Structure and properties of cassava starch-acrylamide graft copolymer
With the continuous development of the wood processing industry,in order to eliminate the hazards of free formaldehyde in traditional wood-based panel adhesives(urea-formaldehyde resin(UF),phenol-formaldehyde resin(PF),and melamine-formaldehyde resin(MF))on human health and the environment,a formaldehyde-free tapioca starch-acrylamide graft copolymer adhesive was synthesized.The tapioca starch-acrylamide graft copolymer was pre-pared using tapioca starch(CS)degraded by sulfuric acid(H2 SO4)and graft copolymerized with acrylamide(AM),and its basic properties were measured.The structures were examined by the Fourier transform infrared spectroscopy(FT-IR),nuclear magnetic resonance carbon spectroscopy(13 C NMR)and X-ray photoelectron spectroscopy(XPS).The curing properties were analyzed by the differential scanning calorimetry(DSC)and scanning electron microscope(SEM),and the effects of the molar ratio of cassava starch basic unit to acrylamide(AM)on the stabili-ty of the tapioca-starch-acrylamide graft copolymer were studied.The results showed that the synthesized starch binder was a milky white emulsion and the polyacrylamide was a transparent homogeneous liquid.The cassava starch-acry-lamide graft copolymer(CS-AAGC)binder synthesized in the first six groups had the appearance of a milky white homogeneous liquid,and the cassava starch-acrylamide graft copolymer binder in the seventh group had the appearance of a milky white jelly.The viscosity of cassava starch-acrylamide graft copolymer binder increased with the increase of the addition of acrylamide and the double-bonded carbon on acrylamide reacted with the hydroxyl group in starch.As the reaction proceeded,the acrylamide and the starch interlocked to form the cassava starch-acrylamide graft copolymer.As the amount of acrylamide increased,the appearance of tapioca starch-acrylamide graft copolymer was white and homogeneous liquid.The adhesive properties of the cassava starch-acrylamide graft copolymer(CS-AAGC)adhesive were also significantly improved,and the corresponding cassava starch-acrylamide graft copolymer showed the best adhesive properties when n(starch basic unit)∶n(AM)=1∶5.The dry shear strength of the plywood prepared by the CS-AAGC adhesive was 1.46 MPa,the 24-h shear strength in(23±2)℃ cold water was 0.87 MPa,and the 3 h shear strength in(63±1)℃ hot water was 0.84 MPa,which satisfied the requirements of the second-grade plywood according to the national standard GB/T 9846-2015"Plywood for general use".
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