Bioresin is a term coined to describe a resin or resin formulation derived from a biological source. Thus, many traditional resins such as protein-based soybean, collagen or casein, or carbohydrate-derivatives from cellulose or starch, natural rubber based adhesives and natural phenolic adhesives such as tannin or lignin may all be classed as bioresins. They are renewable polymers and, with low environmental impact, represent an alternative to existing petroleum-driven systems.
Interest in bio-resin systems stems largely from increasing regulation and public concern for a pollution-free environment, and the need for sustainable alternatives to products based upon a finite petrochemical resource. Commercial thermoset resin production and use is subject to such regulation largely due to the monomer components that form the basis of the formulation. Overwhelmingly, these resins are based on melamine, phenol, urea, formaldehyde, styrene or isocyanate starting materials.
Emissions of formaldehyde, phenol and isocyanate are generally regulated; they are governed in England and Wales under the Pollution Prevention and Control Regulations (2000), SI19, for installations involved in the manufacture of particleboard (PB), oriented strandboard (OSB), medium density fibreboard (MDF) and wood fibreboard. Emissions to air are limited to 5 mg/m3. In particular, the guidance notes that ‘operators should use resins which minimise emissions of formaldehyde wherever possible. The choice of resins used should be continually reviewed to ensure minimum emissions occur. Problems may exist concerning both high formaldehyde levels in the workplace and with the slow release of formaldehyde from the panel products themselves, particularly at the beginning of the product's lifetime.
Bioresin products may offer an alternative, renewable source of thermosetting resins that will begin to address the depletion of finite resources and have better emissions profiles, particularly when formulated without formaldehyde. Though formaldehyde-free materials such as siisocyanate and tannin resins have become available, about 85% of MDF produced today uses formaldehyde resin, corresponding to a European market of approximately 2 million tonnes per annum. In those resins, whilst a reduction in formaldehyde content has been achieved in recent years, it has been at the cost of longer processing times, and decreases in internal bond and bending strengths and an increase in swelling and water absorption of panel products made therefrom. There is, thus, a clear place in the market now for new more environmentally friendly resins that are competitive in price, performance and adaptable to existing composite manufacturing processes.