INDEX Acetal copolymer

The weight average molecular weight of acetal copolymers may be estimated from their melt index (MI, expressed in g/10 min) according to the relation... 

Ultrathene [Quantum], TM for a series of ethylenevinyl acetate copolymer resins for adhesives, conversion coatings, and thermoplastic modifiers. Wide range of melt indexes. Improves specific adhesion of hot-melt, solvent-based, and pressure-sensitive adhesives. 

When Celanese made its first product offerings to the plastics marketplace in 1962, it was with linear acetal copolymers, one having a 9.0 melt index (MI) for injection molding and the other having a 2.5 melt index for extrusion... 

The ethylene vinyl acetate copolymer (EVA) used in these evaluations contained 9% vinyl acetate and had a melt index of 3.2. This and the other polyolefins used were obtained from commercial sources. 

The product mix of autoclave and tubular reactors are similar in terms of LDPE homopolymers (0.910-0.935 g/cc) and some specialty grades of polyethylene such as ethylene/vinyl acetate copolymers up to about 30 wt% vinyl acetate (VA). However, the autoclave process provides higher levels of vinyl acetate (40 wt%) in ethylene/VA copolymers and additional specialty grades of polyethylene such as ethylene/methyl acrylate, ethylene/acrylic acid and ethylene/n-butyl acrylate. Polyethylene molecular weight can be varied over a wide range with the high-pressure process, with Melt Index values (I ranging from 0.15 to 40. 

In Table 2 the property changes which can be expected by a change in melt index for ethylene-vinyl acetate copolymer are listed. It is followed by Table 3 showing the effects of vinyl acetate content on polymer properties. 

Many grades of acetal resins are Hsted in Underwriters Eaboratories (UL) Kecogni d Component Directory. UL assigns temperature index ratings indicating expected continuous-use retention of mechanical and electrical properties. UL also classifies materials on the basis of flammability characteristics homopolymer and copolymer are both classified 94HB. 

Filler-polymer interactions have also been observed in EVA copolymer yielding differences in fire retarding effectiveness between ATH and MH.42 In EVA with 30% vinyl acetate content, magnesium hydroxide had an oxygen index of 46%, whereas aluminum hydroxide gave a value of... 

Talc particles of different lamellarity and specific surface area have been incorporated into polyethylene vinyl acetate (EVA) copolymer/magnesium hydroxide (MH) composite system.63 The fire retardancy of this system has been studied and compared with formulations containing only EVA and MH and formulations containing EVA, MH, and organomodified montmorillonites (oMMT). It was observed that talc with higher lamellar index showed fire behavior similar to that of EVA/MH/ oMMT system with some intumescence. 

Ethylene-copolymer melts generally have a vinyl acetate proportion of approx. 5 to 35% by weight, equivalent to a melt index of Ml216/i9o°c=2 to 500 g/10 min. The melt temperatures in the low-pressure trap range from 160 to 200 °C, depending on the viscosity of the melt. Depending on the polymerization and on the pressure in the low-pressure trap, the melt contains free vinyl acetate (approx. 4000 ppm) in addition to the known ethylene content of... 

The Step 1 product (8 g) was dissolved in 50 ml of benzene and then treated with 2,2 -azobisisobutyronitrile (14.6 mg) and 13.8 g of vinyl acetate and heated to 60°C for 72 hours. The mixture was cooled, and the polymer was precipitated in heptane. After drying the block copolymer was isolated in 47.8% yield having aM of21,500 daltons and a polydispersity index of 1.6. 

The set of concentration differences form the basis for the error index calculation. The values for both peak height and peak area amount to around 2%. This value is quite acceptable considering that the concentration ratios used to develop the calibration parameters were based on the nominal values for the vinyl acetate concentrations in the commercial products obtained from the supplier. The vinyl acetate/vinyl chloride copolymers used in the analysis were stated to contain... 

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