Synergistic Effects Of Pae Complex On The Mechanical And Moisture-proof Properties Of Pulp Molded Products

With the depletion of petroleum resources and the increasing concern on environmental issues,environmentally-friendly bio-based materials have received extensive attention.Especially in recent years,the"plastic ban"policy has accelerated the demand for pulp molded products in the packaging fields.Since pulp molded products are often used as food containers,they need to have excellent mechanical and moisture resistance properties.During the preparation of pulp molded products,oil-and water-proof agents are usually added to the pulp suspension.However,the mechanical and moisture-proof properties of the generated pulp molded products still could not be satisfied for packaging applications.As the most widely used wet strength agent,the excess use of polyamide-epichlorohydrin resin(PAE)would lead to the generation of chloropropanol.In order to reduce the amount of PAE and ensure the good mechanical and moisture-proof properties of pulp molded products,it is necessary to find synergistic additives with PAE.Accordingly,this dissertation discussed the mechanical and moisture-proof properties of pulp molded products by the addition of PAE and cationic starch(CS).In order to further improve the properties of products,PAE and lignin were added into the slurry.The effects of the mixing method of PAE and lignin on the mechanical and moisture-proof properties of the products and the synergistic mechanism between additives were revealed.The main research contents and results are as follows:(1)The effects of the individual and mixed addition of PAE and CS on the tensile strength,wet strength,contact angle,and water absorption of pulp molded products were explored.At the optimum amount of PAE was 2%,the tensile strength,wet strength,contact angle,and water absorption of the pulp molded products were 10 MPa,1.7 MPa,126°,and 61.2%,respectively.When the addition amount of CS was 0.6%,the optimal tensile strength,wet strength,contact angle,and water absorption of the pulp molded products were 6.1 MPa,0.8 MPa,126°,and 74.0%,respectively.The pulp molded products with a PAE and CS content of 1.0%and 0.6%displayed the best performance,that is,their tensile strength,wet strength,contact angle,water absorption,and water vapor transmission rate were 12.2 MPa,2.1 MPa,128°,51.5%,and 639.7 g/m~2·day.(2)To improve the mechanical strength and moisture resistance of the pulp molded products,the effects of hot pressing temperature and lignin addition on their properties were investigated,and X-ray photoelectron spectroscopy(XPS),Thermogravimetric analysis(TGA)and 2D-NMR HSQC techniques were used to reveal the influence mechanisms.The results showed that the best performance of the pulp molded products was achieved when the hot pressing temperature was 160°C and the lignin addition was 30%,with the tensile strength,wet strength,contact angle and water vapor transmission rate of 26.62MPa,4.39 MPa,118°and 617.7 g/m~2·day,respectively.2D-NMR HSQC spectroscopy results showed that the C-C bond content in lignin was the highest at the hot pressing temperature of 160°C,which also indicated that lignin had good bonding properties at this temperature;in addition,lignin had hydrophobic properties,which improved the mechanical strength and moisture resistance of pulp molded products.(3)To further improve the mechanical and moisture-proof properties of pulp molded products,PAE-Lignin composite particles were prepared,and the effects of PAE content on the particle size and zeta potential of the composite particles,and the effects of PAE-Lignin composite particle addition on the mechanical and moisture-proof properties of pulp molded products were investigated.The synergistic mechanism of PAE and lignin in the products was revealed by XPS and SEM.When mixed 0.75%PAE with 0.5%lignin in equal proportions,uniformly dispersed and positively charged PAE-Lignin composite particles were prepared and added to the pulp molded products,and the mechanical and moisture resistance properties of the pulp molded products were optimal when the addition amount was 1.5%,and the tensile strength,wet strength,contact angle,and water vapor transmission rate were 24.9 MPa,11.8MPa,128°,and 11.8 MPa,respectively.The chemical structure of the pulp molded products before and after the addition of PAE-Lignin complex was analyzed,and the results showed that the PAE-Lignin complex improved the mechanical and moisture resistance of the pulp molded products by adsorption and ionic interactions with the pulp fibers.The mechanical strength of the pulp molded products remained almost unchanged after one week in the refrigerator(4°C,75%RH),and degraded about 75%in 100 days under natural environment.