Polyolefin extruder

Today, large polyolefin extruders are built as ZSK MEGAcompounders, mainly as 320, 350, and 380 Me sizes. The reason for this is clear from Fig. 14.8 which shows the same relationship as Figure 14.7, but specifically for polyolefin applications, here with the ZSK Me limit curve for maximum throughput. Normally, the torque limit is only reached with LLDPE and FfDPE if pressure is also built up by the ZSK and the powder from the polymerization reactor is coarse enough to prevent intake problems. With PP or melt-charged LDPE or two-stage machines for bimodal polyethylene, the torque required is well below the Me limit curve. 

The melt (flow) index has become a widely recognised criterion in the appraisal of extrudability of thermoplastic materials, especially polyolefins. It is standardised as the weight of polymer (polyolefin) extruded in 10 min at a constant temperature (190 °C) through a tubular die of specified diameter (0.0825 in. = 2.2 mm) when a standard weight (2.160 kg) is placed on the driving piston (ASTM D 1238). 

T.G. Rials, N.Labbe, S.S. Kelley, and D.J. Gardner. Near infrared spectroscopy assessment of wood-polyolefin extruded composites. In Eighth International Conference on Woodflber-Plastic Composites (and Other Natural Fibers), Madison, WI, 2005. 

Santechem 21-21. [Sanrech] Azodicar-bonamide cone. blowing agent for polyolefins, extruded and inj. molded structural foanL... 

With most homopolymers and copolymers the apparent viscosity is less dependent on temperature and shear stress (up to 10 dyn/cm ) than that of the polyolefins, thus simplifying die design. On the other hand the melt has a low elasticity and strength and this requires that extruded sections be... 

NACE Recommended Practice RP-02-75, Application of Organic Coatings to the External Surface of Steel Pipe for Underground Service NACE Recommended Practice RP-08-85, Extruded Polyolefin Resin Coating Systems for Underground or Submerged Pipe... 

Wet processes involve mixing a hydrocarbon liquid or some other low-molecular -weight substance with a polyolefin resin, heating and melting the mixture, extruding the melt into a sheet, orientating the sheet either in the machine direction or biaxi-ally, and then extracting the liquid with a volatile solvent [6-8]. 

Dry processes involve melting a polyolefin resin, extruding it into a film, thermal annealing, orientation at a low temperature to form micropore initiators, and then orientation at a high temperature to form micropores [9, 10]. The dry process involves no solvent handling, and therefore is inherently simpler than the wet process. The dry process involves only virgin polyolefin resins and so presents little possibility of battery contamination. 

Radical induced grafting may be carried out in solution, in the melt phase,292 29 or as a solid state process.296 This section will focus on melt phase grafting to polyolefin substrates but many of the considerations are generic. The direct grafting of monomers onto polymers, in particular polyolefins, in the melt phase by reactive extrusion has been widely studied. Most recently, the subject has been reviewed by Moad1 9 and by Russell.292 More details on reactive extrusion as a technique can be found in volumes edited by Xanthos," A1 Malaika and Baker et a 21 7 The process most often involves combining a frcc-radical initiator (most commonly a peroxide) and a monomer or macromonomer with the polyolefin as they are conveyed through the extruder. Monomers commonly used in this context include MAII (Section 7.6.4.1), maleimidc derivatives and malcate esters (Section 7.6.4.2), (meth)acrylic acid and (meth)acrylate esters (Section 7.6.43), S, AMS and derivatives (Section 7.6.4.4), vinylsilancs (Section 7.6.4.5) and vinyl oxazolines (Section 7.6.4.6). 

With a history of more than 25 years, the free radical-induced grafting of MAH onto polyolefin substrates is one of the most studied polyolefin modification processes.29 "29, 302 The process has been carried out in the melt phase, in various forms of extruders and batch mixers, and there are numerous patents covering various aspects of the process. It has also been carried out successfully in solution and in the solid state. The materials have a range of applications including their use as precursors to graft copolymers, either directly, or during the preparation of blends.297... 

Why is most compounding of powder additives with polyolefins achieved via either continuous mixers or twin screw extruders ... 

Most plastics e.g. polyolefins and polystyrenes and their derivatives such as ABS (acrylonitrile-butadiene-styrene) and SAN (styrene-acrylonitrile) are supplied by the manufacturers in ready-to-use form with most of the above-mentioned stabilizers or simply need to be additionally stabilized with other additives, e.g. antistatic agents and HALS stabilizers, as required. On the other hand, in the case of other materials (e.g. PVC) it is the end user who adds the additives, pigments or preparations. This is normally done on fluid or high-speed mixers, although in the past gravity mixers or tumble mixers were also used. The mixture is then homogenized on mixing rolls, kneaders, planetary extruders or twin-screw kneaders and further processed. 

In the case of polyolefins the dispersing performance of single-screw extruders and injection molding machines is not sufficiently to undertake high-quality coloration (fibers, film, tape) with powder pigments or pigment mixtures. 

A dramatic improvement in the performance of PMDA in chain extension of PET is possible if the PMDA is added to the extruder in a concentrate using a polycarbonate (PC) carrier [10]. The reason being that if PMDA is compounded in a PET carrier resin then a premature reaction results leading to ultra-high MW PET and gel problems. Alternatively, if PMDA is compounded in a polyolefin carrier then degradation of the polyolefin occurs whereas, when PMDA is compounded in a polycarbonate carrier there is no premature reaction because PC contains no acid end groups (rather, -OH end groups instead). Furthermore, PC is quite miscible with PET. 

Co-extruded films of polypropylene or other polyolefins and a flexible polyester are solutions for pouches for intravenous drug-delivery systems. 

The process for making lithium-ion battery separators can be broadly divided into dry - and weH processes. Both processes usually employ one or more orientation steps to impart porosity and/or increase tensile strength. The dry process involves melting a polyolefin resin, extruding it into a film, thermally... 

Harden s (27) market survey of the growth of polyolefin foams production and sales shows that 114 x 10 kg of PE was used to make PE foam in 2001. The growth rate for the next 6 years was predicted as 5-6% per year, due to recovery in the US economy and to penetration of the automotive sector. In North America, 50% of the demand was for uncrosslinked foam, 24% for crosslinked PE foams, 15% for EPP, 6% for PP foams, 3% for EVA foams and 2% for polyethylene bead (EPE) foam. As protective packaging is the largest PE foam use sector, PE foam competes with a number of other packaging materials. Substitution of bead foam products (EPP, EPE, ARCEL copolymer) by extruded non-crosslinked PE foams, produced by the metallocene process was expected on the grounds of reduced costs. Compared with EPS foams the polyolefin foams have a lower yield stress for a given density. Compared with PU foams, the upper use temperature of polyolefin foams tends to be lower. Eor both these reasons, these foams are likely to coexist. 

MELT STRENGTH ANALYSIS FOR EXTRUDED POLYOLEFIN FOAM DEVELOPMENT... 

Patent Number US 6066393 A1 20000523 POLYOLEFIN/IONOMER BLEND FOR IMPROVED PROPERTIES IN EXTRUDED FOAM PRODUCTS... 

A material, such as (a) a terpolymer of propylene, ethylene and butene-1, (b) a polyolefin composition, which includes about 31 to 39% of a copolymer of propylene and ethylene and about 58 to 72% of a terpolymer of propylene, ethylene and butene-1 or (c) a polyolefin composition, which includes about 30 to 65% of a copolymer of propylene and butene-1 and about 35 to 70% of a copolymer of propylene and ethylene, is irradiated and extruded through a die in the presence of a physical expanding agent and a cell nucleating agent to produce a structure having a density, which is at least 10 times less than the initial density of the material. The foam articles exhibit improved flexibility and low temperature toughness compared to conventional propylene polymer materials. 

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