Melt strength enhancers

Polycondensation polymers such as PET are chai acterized by low melt viscosities and low melt sttengdis. Eurthermore, widi PET there is a marked shear liquefaction 

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Melt strength enhancement of PET and PBT for the production of blown polyester foams... 

As a melt viscosity and melt-strength-enhancing additive for modifying PET for film blowing and extrusion blow moulding applications... 

Blends of PC, ABS, and MMBS are useful to form articles with good impact and low gloss. The articles produced are useful as automotive components, bottles, and tool housings. A mixture of randomly branched carbonate polymers and linear carbonate polymers has been suggested (19). MMBS acts also as a melt strength enhancing agent. 

Applications automotive parts, agricultural film, bags, bottles, cast film, cling film, closures, diaper backsheet, drum liners, film, greenhouse film, hoses, lids, melt strength enhancer (Booster) overwrap film, parts of Industrial containers, playground equipment, point of display cabinets, potable water tanks, toys, trash cans, tubing ... 

Figure 5. Melt Strength enhancement of OBC by blending with LDPE... 

PBT-PC blends show increased melt strength allowing them to be easily processed by blow molding and profile extrusion. The PBT-PC blends have been extruded into sheet and thermoformed into parts. Enhanced melt strength allows PBT-PC blends to be foamed. Structural foam grades for injection molding (10-30% density reduction) are commercially available. 

Chlorinated polyethylene was evaluated as a compatibiliser forpoly(vinyl chloride) composites containing 25% or 40% wood flour. The compositions also contained lubricants, a stabiliser and a processing aid. Following blending, the composites were characterised by rheology studies and measurements of melt strength. The addition of chlorinated polyethylene significantly enhanced the processability of... 

Blends of immiscible polymers exhibit a coarse and unstable phase morphology with poor interfacial adhesion. The ultimate properties of these blends are often poorer than those of either component. The poor mechanical properties can be improved with a small amount of an interfacial agent that lowers interfacial tension in the melt and enhances interfacial adhesion in the solid. High-strain properties, such as strength, tensile elongation, and impact strength, especially benefit from compatibilization (I, 2). 

The new metallocene catalysis leads to isomer purity in excess of 96%. It is also possible to produce branched, high melt strength PP, with extensional stress hardening, similar to that of LDPE [Phillips et al., 1992]. The new PP s show the melting point, T = 120-164°C. To enhance the performance, PP is usually blended (in the reactor or outside the reactor) with much more viscous PP-copolymers. As a consequence, one of the most serious industrial problem is homogenization of these materials [Luciani and Utracki, 1996 Utracki andLuciani, 1996]. 

From the three basic categories of polypropylene, namely, homopolymers, heterophasic copolymers, and random copolymers (with ethylene), there are specialty resins with enhanced capabilities for specific applications. Producers of large blow-molded or thermoformed parts can thus utilize grades with high melt strength to fabricate heat-resistant under-the-hood automotive parts. 

Properties of CPE are related to the content of chlorine. Traditionally, CPE containing 36% chlorine was used (and it is still used today) because of its better elasticity and less compatibility with PVC. More recently, CPE containing 25% chlorine is used because it promotes faster fusion and enhances the melt strength of the formulation. Faster fusion permits the partial or complete elimination of oxidized polyethylene, which is frequently used as fusion promoter. CPE has similar vulnerabilities to PVC, therefore regular PVC thermal stabilizers also stabilize CPE without a need to include special stabilizers. " ... 

Addition of impact modifier also frequently affects other properties than impact strength. It was already reported that filler intake can be increased and the rate of flow is increased. Addition of impact modifier lowers flame resistance of PVC (with the exception of when CPE is used) because impact modifiers are more flammable than PVC. Impact modifiers aid in dispersion of additives, modify the elasticity of melt, and enhance the processing window.Some impact modifiers help to improve the surface of calendered film and preserve the shape of molded and extruded products. At the same time, impact modifiers may increase die swell (e.g., Metablen P). 

Using CPE-25 opens new possibilities not available with CPE-36. It gives faster fusion and enhanced melt strength without reduction of impact strength and weathering performance. 

It was mentioned that the incorporation of nanoclay had only a minor effect on melt strength however it increased the tensile modulus. On the other hand, Cole-Cole plot of the melts showed that the chain extender can promote the development of chain branching by time. The use of an epoxy based multifunctional chain extender resulted in significant enhancement of the melt strength and processability of the blends even at 30 wt% PBSA (Fig. 7.39b). These blends also exhibited interesting mechanical properties (Eslami and Kamal 2013a). 

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