HOMOGENIZING MULTIMODAL POLYMER

• Main Authors: SVEIN, STAAL EGGEN, ARNE SYRE
• Format: Patent
• Language: English
• Published: 22.09.2003
• Edition: 7
• Subjects: AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F,C08G; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING; CHEMISTRY; COMPOSITIONS BASED THEREON; GENERAL PROCESSES OF COMPOUNDING; INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS; MAKING GRANULES OR PREFORMS; METALLURGY; ORGANIC MACROMOLECULAR COMPOUNDS; PERFORMING OPERATIONS; PREPARATION OR PRETREATMENT OF THE MATERIAL TO BESHAPED; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIALCONTAINING PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDEDFOR; SHAPING OR JOINING OF PLASTICS; THEIR PREPARATION OR CHEMICAL WORKING-UP; TRANSPORTING; WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE, IN GENERAL; WORKING-UP

A method of homogenizing polypropylene using twin counter-rotating screws with a melting stage and a separate downstream mixing phase. The polypropylene is melted to at least 5° C. above its melting point in the melting stage and passed through a gate valve into the mixing section. The elongational stress applied to the polymer in the mixing section is at least 20% greater than that of conventional counter-rotating extruders and causes a Henchy strain of between 1.5 and 2.5 in the polymer. This causes significant strain hardening within the polymer sufficient to break up gels within the polypropylene, thereby producing a polymer with no visible white spots.