| As the leading product of adhesive for wood industry,formaldehyde adhesive has a series of problems such as formaldehyde emission,environmental pollution and health hazard in the process of preparation and in application.Thus,environmentally friendly wood-based bioadhesives have become the research focus of scholars all over the world,and vegetable protein-based adhesives are the focus of many researches.Soy protein-based adhesives are the widely investigated and have been commercialized.However,the research and application of cottonseed protein-based adhesives are less than soy protein-based adhesives.In this thesis,the cottonseed protein was structurally modified with SDS,urea,sodium hydroxide and several kinds of polyquaterniums,and its the functional groups were further cross-linked with cross-linking reagent.The modification was carried out to improve the water resistance of the defatted cottonseed powder adhesive.The modification mechanisms of the adhesive were analyzed by FT-IR,TG-DSC and SEM,and it is applied to the production of plywood with different tree species.The main results and conclusions of this paper are as follows:(1)The defatted cottonseed meal with a particle size of 140 mesh is suitable for the preparation of cottonseed protein adhesive;the water absorption and dissolution rate of the adhesive prepared by the modified defatted cottonseed meal are increased,and the change of the bonding strength is related to the specific modifier.Among them,SDS had the best modification effect on cottonseed protein: the water absorption rate,dissolution rate,dry-bonding strength,and water-resistant bonding strength were increased by 367.67%,54.92%,54.64%,and 39.47%,respectively,when the adhesive sample was modified by 3.00% mass concentration of 30% SDS solution.(2)After the defatted cottonseed powder was treated with 3.00% SDS solution,the water absorption and dissolution rate of the adhesive prepared by adding cross-linking agent were decreased,and the bonding strength was improved to some extent.When the PAE dosage was 2.78%,the effect was obvious,but there is no significant difference between the water-resistant bonding strength and the PAE dosage of 1.92%.Compared with the modification effect of SDS,the water absorption of the cottonseed protein adhesive further modified by 1.92% PAE decreased by 291.76%,the dissolution rate decreased by 81.21%,and the dry glue strength of the produced plywood increased by 6.00%.It reached 1.59 MPa,and the water-resistant bonding strength increased by 96.23% to reach 1.04 MPa.(3)The FT-IR,TGA-DSC and SEM characterization methods were used in the preparation process of the adhesive.The results showed that the cottonseed protein was affected by SDS modification,the globulin structure was opened,and the exposed hydrophilic group.The main reason for the increase of water absorption rate and dissolution rate;after adding PAE,the hydrophilic groups exposed on the structure of cottonseed protein,such as hydroxyl group,carboxyl group,amino group,etc.,are chemically cross-linked with PAE resin,and the hydrophilic group is reduced,which is greatly improved.Water resistance of adhesives.(4)The results of orthogonal test show that the best hot pressing technique for making 3-ply plywood with modified cottonseed protein adhesive is hot pressing temperature 150 °C,hot pressing pressure 1.5 MPa,hot pressing time 260 s or 0.85 min/mm.(5)The modified the defatted cottonseed meal adhesive was combined with the best hot pressing process to make Poplar and Pinus massoniana plywood with different layers.The results showed that the highest dry-bonding strength of the three-layers plywood was 2.17 MPa for Poplar plywood and the highest water-resistant bonding strength was Pinus massoniana.The five-layers plywood has a best dry-bonding strength of 2.50 MPa,and 1.08 MPa for best water-resistant bonding strength.The highest dry-strength and water-resistant bonding strength of the seven plywood are Pinus massoniana plywood,which are 3.85 MPa and 1.22 MPa,respectively. |
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