The Effect of the Use of Full Body Harnesses on Their Protective Properties
A full body harness is a component of personal systems protecting against falls from a height. To ensure users’ safety, the harness must retain its protective properties during its whole service period. All the elements of a harness (webbings, threads, metal buckles, etc.) are exposed to destructive factors. Harnesses stored and used for a few years were tested. The paper discusses the most frequent types of damage and their effect on the essential resistance parameters. The effect of atmospheric conditions, sunlight, mechanical damage and dust on the parameters of webbings was tested. Conclusions on the main causes of the loss of the protective properties of harnesses are drawn; periodic checks of the physical conditions and guidelines for estimating acceptable service time are recommended.
Comparison of the UV-degradation chemistry of polypropylene, polyethylene, polyamide 6 and polybutylene terephthalate
The photodegradation mechanism of polymers highly depends on the type and concentration of chromophores present. This influence is studied by making a comparison between the UV-degradation of PE, PP, PA6 and PBT and the thermooxidative degradation of PP at a comparable temperature. The degradation processess are followed by determining the oxygen uptake, CO, CO2 and peroxide formation. During UV-degradation of PP, PE, PA6 and PBT the oxygen uptake is linear in time without an induction period. The oxidation rate of PP is higher than that of PBT, which is slightly higher than the oxidation rate of PA6, while that of PE is the lowest. The determined amount of peroxides depends on the ageing time. For the UV-degradation this does not lead to the expected increase of the oxidation rate, as is the case with thermooxidation of PP. Only a limited proportion of the peroxides formed during the UV-degradation decomposes into radicals. The oxidation rate is mainly determined by other radical forming reactions. In the case of PE and PP this is probably initiation by polymer-oxygen Charge Transfer Complexes (CTCs) and for PA6 and PBT direct photolysis of the amide or the ester linkage, respectively. Thickness degradation profiles show that the UV-degradation processes of PP and PBT are heterogeneous. For PP this is due to oxygen diffusion limitation, while in the case of PBT it is the result of absorption of the UV-light.
Some aspects of polyethylene photooxidation
The hydroperoxides produced by thermal oxidation of LDPE films were used to study their photolysis. Product analysis, kinetics of hydroperoxide decomposition and product formation as well as experiments with model compounds point to new mechanisms of hydroperoxide photolysis. Intermolecular as well as intramolecular decomposition mechanisms are proposed. In polyethylene, these reactions are essentially non-initiating. In addition, it is confirmed that ketones such as those formed by oxidation of polyethylene do not have a significant initiating effect. Reactions of excited charge-transfer complexes polyethylene-oxygen are proposed to account for initiation of photo-oxidation. One of these reactions yields trans-vinylene groups and hydrogen peroxide whose direct decomposition or subsequent photolysis will generate hydroxyl radicals. It is found that this reaction is quenched very efficiently by small amounts of HALS (Hindered Amine Light Stabilizers) and by amines in general. It is postulated that quenching is due to energy transfer from the charge-tranfer complex polymer-oxygen to a charge-transfer complex HALS-oxygen or amine-oxygen. The data available so far support such a mechanism.