Abstract
ABSTRACTThe aim of this study is to analyze the various compositions of polyvinyl alcohol (PVA) and starch (S) blends. The blends have been cross-linked with glutaraldehyde to enhance its properties. The hydroxyl groups of PVA and starch react with glutaraldehyde via formation of acetal bonds hence crosslinking could take place. The cross-linking of glutaraldehyde is observed with the help of various analytical methods such as differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). The presence of two highly reactive alpha protons makes glutaraldehyde more reactive and acidic in nature. The higher reactivity of glutaraldehyde, at higher dosages leads to reduction in H-bonding of PVA and starch. The cross-linked blends showed better thermal and mechanical properties. Viscosity, tensile strength, pencil hardness, and ultimate stress were evaluated to estimate the changes due to cross-linking. It was observed that the mechanical properties are directly proportional to the amount of starch as the starch hydroxyl groups are easily accessible for the cross-linking reaction. The cross-linked blend showed better cohesion between its chains, thereby increasing the glass transition temperature. It was reflected in the subsequent increase in tensile strength properties.
Highlights
Starch is a relatively inexpensive and renewable product that can be obtained from multiple plant sources and that has been extensively used as a wood adhesive [1,2]
It was observed that the mechanical properties are directly proportional to the amount of starch as the starch hydroxyl groups are accessible for the cross-linking reaction
The presence of hydroxyl groups in the structure of polyvinyl alcohol (PVA) and S make the reaction with glutaraldehyde feasible
Summary
Starch is a relatively inexpensive and renewable product that can be obtained from multiple plant sources and that has been extensively used as a wood adhesive [1,2]. A few studies have been conducted on the potential of utilizing starch as wood adhesive. Recent studies have focused on formaldehyde-free wood adhesives which are obtained through the reaction between a cross-linker and a blend of starch with other polymers, such as polyvinyl alcohol [8], tannin [9,10,11] and isocyanates [12]. Polyvinyl alcohol (PVA) is a water-soluble biodegradable polymer. It possesses a high crystalline structure [13]. There are a wide variety of crosslinking agents for PVA, such as maleic acid, formaldehyde, and glutaraldehyde [19]
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