Polyolefins polyethylene injection molding

Pigment Red 242 is used in a broad variety of plastics and fiber appHcations, where it provides scarlet coloration with excellent fastness properties. Warping, however, makes it unsuitable for high density polyethylene injection molding. It finds application in inks and to some extent in industrial paints. The relatively new Pigment Red 262 is recommended mainly for rigid PVC, polyolefins, and fibers, where it affords a strong bluish red. 

The use of TAG as a curing agent continues to grow for polyolefins and olefin copolymer plastics and mbbers. Examples include polyethylene (109), chlorosulfonated polyethylene (110), polypropylene (111), ethylene—vinyl acetate (112), ethylene—propylene copolymer (113), acrylonitrile copolymers (114), and methylstyrene polymers (115). In ethylene—propylene copolymer mbber compositions. TAG has been used for injection molding of fenders (116). Unsaturated elastomers, such as EPDM, cross link with TAG by hydrogen abstraction and addition to double bonds in the presence of peroxyketal catalysts (117) (see Elastol rs, synthetic). 

Polyolefins (Polyethylene, Polypropylene) Powder, pellets Tough and chemical resistant. Weak in creep and thermal resistance. Polyethylene maximum use temperature 210 F, polypropylene 260 F. May be injection and extrusion molded, vacuum formed. Low cost. Antistatic sheet and tiles, heat-shrinkable tubing, deicer boots. 

More than 0.3% pigment is required to formulate 1/3 SD HDPE samples. P.Gr.36 is thus much weaker than P.Gr.7 types, although it withstands more than 300°C and is thus equally heat stable. Considerable influence on the shrinkage of injection-molded polyethylene parts necessitates some caution in using P.Gr.36 for this purpose. Many types are difficult to disperse in plastics, especially in polyolefins. 

Substitute for Conventional Vulcanized Rubbers, For this application, the products are processed by techniques and equipment developed for conventional thermoplastics, ie, injection molding, extrusion, etc. The S—B—S and S—EB—S polymers are preferred (small amounts of S—EP—S are also used). To obtain a satisfactory balance of properties, they must be compounded with oils, fillers, or other polymers compounding reduces costs. Compounding ingredients and their effects on properties are given in Table 8. Oils with high aromatic content should be avoided because they plasticize the polystyrene domains. Polystyrene is often used as an ingredient in S—B—S-based compounds it makes the products harder and improves their processibility. In S—EB—S-based compounds, crystalline polyolefins such as polypropylene and polyethylene are preferred. Some work has been reported on blends of liquid polysiloxanes with S—EB—S block copolymers. The products are primarily intended for medical and pharmaceutical-type applications and hardnesses as low as 5 on the Shore A scale have been reported (53). 

Polyolefins. Low density polyethylene and polypropylene have been developed as sheet and hollow fiber mlcroporous membranes, respectively, for use In plasmapheresis. Polyethylene Is made porous by stretching the annealed film ( ), while polypropylene la made porous by coextruding hollow fibers with a leachable plasticizer. Neither membrane has been prepared with small pore dimensions suitable for protein rejection. These polyolefin membranes are characterized by good chemical stability, but require special surfactant treatments to make them wettable. Their low deformation temperature precludes the use of steam sterilization. Because they are extruded without the usual antl-oxldants and stabilizers, their stability la lower than Injection molding formulations of the same polymer. 

Polyolefin - Polyolefins are a large class of carbon-chain elastomeric and thermoplastic polymers usually prepared by addition (co)polymerization of olefins or alkenes such as ethylene. The most important representatives of this class are polyethylene and polypropylene. There are branched and linear polyolefins and some contain polar pendant groups or are halogenated. Unmodified polyolefins are characterized by relatively low thermal stability and a nonporous, nonpolar surface with poor adhesive properties. Processed by extrusion, injection molding, blow molding, and rotational molding. Other thermoplastic processes are used less frequently. This class of plastics is used more and has more applications than any other. Also called olefinic resin, olefinic plastic. 

Specifically, PVC blends with polyethylene, polypropylene, or polystyrene could offer significant potential. PVC offers rigidity combined with flammability resistance. In essence, PVC offers the promise to be the lowest cost method to flame retard these polymers. The processing temperatures for the polyolefins and polystyrene are within the critical range for PVC. In fact, addition of the polyolefins to PVC should enhance its ability to be extruded and injected molded. PVC has been utilized in blends with functional styrenics (ABS and styrene-maleic anhydride co-and terpolymers) as well as PMMA offering the key advantage of improved flame resistance. Reactive extrusion concepts applied to PVC blends with polyolefins and polystyrene appear to be a facile method for compatibilization should the proper chemical modifications be found. He et al. [1997] noted the use of solid-state chlorinated polyethylene as a compatibilizer for PVC/LLDPE blends with a significant improvement in mechanical properties. A recent treatise [Datta and Lohse,... 

A variety of foams can be produced from various types of polyethylenes and cross-linked systems having a very wide range of physical properties, and foams can be tailor-made to a specific application. Polypropylene has a higher thermostability than polyethylene. The production volume of polyolefin foams is not as high as that of polystyrene, polyurethane, or PVC foams. This is due to the higher cost of production and some technical difficulties in the production of polyolefin foams. The structural foam injection molding process, described previously for polystyrene, is also used for polyethylene and polypropylene structural foams (see Figure 2.61). 

Polyethylene Terephthalate. Crystallization is difficult and slow. Particularly for injection molding, 0.5 percent of 3- im metal oxide, metal salt, pigment, or other minerals, and ionomer are mentioned. For thermo formed food trays, 1 to 3 percent of low-MW polyolefin. 

Cao J, Gao X, Shen K (2012) Morphologies and mechanical properties of high-density polyethylene induced by the addition of small amounts of both low- and high-molecular-weight polyolefin under shear stress applied by dynamic packing injection molding. J Macromol Sci Part B 51 2519-2526... 

Reports of lubricants for polyolefins are rare in the technical literature [30,31]. For polyolefins Farbwerke Hoechst AG recommends the use of Wachs PA 520, which improves rheological properties of the melt bulk polymer and the brilliance of the surface of finished products without affecting mechanical properties. Furthermore, it reduces the danger of stress corrosion in thick wall pieces produced by injection molding. It is also suitable for regulating the melt index. Polyethylene (PE), with a molecular weight of 2000, is also recommended as a lubricant for polyolefins by Bareco (Petrolite Corp.). 

---