Abstract
A dual network hydrogel made up of polyvinylalcohol (PVA) crosslinked by borax and polyvinylpyrrolidone (PVP) was prepared by means of freezing-thawing circles. Here PVP was incorporated by linking with PVA to form a network structure, while the introduction of borax played the role of crosslinking PVA chains to accelerate the formation of a dual network structure in PVA/PVP composite hydrogel, thus endowing the hydrogel with high mechanical properties. The effects of both PVP and borax on the hydrogels were evaluated by comparing the two systems of PVA/PVP/borax and PVA/borax hydrogels. In the former system, adding 4.0% PVP not only increased the water content and the storage modulus but also enhanced the mechanical strength of the final hydrogel. But an overdose of PVP just as more than 4.0% tended to undermine the structure of hydrogels, and thus deteriorated hydrogels’ properties because of the weakened secondary interaction between PVP and PVA. Likewise, increasing borax could promote the gel crosslinking degree, thus making gels show a decrease in water content and swelling ratio, meanwhile shrinking the pores inside the hydrogels and finally enhancing the mechanical strength of hydrogels prominently. The developed hydrogel with high performances holds great potential for applications in biomedical and industrial fields.
Highlights
Hydrogels are cross-linked network structure of water soluble polymer or hydrophilic polymer, which can swell in water to capture many times of their original mass [1]
Hydrogels made of single polymers usually display poor mechanical behaviors [13], as we know, single polyvinylalcohol (PVA) hydrogels are hard to meet the requirements of some applications needing high mechanical strengths
As can be seen that the water content in PVA/borax hydrogels without PVP varied from 68 to 80%, while increased obviously with the addition of PVP. This was mainly due to the oxygen atoms of the carbonyl group in PVP could form hydrogen bonds with the H atoms in water molecules, which endowed PVP with strong hydrophilicity to bond with plenty of water
Summary
Hydrogels are cross-linked network structure of water soluble polymer or hydrophilic polymer, which can swell in water to capture many times of their original mass [1]. Hydrogels made of single polymers usually display poor mechanical behaviors [13], as we know, single polyvinylalcohol (PVA) hydrogels are hard to meet the requirements of some applications needing high mechanical strengths. Due to the hydrophilic functional groups in each molecular unit, PVA can form chemically and physically into a crosslinked hydrogel [17]. At the cost of its stability and mechanical properties, PVA can be fabricated into PVA hydrogel by absorbing plenty of water [18]. PVA is very sensitive to borax, and introducing borax as a crosslinker into PVA hydrogel could significantly enhance the malleability but the mechanical property and ductility were still poor [19]. Polyvinylpyrrolidone (PVP) was added to the PVA–borax system to stabilize the network by forming the inter-chain hydrogen bonding [20]. PVP has planar and highly polar side groups owing to the bond of ‘
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