Photoinitiated grafting of methyl methacrylate on highly oriented polyethylene: Effect of draw ratio on grafting

Modification of highly oriented polyethylene was performed using a photoinitiated grafting technique. The samples were first coated with photoinitiator and then exposed to methyl methacrylate vapor under UV light (λ > 290 nm) at 60°C. The extent of grafting was studied as a function of draw ratio. It was found that the extent of grafting decreased significantly as the draw ratio was increased. Control samples of undrawn samples with different thermal histories suggested that there was another factor in addition to crystallinity that influences the extent of grafting. It is proposed that amorphous orientation or taut-tie molecules reduce the photoinitiation process. Gravimetric and attenuated total reflectance-IR measurements indicated that the grafting reaction can occur below the sample surface (or internal grafting) and that the proportion of surface grafting increases with increasing draw ratio.