Noncrystalline Regions Research Articles

The mechanical properties and structure of poly(m‐methylene terephthalate) fibers

AbstractA study has been carried out of the differences in mechanical properties of oriented fibers of poly(ethylene terephthalate) (2GT), poly(trimethylene terephthalate) (3GT), and poly(tetramethylene terephthalate) (4GT). The properties studied include the tensile stress–strain behavior, the recovery from strain, shrinkage at 100°C and the glass‐transition temperatures. The stress–strain curves of the three materials differ markedly. 2GT shows a monotonic increase in stress with increasing strain up to failure, which occurs at ∼20% strain, and the oriented fibers possess a comparatively high initial modulus. 3GT shows a much lower initial modulus and there is an inflection in the stress–strain curve at about 5% strain. The stress–strain curve of 4GT shows a number of distinct features. Although the initial modulus of 4GT is similar to that of 3GT, the stress–strain curve shows a pronounced plateau in the region between 4% and 12% strain. At higher strains the stresses rise rapidly before failure. These features of the stress–strain curves in the three polymers can be related to previous studies where the x‐ray diffraction spectrum and the Raman spectrum have been examined for fibers under stress. The ranking of both the recovery and shrinkage behavior of these materials is in the order 3GT > 4GT > 2GT. These results can also be understood in terms of the results of the previous structural studies, and it is concluded that the molecular conformations in both the crystalline and noncrystalline regions play a key role in determining the mechanical behavior.

TEMPERATURE DEPENDENCE OF THE THERMAL CONTRACTION OF ORIENTED POLY (ETHYLENE TEREPHTHALATE) FILMS

Highly drawn poly (ethylene terephthalate) (PET) films were crystallized in air at Ta=130-180°C for one hour. These films (named O. S.) shrunk freely by heating in air at Tc=200, 220 and 230°C for 30min. and the changes in x (degree of crystallinity), _??_ (Scherrer's size of crystallite), L (long period), f (X-ray orientation degree), l (length of film) and S (thermal shrinkage) were traced. Plotting these parameters against ΔTr=Tc-Ta, changes in temperature causing films to contract, the following results were obtained:(1) Relation between S(Tc) and ΔTr, was approximately linear (Fig. 5).(2) The rate of increment of x, _??_, L was nearly proportional to ΔTr (Fig. 4, Fig. 7-9 and Fig. 13).(3) The rate of decrement of n=1/_??_ and the rate of increment of r=(L-_??_) was also nearly proportional to ΔTr, (Fig. 11 and Fig. 18).The results of (1) and (2) showed that the higher the degree of crystallinity of O. S., the lower the amount of shrinkage decreased. Assuming the structure of the annealed PET film as the two-phase model of alternating crystalline and non-crystalline regions, the results of (2) and (3) indicated that thicknesses of each lamellar and inter-lamellar regions (_??_ and r) increased on contraction thermally, whereas the numbers of layers of lamellae (n) in the drawn direction of film became smaller. These contractive behaviors seemed to be reasonable compared with the temperature ranges of crystallite-recrystallization into lamellae of PET films2).

Effect of fungal degradation on mechanical properties of cellophane

AbstractChanges in dynamic mechanical properties of cellophane films due either to fungal attack or to hydrochloric acid hydrolysis have been measured. It appears that damage caused by cellulase enzymes that are released from a fungal overgrowth is localized in noncrystalline regions. These effects include a substantial reduction in elastic modulus, a reduction in temperature at which relaxation processes involving chain segmental mobility occur, and a broadening of loss tangent peaks due to segmental mobility and to rotations of methylol groups. Comparing results obtained from cellulase hydrolysis with those obtained from acid hydrolysis, it is clear that enryme attack proceeds by a characteristic and selective process. Implications regarding the embrittlement often seen to accompany biodegradation are discussed.

Translation of silk fibroin messenger RNA in an Ehrlich ascites cell-free extract.

RNA identified by its base composition and T1 RNase oligonucleotide pattern as the message for silk fibroin was purified from mature posterior silk glands of Bombyx mori larvae and used to direct polypeptide synthesis in an Ehrlich ascites cell-free extract. Fibroin mRNA stimulated [3-H]alanine incorporation about 3- to 4-fold in the presence of 80 mM K+ and 4 mM Mg-2+. The stimulation was reduced in the presence of 5 times 10-minus 6 to 10-minus 4 M aurintricarboxylic acid, an inhibitor of the initiation of protein synthesis. The cell-free products were heterogeneous in size, including peptides as large as 100,000 daltons. They co-precipitated with carrier fibroin sequences after digestion with trypsin. A large fraction of the polypeptides synthesized in response to fibroin mRNA was precipitated by antiserum directed against amino acid sequences in noncrystalline region polypeptides of fibroin. Furthermore, after digestion with chymotrypsin, a major fraction of the cell-free products specifically co-precipitated with crystalline region sequences of native fibroin. The size and amino acid composition of the fibroin crystalline region polypeptides isolated from the cell-free products were similar to those from native fibroin.

Thermodynamic Stability and Melting of Crystals in a Bulk Polymer

A lattice theory is developed for a partially crystalline polymer on the assumption that an equilibrium between crystalline and noncrystalline regions is attained under a limited condition. The two extreme cases, where the noncrystalline part is exclusively composed of either chain loops or tie chains connecting different crystals, are treated by considering both intra- and interchain interactions along with the amorphous chain length distribution. The rise in the melting point of a bulk crystalline polymer on stretching is well explained by applying an appropriate criterion to it.

The Radiation Grafting of Silicone onto Rayon and Acetate

The method of radiation grafting of silicone onto cotton was applied to rayon and acetate with the following results : 1) Although, as known, grafting usually occurs at the noncrystalline region of the polymer, both the rate of grafting and the crystallinity of cotton are greater than those of rayon. Therefore, in this system the grafting does not depend only on crystallinity. 2) The rate of grafting on rayon is less than on acetate. The concentration of peroxide formed by 1.9 Mrad of γ-irradiation is 0.52 X 10-2 mol/l in rayon and 1.30 X 10-2 mol/l in acetate. The radiation sensitivity is increased by the acetylation of. OH-groups in cellulose. It is concluded that the grafting of this system depends on the number of radicals formed. 3) The water repellency properties of silicone-graft-rayon-and-acetate show that the structure of the grafted silicone on the surface of the base polymer by irradiation differs from that of the coated silicone prepared by heating in the presence of a catalyst.

Amorphous structure heat: Temperature dependence of heats of solution for polystyrene in toluene and ethylbenzene

Abstract When a polymer is dissolved in a solvent, the heat measured is a sum of a polymer-solvent interaction term and a term related to the structure that existed in the solid polymer relative to its amorphous liquid state. This latter contribution, termed the “residual” heat, can have an endothermic contribution due to the fusion of crystalline regions and an exothermic contribution due to the disruption of structure in noncrystalline amorphous regions. For atactic polystyrene between 30 and 110°C, it is shown that the “residual” heat is exothermic, decreases linearly with temperature differences below Tg, and extrapolates to zero in the vicinity of Tg. The existence of an exothermic heat above Tg is probably related to a 160°C transition in polystyrene. This “residual” heat was further observed to be independent of the pressure at which the polystyrene was glassified.

Near‐infrared spectrum of cellulose: A new method for obtaining crystallinity ratios

AbstractAbsorption bands in the near‐infrared (NIR) spectrum of cellulose were correlated with crystalline and noncrystalline regions and used to derive a new crystallinity ratio. NIR crystallinity ratios of both natural and regenerated celluloses were measured and compared with x‐ray diffraction values. The data indicates that the NIR crystallinity ratio may also depend upon crystallite size.

The Crystalline State of Macromolecular Substances

AbstractUnlike low molecular weight substances, high polymers do not crystallize completely. However long the crystallization process is continued, they still consist of a mixture of crystalline and non crystalline regions. In the undrawn material, these regions form larger units which are known as spherulites. Questions that are of special interest concern the arrangement of the chains in the noncrystalline regions, the causes of chain folding, and the imperfections in the crystals. The incomplete crystallization is a consequence of kinetic inhibitions. This can be deduced from the fact that the crystalline fraction increases with rising crystallization temperature. If polymerization is carried out in the solid crystalline state, one obtains a completely crystalline polymeric material.

Effect of morphology on the dynamic mechanical properties of a semicrystalline polysiloxane

AbstractThe dynamic mechanical properties of semicrystalline poly(tetramethyl‐p‐silphenylene siloxane) in three morphological preparations were measured over the wide frequency range of about 0.002 Hz to 500 Hz and the temperature range of about − 190°C to 100°C. The three samples were all isothermally crystallized at 125°C. Two samples had a spherulite size of 25 μ diameter but differed in the time allowed for secondary crystallization. The other sample had a smaller spherulite size. By assuming compliance additivity, the viscoelastic behavior could be separated into five relaxation processes with an indication that a sixth existed at low temperature. Two processes called γ1 and γ2 could be resolved at low temperatures. The γ1 process was associated with the amorphous region since the peak strength was affected by the rate of cooling through the glass transition region; the γ2 peak, unaffected by cooling rate, is attributed to the crystalline part. In the high‐temperature region, the β peak is associated with the glass transition and has a shape and location that is essentially independent of the morphology. The highest temperature α2 process, whose maximum was not observed in the experimental range covered, is attributed to the crystalline region and is sensitive to changes in crystallization history. The strength of the α1 process unlike that of the other processes was found to be a function of temperature; it was associated with the noncrystalline region.

Multiple relaxation in α- and γ-loss bands of polyethylene

Abstract Dielectric and NMR behavior of linear polyethylene was observed in the α-and γ-loss bands in order to investigate the nature of the multiple loss patterns of these loss bands. The results obtained are compared with those of mechanical measurements. In the dielectric behavior of oxidized linear polyethylene, three relaxations are found in the γ-loss band, while only one relaxation is found in the α-loss band. The β-relaxation is found as a plateau region between the α-and γ-loss bands. The loss pattern of the α-loss band is different from that for the mechanical case which is composed of three relaxations. The effects of difference in morphology, addition of diluent, and heat treatment on the multiple loss patterns are examined. The results suggest that there are two noncrystalline regions in the exterior part of lamellae, including lamellar surfaces, and the two modes of molecular motion in each of these regions are responsible for each pair of relaxations; of the three relaxations found in the γ-loss band the γ2-relaxation is related to the dielectric α-relaxation, while the γ1-relaxation is related to the β-relaxation. The relation between the two relaxations in each pair is similar to that between the primary relaxation due to micro-Brownian motion and the local mode relaxation of amorphous polymers which are caused by the two modes of motion of the same molecules. The γ3-relaxation seems to be caused by some different mechanism.

Quantitative structural characterization of the deformation and shrinkage of isotactic polypropylene fibers and films

Abstract A quantitative determination has been made of the structural elements which control deformation and shrinkage processes in isotactic polypropylene fibers and films. It is found that strain processes such as fabrication draw and shrinkage are controlled by the noncrystalline region of this highly crystalline polymer. Quantitative structure-property correlations are obtained for the polymer, which reveal the interactions between temperature, strain, and orientation. The thermal activation energy of the noncrystalline chains is also determined from these solid-state structure measurements.

Dielectric relaxation of polyethylene below 4° K

Measurements of tanδ for polyethylene for frequencies around one kHz down to temperatures of 4.2° K show an increase in the dielectric loss (Fallou andBobo) (1). We have repeated these measurements with very sensitive equipment over a range of frequencies up to several kHz and down to temperatures of 1.2° K. We find maxima in tanδ as a function of temperature and frequency. It thus seems possible for there to be an activated mechanism at these very low temperatures. The values of the activation energy are of the order of only some cal/mol instead of the more usual kcal/mol. The loss peaks are observed in “as received” material, i. e. fabricated films and pressed plates. Additives and contaminations do not seem to play any role. The loss peaks are observed in stretched, particularly stretched crystalline, material. The dielectric losses vanish for melted and then slowly cooled or quenched material. Molecular rearrangements in the interface between crystalline and non-crystalline regions of the material may play a role in causing these losses.

Mechanical anisotropy in oriented polypropylene

Abstract The low strain mechanical anisotropy of various oriented samples of isotactic polypropylene has been determined over a wide range of temperatures. The samples were prepared by cold drawing, cold drawing followed by annealing at selected temperatures, hot drawing, and hydrostatic extrusion. Modulus measurements and dynamic mechanical measurements were combined with wide-angle and small-angle X-ray diffraction data in attempts to relate the mechanical anisotropy to the morphological structure. In the temperature range studied, the mechanical anisotropy is affected mainly by the B-relaxation process. For cold-drawn material, the effect of annealing on the anisotropy has been interpreted in terms of the relaxation of the noncrystalline regions and the development of the lamellar texture. This allows interlamellar shear to occur at temperatures above the B-relaxation in highly annealed samples, so that the a-relaxation then shows the loss anisotropy predicted by a simple model for an interlamellar she...

Investigation of the glass transition and melting of polymers by nuclear magnetic resonance

AbstractInvestigations of the glass transition and melting of partially crystalline polymers by nuclear magnetic resonance provide valuable information on the nature of noncrystalline regions. The broad line NMR signal was separated into a narrow component and a broad component by using a new method which does not imply the ambiguity usually present. From the intensity of the narrow component the mobile fraction was determined. This fraction was extrapolated to “infinite” temperature. By subtracting the mobile fraction from the noncrystalline fraction, the noncrystalline rigid fraction was obtained. Comparison of the measured second moments of the two components of the NMR line with calculated second moments of chains with fixed ends shows the following: The mobile fraction is formed by chains with either one end fixed or both ends fixed in a comparatively small end‐to‐end distance (for example, loops with adjacent reentry); the noncrystalline rigid fraction is formed by chains whose ends are fixed in a comparatively large or medium end‐to‐end distances (for example, tie molecules connecting different crystals).More detailed information on the chains forming the mobile fraction as well as on the structure in the melt was obtained by high resolution NMR. It was shown that near range order in the melt, for example, the formation of bundles of parallel chains, causes deviations from the lorentzian shape of the NMR line. During primary crystallization the chains within the bundles of parallel chains crystallize. During secondary crystallization, extremely mobile chains outside these bundles are incorporated into the crystals.

The morphological consequences of annealing high‐density polyethylene in solvents

AbstractWhen a semicrystalline polymer imbibes solvent molecules at near‐ambient temperatures it is very probable that the crystalline regions are not affected. The noncrystalline regions swell to accommodate the solvent and may also undergo structural changes which are not reversed on removing the solvent. If this happens, the sorptive capacity of the polymer is permanently changed. Pretreating a polymer membrane with liquid solvent has the same effect on sorption measurements as pretreatment with the corresponding saturated vapor only when special precautions are observed. High‐density polyethylene films were used throughout the investigation, and p‐xylene was the organic permeant. Numerous measurements of sorption and permeation rates were made, and the results are discussed in terms of a new model for the behavior of noncrystalline chains in a semicrystalline polymer. The shorter tie molecules running between the crystalline lamellae appear to be of crucial importance, and slight modification of these may have a large effect on the sorptive capacity of the sample as a whole. The possibility of solvent molecules clustering in the swollen polymer is considered in an Appendix.

Polytetrafluoroethylene: Effects of γ‐radiation on fine structure

AbstractThe structure of granular polytetrafluoroethylene has been studied by electron microscopy. On the basis of the texture of surfaces resulting from fracture a model of the structure is proposed which suggests that PTFE consists of extended chain crystals with both inter‐ and intra‐lamellar noncrystalline regions. The effects of γ‐radiation on the structure have been investigated by examining the texture of irradiated fracture surfaces and also the texture produced by post‐irradiation fracture. The irradiations have been performed in vacuo and in oxygen. In both atmospheres PTFE undergoes degradation with a concurrent increase in crystallinity. However, the texture of the surfaces of high crystallinity PTFE, prepared by radiation, differs markedly to the texture of fracture surfaces of high crystallinity PTFE prepared by thermal annealing. It is proposed that radiation causes rupture of bonds in the interlamellar (chain fold) and intralamellar regions, resulting in the production of chain ends and interlamellar links. Due to scavenging of the free radicals, interlamellar linking is pobably a minor process with irradiation in oxygen. These chemical changes cause modifications to the extended chain lamellar crystals and consequently alterations to the physical properties of the polymer.

Non-crystalline Region in Fiber Structure

Non-crystalline Region in Fiber Structure

Morphology of polyethylene microfibrils and “shish kebabs”

Abstract Gold decoration was applied to elucidate the morphology of annealed and unannealed oriented structures produced by shearing of polyethylene single crystals of known thicknesses, and the morphology of drawn and undrawn “shish kebabs” obtained by stirrer-induced crystallization. Distinct Au periodicities were observed perpendicular and parallel to the unannealed oriented structure, revealing distinctly the presence of microfibrils and an alternation of crystalline and noncrystalline regions within a given microfibril of which the periodicity is, however, found to be much larger than the corresponding original crystal thickness. Annealing resulted in fibrils being completely replaced by lamellae standing edgewise with the Au particles decorating directly on top of the edge but concentrated mainly on the folds leaving the crystalline region almost entirely void of gold. Deformation studies revealed an unusual ductility associated with the shish kebab structure, with the kebab splitting first, then di...

NMR observations of drawn polymers. VIII. Doubly oriented nylon 66

AbstractA wide‐line NMR study of chain segmental motion in nylon 66 has been made on a rolled sheet having “double orientation.” In this sheet the crystallite c axis, i.e., the molecular chain axis, is oriented preferentially along the roll direction, and the crystallographic (010) plane lies predominantly parallel to the roll plane, or the plane of the sheet. The direction of the applied magnetic field with respect to the sheet is characterized by two angles, the polar angle γ subtended by the roll direction and the magnetic field, and an azimuthal angle ϕ. NMR spectra were taken at various values of the angles γ and ϕ and at three temperatures −196°C, 20°C, and 180°C. The second moments of the absorption spectra taken at 180°C were compared with theoretical predictions of second moments based on two models for the high‐temperature segmental motion (called the αc process) in crystalline regions of nylon 66. One model consists of rotational oscillation with amplitudes δ of segments around their axies. The second model is denoted 60° flip‐flop motion and consists of rotational 60°C jumps of the segments around their axes between two equilibrium sites with the possibility that the segments also oscillate with a general amplitudes δ around each site. The experimental results are consistent with fairly large amplitudes δ, in which case both models approach the limiting case of full segment rotation. For this reason the experiments do not allow a distinction between the two models. From the second moments at −196°C and 20°C the decrease in second moment due to the low temperature segmental motion, the γ process, is obtained. This motion occurs in noncrystalline regions of nylon 66 and is found to cause a decrease in second moment which is strongly dependent on the two angles γ and ϕ, implying double orientation of the noncrystalline segments. It is suggested that at low temperatures the noncrystalline segments become immobilized in sites dictated by the crystallite orientation through the extensive hydrogen bonding known to exist in nylon 66.