Resumen de Synthesis and characterization of polycarbonates from epoxidized vegetable oils, propylene oxide and carbon dioxide
The current research is primarily focused on the preparation of a polycarbonate using epoxidized linseed oil (ELO) and epoxidized soybean oil (ESO) as feedstocks. The presence of unsaturation in vegetable oil structure enables chemical modifications to introduce epoxy group which further used to synthesize polycarbonate via catalytic copolymerization with carbon dioxide (CO2). In this study, with the presence of heterogeneous catalyst a mixture of epoxidized vegetable oil and propylene oxide (PO) were reacted with CO2. Synthesis of polycarbonate via this pathway helps to lessen the reliance on petroleum-based feedstocks and besides employing renewable raw materials meets the 7th principle of 12 Principles of Green Chemistry that contributes to sustainability in chemistry.
The research work is divided into four phases. The first phase comprises preliminary studies whereby preparation of a heterogeneous catalyst for the copolymerization of epoxide with CO2 were made. Catalyst screening tests showed that cobalt- zinc double metal cyanide (Co-Zn DMC), a heterogenous catalyst commonly employed in the copolymerization reaction was feasible for cyclohexene oxide (CHO)/CO2 and PO/CO2 copolymerization. Then in-situ epoxidation of unsaturated fatty acids using selected vegetable oils were carried out to modify vegetable oil to epoxidized vegetable oil. The molar ratio of 0.4:0.1:1.7 (organic acid: double bonds: hydrogen peroxide) were applied and the epoxidation reaction took place at 70ºC for five hours. No formation of polymer was observed from the terpolymerization of epoxidized olive oil (EOO), epoxidized palm oil (EPO) and epoxidized sunflower oil (ESFO) most likely due to the low content of epoxy group of the epoxide oils used. However, from the preliminary studies a promising result were obtained from both ELO and ESO whereby a polymer has been successfully developed from the copolymerization reaction.
The second phase of the work is focused on the copolymerization of ESO, PO and CO2 catalyzed by Co-Zn DMC. Products comprises of mixture of poly(propylene carbonate), cyclic carbonate and polyether unit. The Mn of the polymeric products recorded is 6498 g. mol-1 with the percentage incorporation of ESO in the polymer is only 7.8%.
The third phase of the work is dedicated on the development of a poly(carbonate-co-ether) using ELO as the starting material. The terpolymerization reaction were conducted at fixed CO2 pressure of 5 MPa and various catalyst loading, reaction temperature and reaction time. At CO2 pressure of 5 MPa, reaction temperature of 60ºC, reaction time of 24 h and catalyst loading of 0.2 g, the resultant polymer with maximum Mn of 6.21 x 105 g.mol-1 and PDI of 1.05 was recorded.
Finally, the ability of the synthesized polymer to degrade was study under aerobic condition. The aerobic biodegradation of the test materials was determined under controlled composting conditions by analysis of evolved CO2 using an in-house built direct measurement respirometric (DMR) system. Results from this study discloses that 44.6% of PC-ELO and 51.8% of PC-ESO were degraded at the end of trial period. Both polymers were able to degrade most likely due to the co-monomer employed in the copolymerization reaction are renewable and bio based.
