Retardant blend polyethylene

A manufacturer considering using a thermoplastic elastomer would probably first consider one of the thermoplastic polyolefin rubbers or TPOs, since these tend to have the lowest raw polymer price. These are mainly based on blends of polypropylene and an ethylene-propylene rubber (either EPM or EPDM) although some of the polypropylene may be replaeed by polyethylene. A wide range of blends are possible which may also contain some filler, oil and flame retardant in addition to the polymers. The blends are usually subject to dynamic vulcanisation as described in Section 11.9.1. 

Phosphorus -bromine flame retardant synergy was demonstrated in a 2/1 polycarbonate/polyethylene blend. These data also show phosphorus to be about ten times more effective than bromine in this blend. Brominated phosphates, where both bromine and phosphorus are in the same molecule, were also studied. In at least one case, synergy is further enhanced when both phosphorus and bromine are in the same molecule as compared with a physical blend of a phosphorus and a bromine compound. On a weight basis, phosphorus and bromine in the same molecule are perhaps the most efficient flame retardant combination. The effect of adding an impact modifier was also shown. 

Convincing evidence for phosphorus/bromine synergy has now been found in a 2/1 polycarbonate/polyethylene terephthalate blend. Phosphorus and bromine blends were studied as well as compounds which have both elements in the same compound. The relative flame retardant efficiencies of phosphorus and bromine are also reported. 

A 2/1 blend of polycarbonate and polyethylene terephthalate (PC/PET) was flame retarded with bromine, phosphorus, a blend of bromine and phosphorus, and compounds containing both phosphorus and bromine in the same molecule. All compositions contained 0.5 % Teflon 6C as a drip inhibitor and where specified 5 % of an impact modifier. 

We previously reported that brominated aromatic phosphate esters are highly effective flame retardants for polymers containing oxygen such as polycarbonates and polyesters (9). Data were reported for use of this phosphate ester in polycarbonates, polyesters and blends. In some polymer systems, antimony oxide or sodium antimonate could be deleted. This paper is a continuation of that work and expands into polycarbonate alloys with polybutylene terephthalate (PBT), polyethylene terephthalate (PET) and acrylonitrile-butadiene-styrene (ABS). 

Qu, B. and Xie, R. 2003. Intumescent char structures and flame-retardant mechanism of expandable graphite-based halogen-free flame-retardant linear low density polyethylene blends. Polymer International 52(9) 1415-1422. 

The most important commercial blends of BPA-PC are poly(acrylonitrile-butadiene-styrene) (PC/ABS) and polybutylene terephthalate (PC/PBT) or polyethylene terephthalate (PET). Commercial grades of PC/ABS include CYCOLOY (GE), Bayblend (Bayer), and PULSE (Dow). PC/ABS blends exhibit improved flow and processability and enhanced low-temperature impact strength in comparison to PC (Fig. 3). These blends are widely used in applications requiring enhanced impact resistance, such as interior automotive parts and computer and electronics applications such as computer housings and cell phones. Non-halogenated flame-retardant PC/ABS blends are widely available. Poly(acrylic-styrene-acrylonitrile) (PC/ ASA) blends (GELOY , GE Luran , BASF) provide improved weatherability for outdoor applications such as exterior automotive parts, but exhibit reduced impact performance at low temperatures in comparison to PC/ABS. PC/PBT or PET blends (XENOY , GE Makroblend , Bayer) provide enhanced chemical resistance and weatherability for applications such as lawn and garden equipment and automotive bumpers and fasdas. 

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,... 

This chapter covers fundamental and applied research on polyester/clay nanocomposites (Section 31.2), which includes polyethylene terephthalate (PET), blends of PET and poly(ethylene 2,6-naphthalene dicarboxy-late) (PEN), and unsaturated polyester resins. Section 31.3 deals with polyethylene (PE) and polypropylene (PP)-montmorillonite (MMT) nanocomposites, including blends of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and high density polyethylene (HDPE). Section 31.4 analyzes the fire-retardant properties of nanocomposites made of high impact polystyrene (HIPS), layered clays, and nonhalogenated additives. Section 31.5 discusses the conductive properties of blends of PET/PMMA (poly (methyl methacrylate)) and PET/HDPE combined with several types of carbon... 

Fire retardants used in polystyrene (PS) include montmorillonite clay, polytetrafluoro-ethylene (PTFE) [8], bromine-based flame retardants such as brominated bisphenol A [9], brominated phenyl oxide or tetrabromophthalic anhydride, or magnesium hydroxide [10,11]. Sanchez-Olivares and co-workers [12], in their study of the effect of montmorillonite clay on the burning rate of PS and PS-polyethylene terephthalate blends, showed that increased combustion rate accompanied the incorporation of montmorillonite particles in high-impact polystyrene (FlIPS) formulations. 

Stackman [29] carried out a study to find systems suitable for reducing the flammability of polyethylene terephthalate (PET) and poly-1,4-butylene terephthalate (PBT) while retaining the chemical and physical properties of the original polymers. The additives used were phosphine oxides, phosphonates and phosphates and their activity was assessed by means of an oxygen index test. Most of the phosphorus esters were found to be volatile under the blending conditions and both the halogenated phosphorus esters and halogenated derivatives of phosphorus oxide proved to be ineffective as flame retardants. 

The effects of an organoclay and alumina trihydrate (ATH) and/or magnesium dihydroxide (MDH) on the fire retardancy of a ethylene-vinyl acetate (EVA) and low-density polyethylene (LDPE) blend were assessed by TGA and the cone calorimeter (Zhang et al. 2009). 

Another type of TPU/Polefinic blend that has been evaluated is the chlorinated polyethylene (CPE)/TPU blend, which is limited to TPUs that have low thermal processing temperature (<200°C) because of the thermal instability of CPE. The use of small amounts of CPE improve processing and mold release properties of TPU while small amounts of TPU in CPE result in good strength properties and processing characteristics [53], These blends can be used in applications where fire-retardant characteristics and/or low temperature flexibility of the materials are required. 

The significant advantages of products produced from chlorinated polyethylene are their improved resistance to chemical extraction, plasticizer volatility, and weathering. Products made from chlorinated polyethylene do not fog at higher use temperatures and can be made completely flame retardant. They do, however, exhibit chemical instability similar to that of polyvinyl chloride (PVC). They may be used as primary compounding materials or as blending resins with PVC, high- and low-density polyethylene, and other polymers. They are cross-linkable by irradiation or chemical means. 

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