Starch-Based Thermoplastic Wood

Cellulose-based composites are one of the major materials for the worldwide construction industry. There are almost no buildings which do not contain them as a major component. They are constructed of wood fibres or chips held together with typically 15 % by weight of a thermoset resin. One significant advantage of these materials is that they use waste products from the pulp and timber industries and so they are significantly less expensive than virgin timber. Almost all of the resins used in fibreboard are either urea-formaldehyde (UF) or phenol-formaldehyde (PF) and these are the main issue associated with their widespread use. Fibreboard is known to slowly release of formaldehyde, often into the enclosed domestic environment and formaldehyde is a known carcinogen and so efforts are underway to find alternatives to UF and PF resins. This project will use simple plant starch with other non-toxic modifiers to bind the woodflour and thus make a sustainable, recycleable and ultimately compostable material. The project will make large sheets of starch-based thermoplastic wood and test their applicability with a major High Street retailer. Samples will be produced and a significant publicity campaign will be carried out using the data produced by this project.

Fibreboard is produced through the high temperature and high pressure compaction of wood fibres with wax and a thermoset resin and typically has a density of 700 to 850 kg m-3. Fibreboard is the largest sector of the UK synthetic board production market and in 2010 MDF output was nearly 0.8 million m^3; less than half of the UK usage of MDF. The main issue associated with MDF use is the large quantity of dust particles produced during machining and the release of formaldehyde in an enclosed environment both posing significant health risks after manufacture. Formaldehyde has been classified as a "known human carcinogen" producing nasal sinus cancer and nasopharyngeal cancer and a possible link with leukemia has been established. Many organisations are seeking alternatives to MDF, an issue that the current proposal addresses.
The 2010 UK market of fibre- and particle-board is valued at £1.04 bn a 10 to 15 % growth on the previous year equating to approximately 3.5 million m3 of board and over 250 tonnes of formaldehyde. From an environmental perspective this is a significant issue and the use of waste materials such as grey starch and glycerol to replace urea- and phenol-formaldehyde would be a significant improvement. The UK market for MDF is only about 2% of the world market which is in the region of 65 million m3. Clearly even a small intervention in a market of this size would be significant in terms of the value and environmental impact.
The use of starch as a binder would permit waste materials to be employed for material production. The fact that they are thermoplastics enables them to potentially be recycled and ultimately composted. Success of these materials would be one of the most significant advances in the timber industry for 50 years. It has the potential to be used worldwide since most countries have a local source of waste starch and waste fibre. Some of the most significant agricultural waste sources include bagasse, rice straw and coir, all of which could be used in this type of application.
In addition to a significant impact in an important construction sector the study will provide useful academic information on the plasticisation of starch. It will provide generic data which can be used for all starch-based composites. The use of in-situ XRD analysis with a QCM study will provide new insight into the mechanism and kinetics by which salts unzip the hydrogen bonding structure between carbohydrate chains.