Embrittlement times

Table 3 UV-Embrittlement Times (EMT) of PP and LDPE Films Containing Different Concentrations of Antioxidants (processed in an internal mixer at 190°C and 150°C, respectively, and exposed to UV light in an accelerated sunlamp-blacklamp UV aging cabinet)...

To extend this model to the prediction of embrittlement time, one needs first to identify the causal chain leading to embrittlement, second to express mathematical relationships corresponding to the elementary links of the chain, and third to define pertinent end life criteria. According to previous studies (2,3,4), two causal chains are possible in the case under study (Figure 1). 

Table 3 Comparison of embrittlement times during photo-oxidation with catalyst residues for polypropylene samples ...

Figures Variation in (1) relative initial intensity of Sanduvor NPU (at 265 run) (2) embrittlement time of polypropylene films containing 0.1% Sanduwr NPU (3) initial hydroperoxide concentration of the same polypropylene films, with heating time...

Foams are expected to be slower than films owing to thickness and opacity. The UV-degradable formulations listed here are not necessarily those which are to be used in commercial products. In addition, comparison of embrittlement times is not intended to relate to the relative merits of the various materials. ... 

Degradable Polystyrenes. The Ecolyte "Fast" polystyrene foam has a higher concentration of photosensitive vinyl ketone comonomer than the Ecolyte "Slow" foam and as a result has a shorter irradiation time to embrittlement as listed in Table I. The "Fast" foam was brittle after one month outdoor exposure or 275 hr xenon arc irradiation. The outdoor exposure was facilitated by wind and rain erosion. Turning the sample over after 35 hr xenon irradiation lowered the embrittlement time to a remarkably short period of 70 hr considering the thickness and opacity of the foam. Similarly the "Slow" foam had its xenon embrittlement time reduced from 21+00 hr to only 600 hr by turning the foam over after each 2l+ hr irradiation period. To obtain a better idea of the rate of... 

Embrittlement Times of HlRh-Denslty Polyethylene Films Treatments ... 

Degradable Low-Density Polyethylene (LDPE) Films. Typical xenon arc embrittlement times for unstabilized low-density polyethylene are l600-2UOO hrs. The controls chosen for this research are listed in Table II the thin LDPE garment bag embrittled in 1820 hr and the EcoPlastics LDPE control became brittle after 2075 hr xenon irradiation. The thin garment bag was not brittle, as determined by a fold test, after 18 months outdoor exposure. The Dupont "Sclair" LDPE control listed in Table II was unusual since it had short embrittlement times of 1175 hr in the Weather-Ometer and 6.5 months outdoors. This film was used as a yardstick to measure the Degradable LDPE films since a Degradable Plastic should not last more than 6 months, perhaps less, outdoors and 1200 hr in the xenon arc Weather-Ometer. 

In a second experiment the functional lifetime of the Degradable LDPE Plastics was examined. The functional lifetime was defined as the xenon arc irradiation time required to reduce the percent elongation at break by 9/10. These values listed in Table II are determined from the elongation as a function of irradiation time curves in Figs. 2 and 3. The order of increasing time by which films reach 10% of their original elongation is quite similar to the order of embrittlement times. Thus, the former can be used as a convenient indicator of relative susceptibility to brittleness. 

It is a fact that actinic deterioration of Degradable Plastic films will, in due course, lead to the crumbling of them into fine particles. Such disintegration obviates the plastics litter problem and provides the possibility of a solution to the agricultural plastics residue situation. There is evidence in this paper and elsewhere ( ) that there are commercially viable formulations with which packaging (and related) plastics can be made to have controlled, short embrittlement times outdoors but no indoor stability problems. 

PP. Embrittlement times always change most rapidly in mildly oxidised polymers containing little or no carbonyl. This finding is consistant with the observation that added long chain dialkyl ketones are not sensitisers for polypropylene photo-oxidation (30) although aromatic ketones are (22, 30). 

Figure 3, Relationship between carbonyl content and embrittlement time of...

Table 2 Effect of different metal dithiolates on the photostability (embrittlement time, EMT) of PP processed at 190°C (For structures, see Table 1)...

Stabilizer system Concentration (xl0 M100g i) Photo-embrittlement time (hr) References... 

Ec the embrittlement time of control, Ei the embrittlement time of antioxidant 1, and E2 the embrittlement time of antioxidant 2. 

Compound Number m.p. (b p,) °C Light Stability3 embrittlement time (hours)... 

STABILIZER CONCENtRATION g/lUUg EMBRITTLEMENT TIME.hr UNEXTRACTED EXTRACTED ... 

Embrittlement Times of High-Density Polyethylene Films... 

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