TABLE OF CONTENTS The free surface energy for PE is 10 J (at 20 C). The critical surface tension for LDPE ranges between 25.5 and 36 mN/m, while for HDPE it varies between 28 and 34.1 mN/m.
PE, being inert and non-polar, shows low adhesion, i.e., little tendency to bond to a smooth surface. Treatments such as flaming or high-energy irradiation introduce polar groups (carbonyl) into the PE surface and improve bonding properties. The coefficient of friction is situated at the lower limit close to that of PTFE. Blocking, defined as that adhesion between layers of film or sheet that prevents their being separated, is a characteristic noted in PE. Slip and anti-blocking agents can be used.
Impact properties are greatly influenced by the testing variables such as stress distribution, testing speed, and temperature, so that different tests may give quite different results.
In many applications polyolefins are integrated in different components and composite materials, or they are subjected to more or less aggressive media. Two opposite surface characteristics are usually required:
high surface energy, strong wettability, and polar surface are used for adhesion with other macromolecules, metals, adhesives, paints, and varnishes; and
low surface energy, weak wettability, and on a non-polar surface are usually required for some biological and industrial applications.
Several practical and economical methods have been developed over the years in order to modify PE surfaces for improved adhesion, wettability, printability, dye...
