Study On Preparation And Properties Of Modified Cottonseed Protein Adhesives

In 2018,the consumption of formaldehyde-based adhesives reached 16.41 million tons(100% solids content),accounting for more than 90% of the total wood adhesives.Formaldehyde-based adhesives use non-renewable resources such as petroleum as raw materials.There are different levels of formaldehyde release problems during production and use.With the continuous depletion of petrochemical resources and people's emphasis on environmental protection,the development of an environmentally friendly adhesive with renewable biomass resources as the main raw material has important practical significance and practical value.Cottonseed meal is the remainder of cottonseed oil,and its protein content is second only to soybean meal.At present,China produces about 11 million tons of cottonseed each year,and the remaining cottonseed meal after cottonseed oil extraction is as high as more than 6 million tons.If cottonseed meal can be used as the main raw material for the preparation of protein adhesives,it will not only reduce the cost of adhesives but also Use cottonseed meal for high added value.In this study,cottonseed meal was used as the raw material,and the modified cottonseed protein adhesive was prepared under different processes as an adhesive base material after washing with water.The main research contents are divided into four parts: urea modification,urea composite modification with three modifiers,optimization of modifier and urea composite modification process,and blend modification of isocyanate and cottonseed protein adhesive.Through experiments,the effects of reaction temperature,urea concentration,type and amount of modifiers on the properties of cottonseed protein adhesives were discussed,and cottonseed protein adhesive modification methods that met the requirements of different bonding strength and water resistance properties were obtained.Through infrared analysis and thermogravimetric analysis of cottonseed protein adhesive,the relationship between the structure and performance of cottonseed protein adhesive was discussed,and the modification mechanism was revealed.The conclusions of the study are as follows:(1)The wet bonding strength of cottonseed protein adhesive prepared with urea as a modifier at 70°C reaction temperature and 1mol/L and 3mol/L urea concentration is 0.74 MPa and 0.71 MPa,respectively,reaching the national class II Plate standard.(2)Among cottonseed protein adhesives prepared by using three modifiers and urea respectively,SDS and urea have the worst composite modification effect,and the adhesive modified by glyoxal and urea has water resistance.There is a certain improvement,but these two types of adhesive-bonded plywood do not meet the national class II board standards.Adhesive glued plywood prepared by the composite modification of zinc oxide and urea can reach the standard of class II sheet,and when the urea concentration is 3mol/L,the amount of zinc oxide is 8%,and the reaction temperature is 55°C,the wet The bonding strength reached the maximum(1.19MPa).(3)Glue properties of cottonseed protein adhesive modified and optimized by zinc oxide and urea have been improved.Under the conditions of urea concentration of 2mol/L,zinc oxide addition amount of 8%,and reaction temperature of 55°C,the wet bonding strength reached the maximum value(1.30MPa).(4)With the addition of zinc oxide,the solid content and pH value of the adhesive increase,and the viscosity and adhesive strength increase first and then decrease;as the urea concentration increases,the adhesive strength of the adhesive decreases;The adhesive strength of the adhesive prepared at lower temperature(55°C)is better than the adhesive strength of the adhesive prepared at higher temperature(65°C).(5)Infrared test results show that chelation of zinc oxide with cottonseed protein molecules produces chelate compounds with stable ring structure.Thermogravimetric analysis shows that the addition of zinc oxide can improve the thermal stability of cottonseed protein adhesives.(6)With the increase of the amount of isocyanate added,the solid content and viscosity of the blended modified zinc oxide-urea cotton seed protein adhesive increase.When the amount of isocyanate added is greater than 30%,the prepared plywood can reach the national class I sheet standard.(7)The raw material cost of the zinc oxide-urea composite modified cottonseed protein adhesive prepared by the optimal process in this study is about 1230.8 yuan/ton,and the raw material cost of the adhesive modified by isocyanate blending is about 3348.8 yuan/ton,compared with the corresponding level of adhesives in the market has a certain price advantage,can produce better economic and environmental benefits.