Effect of boric acid on poly vinyl alcohol- tannin blend and its application as water-based wood adhesive

Abstract

The work presented here focusses on developing adhesive by blending tannin and polyvinyl alcohol (PVA) in water. To furthermore enhance the properties crosslinking is carried by using boric acid at varying concentrations. Presence of free hydroxyl groups in PVA and tannin acts as a site for crosslinking reaction. The empty p orbital of trivalent boron atom attracts nucleophilic hydroxyl groups of PVA and tannin, hence are expected to form crosslinks. The interaction of boric acid with the blend was confirmed by FTIR spectra studies. The acidic pH favoured the reaction and its effects were observed by increase in viscosity and glass transition temperature (Tg). Films cased with the crosslinked blend demonstrated less hydrophilic behaviour from water contact angle test also increment in pencil hardness value and stress-bearing capacity. Adhesive performance properties like wet tack and time-dependent tensile lap shear strength on softwood and hardwood specimens were evaluated. The crosslinking-enhanced cohesion by reducing the free volumes between the chains and due to this, enhancement in tensile strength on bonded wood substrates was observed. Overall, it was found that the adhesive prepared by crosslinking PVA/tannin blend with boric acid is suitable for wood adhesive application.

The Enhanced Moisture Absorption and Tensile Strength of PVA/Uncaria gambir Extract by Boric Acid as a Highly Moisture-Resistant, Anti-UV, and Strong Film for Food Packaging Applications

“…However, due to its hydrophilic nature, PVA is sensitive to moisture [20]. Previous studies introduced boric acid into PVA to improve the moisture resistance of the blend film [20,21]. Boric acid can form strong hydrogen bonds with PVA molecules, reducing the hydroxyl groups' hydrophilicity [21,22].…”

Tannin as a renewable raw material for adhesive applications: a review

“…207,208 Free hydroxyl groups of wattle tannin can be modified chemically by blending with PVA and crosslinking with boric acid. 120 Selection of similar crosslinkers and blending with a compatible commercial binder (PVA) can partially reduce the dependency of petrochemical derived binders. Recent inclusion of a circular economy and green protocol limits the usage of toxic substances, 151 which has made researchers and industries working on wood adhesives promote bio-derived adhesives.…”

Progress in the development of solid-state electrolytes for reversible room-temperature sodium–sulfur batteries

“…231 These are materials that impart a characteristic property to the polymer matrix. 193,237 Moreover, since SPEs have inherently lower ionic conduction values than ISEs, fillers that contribute to ionic conduction are usually added. 238 Filler incorporation at optimum level decreases crystallinity of the polymer, thereby enhancing the polymer chain mobility.…”