Abstract: The infrared spectra of highly crystalline samples of cellulose containing the lattice types I, II, and III were compared with one another and with the spectrum of amorphous cellulose in the 850–1500 cm.−1 region. The spectra of cellulose II and of amorphous cellulose showed interesting similarities at 1420, 893–897, and 1111 cm.−1, three bands which others have used to follow changes in crystallinity and lattice type because the spectrum of cellulose I differs distinctly at these points from that of amorphous cellulose or cellulose II. The similarity between amorphous cellulose and cellulose II prevents the use of these bands for crystallinity determination in samples with mixed lattice types–for instance, partly mercerized cotton. An explanation is offered for the resemblance of the two spectra, based on the hypothesis that a rearrangement of intramolecular hydrogen bonds, tending to stabilize a different conformation of the cellulose chain, occurs upon destruction of the native cellulose I crystal lattice.

Abstract: The relationship between the cut growth and fatigue failure of natural rubber vulcanizates under repeated loading is examined. The cut growth behavior has been investigated using several types of test piece, and the results are shown to be consistent when interpreted in terms of the tearing energy concept developed previously. The most comprehensive data have been obtained by measuring the growth of a small cut in the edge of a strip cycled in simple extension. It is found that the cut growth per cycle is approximately proportional to the square of the maximum tearing energy attained during the cycle. Using this relation, the fatigue life of a specimen containing a small cut is deduced from elasticity theory as a function of initial cut size and maximum strain. Experimental results give good agreement with theory. A similar strain dependence is found for the fatigue life of die-stamped dumbbell test pieces with no intentionally produced flaws; this is consistent with the mechanism of failure bein...

Abstract: Tensile fatigue failure of a gum vulcanizate of noncrystallizing SBR can be accounted for by the growth of small flaws initially present in the rubber. Fatigue of crystallizing natural rubber was shown in Part I to be attributable to the same cause. Cut growth results are interpreted in terms of the tearing energy theory of Rivlin and Thomas. SBR exhibits cut growth under both static and dynamic conditions; in each case the rate is approximately proportional to the fourth power of the tearing energy. Variation of the dynamic cut growth rate with frequency can be explained by the summation of a timedependent static component of growth and a cyclic component not dissimilar to that occurring in natural rubber. Fatigue failure, under both static and dynamic conditions, is predicted from the cut growth results. These predictions are found to account quantitatively for experimentally observed fatigue lives when a suitable value is assumed for the initial flaw size. Fatigue lives at different temperatures correlate well with cut growth results obtained by Greensmith and Thomas over the same temperature range. The results are compared to those obtained previously for natural rubber, and possible reasons for the differences in fatigue behavior of crystallizing and noncrystallizing rubbers are discussed.

Abstract: The reaction of pyromellitic dianhydride with a solution of a primary diamine in a solvent such as dimethylacetamide gives a viscous solutionof a polypyromellitamic acid of high molecular weight. The viscosity of the solution decreases greatly when it is aged at 35°C. Higher temperatures or the presence of water, excess amine or excess anhydride accelerate the rate of decline. A rapid early drop in viscosity has been found to be due primarily to hydrolysis by adventitious water and to exchange reactions of amine or anhydride groups with the o-carboxyamide linkage. Slow decline over a long period of time results from hydrolysis by water produced in the slow conversion of polypyromellitamic acid to polypyromellitimide. Degradation by hydrolysis also occurs when polyimide films are cast by heating the solution. The effect can be minimized by casting thin films, from which water can diffuse rapidly, or by using a chemical method, such as treatment with acetic anhydride and pyridine, to remove the water produced in imidization.

Abstract: The faint emission of light by various classes and types of polymers when heated in the presence of oxygen, oxyluminescence, was studied by means of a photomultiplier tube and sensitive microammeter. Among the polymers with a carbon-carbon backbone, the polymers having the greater number of tertiary carbon atoms generally showed greater intensities of luminosity. Polystyrene was a notable exception to this generalization. The shape of the luminosity versus time curves varied with the type of polymer. It was also found that the emission of light did not stop instantly when the oxygen atmosphere was replaced by an inert gas, but rather followed an exponential type of decay. The rate of decay appeared to be different with different types of polymers. The intensities of luminescence and the times required to reach maximum or steady state luminescence were compared with oxygen uptake data for various polymers. In general there was a qualitative, but not necessarily quantitative correlation between the luminous intensities and polymer stabilities in the presence of oxygen.

Abstract: The change in melt flow properties, as determined by melt index measurement, as a function of shear history, has been measured for linear polyethylene. It is shown that a drop in melt index occurs when a polymer sample which has had no previous shear history is melted and subjected to shear mixing. This fact is attributed to a molecular homogenization of a previously unmixed blend. An analytical model of the laminar flow in a pipe of concentric adjacent fluids with different viscosities is presented. The model indicates that the effective viscosity of this non-homogeneous system is much lower than the viscosity of fan intimate blend of the same viscosity of an intimate blend of the same viscosity fluids.

Abstract: The interaction of carbon blacks with high polymers during the mixing process was studied by using fillers having a wide range of surface characteristics. Glass beads, Graphon, high-structure blacks, and heat-treated blacks were mixed with elastomers in the Brabender Plasticorder. With the use as a rubber matrix of a high polymer that did not materially change during the mixing process in molecular weight or viscosity, excellent correlation was found between final torque required for mixing and black structure and between peak torque and bound rubber. Increasing interaction was shown to lead to increased mixing torque, increased Mooney viscosity, increased modulus, and higher state of cure, as measured by swelling. If the high polymer matrix breaks down during the mixing process these influences of interaction are mostly obscured by diminishing molecular weight.

Abstract: The solubilities of nitrogen, oxygen, argon, methane, and carbon dioxide in thin films of crystalline oriented poly(ethylene terephthalate) in the glassy state were studied by the static sorption method. High pressure sorption isotherms were obtained for carbon dioxide. Results indicate that, above a certain film thickness, solubilities of all gasses in the crystalline oriented polymer (Mylar) are virtually identical to those in the unoriented crystalline polymer. Solubility constants are correlated with gas force constants, ϵ□k, and the heats of sorption obtained for methane and carbon dioxide are nearly the same for both the oriented and unoriented films. The sorption isotherms obtained for carbon dioxide are nonlinear but may be well described by considering dual sorption modes. One of these, ordinary dissolution, is described by Henry's law, while the other, “hole filling,” is characterized by a Langmuir expression. Solubilities of carbon dioxide in the thinnest oriented films (1 mil) are markedly higher than in the unoriented film. Analysis of the sorption data indicates that both the hole saturation constant, and the hole affinity constant, are larger in the 1-mil oriented film. The amorphous phase appears to be different also, exhibiting a larger capacity for dissolved gas. Different thermal history, relating to the manufacture of the film, is advanced as a possible explanation for increased solubility.

Abstract: The effect of pigments on the vapor sorption characteristics of a noncrosslinked polymer [poly(vinylacetate)] and a highly crosslinked polymer (epoxy type) were investigated. The fillers used in this study were a polar surface (titanium dioxide) and a nonpolar surface (copper phthalocyanine blue). With both polar and nonpolar fillers, a marked decrease in the sorption of organic vapors was noted at low relative pressures, even with very low filler content. At high vapor pressures, the sorption isotherm of the filled polymer approaches that of the unfilled polymer. It was also noted that the shape of the sorption isotherm of the filled polymer closely resembles that of the pure polymer below its glass transition temperature. The experimental results are discussed in terms of the partial immobilization of the polymer segments in the presence of fillers, as a result of the reduced number of possible configurations of the polymer chains.

Abstract: An apparatus has been developed for measuring the dilatation of specimens tested in uniaxial tension in a constant volume chamber by determining the change in the volume of air around the specimen through precise measurement of air pressure. The dilatometer can be used on standard testing machines and has shown reproducible values at testing speeds from 0.66 to 666%/min., and temperatures from −75 to 210°F. Typical stress strain curves are shown with the simultaneously recorded dilatation versus strain.

Abstract: The OH OD exchange reaction between deuterium oxide vapor and cellulose has been studied for thirteen different types of cellulose; the extent of exchange in a cellulose was determined by measuring the increase in the dry weight of the sample. With each cellulose the deuteration reaction was in two stages, a rapid stage followed by a slow stage; the material that exchanges during the rapid stage is the infrared-amorphous fraction of the cellulose, and therefore values for the amorphous fractions of the thirteen samples could be obtained. These amorphous fractions were found to be linearly related to the moisture regains of the samples. There is tentative evidence that the cellulose II samples absorb slightly more water into a unit amount of amorphous material than cellulose I samples.

Abstract: A technique is described for determining the density of polyolefin film from refractive index measurements. The procedure involves the measurement of the refractive indexes (nx, ny, and nz) along the three major axes of a film sample and conversion of the arithmetic average refractive index to a density value. The refractive index data are also used to calculate the per cent crystallinity and birefringence in the film.

Abstract: A theory of tensile rupture in a noncrystallizing rubber, a particular instance of a more general theory of rupture in simple extension, is outlined. The theory assumes that failure takes place by growth of a crack from some imperfection in the material where the stress is high locally. The imperfections are considered as being equivalent, in terms of stress concentration effects, to small cracks initially present in the material, and the conditions for crack growth to occur are then treated on the basis of the tearing energy criterion of Part I. It is assumed, by analogy with tearing on a macroscopic scale, that the crack grows continuously with time at a rate, dc/dt, given by: dc/dt = ATn, where A and n are constants and T is the energy expended per unit increase in crack length, per unit thickness of specimen. The predicted relationships of the breaking time to the stored energy density and initial crack length for specimens tested by stretching at uniform rates and by holding at fixed extensions are first compared with the results of model experiments on test pieces containing small tears and cuts. Values of A and n derived from tear test data are used in the theoretical relationships, and it is shown that there is fair agreement with experiment. Results of tests on tensile test pieces containing no deliberately introduced tears or cuts are then shown to be consistent with a failure mechanism of the above type. It appears, however, that the tearing energies in tensile rupture are lower than those observed in tear tests, and reasons for this difference are discussed.

Abstract: Vinyl aromatic polymers such as polystyrene can be made nonflammable by the addition of halogen compounds. The amount of halogen required to make such polymers nonflammable can now be greatly reduced by the addition of small amounts of certain free radical initiators. Normally about 5 phr of acetylene tetrabromide (parts of additive per hundred parts of polymer) must be added to polystyrene to obtain a self-extinguishing polymer. Only 0.5 phr of acetylene tetrabromide is required if 0.5 phr dicumyl peroxide is added. This synergistic effect has been observed with a series of peroxides, hydroperoxides, azo compounds, quinone imines, benzothiazole sulfenamides, disulfides, and a bibenzyl compound. The synergistic mechanism seems to be based on a series of reactions involving attack of the polymer by the initiator and subsequent reaction between polymer fragments and the halogen compound. The result is a delay in the loss of halogen from the polymer mass and thus a more efficient use of the halogen additive for flame quenching. Known inhibitors of free radical reactions have a detrimental effect on the synergistic mechanism.

Abstract: The oxyluminescence of polypropylene and polyethylene stabilized with various amounts of 4,4′-thiobis(3-methyl-6-tert-butylphenol) were studied and compared with oxygen uptake data. It was found that there was a correlation, although not linear, between the two methods. In the case of the stabilized polypropylenes, a pronounced aging effect was noticed. The oxyluminescent behavior of stabilized polyethylene was somewhat different from that of stabilized polypropylene. The temperature coefficients of the oxyluminescence of polypropylene, polyethylene, nylon 6, polystyrene, polyurethane and polymethyl methacrylate were obtained. From these data the apparent activation energies for the light-emitting reaction were calculated. For the olefin polymers, these values are close to the activation energies of the oxidative degradation reaction obtained by other means. Both polyethylene and polymethyl methacrylate have different activation energies below their transition points as compared to higher temperature, indicating a different mode of reaction in the solid state from that occurring in the melt. An interesting transition luminescence, which was more pronounced in the absence of oxygen, was observed in the case of polyethylene.

Abstract: The thermal dehydrochlorination of PVC has been examined on some samples prepared by fractionation of a commercial PVC, and some other samples obtained by polymerization at different temperatures. The results disagree with the concept of a continuous dehydrochlorination from one side to the other of the chain, that necessitates initiating structural anomalies in the macromolecule itself.

Abstract: On assuming that the two polymer components are poorly compatible or incompatible and from semimicro heterogeneous systems composed of homogeneous phases of each component, two kinds of generalized models which relate the degree of mixing of the two phases to the mechanical behavior of the systems were proposed. In this phenomenological theory, the chemical interaction between the two polymer components was negelcted, and the stress or strain distribution along the boundaries between the two phases was much simplified. This might give serious error when the mixed phases become small and the surface effect, instead of volume effect, becomes significant. The mechanical mixtures can be classified by the manner of mixing of the two phases of A and B components as follows: A islands in B matrix, B islands in A matrix, A matrix-B matrix, and A islands-B islands mixing. The mechanical properties of the mixed systems are affected not only by those of each component and their volume fraction in bulk, but strongly by the manner of mixing. The terminology used here, as the degree of mixing, is one of the representations of the manner of mixing in terms of distribution function of partial volume fractions of each component in the mixed system. The analysis of some mixed systems of two polymer components gave the following results. The mixed systems cast from acetone solution of poly(vinyl acetate) and poly(methyl methacrylate) give mechanical mixtures of the islands-in-matrix type mixing. A phase conversion from PMMA islands in PVAc matrix to PVAc islands in PMMA matrix occurs at about 70% volume fraction of PMMA due to the hexagonal close packing of PMMA islands in PVAc matrix with increase of volume fraction of PMMA On the other hand, the systems cast from mixtures of acetone solution of PVAc and lightly crosslinked PMMA fine particles give mechanical mixtures of the matrix-matrix type mixing. The mixed systems of polystyrene and 30/70 butadiene–styrene copolymer, which have been classified by Tobolsky as polyblends, might also be a type of mechanical mixture classifiable as matrix-matrix mixing. However, the manner of mixing should be much modified by the chemical interaction between the two components.

Abstract: Three recently published x-ray methods for determining the crystallinity of poly(ethylene terephthalate) are discussed and compared with density and infrared methods The effect of crystallite size is shown to account for most of the disagreement among the several methods A short method of estimating crystallinity from x-ray diffraction, suitable for counting techniques and requiring only two measurements, is presented and compared with the density method

Abstract: The curing of hexakis(methoxymethyl)melamine (HMM) alone and in blends with functionally substituted acrylic polymers was monitored by means of torsional braid analysis, infrared spectroscopy, weight change, and analysis of the volatile by-products. HMM alone, when heated with a strong acid catalyst, forms thermoset condensation polymers which evidently have the same methylene-bridged structure as conventional melamine-formaldehyde resins; the major elimination product is methylal. When HMM is blended with an acrylic polymer containing methacrylic acid units, the acrylic chains are crosslinked by elimination of methanol and formation of methylene ester linkages between the acid groups and the melamine. The crosslinking reaction proceeds with or without strong acid catalysis and is many times faster than the self-condensation of HMM. Acrylic polymers containing primary hydroxyl groups (derived from 2-hydroxyethyl methacrylate) also undergo acid-catalyzed reaction with HMM, and at a rate so much faster than analogous carboxylated polymers, that storage stability of the catalyzed resin becomes a serious problem. If a weaker catalyst, such as phthalic anhydride, is used, the curing reaction is very much slower. In order to develop the maximum number of new linkages, according to any of the experimental criteria, all of these systems must be heated for longer times, or at higher temperatures, than are customarily used in thermosetting resin technology. Thus the known utility and durability of such acrylic/melamine resins are achieved with only a fraction of the total number of crosslinks which are potentially capable of formation.

Abstract: The reaction of industrially available “prepolymers,” containing one or several isocyanate groups per chain, with tert-butyl hydroperoxide yielded long-chain peroxycarbamates. These were found able to initiate the polymerization of a wide variety of vinyl monomers as well as dienes leading to a new class of block polymers of very interesting physical properties. Polyether and polyester “prepolymers” with one, two, or three isocyanate functionalities were linked chemically to polystyrene, polymethyl methacrylate, poly-n-butyl acrylate, polyarylonitrile, and polyisoprene. The formation of block polymers was proved by both physical and chemical methods. Their mechanical properties were illustrated by means of torsional modulus–temperature curves. The effect of varying composition and of a crosslinking agent on the elastic modulus was examined. Tentative reaction mechanisms were also presented.

Abstract: A study was made of the rheological behavior of 35 samples of nylon 6 polymers of molecular weights varying from 4,000 to 40,000. A capillary extrusion rheometer was employed, and flow curves extending over a large range of shear rates were obtained. The effect of temperature, shear rate, and molecular weight on viscosity is reported, and some peculiarities of the flow behavior of nylon 6 polymers are discussed.

Abstract: A continuum theory of nonlinear viscoelastic behavior has been developed which is applicable to the quantitative description of the rheological properties of high polymeric materials. Particular classes of deformations have been investigated. Special emphasis has been placed upon nonlinear effects in viscoelastic fluids such as normal stresses and variable viscosity. Two new classes of flows are defined: sufficiently smooth flow and isoelastic flow.

Abstract: Many derivatives of phenyl salicylate turn yellow when they are exposed, in solution, to ultraviolet light. This limits their usefulness as ultraviolet stabilizers for plastics. Evidence is presented to support the postulation that the yellowing is due to the formation, by a photochemical ortho rearrangement, of a derivative of 2,2′-dihydroxybenzo-phenone. Aromatic salicylates, such as 2,6-dialkylphenyl salicylate, in which the ortho rearrangement is blocked, are found to be nonyellowing stabilizers, although less effective than the better yellowing varieties, such as p-octylphenyl salicylate. Loss of stabilizer by volatilization, either in compounding or during subsequent exposure, is shown to be an important factor in limiting the effective performance of the stabilizer.

Abstract: Cast linear polyethylene films subjected to dry and solvent annealing display markedly different sorption and difusion barrier properties than do untreated films. The subsequent sorption of liquid o- and p-xylene and cis- and trans-acetylene dichloride per unit volume of amorphous polymer increases as the annealing temperature and/or treating solvent concentration increases. Integral diffusivities calculated from sorption and steady-state permeation rates show a monotonic increase with sorption per unit volume of amorphous polymer. The concentration dependence, however, is less marked than observed in similar systems at low permeant activity. Apparently the above treatment reduces the effective crosslinking imposed by the crystallites on the amorphous polymer chains through disentangling and incorporating some of these chains into crystallites. Thus the polymer is capable of a greater degree of swelling when brought into contact with a compatible liquid in a spite of a higher degree of crystallinity. The low concentration dependence of the diffusivities is probably due to heterogeneous distribution of excess permeant in a treated film. If the excess permeant were preferentially sorbed in regions of low polymer concentration then the above observations could be explained. Long-duration, osmotic stress-induced swelling and recrystallization have been cited to account for time-dependent permeation rates in treated and untreated films.

Abstract: Determinations of the degree of chemical crosslinking and crosslinking efficiency values E (i.e., the number of sulfur atoms combined in the network per chemical crosslink present) have been used in conjunction with the chemical probes triphenylphosphine and sodium di-n-butyl phosphite to establish the structural features of sulfur links in vulcanizate networks derived from a variety of accelerated natural rubber–sulfur systems, from a cis-1,4-polyisoprene–TMTD–zinc oxide system, and from natural rubber and ethylene–propylene rubber crosslinked with a dicumyl peroxide–sulfur system. The triphenylphosphine converts polysulfide links into monosulfide and, to a lesser extent, disulfide links. The values of E′, i.e., the number of sulfur atoms combined in the network per chemical crosslink present after triphenylphosphine treatment are, therefore, a measure of the extent of main-chain modification in the network by cyclic monosulfide groups and/or pendant groups of the type: SxAccel. (where x ≥ 1 and Accel. is an accelerator fragment). Sodium di-n-butyl phosphite cleaves di- and polysulfide crosslinks but leaves monosulfide and carbon–carbon crosslinks intact, and thus determination of the degree of chemical crosslinking before and after treatment with this reagent yields estimates of these two different classes of crosslinks. The combined results indicate that the efficiency of utilizing sulfur for crosslinking and, therefore, the structural complexity of the derived networks are very sensitive to the nature of the vulcanizing system (type and relative concentrations of crosslinking agent, accelerator, and activator) and vulcanizing conditions (time and temperature of cure). In general, the proportion of crosslinks which are di- and/or polysulfidic decreases with increasing cure time, and for the accelerated sulfur systems the structural complexity of the network increases with cure time, especially at higher vulcanizing temperatures and with low concentrations of fatty acid activator.

Abstract: The water sorption by adult and embryonic native and insoluble collagen was investigated, along with that of calfskin gelatin Greater sorption was obtainable with the collagen fractions than with gelatin, but the technique could not distinguish the fractions themselves The suggestion is made that the greater sorption by collagen over gelatin and differences in apparent wettability between the adult and embryonic insoluble collagen might be explained by the formation of helical grooves with aging Density measurements of the collagen fractions indicate that collagen becomes more crystalline with aging This also applied to the insoluble collagen These results are consistent with the view that differences in collagen solubility are due to differences in molecular ordering The density of the insoluble collagens and gelatin passes through a maximum at 3–4% sorbed water The phenomenon is explained on the basis of water bridges comprised of a single water molecule double hydrogen bonded to closely aligned chains A discussion is presented in this connection A calculation based on the density yields a molecular volume of 432 × 10−19 cm3 For tropocollagen This is in agreement with the molecular dimensions and consistent with the idea that collagen is formed from an aggregation of the monomer

Abstract: The insolubilization of polyvinyl alcohol by potassium dichromate on exposure to light has been investigated. Ultraviolet spectrometry shows that secondary hydroxyl groups are oxidized to ketone groups but insolubilization is attributed to crosslinking of polymer chains by co-ordination of alcohol groups to “nascent” chromic ions formed by reduction of the dichromate. Exposure to air saturated with water vapor eliminates the carbonyl absorption maxima from the ultraviolet spectrum of polyvinyl alcohol film but the spectrum can be restored by heating: this phenomenon is independent of the crosslinking reaction.

Abstract: When well oriented and crystallized high density polyethylene film was redrawn, slip deformation and twin deformation, the mode of which depends upon the redrawing angle to the original drawn structure, could be observed. When the redrawing angle is very small, single slips, the direction of which is [001] to the original drawn structure, and homogeneous deformation bands attached to them are usually observed. The [001] directions of slipped and unslipped regions are slightly at an angle to each other. As the redrawing angle approaches a right angle, kink bands can be observed. From these results we may conclude that the structure of this drawn polyethylene film is very similar to that of a single crystal or metal.