Abstract
Polyurethane adhesives made from synthetic chemicals are non-biodegradable, costly and difficult to find raw materials from local market. To avoid solid pollution problem, cost effectiveness and easy availability of raw materials, biomaterials based polyurethane adhesives are used in current industrial interest. Direct use of castor oil in polyurethane adhesive gives limited hardness. Modification on active sites of castor oil to utilize double bond of unsaturated fatty acid and carboxyl group yields new modified or activated polyols, which can be utilized for polyurethane adhesive formulation. In view of this, we have synthesized polyurethane adhesives from polyester polyols, castor oil based polyols and epoxy based polyols with Isocyanate adducts based on castor oil and trimethylolpropane. To study the effects of polyurethane adhesive strength (i.e. lap shear strength) on wood-to-wood and metal-to-metal bonding through various types of polyols, cross-linking density, isocyanate adducts and also to compare adhesive strength between wood to wood and metal to metal surface. These polyols and polyurethanes were characterized through GPC, NMR and IR-spectroscopy, gel and surface drying time. Thermal stability of PU adhesives was determined under the effect of cross-linking density (NCO/OH ratio). The NCO/OH ratio (1.5) was optimized for adhesives as the higher NCO/OH ratio (2.0) increasing cross-linking density and decreases adhesion. Lower NCO/OH ratio (1.0) provideslow cross-linking density and low strength of adhesives.
Highlights
The adhesives based on polyurethanes used by a wide range of application like woodworking, furniture building/ restoration, boat building/ repair, cabinet making and millwork, stone working, tile and other masonry, light aircraft building/ repair, crafts, and many others
In the view of this the present work describe the performance of castor oil based novel polyurethane adhesive system for wood to wood and metal to metal bonding by using polyester polyols, castor oil-polyester polyols and epoxy-polyester polyols with different isocyanate adducts having different NCO/OH ratio
Gel time decreases as the NCO/OH ratio increases in all the cases;
Summary
The adhesives based on polyurethanes used by a wide range of application like woodworking, furniture building/ restoration, boat building/ repair, cabinet making and millwork, stone working, tile and other masonry, light aircraft building/ repair, crafts, and many others. For many years researches have been trying to develop the properties of polyurethane adhesives for different application area via, modification and combination of various polyols as well as isocyanates adducts. Modification in hydroxyl terminated polyols based polyurethane has been studied extensively as they could be effectively used as adhesive[4,5]. The adhesive properties of polyurethane from modified castor oil or its derivatives are studied under the different variation in composition[31,32,33]. In the view of this the present work describe the performance of castor oil based novel polyurethane adhesive system for wood to wood and metal to metal bonding by using polyester polyols, castor oil-polyester polyols and epoxy-polyester polyols with different isocyanate adducts having different NCO/OH ratio. The adhesive strength (Lapshear strength) of these polyurethanes were measured under the effects of chain length, isocyanate adducts, cross linking density and types of polyols to determine the effects of cross-linking density on thermal stability, gel and surface drying time on polyurethane adhesives
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