Adhesion enhancement of polyolefins by diamond like carbon coating and photografting polymerization

Polyolefins, such as polyethylene (PE) and polypropylene (PP) are widely used materials with low adhesion property. Diamond-like carbon (DLC)-deposited polyolefins are especially attractive for the effective control of the surface and the mechanical properties of the polyolefins, where the adhesion between the DLC and the polyolefins is the key parameter that determines the major properties. Recently we have found that the low-adhesion surfaces of some polyolefins such as high-density PE (HDPE) and linear low-density PE (LLDPE), could be drastically modified to show a good adhesion after diamond-like carbon (DLC) coating, although some other polyolefins such as low-density PE (LDPE), isotactic polypropylene (iPP), and syndiotactic polypropylene (sPP) could not be surface-modified for higher adhesion property by DLC coating, which was due to the low adhesion between polyolefins and DLC. To overcome the problem, photografting polymerization was introduced to improve the low adhesion property of LDPE, iPP, and sPP. The adhesive strengths between the polyolefins and the DLC films were remarkably increased by photografting acrylic acid (AA) onto the polyolefin surface before DLC coating. In addition, the fracture of the base polymer was observed for AA-grafted polyolefins synthesized at the grafting time of ~ 15–30 min, indicating the strong adhesive force between photografted polyolefins and DLC.Furthermore, the adhesion forces between DLC and other widely-used polymer materials, such as polystyrene (PS), polymethylmethacrylate (PMMA), polyethyleneterephthalate (PET), polyurethane (PU), and polydimethylsiloxane (PDMS) which were all rather not easy to directly deposit DLC, were also found remarkably increased by photografting AA onto the polymer surfaces before DLC coating.

► Acrylic-acid photografting polymerization was introduced.
► The polymerization method was used as a new way of surface treatment.
► The method significantly improved the adhesion between DLC and widely-used polymers.
► The method would lead to an invention of a new functional DLC–polymer material.