“Research on the mechanism to improve the surface adhesion of polyethylene by techniques of high environmental performance based on atmospheric plasma” 

ABSTRACT

Currently, the polyethylene is one of the thermoplastics of higher consumption in the world with an estimated annual demand of 60 million tons. The high demand of polyethylene has been directly linked to its versatility, good physical properties and the economic competitiveness of their production processes. Furthermore the polyethylene is considered the cheapest polymer. Several strengths confirmed as a suitable material for many applications: its low density, good chemical and mechanical resistance, lack of odor, non-toxicity, low permeability to water vapor and good electrical properties. Due to this balance between chemical, physical and economic properties, polyethylene can be found in many industrial sectors of both high and low technology content.

However, it has certain limitations in its applicability due to its own properties. One of the major limitations of polyethylene is given in industrial sectors that demand high quality materials and performances, and, also a greater technological content, such as automotive sector, construction, food industry, interior or sports applications. The products for these sectors require an improved of the adhesive properties. But not only polyethylene but the whole of other polymeric materials, that, due to its chemical nature, does not have good adhesive properties. Due to this demand in industry a search is required to improve wettability properties of the polyethylene.

In this paper we have used an atmospheric plasma process to improve wettability and adhesive properties of polyethylene sheets. The improvement in adhesive properties was studied by changes in surface energy through the determination of contact angle. The measures were made for different treatment conditions depending on the rate treatment and the distance between the nozzle and the polyethylene substrate. The action of atmospheric plasma is analyzed by chemical and physical changes. The variation of physical properties is measured by the variation of morphological changes and roughness. On the other hand, a study of the maximum peel strength "T" and shear has been performed, for polyethylene/polyethylene joins previously treated under different conditions of atmospheric plasma. Finally, the effect of storage time has been studied to establish the durability of the process to give an answer to a real industrial need. The study has been made by analyzing the hydrophobic recovery substrate calculating the surface energy and the shear tests.

The results show that plasma treatment at a low treatment rate and a low distance between nozzle/substrate improves substantially the wettability of polyethylene sheeting. The main mechanism of action of the plasma surface activation is by insertion of polar species, as evidenced by XPS study. These species are highly reactive, which results in loss of wettability observed in the study of aging. In addition there are also physical changes as demonstrated by increased roughness and mass loss, which contribute positively to improving the adhesive properties. In general, we can conclude that the plasma treatment is a very interesting from the standpoint of economic and environmental, as it is a process easily implemented in a production process that does not generate waste.