Poly deterioration

The actual time required for poly-L-lactide implants to be completely absorbed is relatively long, and depends on polymer purity, processing conditions, implant site, and physical dimensions of the implant. For instance, 50—90 mg samples of radiolabeled poly-DL-lactide implanted in the abdominal walls of rats had an absorption time of 1.5 years with metaboHsm resulting primarily from respiratory excretion (24). In contrast, pure poly-L-lactide bone plates attached to sheep femora showed mechanical deterioration, but Httie evidence of significant mass loss even after four years (25). 

Dissolution/reprecipitation processes were evaluated for the recycling of poly-epsilon-caprolactam (PA6) and polyhexamethyleneadipamide (PA66). The process involved solution of the polyamide in an appropriate solvent, precipitation by the addition of a non-solvent, and recovery of the polymer by washing and drying. Dimethylsulphoxide was used as the solvent for PA6, and formic acid for PA66, and methylethylketone was used as the non-solvent for both polymers. The recycled polymers were evaluated by determination of molecular weight, crystallinity and grain size. Excellent recoveries were achieved, with no deterioration in the polymer properties. 33 refs. 

The identification and quantification of potentially cytotoxic carbonyl compounds (e.g. aldehydes such as pentanal, hexanal, traw-2-octenal and 4-hydroxy-/mAW-2-nonenal, and ketones such as propan- and hexan-2-ones) also serves as a useful marker of the oxidative deterioration of PUFAs in isolated biological samples and chemical model systems. One method developed utilizes HPLC coupled with spectrophotometric detection and involves precolumn derivatization of peroxidized PUFA-derived aldehydes and alternative carbonyl compounds with 2,4-DNPH followed by separation of the resulting chromophoric 2,4-dinitrophenylhydrazones on a reversed-phase column and spectrophotometric detection at a wavelength of378 nm. This method has a relatively high level of sensitivity, and has been successfully applied to the analysis of such products in rat hepatocytes and rat liver microsomal suspensions stimulated with carbon tetrachloride or ADP-iron complexes (Poli etui., 1985). 

Poly(ethylene terephthalate), (PET), is a thermoplastic polymer widely used in the production of fibers and films on exposure to near ultraviolet light, PET fibers tend to lose their elasticity and break easily PET films become discolored, brittle and develop crazed surfaces. Such deterioration in properties has been attributed to photochemical reactions initiated by the... 

Limited testing on chlorine sensitivity of poly(ether/amidel and poly(ether/urea) thin film composite membranes have been reported by Fluid Systems Division of UOP [4]. Poly(ether/amide] membrane (PA-300] exposed to 1 ppm chlorine in feedwater for 24 hours showed a significant decline in salt rejection. Additional experiments at Fluid Systems were directed toward improvement of membrane resistance to chlorine. Different amide polymers and fabrication techniques were attempted but these variations had little effect on chlorine resistance [5]. Chlorine sensitivity of polyamide membranes was also demonstrated by Spatz and Fried-lander [3]. It is generally concluded that polyamide type membranes deteriorate rapidly when exposed to low chlorine concentrations in water solution. 

Lee and coworkers report on a photo-initiated polymerization for the preparation of poly(butyl methylacrylate-co-ethylene dimethylacrylate) within fused silica capillaries. UV light-initiated polymerization is well suited to monolith formation in restricted spaces since polymer forms only in those areas that are exposed to irradiation. This leads to far greater control over the length and size of the monolithic column formed. The resulting columns are robnst since their separation ability does not deteriorate with time or number of injections and their reprodncibility is excellent. ... 

Composite propellants consist of an oxidizer (AP/AN/ADN), a metallic fuel such as Al, Mg etc and a binder, usually a polymer which also serves as a fuel. Vacuum stability tests (VSTs) suggest that composite propellants are intrinsically more stable than SB, DB and propellants. However, use of more exotic ingredients such as oxidizers (ADN and hydrazinium nitroformate, HNF), binders [poly([NiMMO)] and poly([GlyN)] are likely to introduce severe compatibility-related problems [30, 31]. Some recent research in this direction indicates that stability of such propellants is largely determined by the chemical and mechanical properties of propellants. However, early evidence of deterioration generally comes from a change in their mechanical properties rather than from chemical investigations [32]. 

Films made from TPX exhibit an insufficient heat sealability. A widely adopted solution for improving such insufficient heat sealability is addition of a low density poly(ethylene) (LDPE) homopolymer or an ethylene propylene copolymer. However, the addition of these polymers only result in little improvement in their heat sealability. Instead, the addition results in poor dispersion and deteriorated impact resistance (23). 

M thiocyanate solution. The lifetime of these electropolymerized electrodes (at least 2 months) is a significant improvement over that of PVC-based electrodes that use cobalt porphyrins (28, 29). The latter electrodes were selective toward thiocyanate, but the slopes of the calibration curves deteriorated substantially in less than one month. The improved lifetimes of the poly[Co(o-NH2)TPP] electrodes may be attributed to the covalent fixation of the ionophore to the polymeric matrix ... 

Some polymers show discoloration as well as reduction of the mechanical properties (e.g. aromatic polyesters, aromatic polyamides, polycarbonate, polyurethanes, poly (phenylene oxide, polysulphone), others show only a deterioration of the mechanical properties (polypropylene, cotton) or mainly yellowing (wool, poly(vinyl chloride)). This degradation may be less pronounced when an ultraviolet absorber is incorporated into the polymer. The role of the UV-absorbers (usually o-hydroxybenzophenones or o-hydroxyphenylbenzotriazoles) is to absorb the radiation in the 300-400 nm region and dissipate the energy in a manner harmless to the material to be protected. UV-protection of polymers can be well achieved by the use of additives (e.g. nickel chelates) that, by a transfer of excitation energy, are capable of quenching electronically excited states of impurities (e.g. carbonyl groups) present in the polymer (e.g. polypropylene). 

Especially above room temperature many polymers degrade in an air atmosphere by oxidation that is not light-induced (heat ageing). A number of polymers already show a deterioration of the mechanical properties after heating for some days at about 100 °C and even at lower temperatures (e.g. polyethylene, polypropylene, poly(oxy methylene) and poly(ethylene sulphide)). 

AChE was sandwiched with poly(diallyldimethyl-ammonium chloride) layers on the surface of CNTs. The OP biosensor thus developed was used to detect paraoxon (Figure 55.7) as low as 4 x 10 M with a 6 min response time in flow injection analysis. A high stability of the sensors was also a merit of this biosensor no deterioration in the response was observed after 1 week of eontinuous use of the sensor. Only a 15% deerease in the aetivity of the enzyme was observed after 3 weeks, though the authors... 

Deterioration of the properties of amorphous poly-DSP and poly-P 2 VB on exposure to sunlight in the air is another striking abnormal behavior which is observed neither in the corresponding as-polymerized polymer crystals nor in the polymer in solution69. ... 

Experimental approaches have been reported by two groups. The group at Gunma University (25) synthesized a prototype of ladder polymers, poly(bicyclosilane)s. Polymers with three, four, and five ladder steps were synthesized, and the bathochromic shifts were measured, Ikehata et al, (26) attempted substitutional doping by thermal neutron irradiation of (SiH) ladder polymers synthesized through the reduction of trichlorosilane with lithium in THE (tetrahydrofuran). Thermal neutron capture by Si will yield P in this process for total flux amounts of up to 10 /cm. The concentration of phosphorus impurity is 0.1 ppm. No serious deterioration was caused by strong neutron irradiation. However, in this study, the detailed properties... 

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