Dart impact strength

Blending with LLDPE is used to upgrade the properties and improve the processing of conventional LDPE. For example, by adding 25% of ethylene—1-butene LLDPE resin with I2 of 0.5 to conventional LDPE resin, the dart impact strength of 75 p.m film is increased from 490 to 560 g, the puncture strength from 41 to 49 J /mm (770-920 ft-lbf/in.), and the tear strength from 43 to 63 N /mm (246—360 ppi). CompositionaHy uniform VLDPE resins are used in blends with HDPE, commodity LLDPE, and polypropylene (PP) (70,71,89). 

Tables 4—6 Ust ASTM methods used for the characterization of PB and PMP. A number of specialized methods were developed for testing particular articles manufactured from polyolefins several of these determine the performance of PB and PMP film, including the measurement of the film s dart impact strength and tear strength. Dart impact strength is measured by dropping a heavy dart with a round tip on a stretched film. Tear resistance, which reflects the film s resistance to tear propagation, is measured with the Ehnendorf tear tester. Two values for the tear strength are usually reported, one in the machine dkection of the film and the other in the transverse dkection. Pipes manufactured from PB are tested by pressurizing them internally with water the time-to-burst failure is determined at various temperatures (46). The standard test method for haze and luminous transmittance (ASTM D1003) is used for the measurement of PMP optical characteristics.

To improve the end use performance and make the processability easy, control of MW and MWD as well as the use of.more than one comonomer has been reported for LLDPE [28]. Union Carbide s high MW-LLDPE with broad MWD is a 1-hexene-based resin, and its film provides superior (about 30-50% higher) tensile strength, puncture resistance, and dart impact strength than conventional 1-hexene-based resin, but with lower tear resistance in the transverse direction. The broad MWD makes the resin processability easy on the conventional extruder. 

Figure 16 Dart impact strength of HMW-HDPE films. Source Ref. 132.

Dartanol, 24 536 Dart impact strength, 20 429 Darzens-Claisen condensation, 14 570 Darzens condensation, 10 505 DAS antibody, 14 145, 147 DAS-hemisuccinate (DAS-HMS), 14 144 DASH-Sodium Study, 22 813 Data, growth of, 21 612-613. See also Decay data... 

Figure 12.15 Effect of process conditions on the dart impact strength of an article molded in an injection molding-grade HIPS...

Table II. Kilolangley to 50% Retention of Dart Impact Strength...

Graph 30-01. Dart impact strength of various poiyoiefins and ExxonMobii Exact POP. 

Toughness Dow Primacor copolymers have rugged physical properties. Ultimate tensile strength is comparable to that of LLDPE, while dart-impact strength is substantially greater,... 

LLDPE has become a key PO for blown film, but not without some difficulties in establishing methods for maintaining bubble stability and gauge consistency. Typically, LDPE is blended with the LLDPE to inaease melt strength and bubble stability, but this can reduce tensile tear, and dart-impact strengths. Alternatively, process developers have turned their attention to a melt-strength additive (MSA) developed by DuPont Canada in the 1980s particularly for when bubble stability is a problem. 

With increasing spherulite size, the tensile yield strength and tear strength increase and the elongation and pimcture resistance deteriorate. In the case of films containing p-crystals, the dart impact strength increases with increasing p-crystal content. 

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