| With the improvement of people’s living standards and environmental awareness, starch-based aqueous polymer isocyanate wood adhesives (starch-based API) are widely used in wood industry. In order to overcome the shortcomings of traditional starch-based adhesive such as poor water resistance, firstly the corn starch was modified, and then starch-based API was prepared. Also impact on the using environmental, gluing performance of starch-based API decline and its use was affected. Revealing effects of environmental factors such as wet and thermal on aging the mechanism and regularity of wood products, aging resistance of starch-based API and durability of glued products were further improved.Modified starch was prepared by acid-catalyzed hydrolysis and oxidation starch in this study and the best synthesis scheme of starch-based API was optimized by orthogonal test for emulsifiers, polyvinyl alcohol and P-MDI as the main factor and compression shearing strength as indicators. Chemical analysis and instrumental analysis methods were used to characterize its performance. The effect of aging treatment conditions on the starch-based API adhesive and its products was analyzed. The influence of the different surface treatments on bonding properties of starch-based API was revealed. The service period of starch-based API was revealed and useful life of bonding products for starch-based API was forecast Specific contents are as follows:(1) Corn starch was oxidized by using ammonium persulfate and modified starch was prepared by addition of ethylene glycol and maleic anhydride. The best synthesis formula of starch-based API adhesive was optimized by orthogonal test for emulsifiers, polyvinyl alcohol and P-MDI as the main factor and compression shearing strength as indicators. The results showed that:compression shearing strength of wood glued products for starch-based API adhesive obtained by the best formula can meet fully the requirements of JIS-K6806. Modified starch and starch-based adhesive properties were characterized by chemical analysis and SEM and FT-IR. The results showed that its physical and chemical properties met standard and actual needs. SEM analysis showed:starch surface was certain damaged by acid hydrolysis and oxidization and occurred reaction during the synthesis of the main agent and attached to the starch surface. The starch molecules integrated tightly in together during synthesizing starch-based API adhesive. FT-IR analysis results showed:acid and oxidization starch only increased reactivity corn starch and did not change its structure, however the spectrum of the main agent and starch-based API adhesive had the new absorption peak generation, which showed that chemical reaction occurred in the synthesis process.(2) The starch-based API film and saled API film were treated by acceleration aging and hygrothermal aging and its structure was characterized by FT-IR, TQ DSC, SEM and EDS. FT-IR showed that untreated film had considerable untreated isocyanate group and isocyanate groups in the treated film disappeared in different cycles. Starch-based API adhesive durability analyzed from the point of view of quality loss, the thermal stability of film was not the same because of the different treatment approach. The much higher of hygrothermal aging treatment temperature got, the more stable film got. In addition, degradation rate of film treated was also different, in the same mass loss premise, the degradation rate of film was not the same when hygrothermal aging treatment temperature was different. But under the same hygrothermal aging temperature, the degradation rate of film for the different processing cycle was basically the same. The glass transition temperature of the starch-based API was analyzed under different hygrothermal aging temperature. The results showed that as the temperature rising and hygrothermal aging cycle extending, starch-based API glass transition temperature was reduced. Aging treatment effect was analyzed from bonding performance of glued products. The results showed that compression shearing strength of the untreated samples increased initially and then stabilized with the placement period increasing. The decline of compression shearing strength for accelerated aging specimens was faster than that of hygrothermal aging. While the different hygrothermal aging treatment temperatures, as the process temperature rising, the decline rate of compression shear strength became much faster. As the hygrothermal aging temperature rising and hygrothermal aging cycle extending, destruction of bonding joint for starch-based API adhesive increased at the different level. With hygrothermal aging temperature and the aging period, the starch-based API bonded joint damage in the form of varying degrees of increase. EDS analysis showed that the oxygen content of the bonded joint changed differently with hygrothermal aging treatment temperature and aging cycle, which indicated that moisture diffused into the adhesive joints during the hygrothermal aging process. As the hygrothermal aging temperature rising and hygrothermal aging cycle extending, the water absorption of starch-based API treated by hygrothermal aging increased.(3) The surface treatment can improve the durability of adhesive joints. So the substrate were carried out sanding, chemical oxidation and coupling process. The effect of the different treatment methods on bonding property was analyzed. Process parameters were sandpaper 1000 mesh, chemical oxidant concentration of 20%, the coupling agent concentration of 3%. The wood surface treated can improve its bonding properties. By XPS analysis, sanding just changed the wood surface roughness, its composition had not been changed. Wood surface polar was modified by chemical oxidation treatment, however wood surface formed a transition layer by coupling agent treatment. The elements valence and content of wood surface treated by the above methods occurred variety. FT-IR analysis showed that wood sanded preserved characteristic peaks of untreated wood samples, and wood some peaks of chemical oxidation and coupling agent treatment had disappeared. After surface treatment of wood was treated by hygrothermal aging, water absorption of adhesive joints decreased, decrease range in turn was coupling agent> chemical oxidation> sandpaper, while damage form of bonded joints were also different.(4) Moisture diffusion coefficient of adhesive joint was reduced after the surface treatment, which described surface treatment can effectively reduced moisture diffusion rate in the bonding joint. Thus, the surface treatment can improve the durability of the bonding joint. Relational expression of hygrothermal aging temperature and service life of adhesive joints for API was deduced. Time of reaching the service under different hygrothermal aging conditions was calculated. Relational expression of hygrothermal aging temperature and glass transition temperature and water absorption were derived under different hygrothermal aging conditions. The glass transition temperature and water absorption were calculated when bonding joint reached service period under different hygrothermal aging conditions. |
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