A wide range of polyols that is used in polyurethane industries originated from petroleum-based chemicals. Most of the petroleum-based polyols fall into two classes, i.e. hydroxyl-terminated polyethers and hydroxyl-terminated polyesters. The polyesters are prepared by reaction of dibasic acids such as adipic acid, sebacic acid or phthalic acid with diols such as ethylene glycol or with higher functionality alcohols such as glycerol. On the other hand, polyether polyols of most interest in solid polyurethane are the polypropylene glycols and the polytetramethylene glycols. In both cases, the manufacture involves the addition polymerisation of the monomeric epoxide
The oil palm industry can be further strengthened through products diversification that can be produced within the sector itself. Currently, 80% of palm oil is utilised in the food industry, whereas only about 20% is utilised in the non-food industries, mainly in the production of oleochemicals such as soap.
Other than surfactants and soaps, vegetable oils like palm oil being triglycerides of fatty acids, have a number of excellent properties which could be utilised in producing valuable polyurethane (PU) products. With the continuous escalation in price of crude oil, polyols based on vegetable oils are increasingly becoming more viable alternatives to the petrochemicals polyols. It is known that PU products are very versatile as they continue to make positive contribution to improve our living standards, whether as automotive components, house-hold furniture, elastomers for shoes, coating materials, sealants or as adhesives.
As the world's petroleum resources are depleting coupled with pressure from environmentalist organisations, scientists worldwide have been looking into renewable/sustainable raw materials to replace petroleum-based polyols. Natural oils, which can be derived from both plants and animals sources, making them an ideal alternative chemical feedstock.
According to Erhlich (1959), the naturally occurring castor oil is the most satisfactory raw material for urethane reaction as the trifunctionality of castor oil contributes to the toughness of the polymer structure and the long chain fatty acid imparts flexibility and water resistance. In order to use other natural oils as polyols for polyurethane production, multiple hydroxyl functionality is required. Hydroxyl functionality naturally occur in castor oil and can be introduced synthetically in other natural oil with unsaturated sites by epoxidation followed by ring opening with alcohols, amino alcohols or acids.
The preparation of polyols from animal and vegetable based triglycerides has been described in many prior art. For an example, U.S. Pat. No. 3,637,539, describes a process whereby a mixture of triglycerides of C6 to C24 is heated with dialkanolamine to produce polyols for the production of good quality rigid polyurethane foam.
Bilyk et. al. (1974) claimed that polyols of higher hydroxyl content can be prepared by reacting epoxidised tallow with trimethylolpropane in the presence of p-toluene sulphonic acid.
British patent application (publication no. GB 908500) discloses a process for preparing polyesters from epoxy-containing monoglycerides, in which epoxidised triglycerides are subjected to glycerolysis in the presence of pyridine, resulting a mixture of predominantly epoxidised monoglyceride. The mixture is then reacted with dibasic acids for at least 17 hours at 150° C. to give polyester resins with various physical properties depending on the type of dibasic acids used in the preparation. GB 908500 also described that the preparation of epoxidised triglycerides are done through any known method such as reaction between peracids with the unsaturation of triglycerides. However the common methods of preparing monoglyceride from non-epoxidised glycerides are not readily adaptable to the treatment of epoxidised triglycerides, as the oxirane group will undergo ring opening in the presence of most catalysts generally employed in any known methods for preparing monoglycerides. In addition, it was revealed in GB 908500 that a possible method for obtaining epoxidised partial glycerides by epoxidising a monoglyceride of unsaturated fatty acids is not satisfactory for preparing an epoxidised monoglyceride as the presence of free hydroxyl group on partial glyceride interferes with the epoxidation reaction, which resulted in no appreciable amount of epoxy-containing monoglyceride is formed.
Accordingly, it is an object of this invention to provide such a method of synthesis that produces predominantly monoglyceride from unsaturated fatty acids or its corresponding triglycerides and polyhydric alcohol.
It is a further object of this invention to provide such a method of synthesis that involves epoxidising monoglyceride of unsaturated fatty acids to yield appreciable amount of epoxidised monoglyceride, which prior art has not be able to achieve.
It is another object of this invention to provide such a method of synthesis that converts epoxidised monoglycerides of unsaturated fatty acids to yield polyol monomer by means of ring opening with polyhydric alcohols.