Scientists develop polyurethane plastics from rapeseed oil

An intensive world-wide effort to develop technology for manufacturing plastics from vegetable oil, rather than petroleum, has led researchers in Canada to a process for making polyurethane (PUR) plastic sheets from canola (rapeseed) oil.

Given the wide-spread use of PUR plastics in our daily lives, this can be seen as an important development. The breakthrough adds to a growing series of plant-based alternatives to petroleum based plastics. Last week, researchers from Brazil announced they successfully produced polyethylene (PE) from sugar cane (earlier post). With the new PUR plastic, we now have a bio-based alternative for most of the commonly used plastics.

In their study scheduled for publication in the July 9 issue of Biomacromolecules, Suresh S. Narine and Xiaohua Kong report on the properties of their vegetable-based PUR sheets. An open access ASAP version of the article is already online.

Polyurethanes are one of the most interesting classes of copolymers, which can vary from rubbery materials to glassy thermoplastics and from linear polymers to thermosetting plastics. The versatile PURs are widely used in liquid coatings and paints, adhesives, flexible foam in upholstered furniture, building insulation, shoes, and automotive interiors.

The process
The PUR sheets were produced with an improved version of a process in which canola oil is treated with ozone to make the chemical raw materials for PUR. This ozonolysis technology has been industrially established and has been used earlier to produce azelaic acid and pelargonic acid from commercial-grade oleic acid. Generally, the process of producing acids is carried out in carboxylic acid. To produce alcohols using this technology, the conversion of the ozonide to acids during ozonolysis should first be prevented. The researchers achieved this by using a nonacid solvent. The products of such ozonolysis (the ozonide) have been further reduced to aldehyde using a reductive agent and subsequently hydrogenated to produce the alcohols.

The scientists then used this ozonolysis- and hydrogenation based technology to produce polyols with terminal hydroxyl groups from vegetable oils and used them successfully to produce PUR elastomers and foams which had better thermomechanical and mechanical properties than the corresponding PUR made from commercially available biobased polyols. This first generation of polyols was not suitable to produce PUR plastics due to their relatively high acidity content:
biofuels :: energy :: sustainability :: petroleum :: rapeseed :: canola :: plant oil :: bioplastic :: polyurethane :: bioeconomy ::

The researchers have now improved the technology, optimized the process and produced a new generation of polyols from canola oil with lower acidity and hydroxyl number close to what is theoretically achievable. The polyols were suitable for the production of a wider range of PUR materials including PUR plastics.

In their article, the scientists describe the process as low-cost without the need for complicated technology, and said that it produces PUR sheets with "excellent" mechanical properties.

"It is reasonable to believe that the vegetable-based PUR could be a potential candidate to replace or practically replace petroleum-based PUR, in sensitive and high end applications such as in the biomedical area," the report says.

In 2006 world consumption of polyurethanes stood at 8.9 million tonnes.

The number of bio-based platform chemicals is growing steadily. We now have replacements for virtually all basic compounds used most commonly in the petrochemical industry as far as plastics are concerned.

Green alternatives now exist for some major types of plastic: for low and high density polyethylene (LDPE/HDPE) and polypropylene (PP), polyethylene teraphthalate (PET), and polyvinyl chloride (PVC). In fact, in several cases, the bio-based alternatives outperform their petroleum rivals on many properties (for an example, see Rilsan, a very robust castor bean oil based polyamide).

References:
Xiaohua Kong and Suresh S. Narine, "Physical Properties of Polyurethane Plastic Sheets Produced from Polyols from Canola Oil", Biomacromolecules, ASAP Article 10.1021/bm070016i S1525-7797(07)00016-5 June 6, 2007.