Green nanocomposites based on renewable plant oils have been developed. Curing of epoxidized plant oils in the presence of organophilic montmorillonite produced triglyceride−clay nanocomposites showing flexible property. A nanocomposite with homogeneous structure was obtained, in which silicate layers of the clay were intercalated and randomly distributed in the polymer matrix.
Epoxide-containing polyesters were enzymatically synthesized via two routes using unsaturated fatty acids as starting substrate. Lipase catalysis was used for both polycondensation and epoxidation of the unsaturated fatty acid group. One route was synthesis of aliphatic polyesters containing an unsaturated group in the side chain from divinyl sebacate, glycerol, and the unsaturated fatty acids, followed by an epoxidation of the unsaturated fatty acid moiety in the side chain of the resulting polymer. In another route, epoxidized fatty acids were prepared from the unsaturated fatty acids and hydrogen peroxide in the presence of lipase catalyst, and subsequently the epoxidized fatty acids were polymerized with divinyl sebacate and glycerol. The polymer structure was confirmed by NMR and IR, and for both routes, the high epoxidized ratio was achieved. Curing of the resulting polymers proceeded thermally, yielding transparent polymeric films with high gloss surface. Pencil scratch hardness of the present films improved, compared with that of the cured film obtained from the polyester having an unsaturated fatty acid in the side chain. The obtained film showed good biodegradability, evaluated by BOD measurement in an activated sludge.
This study deals with the preparation and properties of a new class of organic-inorganic hybrids from renewable resources. The hybrids were synthesized by an acid-catalyzed curing of epoxidized triglycerides in the presence of an organophilic montmorillonite (a modified clay). The mechanical properties were improved by the incorporation of clay in the oil-based polymer matrix. The reinforcement effect due to the addition of clay was confirmed by dynamic viscoelasticity analysis. The hybrids showed relatively high thermal stability. The co-curing of epoxidized soybean and linseed oils in the presence of clay produced hybrids with controlled mechanical and coating properties. The barrier property of the hybrid towards water vapor was superior to that of the oil polymer. The development of the present hybrids consisting of inexpensive renewable resources, triglyceride and clay is expected to contribute to global sustainability.
KEY WORDSEnzymatic Polymerization / Immobilized Lipase / Polyester / Lactone / Lipase is an enzyme that catalyzes hydrolysis of fats (fatty acid triglycerides) in living cells. In a nonaqueous medium, on the other hand, lipase can act as catalyst for esterification and transesterification. 1 This characteristic property has been applied to lipasecatalyzed ring-opening polymerization and polycondensation under mild reaction conditions to biodegradable polyesters and polycarbonates. 2-9 Enantio-and regioselective polymerizations have been achieved via lipase catalysis to give functional polyesters, most of which can not be synthesized by conventional chemical catalysts. [10][11][12][13][14][15] Candida antarctica lipase (lipase CA) immobilized on macroporous acrylic resin (Novozym 435) is industrially developed for modification of triglyceride oils. Previously, we first demonstrated highly efficient catalysis of Novozym 435 for polymerization of lactones; 16 a small amount of this enzyme (less than 1%) induced the polymerization of ε-caprolactone (ε-CL) and the polymerization rate using Novozym 435 was much larger than that by other commercially available lipases under the similar reaction conditions. Furthermore, Novozym 435 could be repeatedly used for the polymerization of ε-CL. 17 In the range of 5 cycles, the polymerization results hardly changed.Activity of immobilized enzyme catalysts is well known to depend on their support properties such as hydrophilicity and porosity. 18 In this study, we have screened the enzyme support for development of the immobilized lipase catalyst for efficient production of polyesters. 19 RESULTS AND DISCUSSIONIn this study, four polymeric and one ceramic supports have been employed (Table I). All the supports are powdery in the diameter larger than 100 µm and have porous structures. There were no functional groups † To whom correspondence should be addressed. Scheme 1.in the polymer supports (sample A-D) and the phenyl group was introduced on the surface of the pore in the ceramic support (sample E). The immobilization was carried out by mixing an aqueous solution of lipase CA and the support in a phosphate buffer of pH 7.0. The amount of protein fixed onto the support was calculated from the difference of protein content in the solution before and after the immobilization (Table II). The immobilized protein content scarcely depended on the support type except sample C, suggesting that a support with small poresize is not suitable for the immobilization of lipase CA. For reference, the amount of the immobilized protein of Novozym 435 was 175 mg g −1 support (data from supplier).In order to examine the catalytic activity of the present immobilized lipases for the polyester synthesis, the polymerization of ε-CL was performed in toluene at 60 • C for 1 h (Scheme 1). The lipase immobilized on polypropylene (sample B) showed the highest activity. An immobilized lipase on porous polypropylene was reported to catalyze ester hydrolysis and esterification. [20][21][22] Samples D and E ...
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