Plasma treatment disadvantage

A disadvantage with conventional plasma treatment techniques is the requirement for treatments to take place in a vacuum, adding to the equipment costs. However, if a dielectric material is placed between the electrodes of the plasma equipment, then treatment can be performed at atmospheric pressure. This method is known as a dielctric barrier discharge treatment and has been the subject of some recently reported studies. 

Pretreatment methods such as flaming, corona treatment, or ND plasma treatment are not useful, or even disadvantageous, with cyanacrylate adhesives due to the formation of acidic cleavage products or components on the surface. 

Better effects on complicated PP parts are produced by a low-pressure plasma treatment in oxidizing gases, such as oxygen. The disadvantage of the plasma process (pressure 0.01-1 mbar, lOMhz, 500 W) is that the plasma chamber after the positioning of the parts must be evacuated and filled with the plasma gas. This process is discontinuous and needs approximately 1.5 min or more for a filled chamber (see also the chapter Surface modification of polypropylene by plasma in this book). 

In spite of these disadvantages, plasma treatment of polymers is an attractive process to produce the required surface modification. By using different types of gas, various chemical functionalities can be introduced on the surface. In general, more uniform surfaces are produced by plasmas than by flame and corona treatments. The modification is typically confined to the surface without changing the bulk physical and chemical properties of the pol)uner. 

In this study, the surface of poly(dimethylsiloxane) membranes was modified by APG plasma. Poly(dimethylsiloxane) membranes have both the advantage of high permeability and the disadvantage of low selectivity. First, the effect of the APG plasma treatment on CO2 permeability and CO2/CH4 selectivity was investigated in detail. Then the surface structure of the membrane was analyzed and the relationship between the selectivity of CO 2 and surface structure was studied. The results were compared with those for low pressure plasma treatment by Ar, since no data on He plasma treatment of poly(dimethylsiloxane) membranes are available. 

A number of chemical and physical surface treatments have been developed for polymeric materials in recent years. Due to the disadvantage of chemical treatments, physical surface treatments are preferred to modify the surface of polymeric materials (Petrie 2006). Plasma surface treatment is often the preferred way to treat the surfaces as it offers more stable and longer-lasting surface-energy enhancement than any other treatments (Rotheiser 1999). However, conventional plasma treatment also has shortcomings. It requires a low pressure (partial vacuum), and thus the parts must be processed in a vacuum chamber, restricting the part size. Atmospheric-pressure plasma has been developed to operate at near ambient temperature and atmospheric pressure, eliminating the expensive vacuum systems. 

Poly(ethylene glycol) (PEG) molecules attached to adenosine deaminase (ADA) have been used in patients exhibiting symptoms of the severe combined immunodeficiency syndrome (SCID) caused by ADA deficiency. The modified enzyme has a plasma half-life of weeks as compared to the unmodified enzyme (minutes) (248). PEG-L-asparaginase has induced remissions in patients with non-Hodgkin s lymphoma (248). However, one disadvantage of PEG-enzyme treatment is its expense, ie, a year s treatment costs about 60,000 (248). 

The use of vincristine to treat thrombotic thrombocytopenic purpura has also been reported to be successful 14,18). This rare disease of sporadic thrombosis of small vessels with consequent intravascular hemolysis has been successfully treated recently with both plasma exchange and plasma infusion. However, there are obvious disadvantages to plasma infusion, including volume overload, transmission of infection, and cost and scarcity of plasma. Several patients have been successfully treated with vincristine alone or in association with plasma therapy. At present, however, this treatment should probably not be used alone because of the high success rate of plasma infusion and/or exchange. 

This occurs in hypopituitarism. In theory the best treatment is corticotropin, but the disadvantages of frequent injection are such that hydrocortisone is preferred. Usually less hydrocortisone is needed than in primary insufficiency. Special sodium-retaining hormone is seldom required, for the pituitary has little control over aldosterone production which responds principally to plasma potassium concentration and to the renin-angiotensin system. Thyroxine and sex hormones are given when appropriate. The general conduct of therapy does not differ significantly from that in primary adrenal insufficiency. 

---