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Surface coatings and metathesis: new opportunities
thesisposted on 2017-01-24, 00:46 authored by Kosowska Rengarajah, Zuzanna Ewa
The paint industry is currently facing legislative pressure to reduce volatile organic compound (VOC) content and the use of other harmful chemicals in coating products. There is also increasing consumer demand for paints with superior coating and finish quality as well as ease of use. This thesis reports on the development of novel coatings from renewable feedstocks through the use of well controlled olefin metathesis. The coating industry, like many others that rely on crude oil derivatives, also has to cope with increasing costs of crude oil derived materials. To overcome this, as well as to meet increasing pressures to utilize sustainable technologies, the development of improved alkyd paints for the market was proposed. Alkyd paints are partly based on vegetable oils and are thus relatively cheap and “green” to produce. Their loss in market share over the past two decades is partly due to the improvements in competing types of paints, their high VOC (volatile organic compound) content (introduced via formulation) and their inferior ageing properties. A collaborative project between Monash University and DuluxGroup has resulted in the development of an efficient curing methodology to generate alkyd coatings through olefin metathesis. Metathesis-induced curing of films generates coatings which possess a lower propensity for yellowing and embrittlement compared to conventional alkyds. Industrially available solvents were investigated for their compatibility with the curing system. Ethyl acetate (containing traces of acetic acid) was found to be a suitable solvent for both olefin metathesis and dilution of alkyd resins. Alkyds based on natural vegetable oils and vegetable oils modified by prior metathesis with 2-butene, were then cooked (i.e. triglycerides were heated with a polyol and phthalic anhydride in the presence of minimal amounts of an azeotroping solvent). The conventional scale (3-5 kg) of the cooks was prohibitive and preparation of alkyd resins on a smaller scale was devised. Initially this was done using microwave technology, then a conventional small scale method (<1 kg) was established. This allowed rapid evaluation of resultant resins. Characterisation of the resins was carried out using Acid Value measurements and GPC, and evaluation of metathesis curing was carried out by touch tests on microscope slides. The curing rate was also investigated by headspace MS monitoring of released 2-butene throughout curing of a butenolysed resin. Novel, modified second generation Hoveyda-Grubbs’ type catalysts were also assessed. It was anticipated that modified resins would perform better as the evaporation of 2-butene from the film would drive the cross-metathesis curing reaction to completion. Significantly, the research also developed processes for preparing acceptable films from unmodified alkyds. The potential to use unmodified alkyds makes this technology more attractive as it would be easier and cheaper to apply. Potential economic benefits stem from the replacement of imported petrochemical feedstocks with Australian agricultural products in the coating and materials industries, and the development of high performance products with the potential for export.