Natural adhesives are commonly used adhesives in our daily lives. According to different sources, they can be classified into animal adhesives, plant adhesives and mineral adhesives. Among animal adhesives, there are hide glue, bone glue, shellac, casein glue, albumin glue, fish bladder glue, etc.; among plant adhesives, there are starch, dextrin, rosin, gum arabic, natural rubber, etc.; and among mineral adhesives, there are mineral wax, asphalt, etc. Due to their abundant sources, low cost and low toxicity, they are widely applied in the processing of furniture, bookbinding, packaging and handicrafts.
Inorganic Adhesives
Adhesives prepared with inorganic substances such as phosphates, phosphates (it seems there is a repetition here, you may check), sulfates, borates, metal oxides, etc. as the adhesive materials are called inorganic adhesives. Its characteristics are as follows:
(1) It can withstand high temperatures, and can endure temperatures of 1000°C or even higher.
(2) It has good anti-aging properties.
(3) The shrinkage rate is small.
(4) It is brittle, and its elastic modulus is one order of magnitude higher than that of organic adhesives.
(5) It has poor water resistance and poor resistance to acids and alkalis.
Lignin Adhesives
Lignin is one of the main components of wood, accounting for about 20-40% of the wood, second only to cellulose. It is difficult to extract lignin directly from wood, and its main source is the waste liquid from the pulp production process, which is extremely rich in resources. Lignin is not used alone as an adhesive. Instead, phenolic resin polymers obtained by the reaction of the phenolic groups of lignin with formaldehyde are used as adhesives. To improve the water resistance, it can be used in combination with compounds such as cycloaliphatic isocyanate , epoxy isocyanate, phenol, resorcinol, etc. Lignin adhesives are mainly used for bonding plywood and particleboard. However, it has a high viscosity and a dark color. After improvement, its application range can be expanded.
Starch Adhesives
Since the 21st century, the good environmental performance of materials has become a major feature of new materials. As a non-toxic, harmless, low-cost, biodegradable and environmentally friendly natural renewable resource, starch has been increasingly widely used in various industries. In particular, in recent years, the production technology of the global adhesive industry has been developing towards the directions of energy conservation, low cost, non-toxicity, high viscosity and solvent-free.
As a green and environmentally friendly product, starch adhesives have attracted widespread attention and great importance in the adhesive industry. In terms of the application and development of starch adhesives, starch adhesives made by oxidizing corn starch have a promising future and are the most studied and applied.