Tear resistance

Tear resistance of plastic film or sheeting is a complex function of its ultimate resistance to rupture. Basically, very low rate of loading—51 mm (2 in.)/min—is employed and is designed to measure the force to initiate tearing. The maximum stress or force (that is generally found near the onset of tearing) required to tear the specimen is recorded as the tear resistance value in newtons (or pounds-force) [41,42]. 

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Tear Resistance. The resistance of an elastomer to tearing is affected by the particle size and shape of the filler it contains. Tear resistance generally increases with decreasing particle size and increasing sphericity of fillers. 

The clean, durable, nondust-forrning character of polyethylene foam has led to its acceptance in packaging missile parts (230). Polyethylene foam sheet has also displaced polystyrene foam sheet for packaging glass bottles and containers because of its greater resUiency and tear resistance. 

Even though separation may not be the primary function for which the geotextde is instaded, in almost every case the geotextde does perform as a separator. For the separation function, the physical properties of concern are primarily strength-related, including wide width, puncture resistance, and tear resistance. 

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.

The even-numbered carbon alpha olefins (a-olefins) from through C q are especially useful. For example, the C, C, and Cg olefins impart tear resistance and other desirable properties to linear low and high density polyethylene the C, Cg, and C q compounds offer special properties to plasticizers used in flexible poly(vinyl chloride). Linear C q olefins and others provide premium value synthetic lubricants linear 145 olefins are used in... 

Nonwood fibers are used in relatively small volumes. Examples of nonwood pulps and products include cotton Enters for writing paper and filters, bagasse for cormgated media, esparto for filter paper, or Manila hemp for tea bags. Synthetic pulps which are based on such materials as glass (qv) and polyolefins also are used (see Olefin polymers). These pulps are relatively expensive and usually are used in blends with wood pulps where they contribute a property such as tear resistance, stiffness, or wet strength which is needed to meet a specific product requirement. 

Silica. The main uses of siUca are in the treads of off-the-road tines for improved chunking and tear resistance and as a component of the bonding system for brass and 2inc-plated steel cord. These are commonly used in radial passenger and tmck tire belt skim stock. In addition the body pHes of steel radial tmck tires, hoses and belts, and footwear use significant volumes of siUca as a reinforcing filler. 

There is a definite trend in the suppHer industry to develop multifimctional materials with value-added properties. One suppHer has introduced a modified hydrocarbon resin that softens, improves filler incorporation, improves mill banding, and increases tack in the green compound while imparting increased low strain (<100%) stiffness, significantly improving tear resistance in the vulcanized compound. 

For both the tongue and Elmendorf test methods, it is important to observe the behavior of the specimen as the tear is propagated. In cases where the yams in the test direction are much stronger than the perpendicular yams, it is sometimes difficult or impossible to propagate the tear in the desired direction. In this case, a crosswise tear results. Tear resistance is primarily a function of fabric constmction. Loose, open weaves such as cheesecloth tend to resist tear, whereas tight weaves tend to tear easily. In the open weave, the concentrated force field at the point of tear is dissipated by the compliance of the fabric stmcture to accommodate the stress field, thereby distributing the force over a greater number of yams. 

Testing. Various test methods are provided by ASTM (16). These iaclude pigment tests of importance such as chemical analysis, presence of oversize particles, oil absorption, particle size distribution, degree of dispersion, presence of soluble components, etc. Numerous tests are also given by ASTM for the properties of filled and unfilled polymers. These iaclude, for example, such properties as impact resistance, stiffness, viscosity, tear resistance, hardness, color, and electrical resistivity. 

Tear resistance Excellent Fair Excellent Good Fair to Good Fair Poor Fair... 

This lower has a number of ramifications on the properties of polybutadiene. For example, at room temperature polybutadiene compounds generally have a higher resilience than similar natural rubber compounds. In turn this means that the polybutadiene rubbers have a lower heat build-up and this is important in tyre applications. On the other hand, these rubbers have poor tear resistance, poor tack and poor tensile strength. For this reason, the polybutadiene rubbers are seldom used on their own but more commonly in conjunction with other materials. For example, they are blended with natural rubber in the manufacture of truck tyres and, widely, with SBR in the manufacture of passenger car tyres. The rubbers are also widely used in the manufacture of high-impact polystyrene. 

Thermoplastic polyurethane elastomers have now been available for many years (and were described in the first edition of this book). The adipate polyester-based materials have outstanding abrasion and tear resistance as well as very good resistance to oils and oxidative degradation. The polyether-based materials are more noted for their resistance to hydrolysis and fungal attack. Rather specialised polymers based on polycaprolactone (Section 25.11) may be considered as premium grade materials with good all round properties. 

General advice on the suitability and degree of resistance of glove materials are summarized in Table 13.12. In all cases, however, in addition to the necessary mechanical properties (i.e. resistance to abrasion, blade cut resistance, tear resistance and puncture resistance rated according to European Standard EN 388), consideration should be given to the resistance to the specific chemicals involved. 

Polymer chains with sulphur atoms, improving breakdown of polychloroprene during mastication, increasing tear resistance and dynamic behaviour. 

One-step vulcanization, wide range of curing conditions, high loading elasticity, snappiness, no deformation, weatherability. ozone resistance, heat resistance, tear resistance, coating performance, adhesive properties, skid resistance, abrasion resistance... 

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. 

Both tear resistance and hysteresis increase on incorporation of silica, but the effect is less pronounced as compared to the stress-strain properties. Tension set of the ZnO-neutralized m-EPDM system is low (around 20%) and incorporation of filler causes only a marginal increase in set due to chain slippage over the filler surface, as previously discussed. Measurement of physical properties reveal that there occurs an interaction between the filler surface and the polymer. Results of dynamic mechanical studies, subsequently discussed, support the conclusions derived from other physical properties. 

There are other types of impact tests for shock loading where energy is required to cause complete failure is reported. Each has their specific behaviors that can be related to specific product performance requirements. Tests include ball burst, ball or falling dart using different weights and heights, bag drop, bullet-type instantaneous impact, Charpy, dart drop, Mullen burst, tear resistance, and tub (2). 

Urethane Liquid Exceptional abrasion, cut, and tear resistance. Poor moisture and heat resistance. Variety of formulations leading to different properties including range of durometers without plasticizers. Antistatic rollers and tires, hose for transfer of flammables, strain gages, pressure transducers. 

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