components, possibly from fossil sources, to produce polyesters, polyamides and polyurethanes.

Typical reinforcing fibres include flax, hemp, jute, kenaf, sisal and abaca as well as wood fibres from waste (WPC) from the wood and paper-processing industries, and reprocessed cotton.

It is only through the correct compounding that biopolymers are tailor-made for the relevant application. The main areas of application for biopolymers, often as blends with biodegradable plastics (also from fossil raw materials), are films, fibres, non-wovens, thermoplastics, adhesives and basic materials for dispersions. Target products include packaging and coatings for paper and board composites, sacks and bags for collecting biowaste, as well as catering products and products for horticulture and landscaping. Special areas of application in medical technology are surgical thread, hard and soft tissue implants and the encapsulation of active ingredients, for which PLA, PHB and their copolymers can be used. Their big advantage in such applications is that the mechanical properties and decomposition rate can be individually adjusted. Proteins, natural resins and waxes are frequently used for the manufacture of adhesives, paints and other surface coatings.

Natural fibre composites have gained major importance as lightweight construction materials and have been used for many years in the automotive industry, especially in car interiors for high-quality door structures and dashboards. They are also used for underbody protection and in driver‘s cabins in trucks. Like natural fibres and natural fibre composites, WPCs have gained an increasing foothold in the building industry, and their popularity is growing all the time.

The adjustability of the mechanical properties and decomposition rates of biopolymers illustrates that, with the right research, they can also be made suitable for the production of durable, high-quality plastics. Walkman and mobile phone housings made of biopolymers are already on the market.

There are currently two main challenges when it comes to stepping up the use of renewable raw materials. One is to make greater use of biological waste products such as lignin, and the other is to identify natural locations that do not compete with forestry and agriculture. These include marine plants of all kinds, which are noted for their rapid growth rates and serve as an effective carbon sink. The production of renewable raw materials such as cellulose and PHB through micro organisms also has considerable potential. It is possible either to produce biopolymers in a fermenter or to transfer the corresponding genes of the micro organisms to plants so that the biopolymers can be harvested in the traditional way. Here, genetically modified plants can be grown on set-aside agricultural land, so that there is no competition with crops and plants for the food sector.

Apart from conserving fossil resources and the CO2-neutral utilisation of biopolymers (from cradle to grave), renewable raw materials offer a major opportunity for the development of innovative products and processes and they also increase the reliability of feedstock supplies. There are thus good reasons for the plastics industry to look today at the enormous potential of renewable raw materials, and not to miss the boat in this expanding field.


*Biopolymers are natural high molecular-weight substances. Plastics based on biopolymers are often described as bioplastics. In contrast, biomaterials are materials that are used in contact with the biosystem, the human body.
Renewable raw materials and plastics made of renewable raw materials - Vita Prof. Dr. Dr. h.c. Heinrich Hartwig Höcker