Polyethylene blowing agents

Polyethylene. This is essentially a closed-ceU insulation manufactured at 448 2 K by an extmsion process. A blowing agent and nucleating agent are employed to control the ceU size, and primary use is in insulating pipelines for hot and chilled water lines, air conditioning, and processing systems. 

Blowing agents for producing foam mbber, polyethylene, and vinyl chloride are made from chloroformates, hydra2ine, and a base. Eor example. 

Products with very low dielectric constant (about 1.45) can be obtained by the use of cellular polymers. Blowing agents such as 4,4 -oxybisbenzenesulphono-hydrazide and azocarbonamide are incorporated into the polymer. On extmsion the blowing agent decomposes with the evolution of gas and gives rise to a cellular extrudate. Cellular polyethylene is a useful dielectric in communication cables. 

Eoams were extruded from low density polyethylene (LDPE) and blends of LDPE with syndiotactic polypropylene (sPP), using isobutane as the blowing agent. The extruded materials were characterised by measurement of dimensional stability at room temperature, density, tensile properties, dynamic stiffness, and crystallinity determined by differential scanning calorimetry. The sPP, with a slow crystallisation rate, did not interfere with the expansion of the LDPE, and enhanced the temperature resistance by in-situ crystallisation. The blends were flexible, dimensionally... 

A chemical blowing agent was well dispersed in a linear low density polyethylene matrix, in pellet form. The pellets were rotationally moulded to produce foams, the morphology of the foams being studied using optical microscopy. The quality of the cell structures in terms of cell size, cell population density and volume expansion ratio was superior to that of foams produced by drying blending. 28 refs. 

Ba azide has not been used as an expl, bur it has been used in the manuf of fluorescent lamps and radio tubes (Ref 12a 19)- It has also found use as a blowing agent during the vulcanization of cellular rubber (Ref 22). The expl reaction of Ba azide is prevented by adding gelatin, machine oil or Neugen (polyethylene glycol laurate)... 

Cross-linked polyethylene foams are produced by eilher radiation or chemical cross-linking of an extruded expandable sheet containing a chemical blowing agent. These products have finer texture and a softer, more resilient feel than extruded low density polyethylene foams and are used in comfort cushioning and cushion packaging applicutinns. 

OBSH A blowing agent for chloroprene rubber, polyethylene resin or polyvinyl chloride resin. 

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