Polyamide deterioration

These polymers possess enhanced solubility compared to the aromatic polyamides with no deterioration in thermal stability. Their Ts vary from... 

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 best performing coatings were the vinyl ester, the bisphenol A epoxy cured with an aliphatic amine, and a novolac epoxy cured with a mixed aromatic/cycl oal i phati c amine. The saturated polyester, and a bisphenol A epoxy cured with a polyamide amine showed significant deterioration of the coating material in the acid, and corrosion of the underlying steel. Two types of novolac epoxies cured with aromatic amines showed intermediate performance. 

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. 

The chemical sensitivity or life expectancy of reverse osmosis membranes is very important for manufacturing application. Thus chlorine is the most well known reagent for water disinfection. Glaster et al. 61 inspected the influence of halogens on the performance and durability of reverse osmosis membranes. Cellulose acetate was unresponsive to halogen agents but polyamide-type membranes deteriorated rapidly when exposed to halogens. 

With conventional paint systems rather poor adhesion is obtained with acetal and the polyolefin plastics adhesion with polyamide normally is good at first but under adverse conditions can deteriorate. In general, ABS and polycarbonate do not give comparable difficulties. 

In recent years, remarkable progress has been made in the syntheses of aromatic and heterocyclic polymers to search a new type of radiation resistant polymers. Sasuga and his coworkers extensively investigated the radiation deterioration of various aromatic polymers at ambient temperature [55-57] and reported the order of radiation resistivity evaluated from the changes in tensile properties as follows polyimide > polyether ether ketone > polyamide > polyetherimide > polyarylate > polysulfone. 

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). 

Recent tests by Sun (32) have shown that polyimide membranes have higher rejection rates than those of polyamide membranes, but polyamide membranes have higher flux. The highest flux obtained with hexane miscella and polyamide membranes was 6.6 LMH. The phosphorus rejection rates of 98.1-99.3% were obtained with hexane miscella. The addition of surfactants increased the phosphorus rejection rate from 83.3-78.7% to 96.4% with IPA miscella. The added surfactants facilitated the formation of large phospholipid clusters. Koseoglu et al. (33) reported that membranes made of polyamide were least affected by hexane, but that a membrane made from a fluorinated polymer was deteriorated by hexane. 

In the process of polyamidation foaming of the polymer was not observed. Thermal stability of the dyes is satisfactory at warming - up for 48 hours and this shows that their introduction at the stage of - caprolactam polyamidation does not deteriorate PCA properties. 

During the first 100 h of oxidation there were no significant differences between the samples, i.e. they all seemed unaffected by thermo-oxidation and no influence of repeated processing was found [65]. However, after 500 h of thermo-oxidation, all recycled samples showed a marked deterioration in tensile strength whereas the virgin material remained unaffected. The magnitude of the decrease in tensile strength corresponded well to the number of times the material was extruded. After 1200 h of thermo-oxidation the deterioration in mechanical properties was even more pronounced and at this point the polyamide 6.6 recycled three times retained only 20% of its... 

Considerable data have been published on the deterioration of some specific properties of polyamides as a consequence of natural or artificial weathering but few papers have been concerned with mechanistic photochemistry of these polymers. The results of Sharkey and Mochel [101] on the photo-oxidation of amides have opened the way to a better understanding of the problem. These authors have suggested that the primary photochemical step in the photolysis of amides is the breaking of the CO—NH bond with the formation of two free radicals which preferentially abstract hydrogen atoms from the methylene groups adjacent to the nitrogen namely,... 

Floors ana walls of structures are obvious areas where epoxy systems may be utilized to prevent deterioration from abrasion and chemical attack. Such systems are now to be found in original specifications. VTall surfaces may be coated viith epoxy systems based on solid resins dissolved in solvents and hardened with polyamines and/or polyamides. Porous surfaces, such as concrete blocks, are first prepared viith fillers to provide a smooth surface for application of coatings. 

Polymers containing hydrolysable groups or which have hydrolysable groups introduced by oxidation are susceptible to water attack. Hydrolyzable groups such as esters, amides, nitriles, acetals, and certain ketones can react with water and cause deterioration of the polymer. The dielectric constant, power factor, insulation resistance, and water absorption are most affected by hydrolysis. For polyesters, polyamides, cellulose, and cellulose either and esters, the hydrolysable groups are weak links in the chain, and hydrolysis of such polymers can cause serious loss of strength. A summary of water absorption characteristics of common plastic and rubbers is presented in Table 1.15. 

Because of the relatively low temperature of decomposition, DTA can be used to make foams with a uniform cellular structure without deterioration of the polymer. The disadvantages of DTA are, however, poor dispersive abihty in mixtures and sensitivity to moisture. Nevertheless, DTA is used in foaming PVC (especially for thin walled articles), polyurethane, polystyrene, polyamides, and siloxane rubbers. 

Mechanical Properties Chen et al. [2007] smdied the dynamic mechanical properties of films prepared by the solution casting method of PHBHV reinforced with HAp. The results indicated that at 75°C the storage tensile modulus of the polymer matrix, E , almost doubled by incorporation of 30 wt% HAp. The decrease in tan S was attributed to the hindrance of polymeric segment mobility by the nanofiller. Polyamide-69 has been reinforced with up to 10 wt% HAp [Sender et al., 2007]. The DMA results have pointed out an enhancement of the mechanical properties as a function of HAp content up to 5 wt% above this limit they deteriorated, probably due to the HAp agglomeration. 

Polyamides are susceptible to degradation by heat, oxygen, light, and chemical agents. During melt processing, thermal, oxidative, and hydrolytic processes may be operative that may also contribute, in addition to photochemical degradation, to the deterioration... 

Recycling has a dramatic influence on the mechanical and thermal properties of unstabilised polyamide 66. However, glass fibre reinforced polyamide 66 may be recycled up to four times without any significant deterioration in the performance of the material. Proper amounts and combinations of processing additives and antioxidants, together with optimised processing parameters, make it possible to recycle polyamides without significant losses of mechanical properties. 

Pg. 4 - Para 2. CTBN as free dibasic acid does deteriorate all amine, amidoamine or polyamide cured epoxy adhesives if it exists as free acid. This is why the overwhelming majority of instances adducts CTBN and epoxy first. No free acid. 

Poly(imide-co-amides) are easier to produce and to process than aromatic polyamides or polyimides. Like these, they are used in particular for electrical insulation coatings. As the ratio of imide/amide increases, the thermal stability of the copolymers increases, but the flexibility of the product deteriorates. 

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