Properties And Application Of Acid-thinned Acetylated Cassava And Waxy Maize Starch In Adhesives

Cassava and waxy maize starches were used as raw materials, acid pretreatment beforethe acetylation was introduced in the preparation of the modified starches. The correspondingphysicochemical properties of the modified starches were then investigated. Then themodified starches were graft-copolymerized with compound monomers, crosslinking agentand modifying agent were added into compound modified starch slurry to prepare theadhesives. The paper studied the condition of graft-copolymerize, formula of adhesives andpreparation technology, and the adhesives were compared with white latex.First, the physicochemical properties of the acid-thinned and acetylated starches wereinvestigated and were compared with single processed starches, the morphological andstructural changes of the modified starches were also observed and analyzed. The resultsshowed that: the modification by acid thinned and acetylation improved the pastetransparency and retrogradation obviously, enhanced the cold and hot paste stability;decreased the swelling power, gelatinization temperature and peak viscosity; the modifiedstarch had no difference with the crystalline pattern and the granular structure.After that, the acid-thinned acetylated waxy maize starch was prepared with differentconcentration of hydrochloric acid as pretreating methods, the corresponding physicochemicalproperties of the modified starches, including the viscosity、transmittance and the swellingpower were then investigated, the morphological and structural changes of the modifiedstarches were also observed and analyzed. The study on characteristics indicated that thefreeze-thaw stability, swelling power and paste viscosity of the modified starch weredecreased obviously, the modified starches was of lower gelatinization temperature thancorresponding acid-thinned starches but higher than acetylated starch, the retrogradation andpaste stability was improved, the paste transparency and solubility were increased, thecrystalline pattern unchanged.Second, reaction of grafting copolymerization of vinyl acetate onto the modified starchwas investigated and the graft copolymer of starch was characterized. The optimumtechnology parameters was: chose the waxy maize starch as the materials, the concentrationof hydrochloric acid was0.75mol/L, acetic anhydride6%, content of starch was25%, the amount of vinyl acetate was30mL,adding time was1.5h, reaction time was3h, the amount ofinitiator was2.5%of the starch weight, temperature was70℃. The dry and wet shearingstrength of adhesives reached3.7MPa与2.1MPa. Infrared Spectrum and X-ray diffractiondemonstrated that crystal structure of reaction product disappeared and starch grafted withmonomers successfully.Third, based on the technology of the graft copolymerization, the crosslinking agent,modifying agent and gelatinization temperature were studied, the optimum technologyparameters was: PVA, crosslinking agent, sodium borate, carbamide were40%、0.5%、0.6%、30%respectively of the starch amount and gelatinization temperature was75℃, in thiscondition the dry and wet shearing strength of adhesive reached4.5MPa and3.2MParespectively.Finally, characteristics of this adhesives were compared with white latex bought from themarket and acid-thinned starch adhesives. Characteristics on appearance、viscosity、dry time、wood polluting、ash content、solid material content、resistant-shear stability were close towhite latex; the freeze-thaw stability was inferior to white latex but met with the operatingrequirements; the mobility was improved greatly, this adhesive was semi-solid flow regimesubstance and displayed the typically pseudoplastic fluid.