Melt fracture behavior of polypropylene-type resins with narrow molecular weight distribution. II. Suppression of sharkskin by addition of adhesive resins

Standing on a hypothesis that the sharkskin of a polymer with a narrow molecular weight distribution at extrusion processing originates from a stick-slip of the polymer at the die wall, the suppression of the sharkskin was tried by means of suppressing the slip by the addition of adhesives. To polypropylene (PP)-type resins with narrow molecular weight distributions such as a PP-type thermoplastic elastomer, PER and a controlled rheology PP were added small amounts of adhesives such as maleated PP, maleated PER, reactive polyolefin oligomers, ethylene/ethylacrylate/ maleic anhydride (MAH) copolymer, ethylene/vinyl acetate copolymer, and styrene/ HAH copolymer, and their melt fracture behaviors at capillary extrusion were observed. It was found that the sharkskin of the PP-type resins with narrow molecular weight distributions was suppressed by the addition of the adhesive resins with good adhesion to metal. The suppressive effect of the sharkskin was generally the more remarkable by the higher loading of the adhesives with the higher AIAH content. This is the direction of increasing adhesion. From this fact, it was assumed that the sharkskin of the PP-type resins with narrow molecular weight distribution does not originate from a periodic growth and relaxation of tensile stress at the extrudate surface but from a stick-slip at the die wall. Based on this mechanism, it may be said that the sharkskin can be suppressed by both ways of directions of promoting and suppressing the slip at the die wall. The former way is the previously known method, and the latter way is the method proposed in the present study. (C) 2002 Wiley Periodicals, Inc.