Dart impact

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 12 Dart impact (ASTM.D1709) of different copolymers (at constant MW). Source Ref. 31.

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 demonstrates an opposite effect for dart impact properties. Here, the impact is normal to the orientation in parallel and perpendicular directions, allowing the impact point to be the crack initiator. The less orientation in the article thus provides greater impact strength. 

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