Research on the improvement of the humectability of polymeric films of Low Density Polyetilene (LDPE) by plasma corona. Optimization of laminated with polyetilen foams by lamination processes with hot-melt adhesives for technical applications in the automotive sector

ABSTRACT
During last years, there have been a lot of research initiatives addressed towards the improvement of the adhesive properties of the polymeric materials. In the automotive sector it is very important that the polymeric films can be joined to materials of different nature. The main problem associated to the use of these materials is that they are substrates of low surface energy and they need a surface treatment to increase the moisturizing of their surfaces and to obtain good adhesive joints, a good dyeing and the application of long lasting coatings and laminated. In the case of the adhesion, the objective of the surface treatments is increasing the affinity between the adherents surface and the adhesives surfaces. This way, we can optimize the efficiency of the adhesive joints for obtaining substrates with good adhesive properties, essential condition for obtaining laminated with good technical applications. 

In this work we aim at improving the moisturizing of the polymeric films of LDPE through plasma corona treatment, for obtaining laminated with polyethylene foams through lamination processes with hot-melt adhesives with technical application for the automotive sector. The improvement of the moisturizing has been assessed through the study of the contact angles with different liquids of measure depending on the work power used. The characterization of the surface activity as result of the treatment is made through the spectroscopy infrared by Fourier transformer with Total Reflectancy Attenuation (FTIR-ATR) and the photoelectronic spectroscopy of X-rays (XPS) that allow to indentify the phenomena of the surface functionalization. In a parallel way, the phenomena of abrasion associated to the treatment aggressiveness will be identified and quantified by the scanning electronic microscopy (SEM) and the atomic force microscopy. As a complement, the homogeneity of the treatment will be determined depending on the amplitude and the time (reproducibility). Furthermore, the samples treated with plasma will be submitted to an aging procedure for estimating the durability of the treatment.


The moisturizing of the LDPE film improve a lot when the power of the corona discharge increase, reaching the best results for powers of 600W. In this sense we can assess that the surface functionalization process is based in the introduction of different polar species that are highly unstable. Due to that, when submitting the samples to an aging process it is produced a lose of hidrofilic behaviour, known as hidrofobic recovery.


The LDPE film laminated-foam of PE reticulated present good behaviour of the adhesive joints against the durability of the aging process, even for long cycles and aggressive service conditions. The curing time is a main parameter against the final mechanic behaviour of the laminated material. Finally, we can conclude that plasma treatment by corona discharge is an advantageous process to work in a continuous way with an improvement in the moisturizing of polymeric films and consequently an improvement of their adhesive properties.