Improvement of mechanical properties by cold plasma treatment of bonded surfaces

Abstract

In nature, matter is found in solid, liquid or gaseous form. At very high temperatures, molecules can absorb an enormous amount of energy, causing them to move in a disordered way. With the absorbed energy, they can dissociate into atoms, and because of their disordered motion, these molecules or atoms can split into ions and electrons. Excessive heating of matter is therefore always accompanied by ionisation, leaving the medium electrically neutral. This ionised state is known as plasma. It is sometimes called the fourth state of matter. Plasmas are therefore mixtures of neutral and/or excited ions, electrons, atoms, radicals or demodules with an internal energy above the neutral state. Sources of plasma can be as follows: naturally occurring in the ionosphere; produced by nuclear reactions; generated by a hyperfrequency source; formed by direct heating followed by confinement in a region of space by a magnetic field; and produced by electrical discharges. Plasma is characterised by the state of its components: density, which is defined by the number of particles per unit volume; kinetic temperature; and degree of ionisation. Plasma can be thermal or out of thermal equilibrium, or 'cold plasma'. Cold plasma is formed, for example, when a gas passes through strong electric fields - electrons are dissociated from the molecules and the gas becomes electrically conductive and glows blue. The paper describes the equipment used to create cold plasma, which was used to treat different surfaces. After treatment, they were bonded with different adhesives and tested for tensile strenght. An improvement in the mechanical properties mentioned above was observed when the surfaces to be bonded were treated with cold plasma compared to surfaces bonded normally. When the impact of cold plasma treatment on elongation, or ε, is examined, it is found that for Fiber Wood samples, cold plasma treatment considerably boosts elongation, increasing it from 0.35% for untreated samples to 0.81% for samples treated with cold plasma. For samples that have been treated with cold plasma, the average value increases significantly from 0.03% to 0.63% when ArbofillFichte material is used. In addition, the application of cold plasma treatment to the surfaces results in an increase in the modulus of elasticity. For example, the modulus of elasticity doubles for Arbofill Fichte samples, going from 113.56MPa for untreated samples to 227.43MPa for cold plasma treated samples; for Fiber Wood, it increases from an average value of 789.52MPa for untreated samples to an average value of 931.62MPa for treated samples.