Showing papers in "Journal of Applied Polymer Science in 1969"

Estimation of the surface free energy of polymers

Abstract: A method for measuring the surface energy of solids and for resolving the surface energy into contributions from dispersion and dipole-hydrogen bonding forces has been developed. It is based on the measurement of contact angles with water and methylene iodide. Good agreement has been obtained with the more laborious γc method. Evidence for a finite value of liquid-solid interfacial tension at zero contact angle is presented. The method is especially applicable to the surface characterization of polymers.

The continuum interpretation for fracture and adhesion.

Abstract: Continuum fracture concept indicating essential surface energy interpretation difference in otherwise similar adhesive and cohesive failures

Attachment of amino groups to polymer surfaces by radiofrequency plasmas

Abstract: Low temperature gaseous plasmas of ammonia or nitrogen–hydrogen mixtures contain NH2 groups, or precursors thereof, formed in the plasma, which experimental evidence strongly suggests, can add to various polymer surfaces. The plasmas were established in the 0.3–1.5 torr range by radiofrequency (13.56 MHz) electrodeless excitation at powers ranging from 50 to 500 W. Samples of polypropylene, poly(vinyl chloride), polytetrafluorethylene, polycarbonate, polyurethane, and poly(methl methacrylate) were investigated. All these polymers added amino groups to varying degrees of amino site densities depending on the choice of plasma parameters and the reactivity of the polymer itself. In every instance the polymer was rendered more wettable, although no quantitative wettability measurements were made. Following the plasma treatment, degrees of amino attachment to the polymer were followed radiometrically and reported in terms of “heparin thicknesses” resulting from ionic heparin 35S attachment to quaternary sites produced from the amino groups. Two implications of such a surface modification are to adhesion and blood compatible materials preparation.

Load–compression behavior of flexible foams

Abstract: The load-compression behavior of a foam reflects its geometric structure and the physical properties of the matrix polymer. Quantitative relations between these parameters have been established in the present study. Based on both theoretical analyses and experimental data obtained on a flexible polyurethane foam, it is shown that the compressive stress can be factored into the product of two terms: (1) a dimensionless function of the compressive strain, ψ(e), calculated from experimental load-compression data and reflecting the buckling of the foam matrix; and (2) a factor, eEƒ, where Eƒ is the apparent Young's modulus of the foam (which is a function primarily of the modulus of the base polymer E0 and of the volume fraction of polymer, φ). Thus the compressive stress behavior of a foamed polymer is determined by E0, φ, and the matrix geometry, the latter described by the function ψ(e). Using these established relations, it now is possible to delineate precisely the structural features a foam mus...

Crazing, yielding, and fracture of polymers. I. Ductile brittle transition in polycarbonate

Abstract: Most thermoplastics far below their glass transition give a brittle fracture when de-formed in uniaxial tension. Bisphenol-A polycarbonates are an exception and deform in a ductile manner. However, it has been observed in Izod impact studies of notched samples that the mode of failure changes from a ductile to a brittle fracture on annealing samples below Tg. It has been found that, when notched samples are stressed, a Griffith type flaw is formed under the notch. The criterion for the ductile brittle transition is evaluated in terms of σG (the stress required to propagate the Griffith flaw), and σy, the yield stress for the polymer. It has been found that the density and yield stress for the samples annealed at various temperatures are dependent upon previous thermal history and in particular on the molecular weiAght. On the basis of these measurements, it is concluded that many of the so-called anomalous effects observed with polycarbonate can be explained.

The glass transition temperature of filled polymers and its effect on their physical properties

Abstract: The glass transition temperature, dynamic shear moduli, and bulk viscosities of Phenoxy PKHH (a thermoplastic polymer made from bisphenol-A and epichlorohydrin) filled with glass beads and Attapulgite clay were investigated. The glass temperature of the polymer increased with increasing filler concentration and with increasing specific surface area of the filler. The data were interpreted by assuming that interactions between filler particles and the polymer matrix reduce molecular mobility and flexibility of the polymer chains in the vicinity of the interfaces. From the measured moduli and the viscosities of the filled and unfilled materials, the modulus reinforcement ratio in the glassy state and the relative viscosity in the viscous state were obtained as functions of the filler type and concentration. The relative modulus for the glass bead composite system follows the Kerner equation, while the clay-filled systems exhibit slightly greater reinforcement. The relative viscosities are strongly temperature dependent and do not follow conventional viscosity predictions for suspensions. It is suggested that the filler has a twofold effect on the viscosity of the composite materials; one is due to its mechanical presence and the other is due to modifications of part of the polymer matrix caused by interaction. Using the WLF equation to express all modifications of the matrix, one can isolate a purely mechanical contribution to the viscosity reinforcement. This mechanical part is approximately bounded by the theoretical predictions of Kerner,32 Mooney, 36 and Brodnyan,41 for suspension viscosities.

The reaction of polypropylene with maleic anhydride

Abstract: An addition reaction of maleic anhydride with polypropylene takes place in the presence of radical reagents or sunlight. The initial rate of the reaction was proportional to the concentration of polypropylene and maleic anhydride, and one-half power of the concentration of the radical reagents. The increase in the temperature from 80 to 120°C increased the rate of the reaction and di-cumyl peroxide was effective as a radical reagent for this reaction. Ionic crosslinked rubber-like polymers were obtained from the reaction of maleic polypropylene with some alkali metal compounds. They showed the characteristic absorption band due to COO⊖ in their infrared spectra.

Activated gas plasma surface treatment of polymers for adhesive bonding

Abstract: Polyethylene, polypropylene, poly(vinyl fluoride) (Tedlar), polystyrene, nylon 6, poly(ethylene terephthalate) (Mylar), polycarbonate, cellulose acetate butyrate, and a poly(oxymethylene) copolymer were treated with activated helium and with activated oxygen. Mechanical strengths of adhesive-bonded specimens prepared from treated and from untreated coupons were compared. Polyethylene (PE) and polypropylene (PP) showed the greatest increases in bond strength. Oxygen and helium were both effective with polyethylene, but polypropylene showed no improvement when treated with activated helium. The results with excited helium parallel the effects of ionizing radiation on these two polymers, as does the appearance of unsaturation bands in the infrared (965 cm−1 in PE, and 887 and 910 cm−1 in PP). Active nitrogen produced excellent bond strength with polyethylene but not with polypropylene. Of the remaining polymers examined, Tedlar, polystyrene, and nylon 6 showed the greatest improvement in bondability after treatment, and Mylar showed moderate improvement. Polycarbonate, cellulose acetate butyrate, and the poly(oxymethylene) copolymer gave approximately two-fold increases in lap-shear bond strength. In several cases, significant differences in response to time of treatment and type of excited gas were found.

Polymer rheology: Influence of molecular weight and polydispersity

Abstract: Literature data on the non-Newtonian flow of bulk polymer and of polymer solutions are correlated on the basis of a four-parameter equation, η = η∞ + (η0 − η∞)/[1 + (τD)m], η being the viscosity at shear rate D, and η0 and η∞ limiting values at D = 0 and D = ∞, respectively. The parameters η0, η∞, and τ all show dependence on molecular weight, and in general there is good correlation between τ and η0. There is evidence that τ is related to a molecular weight higher than the weight-average. The exponent m shows dependence on molecular weight distribution and approaches an upper limit of unity for a monodisperse linear polymer. For linear unblended polymers it may be expressed empirically by m = (Mn/Mw)1/5.

Multiple detectors for molecular weight and composition analysis of copolymers by gel permeation chromatography

Abstract: The use of a single detector in gel permeation chromatography (GPC) for samples of varying composition leads to erroneous conclusions. With certain simplifying assumptions, a gel permeation chromatograph equipped with properly selected dual detectors yields composition and molecular weight distribution information that is meaningful. Examples discussed are a mixture of homopolymers and a sample supposed to have been a styrene–butadiene block copolymer. The ultraviolet absorption is used in conjunction with the refractive index trace to give qualitative information that is much more informative than could be obtained with one detector. Calibration of the relative responses of the detectors to each of the components of the mixture is described, and these calibrations are used to calculate point-by-point composition, molecular weights, and molecular weight averages.

Polymer reactors and molecular weight distribution. VIII. A method of interpreting skewed GPC chromatograms

Abstract: A new-method of interpreting GPC chromatograms which accounts for skewing and symmetrical axial dispersion has been developed. General relationships for a symmetrical axial dispersion correction and for a skewing correction are derived. The method has been verified experimentally for unimodal chromatograms and linear calibration curves over a wide range of GPC operating conditions, polymer molecular weights and polydispersities. Measurements of h and skewing factors were obtained by a once-through technique. The need for performing reverse flow experiments has been eliminated. Artificial oscillations in the corrected chromatogram due to step size (Method of Pierce-Armonas), and to number of terms in a polynomial expansion (Method of Tung and Method of Smith) are eliminated. The method has yet to be evaluated for nonlinear calibration curves and multi-modal distributions. However, suggestions for its application in these circumstances are presented.

Failure mechanisms in peeling of pressure-sensitive adhesive tape

Abstract: Studies on the peel behavior of pressure-sensitive tape comprising a polyester backing and polyacrylate adhesive have shown that, in peeling from a plane glass surface, three fundamentally different modes of peeling may be distinguished, depending upon the rate of pulling. At low rates, deformation by flow of the adhesive appears to determine the peel behavior and the peel force is strongly rate dependent. At high rates, little or no viscous deformation of the adhesive occurs and the peel force is independent of rate. At intermediate pulling rates, cyclical instability of made of failure involving alternate storage and dissipation of elastic energy in the backing, results in the phenomenon of “slip-stick” peeling, in which failure is jerky and regular. Results have been obtained which show how the pulling rates at which transitions from one mode of peel to another occur, and the peel force values for a given type of failure, depend upon such factors as molecular weight of adhesive, thickness of backing film, and angle of peeling.

The photo‐oxidation of polypropylene: Some effects of molecular order

Abstract: : Fractional crystallization was used to separate a commercial, predominantly isotactic, unstabilized polypropylene into fractions of relatively low and relatively high atacticity, but of similar molecular weight. IR spectroscopy was used to follow the photo-oxidations of films formed from these fractions during irradiation in air with light of wavelengths greater than 3000 A. The major oxidation products included hydrogen-bonded hydroperoxides and carbonyl compounds. Films of constant tacticity, but varying morphology were prepared by quenching from the melt. No distinct correlation was found between sample photostability and morphology, as indicated by film density. Films of low atactic content were found to undergo faster photo-oxidation than films of high atactic content, irradiated under identical conditions. This effect is believed to be due to the occurrence of a stereo-dependnt step (or steps) in the oxidative chain, and not due to differences in sampling morphology. The possible nature of the stereo-dependent steps is considered in terms of well-established oxidative chain processes. The effects of polypropylene polymorphism on oxygen permeability are briefly considered. (Author)

Calibration of instrumental spreading for GPC

Abstract: The proper use of the method for correcting instrumental spreading in GPC requires a precise calibration of the spreading characteristics of the instrument. Heretofore, such a calibration could be obtained only through the tedious reverse-flow experiments. A more rapid method of calibrating instrumental spreading is presented in this work. This method uses the leading halves of the chromatograms of several standard polystyrene samples. These chromatograms are normally used in the calibration of molecular weight; additional experimental steps are therefore not required. The calculation of the instrumental spreading characteristics from these chromatograms is also relatively simple. The instrumental spreading characteristics were found to depend on the elution volume but not on the nature of the polymer. Thus, calibration results from using polystyrene standards can be used to treat chromatograms for other polymers. For the present GPC instrument, the spreading was found to reach a maximum at an elution volume near 400,000 in polystyrene molecular weight. The existence of this maximum is in agreement with observations made by other investigators and is and indication that diffusion in the mobile phase is not an important contribution to instrumental spreading. The problem of skewing or tailing is discussed. Indication of skewing was observed for one of the higher molecular weight polystyrene samples but the extent of skewing was not severe at the present flow rate of 2 ml/min.

Studies on dry spinning. I. Fundamental equations

Abstract: One difficulty in analyzing the state of filament in the dry spinning process is that in the boundary conditions required to solve the equations of mass, momentum and energy which are derived on the consideration of balance with respect to infinitesimally small element are not given a priori. The equations which include these boundary conditions in themselves are derived by considering mass, momentum, and energy balances with respect to the entire cross section of filament. These additional macroscopic equations are simplified to a great extent by assuming the flat velocity profile through the cross section of filament. Besides, in the steady state, these macroscopic equations are modified to give the equations of average solvent content, spinning tension, cross-sectional area, and average temperature. When the spinning conditions are given and the physical constants are measured for a given polymer and solvent system, it becomes possible to calculate the state of filament by solving these microscopic and macroscopic equations simultaneously without resorting to actual spinning.

Isothermal pyrolysis of cellulose: Kinetics and gas chromatographic mass spectrometric analysis of the degradation products

Abstract: : The objective of the work was to study the degradation processes of untreated and fire retardant treated cellulose above 300C. The basic overall decomposition mechanism, in terms of three phases of pyrolysis based on weight loss measurements of the untreated cellulose between 315C - 360C, is similar to that observed between 276C - 298C. This observation was supported by measurements on the rates of formation of degradation products directly generated in the time-of-flight mass spectrometer at 298C. A 2% KHCO3 treatment of the white alpha cellulose at 300C increased the rate of volatilization 7-fold. The results of a gas chromatographic-mass spectrometric analysis of the volatile degradation products of the untreated and fire retardant treated cellulose indicated that: There is little difference in either the quality or relative quantity of volatiles generated during the three different stages of pyrolysis; the fire retardant, KHCO3, does not markedly change the types of degradation products having molecular weights below about 110, although it does change their relative concentrations; the initial rapid weight loss in both cases is not due to desorption of water, but primarily to decomposition of the cellulose molecules.

Influence of water on stress corrosion cracking of epoxy bonds

Abstract: Environment assisted fracturing, or stress corrosion cracking of adhesive joints in liquid water or a humid atmosphere was shown to occur at values of applied crack extension force ςa considerably below those required for onset of opening-mode rapid fracture ςc. The minimum value of ςa below which no cracking was observed, ςSSC, was dependent on the relative humidity and the particular adhesive used. For two adhesive systems, the one with the lower hardener content and post cure temperature showed both a lower absolute value of ςSSC and a lower ratio of ςSSC to ςc. The value of ςSSC for both adhesive systems decreased as the humidity was increased. As the relative humidity approached 100%, the value of ςSSC approached its value for liquid water. Values of ςc for the two adhesives differed by a ratio of approximately 2:1. When water was introduced to the crack tip, ςc for the less tough material increased while it was not significantly changed for the tougher material.

Base‐hydrolyzed starch‐polyacrylonitrile (S‐PAN) graft copolymer. S‐PAN‐1:1, PAN M.W. 794,000

Abstract: Starch-polyacrylonitrile (S-PAN) graft copolymer consisting of one part starch and one part polyacrylonitrile (M. W. 794,000) was hydrolyzed with aqueous KOH at 80 and 100°C to polyelectrolytes containing carboxyl and amide functionality but void of infrared-detectable amounts of nitrile. Viscosities of potassium salts of the polyelectrolytes in water were pH dependent with peak viscosities at 8.5. These dispersions were characterized by unusually high viscosities, 15,000 to 26,500 cp at 1% concentration, and by the ability to retain significant viscosities, 300 to 950 cp, upon dilution to 0.03% concentrations. A 1% dispersion of hydrolyzed S-PAN had a viscosity of 5,000 cp in the presence of 8% KCl; however, the depressing effect of added salts on viscosity of aqueous dispersions of hydrolyzed S-PAN increases as the valence of the cation increases.

The pyrolysis of acrylic fiber in inert atmosphere. I. Reactions up to 400°C

Abstract: The pyrolysis of acrylic fiber up to 400°C in an inert atmosphere at 1° and 6°C/min was studied by means of thermogravimetric and differential thermal analysis. The exothermic reaction occuring at 180–300°C was shown to be due to the reaction of nitrile groups by comparing the extent of exotherm with the number of nitrile groups present, determined by infrared spectroscopy. In addition, results of single-fiber tensile measurements, density, and elemental analysis of the pyrolyzed fibers are interpreted in terms of possible molecular structures. The gases evolved on pyrolysis were analyzed for both ammonia and hydrogen cyanide and the liberation of ammonia was attributed to a termination reaction of the polymerization of nitrile groups. The critical conditions necessary for the production of high strength and modulus carbon fiber are discussed briefly in ralation to the chemical changes occurring on pyrolysis.

Young's modulus and secondary mechanical dispersions in polypromellitimide

Abstract: Dynamic mechanical properties were determined in polypyromellitimide at acoustic frequencies over a wide temperature range (80–750°K). Two distinct secondary relaxation effects were found: one (β′) at lower temperature, characterized by a loss maximum at 250°K, and another (β) at higher temperatures with a loss maximum at 400°K. The lower temperature peak is shifted towards higher temperature with increasing frequency following an Arrhenius-type equation (apparent activation energy: 15 kcal/mole); the relaxation strength increases with water content and becomes practically zero when samples dried under vacuum at 200°C are examined. The β′ relaxation process is thus attributed to the presence of adsorbed water molecules. The higher-temperature (β) dispersion, which persists even after dehydration, on the basis of some results obtained for other polymers containing p-oxylphenylene rings in the backbone, is tentatively attributed to torsional oscillations of aromatic rings along the chain.

Spin orientation during acrylic fiber formation by wet‐spinning

Abstract: The molecular orientation acquired during fiber formation of acrylic fibers by wetspinning has been studied. Orientation was detected by measurements of sonic modulus which were converted into an orientation factor. The orientation correlates very well with the ratio of take-up velocity to the freely extreuded velocity. Several mechanisms for the origin of spin orientation are discussed.

Structural characterization of vulcanizates part X. Thiol‐disulfide interchange for cleaving disulfide crosslinks in natural rubber vulcanizates

Abstract: The thiol-disulfide exchange reaction is shown to be applicable to cleavage of disulfide crosslinks in accelerated sulfur vulcanizates of natural rubber. The reaction, in conjunction with the previously reported selective cleavage of polysulfide crosslinks, is used to determine the distribution of crosslink types for several accelerated sulfur vulcanization systems as a function of cure time. Discrepancies between the results and published results obtained using the reagent sodium di-n-butyl phosphite for disulfide crosslink cleavage are discussed.

The stress cracking of polyamides by metal salts. Part I. Metal halides

Abstract: The stress cracking of polyamides (nylons) by a number of metal salts, in aqueous and nonaqueous solutions, has been investigated. Many metal halides and halide-like salts were found to be active stress-cracking agents, while metal acetates and sulfates were inactive. Zinc chloride was found to be most active, and its activity was compared with other metal halides. Using a recording tensometer, time to crack initiation, time to crack-through and time to rupture were determined. These parameters were found to be dependent on temperature, moisture content of the nylon, concentration of the cracking agent and level of stress. High values of all these factors favored rapid cracking. Cracking parameters were shown to be mainly independent of the surface geometry of the nylon and the hydrogen ion concentration of the cracking agent. Metal halides did not appear to cause any chain scission in the nylon and stress cracking was not due to hydrolysis or metal-ion catalysed hydrolysis.

Oxidation of bisphenol a polymers

Abstract: Polysulfone, polycarbonate, and phenoxy resins were aged under thermal and ultraviolet light conditions. Thermoxidative processes in polysulfone and polycarbonate are of such minor significance as not to impart noticeable losses in these materials below 125°C. In phenoxy, however, thermal oxidation above 100°C results in rapid deterioration of all physical properties. This probably results from the low glass transition temperature of this polymer. Photo-oxidation rapidly degrades polysulfone. This appears to be a consequence of scission at the sulfone link. In polycarbonate, however, the only serious result of short-term irradiation is discoloration. For phenoxy resin, crosslinking through reactions at the hydroxyl group is the principal result of photo-oxidation. In all processes the bisphenol A portion of the three polymers appears to play only a small role.

The stress cracking of polyamides by metal salts. Part II. Mechanism of cracking

Abstract: The action of metal halides on polyamide (nylon 6) and secondary amide model compounds has been investigated, using infrared and NMR techniques. Metal halides, which are active stress cracking agents for polyamides, induce characteristic changes in the spectra of both nylon 6 and the model compounds. Two types of changes were observed, depending on the metal halide involved, and on this basis the metal halides have been classified as Type I or Type II. The spectral changes appear to be due to the formation of complexes between the amide group and the metal halide, and structures for these complexes are proposed. Type I metal halides, such as zinc, cobaltII, copperII and manganeseII chlorides, form complexes in which the metal atom is coordinately bonded to the carbonyl oxygen atom of the amide group. These agents cause stress cracking by interference with the hydrogen bonding in the polyamide. Type II metal halides, such as lithium, calcium and magnesium chlorides and lithium bromide in solution form proton donating, solvated, species which act as direct solvents for nylon 6 in a manner similar to phenols and formic acid. Type II agents appear to cause simple solvent cracking.

Transport properties and their correlation with the morphology of thermally conditioned polypropylene

Abstract: Time-lag and static sorption experiments were employed to measure permeability, diffusivity and solubility constants of He, A, and CF4 in polypropylene films cooled at various rates from the melt and subsequently annealed at varying temperatures near the melting point. While solubility constants in films annealed above 90°C showed the normal variation with the amorphous content of the polymer, solubility constants for all unannealed, quenched films were remarkably constant and independent of the rate of cooling. In fact, all quenched films appeared to have the same amorphous content (ca. 41%). The remaining material is believed to be a mixture of monoclinic and hexagonal crystallinity, the volume ratio of the two being a function of the rate of quenching, and changing on annealing, in favor of the more stable, monoclinic form; the transition occurring rather sharply at 90°C. X-ray diffraction provided supporting evidence for the presence of the hexagonal crystals. The diffusion behavior in crystalline polypropylene is normal and Fickian but instead of the usual decline with increasing crystallinity, diffusivities showed definite enhancement in the case of the annealed films, i.e., the expected monotonic decline of D with increasing crystallinity is not observed. This behavior is attributed to a reduction in diffusional impedance through formation of defects in existing crystallites, as the lamellae thicken, in a manner similar to that observed on annealing of polyethylene single crystals. The apparent activation energies of diffusion were essentially constant and independent of thermal history. This suggests that in a highly crystalline polymer diffusion is not so much impeded by the restricted mobility of chain segments but rather by the extremely small dimensions of the available diffusive pathways. In support of the argument that the transport properties of polypropylene are controlled at a level of microstructure well below the characteristic dimensions of spherulities, it was observed that bulk-crystallized polypropylene has a spherulitic structure whose size and texture do not change significantly on annealing.