Preparation and Properties of Starch-based Non-isocyanate Polyurethane Adhesives
A starch-based non-isocyanate polyurethane(DPHU)adhesive was synthesized by a two-step process under solvent-free and catalyst-free conditions.A mine-blocked polyhydroxy urethane(NPHU)prepolymers was synthesized from diamine and bis(six-membered ring carbonate)(BCC),and the prepolymers were further reacted with dialdehyde starch(DAS)by a Schiff-base reaction to synthesize DPHU adhesives.The molecular weight and structure of diamines as well as the effect of DAS addition on their properties were investigated in detail.The results showed that the adhesive properties of NPHU prepolymers decreased with the increase of the molecular weight of the polyether amine.When the relative molecular mass of polyether amine was 230,the lap shear strength of NPHU-D230 prepolymer was up to 5.35 MPa.The presence of the amide bond improved the adhesive properties of NPHU prepolymers.With the increase of DAS addition,the lap shear strength of DPHU showed a tendency of increasing first and then decreasing,and the lap shear strength of DPHU-30 reached up to 6.26 MPa when the DAS addition(in terms of mass fraction)was 30%.The mechanical properties analysis showed that DPHU could be transformed between toughness and rigidity materials by adjusting the DAS addition amount.The DAS addition amount reached up to 70%,the tensile strength of prepared DPHU-70 was as high as 6.74 MPa,and the elongation at break was up to 12.59%.In addition,DPHU had good thermal stability,self-healing properties,and shape memory properties.The glass transition temperature(Tg)of DPHU-0-DPHU-70 increased from16.14℃to31.56℃when the DAS addition increased from 0 to 70%.When the DAS addition was 0-50%,the self-repairing efficiency of the surface scratches of DPHU-0-DPHU-50 could reach more than 90%in 3 min at 50℃.The DPHU spline was folded and the heating-cooling cycle was repeated,and the spline could be restored to its original state in a short time.
starchadhesive propertiesnon-isocyanate polyurethanesSchiff base reaction
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