Making a non-toxic wood glue

Materials World magazine
,
1 Jul 2019

Cambond Ltd Founder Xiaobin Zhao discusses how algae can replace formaldehyde resins in wood panel products.

Industrial resins are essential in the manufacture of certain wood products, including medium-density fibreboard (MDF), particle board and plywood, moulded items such as shipping pallets, and even coatings.

These applications typically rely on synthetic resins made of urea, phenol and formaldehyde. While not harmful they are growing undesirable – formaldehyde is toxic but there are no records of illness from wood exposure, and phenol is sourced from petroleum.

Since the 2015 roll-out of regulatory changes in the USA, EU and China, pressure has been mounting for the wood panel industry to switch to a non-toxic, formaldehyde-free glue to meet stricter environmental standards and lower carbon emissions of manufacturing.

To support this transition, Chinese company Cambond has been working with partners in the construction industry to carry out large-scale trials of a new, bio-based industrial resin. Establised in 2015, the firm is aiming to set-up a base in the UK to lead a move to greater sustainability.

Farming a solution

Using biomass to make bio-based adhesives for wood panels and shipping pallets can result in performance that matches, if not exceeds, that of conventional wood adhesives. Also, crucially, its sustainability credentials are sound. By using agricultural waste as a feedstock it lowers the consumption of oil-based chemicals, along with the carbon footprint of the manufacturing processes.

The agricultural sector is a prime area of material resources, and environmental issues, due to high levels of waste. The industry generates billions of tonnes of crop residue, such as straw, which could be used as feedstock. Agri-waste is carbon-negative but it has not been adopted for many uses in modern construction due to technical and end-product performance limitations. And while it may not be suitable for complex applications, it has proven ideal as a replacement for industrial resins.

Cambond found that performance is improved by using biomass high in protein, for which it used algae – more precisely, a green pond weed from China’s largest lake, Lake Taihu, known for its enormous and problematic algal blooms that grow out of control due to high levels of pollution. To help preserve marine life, thousands of tonnes of algae must be removed from the water and then need to be disposed of each year, providing a renewable material source. Algal biomass has highly sticky properties, achieved by a simple mechanical blending of the algal materials with inorganic and polymeric crosslinking agents to form a solid blend.

The process involves first drying protein-based biomass and large quantites of algae. This is milled into a micrometre powder and mixed with additives to form a dry resin powder. For final formulation, water and additional additives are combined, the solution mixed and then it is applied in the same way as traditional glues in the wood panel manufacturing process.

Protein in biomass

Further development of the bio-resin was achieved through the company’s biomass crosslinking and blocking (BCB) technology.

This was founded on the discovery that protein-containing biomass from a variety of sources, including algae and distiller’s dry grains and solubles (DDGS) in aqueous media, can be crosslinked by isocyanate-containing crosslinking agents to form a water-resistant polymeric network. At the same time, the isocyanate functional groups are blocked by natural phenol groups in algae, or hydroxyl groups from the biomass to protect the isocyanate activities.

The blocked isocyanate groups keep the adhesives stable in aqueous adhesives and are less toxic and more stable than virgin isocyanates. De-blocking of the isocyanate-phenol/alcohol conjugates take place during the heating phase of the manufacturing process of wood composites to create a strong wood-wood bonding effect.

Building strength

Taking the production chain further, it was discovered that it is possible to use biomass, such as straw and bamboo, to make construction materials by processing it into fibres that are then mixed with the bio-resin. This mixture is pressed into moulded door frames, furniture frames or anything that can be formed from plastic to produce a strong end product. The glue could potentially work with any typical biomass building material, unlike urea-formaldehyde which has difficulty binding waxy surfaces like straw.

Seven million tonnes of urea-formaldehyde adhesive is produced in China each year, so there is a large target market. Cambond’s joint venture manufactured 1,000 tonnes of bio-resin in the first six months of production and aims to increase capacity to 100,000 tonnes this year. Work is ongoing to conduct manufacturing trials with several plywood, MDF and furniture production companies in China, India and Europe.

In these trials, the glue was substituted for that used in the existing manufacturing process, to minimise the adoption cost and ensure continuity of wood panel production. Work is ongoing, but expansion into China will be carried out through such joint ventures with regional construction companies.

In the UK, the company is also working with a major wood board manufacturer to complete a further set of trials that could support the set-up of a new facility. Access to suitable biomass feedstock is plentiful in the UK, such as the waste streams from bio-refineries and distilleries (DDGS) in the north-east of England, and sugar beet in the east of England, while other sources of biomass are being explored in collaborations with research institutes.

Research collaboration

Moving further afield, Cambond is participating in Bio4ever – a European Union consortium in Italy investigating the quality and longevity of biomass-based products for the construction industry. This is an interdisciplinary research project dedicated to fulfilling the gaps in knowledge on some of the fundamental properties of novel bio-based building materials.

The two driving objectives of the initiative are to promote the use of bio-materials in modern construction by understanding and modelling its performance and function over time and under weathering conditions, to identify the most sustainable treatments of bio-material residues at the end of life, and improving their environmental impact. The overall goal is to ensure the sustainable development of the wood-related construction industry, taking into consideration environmental, energy, socio-economic and cultural issues.

As an example of the programme’s work, natural weathering is being performed by placing a set of samples on the rooftop of our institute’s building in San Michele all’Adige, Italy. These have been left in a southern exposure and will be collected every three months for one year to examine the effects. A separate research collaboration has been undertaken with the Biocomposite Centre at Bangor University, Wales, which involves the production of MDF using the bio-resin.

Time to change

The global wood panel industry is steadily growing and is forecast to be worth US$174.55bln by 2025, according to Grand View Research data. This level of production requires huge quantities of resin – around 20 millions tonnes annually – in a market that is already mature and is estimated to hit a value of US$6.18bln by 2025.

Despite this economic strength and a compound annual growth rate of 7.7% over the next five years, feedstock from waste could still have a positive effect on the market, as well as helping to control its environmental credentials. Biomass-based adhesives are direct derivatives of renewable biomaterials and they are predicted to be a growth area of the bioproducts industry. There are a number of drivers to encourage adhesive and wood composite manufacturers to switch to bio-based adhesives, including that they:

  • Reduce the generation of hazardous waste, lower chemical emissions and reduce waste disposal
  • Lower insurance costs from reduced risk and savings on systems for emissions control, released agents and other processing
  • Conserve oil and use fewer oil-based products, and
  • Make economic development sustainable, and can be made within existing production facilities so only require minimal process changes.