Strength notched impact

Development of toughened acetals has recendy dourished. One such grade, Delrin lOOST, boasts a notched-impact strength of 900 J/m (16.86 ft-lb/in.) at 23°C, substantially higher than that of nonmodified, general purpose grades (Table 2). 

Charpy notched impact strengths in excess of 55 kJ/m have been reported for alloys with homopolymers and in excess of 20kJ/m for copolymers. 

Melt Index ASTM D.1238 (300 C) g/10 min Notched impact strength ASTM D.256 hod ftlbfin jin Recommended processing method... 

Polycarbonates with superior notched impact strength, made by reacting bisphenol A, bis-phenol S and phosgene, were introduced in 1980 (Merlon T). These copolymers have a better impact strength at low temperatures than conventional polycarbonate, with little or no sacrifice in transparency. These co-carbonate polymers are also less notch sensitive and, unlike for the standard bis-phenol A polymer, the notched impact strength is almost independent of specimen thickness. Impact resistance increases with increase in the bis-phenol S component in the polymer feed. Whilst tensile and flexural properties are similar to those of the bis-phenol A polycarbonate, the polyco-carbonates have a slightly lower deflection temperature under load of about 126°C at 1.81 MPa loading. 

Several blends based on polysulphone materials have been marketed. Probably the most well known is Mindel, originally produced by Uniroyal, acquired by Union Carbide, but now marketed by Amoco. Whilst not exhibiting the heat resistance of the unblended homopolymer, Mindel materials, which are blends of polysulphone and ABS, are lower in cost, easier to process and have higher notched impact strengths. The Mindel A materials are unreinforced, the Mindel B grades contain glass fibre, and the Mindel M grades contain other mineral fillers. A related polysulphone/SAN blend has been marked as Ucardel. 

As with poly(ethylene terephthalate) PBT-based copolymers have been introduced to overcome some of the deficiencies of the homopolymer. For example, the rather low notched impact strength of unreinforced grades has been overcome by partial replacement of the terephthalic acid with a longer chain aliphatic dicarboxylic acid. Improved toughness has also been obtained by grafting about 5% of ethylene and vinyl acetate onto the polyester backbone. 

Table 6 Effect of Cure Inhibitor Concentration on the Charpy Notched Impact Strength (ak) at O C...

It was found that PP-EPDM blends [30] with a slow curing EPDM have a high-impact strength. Effect of tet-ramethyl thiuram disfulfide (TMTD) concentration on the Charpy notched impact strength of PP-EPDM blend is given in Table 8. 

Figure 7 Notched impact strength vs. interparticle distance for PBT-maleic anhydride grafted EOR blends. Source Ref. 58.

The forgings were evaluated by density, microstructure, surface finish, tensile strength, notched impact strength, ductility, and fatigue strength measurements... 

Broutman and McGarry [98] examined the effects of crosslinking on toughness as early as 1965. Bell [99] observed a threefold increase in notched impact strength as the molecular mass between crosslinks was increased. Schmid et al. [100] and Lohse et al. [101] pointed out the dominating effect of molecular strand length on the ultimate properties and the toughness of crosslinked polymers. Later, Batzer et al. [46], Schmid [44], and Fischer et al. [45] compared the behavior of various networks composed of epoxy resins. 

Figure 14.17 Relationship between notched impact strength of PET compounds and their moisture content. The plot emphasizes the need for proper drying of PET resin to reduce the moisture content to below 200 ppm before melt processing. Intensive drying procedures are time-consuming and costly and therefore internal desiccants are often used...

The notched Izod impact strength of PET at room temperature is only 45 J/m. Supertough PET with notched impact strengths up to 1000 J/m can be prepared by melt blending PET with 20wt% of a reactive elastomeric terpolymer (e.g. E-MA-GMA). Pecorini and Calvert [28] have attributed this supertoughness phenomenon to two distinct toughening mechanisms, as follows ... 

Tensile properties and flexural modulus were determined on 20 mil pressed films in accordance with ASTM D882 and D790, respectively. Izod (notched) impact strength was determined on compression molded plaques in accordance with ASTM D256. Water vapor transmission was determined on 5 mil pressed films in accordance with ASTM E96. 

There is no true correlation between the two methods as we can see in Figure 3.5, which displays the notched versus un-notched impact strength of various grades of polycarbonates, acrylics, polyphenylene sulfide and nylon. 

Notched impact strength ASTM D256 (J/m) No break 20-220 54-NB... 

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