Melt strength test

Thermoformability is a property required by the many sheet materials used in the thermoforming industry. These properties are unique for the specific forming methods used, and are best determined by actual thermoforming tests on smaU-scale equipment. The softening or drape temperature of the material, residual stress in the sheet from its manufacture, and its melt strength and viscosity are important parameters relating to this use. 

Extensional Viscosity. AH three types of extensional viscosity can be measured (101,103) uniaxial, biaxial, and pure shear. Only a few commercial instmments are available, however, and most measurements are made with improvised equipment. Extensional viscosity of polymer melts can be estimated from converging flow (entrance pressure) or from a melt strength drawdown test (208). 

TDI isomers, 210 Tear strength tests, 242-243 TEDA. See Triethylene diamine (TEDA) Telechelic oligomers, 456, 457 copolymerization of, 453-454 Telechelics, from polybutadiene, 456-459 TEM technique, 163-164 Temperature, polyamide shear modulus and, 138. See also /3-transition temperature (7)>) Brill temperature Deblocking temperatures //-transition temperature (Ty) Glass transition temperature (7) ) Heat deflection temperature (HDT) Heat distortion temperature (HDT) High-temperature entries Low-temperature entries Melting temperature (Fm) Modulu s - temperature relationship Thermal entries Tensile strength, 3, 242 TEOS. See Tetraethoxysilane (TEOS)... 

A rapid method for determining the melt strength has been developed by Busse (1967). He extruded a polymer melt through a standard orifice at a given temperature and a standard rate. The thread obtained was taken up on a pulley with variable speed. During a test the take-up speed was gradually increased until the thread broke, while the tension was recorded as a function of time. 

Typically, it is desirable for a polymer to have a certain level of melt strength so that it processes well in these types of fabrication operations. Ideally, one would like to characterize the melt strength of a resin using a test method that best captures the type of deformation experienced by a polymer in a commercial fabrication operation. Owing to the complex flows associated with such operations, the approach that is most commonly used is to characterize the melt strength of a polymer in a uniform flow field and then infer from this information its performance in a real fabrication operation. 

The melt index test measures the rate of extrusion of a thermoplastic material through an orifice of specific length and diameter under prescribed conditions of temperature and pressure. This test is primarily used as a means of measuring the uniformity of the flow rate of the material. In this study, the melt flow index (MFI) value increased from 1.35 to 1.69 g/10 min with increase in EMA content from 0 to 10% in the PMMA/EMA blends (Table 5.3). This may be due to the reduction in cohesive strength as well as the plasticizing effect of EMA in PMMA/EMA blends. However, further addition of EMA content above 10% by weight shows no more increase in MFI. 

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