Bonding

Bonding is a technique that connects two or more bonded objects through the micro-force of the adhesive at the interface. The factors that affect the bonding are the base material, the bonding interface, the bonding ability of the adhesive itself, the bonding process and so on.

Difficult-to-stick polymer materials include polyolefins such as polyethylene ( PE ) and polyene ( PP ), and fluorine-containing polymer materials such as polytetrafluoroethylene ( PTFE ) and polyperfluoroethylene ( FEP ). Due to their excellent performance, they are widely used in various fields of the national economy. However, PE, PP and PTFE are non-polar materials, and their applications in many fields are limited due to their low surface energy and poor surface hydrophilicity. Therefore, surface modification of these materials is particularly important. The plasma treatment method has the advantages of fast processing speed, good treatment effect and small damage to the material itself, and has been widely used in surface modification.

Principle of plasma treatment to improve adhesion

The treatment of difficult-to-stick materials by plasma technology is mainly through physical or chemical etching on the surface of the material, the introduction of polar groups on the surface polymerization or grafting to increase the surface roughness of the material and improve the surface polarity, so as to obtain better wettability and adhesion.

The plasma usually acts on the surface layer of the material. According to the different energy density of the plasma and the reactivity of the excited particles, the treatment depth is from several nanometers to tens of nanometers. The energy of the active particles in the plasma ranges from a few electron volts to dozens of electron volts, which is greater than the typical chemical bond dissociation energy in polymer materials ( such as the dissociation energy of C − C is 3.61 eV, C = C is 6.35 eV, C − H is 4.30 eV, etc. ). Therefore, the energy of the plasma is sufficient to cause the fracture and recombination of chemical bonds on the surface of biomass materials, resulting in etching, evaporation, crosslinking, degradation, oxidation and other reactions. From the reported research results, it can be seen that the main mechanism of using plasma to modify the surface of biomass materials to improve the interfacial compatibility of composite materials includes two aspects : one is the physical etching effect. Plasma treatment can form nano-scale nicks and pits on the surface of the material, which is conducive to the formation of good mechanical meshing between the adhesive and the surface of the material ; second, plasma modification can introduce a large number of polar functional groups on the surface of the material, which can promote chemical crosslinking between biomass materials and polymers such as adhesives. 

Comparison of surface energy before and after plasma treatment

Changes in dyne values before and after plasma treatment, PTFE 60 dyne pen