Surface Photografting

Surface modification of polymers has become an important research area in the plastics industry. Many polymers have very good bulk properties and are inexpensive, but many industrial applications - such as adhesion, biomaterials, protective coatings and composites - require special surface properties. Because polymers usually have a low suface energy, they often do not possess the surface properties needed to meet the demands of various applications. Advances in surface treatment have been made to alter chemical and physical properties of polymer surfaces without affecting bulk properties. By photochemical immobilization of functional aryl azides even inert polymers such as polyolefines could be modified. Printability, wettability as well as biocompatibility could be significantly improved by covalent bonding of hydrophilic carbohydrate residues. Increased light stabilitywas achieved by immobilisation of HALS derivatives. We also modified aerosil through covalent bonding of hydrophobic as well as copolymerizable groups. Biocompatibility of aerosil-filled silicon rubber was improved by grafting of heparinoids.


Hydrophilization of PP Surfaces

Polypropylene, which is very inexpensive and easy to process, has excellent mechanical properties, but due to its inert structure and low surface energy the key problems with this material lie in its printability and bondability. To overcome these difficulties, surface modifications such as corona discharge treatment are frequently employed. In a corona discharge system, a plasma is produced when air is ionized by a high electric field. The atmospheric pressure plasma, which is called a corona discharge, causes various chemical and physical changes on the polymer surface. It is well recognized that corona treatment produces surface oxidation. Electrons, ions, excited neutrals and photons that are present in a discharge can react with the polymer surface to form radicals. These radicals react rapidly with atmospheric oxygen. These reactions make possible cross-linking and functionalization of the polymer surface with and without chain scission. The decomposition of hydroperoxide groups produces COH, C=O and COOH groups. Disadvantages are a lack of uniformity and insufficient durability of the modification. By photochemical immobilisation of hydrophilic aryl azides based on carbohydrates such as glucose, sucrose and dextrine an even and permanent surface modification of PP was achieved.

Real-time FTIR spectroscopy was employed for monitoring the photolysis of the azides (decrease of the characteristic azide band). The properties of the modified PP were investigated bycontact angle measurements and by application of special test inks (Arcotec®), suitable for simple and quick evaluation of surface tension of polyolefines.

Polypropylene, which is very inexpensive and easy to process, has excellent mechanical properties, but due to its inert structure and low surface energy the key problems with this material lie in its printability and bondability. To overcome these difficulties, surface modifications such as corona discharge treatment are frequently employed. In a corona discharge system, a plasma is produced when air is ionized by a high electric field. The atmospheric pressure plasma, which is called a corona discharge, causes various chemical and physical changes on the polymer surface. It is well recognized that corona treatment produces surface oxidation. Electrons, ions, excited neutrals and photons that are present in a discharge can react with the polymer surface to form radicals. These radicals react rapidly with atmospheric oxygen. These reactions make possible cross-linking and functionalization of the polymer surface with and without chain scission. The decomposition of hydroperoxide groups produces COH, C=O and COOH groups. Disadvantages are a lack of uniformity and insufficient durability of the modification. By photochemical immobilisation of hydrophilic aryl azides based on carbohydrates such as glucose, sucrose and dextrine an even and permanent surface modification of PP was achieved.

Real-time FTIR spectroscopy was employed for monitoring the photolysis of the azides (decrease of the characteristic azide band). The properties of the modified PP were investigated bycontact angle measurements and by application of special test inks (Arcotec®), suitable for simple and quick evaluation of surface tension of polyolefines.