Films of polyamides were exposed to heat, ultraviolet radiant energy, and different atmospheric conditions. The degradation products were collected in some cases and analyzed by mass spectrometric techniques. The unexposed and exposed specimens were examined by the following techniques to obtain information concerning the changes in chemical and physical structure of the polymer: infrared absorption, ultraviolet absorption , viscosity of solutions, measurement of dielectric constant and dissipation factor, photomicrography, X-ray diffraction, electron microscopy, electron diffraction, and effect of organic liquids. In addition, pyrolysis studies were made and some physical properties were determined. The results of the investigation show clearly that no single method gives a complete picture but that the results from several of the methods give an insight into the mechanism of degradation of poly ami des.Polyamide molecules are relatively unaffected by exposure to moderate temperature (60 0 C). However, loss of water and other volatile materials may cause changes in physcial properties. The effects of exposure to ultraviolet radiant energy are more pronounced, and degradation of the polyamide molecule occurs with accompanying loss of water and other volatile materials that act as plasticizers.The results of this inves tigation show that the general course of the degradation of polyamides is as follows :1. The polymer mol ecules break at the C -N bond of the peptide group creating smaller polymer molecules with the same unit of chemical structure. The fragments broken out are evolved as carbon dioxide, carbon monoxide, water, and hydrocarbons.2. The degree of crystallinity or local order changes, including alterations in hydrocarbon packing, dipole rearrangement, and hydrogen bridging.3. The amount of strongly bound water and/or organic liquids changes. These materials are probably bound by hydrogen bridging to the oxygen of the peptide group. They act as plasticizers for the polyamides. r. IntroductionOne of the major problems facing the plastics industry is the degradation of some plastics when exposed to certain service conditions. This problem has been investigated extensively by accelerated tests involving one or more physical properties. While empirical investigations of this type give information of value, they yield little or no information on the basic changes in the material. As a result, the value of the information now aVi),ilable is not only limited, but in too many instances the information cannot be used to predict behavior in actual service [1).1 The physical changes observed during degradation may result from (1) changes in the chemical structure of the plastic material, and (2) loss or changes in the compounding ingredients. The logical method of attack is to determine the specific chemical reactions involved in the degradation of the plastic and how these reactions are affected by the intensity of the conditions encountered.The degradation of the plastic type of polyamides was investigated as p...
Sin ce p olystyrene is a widely used plastic a nd styrene is an in tegral part of t he m ost wid ely used sy nthetic r ubber (GR-S) , it appears necessary to k now somethi ng of the process of degrada t ion of polystyrene t o a ssist in in terpreting t he d egradation of these materi als in service. P olystyrene films were exposed to h eat at 100° C in a for ced-draft air oven a nd to ultraviolet ra di a nt e nergy at 60° C in air. Chemical st r uctural changes in t he polymer a s a resul t of t hese t reatments were a nalyzed b y st udy of t he infrared spectra between 2 a nd 16 microns , obtained wit h a Ba ird recording infra red spectrop ho tomete r. U lt rav iolet expos ure fo], 200 hours resulted in a bsorpt ions a t 2.9 and 5.8 microns, which a re attributed to hydroxyl a nd carbonyl groups, respectively. H eati ng of t he film for 270 hours at 100° C p rodu ced no signifi can t change in the infra red spectrum. P ro longed heating at. 125° C resul te d in t he dest r uction of t he films by £i ow. The literature and t heory o n t he d egrada t io n of p olys tyrene a re discussed. Several me cha nis ms are postu lated to a ccou nt for the p rod uction of hydroxyl a nd carbonyl p rodu cts in t he p oly mer .
The degradation of polystyrene by heat and ultraviolet radiant energy was followed by mass spectrometric analysis of the gaseous products evolved. Oxygen content, discoloration, and insolubility of the treated polymer were also investigated. The degradation of polystyrene involves two different processes: (1) the breakdown of thermolabile groups formed in the polymer prior to degradative treatment; this breakdown is caused by exposure to heat at 120°C. in vacuo and 115°C. in oxygen and to ultraviolet radiant energy at 120°C. in vacuo and 118°C. in oxygen; it is accompanied by the removal of residual materials such as solvent; and (2) the oxidation of the polymer caused by exposure to ultraviolet radiant energy in the presence of oxygen. The evolution of benzene, methyl ethyl ketone, dimethylbenzenes, and alcohols is associated with the first stage involving the breakdown of thermolabile groups and the removal of residual materials. Compounds such as formaldehyde, formic acid, and acetic acid are produced as a result of oxidation of the polymer. The oxygen content of the polymer was decreased from 0.33 to approximately 0.1 percent by heating at 120°C. in vacuo and at 115°C. in oxygen, and by exposure to ultraviolet radiant energy at 120°C. in vacuo. Ultraviolet treatment at 118°C. in oxygen for 250 hours quadrupled the original oxygen concentration. Discoloration of the polystyrene was definitely noted only on exposure to ultraviolet radiant energy in oxygen and is associated with oxidation of the polymer. The material became insoluble as a result of all heat and ultraviolet treatments. The amount of insoluble material increased with severity of exposure conditions.
he most important engineering aspect of pipe is its T behavior when subjected to internal stresses arising from the transport through it of gases and fluids under pressure. Although a universal consideration with all materials in pipe form, this aspect is one of particular interest for pipe made from plastics because (a) of their relatively low strength compared to that of steel, ( b ) of their plastic nature, and (c) of the short time they have been known and used by man. Other materials such as steel are less plastic in nature at ordinary temperatures and a highly significant point is the fact that they were widely used with many successes and failures before reliable engineering properties and design criteria were developed.The young thermoplastic pipe industry recognized its status and problems when it began to achieve stature in the 1940's. However, in its early stages the applications were in non-critical areas and the output of the small industry was not sufficient to support a large scale engineering research program.As the industry developed and the uses of plastics pipe multiplied, the engineering sophistication required for proper design of plastic pipe for use in pressure applications became more important and more critical. Recognizing that it was not economically practical to develop long-term hydrostatic design stresses through service and also that it was not technically possible to obtain reliable hydrostatic strength properties by the same means, the Thermoplastic Pipe Division of The Society of the
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