Showing papers in "Journal of Polymer Science Part C: Polymer Symposia in 1971"

The use of adsorbed cellulase in the continuous conversion of cellulose to glucose

Abstract: Cellulose strongly adsorbs cellulase at pH 4.0-5.0, 25-50°C, conditions which are optimum for the enzyme action. The adsorbed enzyme is sufficient to digest the cellulose with no replenishment of enzyme even though the liquid phase containing the sugar is continuously removed. As cellulose is digested, the released enzyme is readsorbed on excess or newly added cellulose with retention of activity. Sugars can be separated from the enzyme-cellulose complex by simple filtration or centrifugation or by retaining the enzyme-cellulose complex in a column from which the sugar solution is eluted. Adsorbed cellulase has been used to produce syrups containing 5-14% glucose continuously from stirred reactors containing 10-20% cellulose, or from cellulose columns.

The effect of liquid anhydrous ammonia in the structure and morphology of cotton cellulose

Abstract: The effect of liquid ammonia on cotton fabric was studied using x-ray diffraction (XRD) and electron microscopy. A phase diagram is presented describing the relationship between disordered cellulose, cellulose I, and cellulose III. The transition from cellulose I to III proceeds through the liquid ammonia. Cellulose III is obtained upon drying the ammonia-cellulose without the presence of water. Treatment of the cellulose III or of the ammonia-cellulose with water brings about the formation of cellulose I. The degree of crystalline order achieved in water is enhanced by heating, which is consistent with a glass transition temperature between room temperature and 100°C. The cellulose III crystallites obtained are much smaller than those of cellulose I,16-23Aas against 50-80A The interaction of ammonia with cotton cellulose is faster than with other swelling agents, such as ethylamine. The penetration of ammonia into the secondary wall of the cotton fiber is not only along the concentrical rings, as is the case with water, but also radially across the rings. Prolonged soaking in water increases the crystallite size with simultaneous rejection of swelling water.

Ideas on the ultrastructural organization of the cell wall components

Abstract: The wood cell wall is composed of chemically and structurally different components. The cellulose molecules are smooth long chains, able to aggregate in longitudinal direction to compact fibrils. The polyoses consist of shorter chains with side groups and branching points so that they are not able to aggregate in such a strict order as cellulose. The orientation system of the cell wall and the behavior of isolated polyoses give reason to suppose that the polyoses are not coiled forming globular particles within the cell wall. From the ontho-genetic point of view, lignin is the last component which is incorporated into the cell wall. The different possibilities of branching resulting from the chemical characteristics of the phenylpropanone monomer enables the formation of large molecules embedding the polysaccharide elements and filling up the remaining cavities. The results of chemical and electron microscopic studies are projected into a model representing a possible ultra-structural organization of the components within the wood cell wall.

Tracer study of kinetics and mechanism of hydrolytically induced interfacial failure

Abstract: Analysis of the kinetics of hydrolytic desorption of chemisorbed C-14 labelled polymeric APS (gamma-aminopropyltriethoxysilane, a coupling agent for glass reinforced epoxy resins) from flat silica or borosilicate surfaces, indicated that the polymer probably consisted of short chains each chemisorbed at one end to the surface with little or no cross-linking. A method was developed to determine from kinetic data whether or not more than one type of bond is severed during the desorption process. Application of the method to these results indicated that more than one type of linkage was being hydrolyzed in the desorption of APS. Glass-epoxy adhesive joints were prepared from glass containing various amounts of APS chemisorbed to the surface. In one set of experiments, the amounts were varied through aqueous extraction of increments of the originally deposited material. In a second set, the amounts were varied by adsorption from very dilute solution. The lifetimes of the adhesive joints were measured under static load in hot water. It was found that the maximum lifetime is not dependent on the thickness of the chemisorbed layer, but that it is dependent on the lateral surface concentration of the chemisorbed polymeric units. Examination of the debonded joints for radioactivity indicated that failure resulted from hydrolysis of siloxane bonds in the coupling agent structure.

Chain scission and plastic deformation in the strained crystalline polymer

Abstract: Depending on temperature and load rate an unoriented polymer solid under sufficiently large applied stress either deforms plastically (high temperature, low rate of loading) or undergoes brittle fracture (low temperature, high rate of loading). The fracture proceeds through the areas of minimum strength, i.e., along the boundaries between adjacent spherulites and between parallel lamellae. Very few chains, i.e., interlamella tie molecules and molecules bridging the crack if a crystal lamella is broken, are ruptured during this process. Hence the number of radicals per cm2 of new surface is small, about 1013/cm2. The plastic deformation gradually transforms the sample into the extremely well oriented fiber structure of much higher elastic modulus and strength but of smaller strain to break. The basic element of the fiber structure is the long and narrow microfibril formed by micronecking of the crystal lamella. The microfibril consists of fully oriented folded chain blocks connected by a great many tie molecules obtained by partial chain unfolding in the micronecks. Their number per amorphous layer increases with the draw ratio and so does the tensile strength of the microfibril. Under load the fiber structure breaks at very small strain. The fracture proceeds through the weakest elements of the structure, i.e., through the boundary between adjacent microfibrils and the amorphous layers between subsequent blocks of the microfibrils. With axial stress the fracture must cut at least one full cross section of the fiber and hence rupture about 1014 intrafibrillar tie molecules per cm2. ESR experiments show long before the final break a much higher number of radicals throughout the whole strained sample upto 1017/cm2. The number of broken chains depends on strain and not on stress. One imagines that at every applied strain one breaks the most strained tie molecules which as a consequence of stress concentration have to carry most of the load. The stress concentration caused by the special morphology of the microfibrils and tie molecules reduces the tensile strength of the polymer far below the theoreticall limit calculated for uniform stress field even if one considers that the number of chains passing through the fracture plane is only a fraction of the maximum number calculated with all macromolecules extended and perfectly aligned.

Relationship between structure of drawn polymers and molecular motion

Abstract: In order to study the relationship between structure and molecular motion, drawn polymers are more suitable than isotropic samples since their morphology can be characterized more easily by quantitative methods such as small angle X-ray scattering (SAXS) and electron microscopy (EM). The effects of changes in morphological structure on molecular motion are demonstrated by comparing the results of the SAXS and EM measurements with the dynamic mechanical behavior of drawn polyethylene. In addition the NMR broad line spectra of these samples were analyzed and the influence of annealing conditions and external stress was investigated.

Effect of tension and temperature on crystalline polymer texture

Abstract: A variety of annealing treatments at elevated temperatures have been characterized by a specific infrared absorption assigned to the folded chain segments in polyethylene terephthalate fibers. The higher the annealing temperature, the more regular is the chain folding introduced into the fiber. When a fiber is free to contract, it will have a much larger amount of refolding than one which is held at constant length. Stretching is able to prevent refolding at low temperatures but in these experiments stretching was not able to prevent refolding at the highest temperature. By comparing the above infrared results with small angle X-ray diffraction and broadline nuclear magnetic resonance techniques, it is now possible to give validity to the interpretation that chain folds are major contributors to the long period. The external tension applied to a fiber during an annealing treatment will determine the internal shrinkage tension caused by the molecules during subsequent reheating. If chain refolding is allowed to occur during annealing, the potential for subsequent shrinkage and the amount of internal shrinkage tension are lowered, and higher temperatures are required to activate additional shrinkage. It thus appears that a major contributor to shrinkage and shrinkage tension in an oriented fiber is the refolding of molecules during thermal activation.

Oxidative reactions of cellulose initiated by free radicals

Abstract: Oxidative reactions in cellulose are commonly initiated by thermal, ultraviolet, and high-energy radiations and by chemical oxidation. Long-lived free radicals, formed in cellulose on the localization of energy from thermal, ultraviolet, and high-energy radiations, and short-lived free radicals, formed in cellulose by oxidation, e.g., by ceric ion or redox reactions, were investigated by electron spin resonance spectroscopy. Dehydrogenation and oxidative depolymerization reactions of cellulose are indicated. The physical, chemical, and morphological effects of these free-radical initiated reactions on cellulose are summarized. The formation of free radicals in cellulose also increases the chemical reactivity of cellulose, particularly for chain copolymerization reactions with vinyl monomers. Preparation of cellulose-poly(vinyl) copolymers, using free-radical initiation, yields paper, film, wood, and textile products with new physical and chemical properties.

Rotational isomerism, microstructure and molecular motion in polymers

Abstract: In the first part the microstructure of polymer melts and semicrystalline bulk material is treated on the basis of the bundle model and with molecular parameters. The meander-shaped arrangement of the bundles in the amorphous phase can be founded thermo-dynamically and leads to a radius of the meander of 50 A. Based on this model a molecular theory of the relaxation processes (α, β, γ) is given and experimentally proved for linear polyethylene. In the last part both limiting cases of the deformation behavior are quantitatively derived in a molecular picture: the ideal plasticity illustrated by the yield stress of linear polyethylene and the ideal para-elasticity illustrated by the stress-strain curve of the drawn polyamide fiber.

Dynamic mechanical behavior of partially hydrolyzed ethylene‐vinyl acetate copolymers

Abstract: A dynamic mechanical study has been made of two series of partially hydrolyzed ethylene-vinyl acetate copolymers. Series A contains 75 mole % ethylene and series B contains 59 mole % ethylene. The frequencies employed were 3.5, 11, and 110 Hz, and the temperature range was from −180° to +120°C. Three relaxation regions are discernable in this range and these are labeled α, β, and γ in order of decreasing temperature. The α relaxation is associated with the glass transition of the copolymers. The β relaxation is absent in the unhydrolyzed copolymers and is dependent on hydroxyl content. It is assigned to local motions of hydrogen bonded groups. The γ relaxation is insensitive to hydroxyl content and is assigned to local motions of methylene sequences. The above assignments are supported by the effect of water added to the polymers. Added water decreases the temperatures of the α and β relaxations but does not affect the γ relaxation significantly. The magnitude of the β relaxation is considerably enhanced by water.

Fibrillar lignin or fibrillar pectin

Abstract: Previous work had demonstrated that an ultraviolet absorbing, fibriliar substance is present on the outer wall surface of suspension-cultured cells and between adjacent cells. The fibrils were called lignofibrils on the basis of their resistance to enzyme attack, ultraviolet absorption, alkaline nitrobenzene degradation, and extraction by aqueous dioxane. However, more complete chemical analysis of the fibrils demonstrates that their major component is a linear polygalacturonic acid to which an ultraviolet absorbing compound(s) is attached. The term lignofibril for this material is therefore withdrawn. Extended fibrils exhibit no detectable close-range order by X-ray diffraction. Similar fibrils have now been observed in native tissues, but their biological function is still problematical.

Twisting energy of holocellulose fibers

Abstract: Freely drying fibers exhibit collapse and twist behavior that is only infrequently observed in the formation of a paper web. Anisotropic fiber shrinkage models are employed that enable calculation of the twisting energy of a freely drying fiber as well as the reverse case (dry to wet). The twisting energy appears to be highly significant in relation to the fiber and bond energies associated with paper strength. Some experimental results with southern pine fibers have been obtained using specially designed testing devices.

Distribution of substituents in partially acetylated cellulose

Abstract: The distribution of substituents in a partially acetylated cellulose (DS 2.4) has been determined. 0-Acetyl groups were replaced by 0-methyl groups by using methylsulphinyl sodium and methyl iodide on a product, in which the original free hydroxyl groups had been protected by reaction with methyl vinyl ether. The methylated sugars obtained on acid hydrolysis of this product were converted into alditol acetates and analyzed by GLC-mass spectrometry.

The behavior of cotton cellulose and beech wood in ammonia atmosphere

Abstract: In order to learn more about the plasticization of wood, sorption measurements on cellulose rich specimen, cotton fibers, and bending tests on beech wood were performed in ammonia atmosphere. The results showed that the sorption of NH3 on cotton was substantially hindered at low relative vapor pressure, presumably due to interaction of NH3 with hydrate water. Near the saturation pressure a reduction of the sorption capacity was observed because of developing collapse in the capillary system. In the middle relative vapor pressure range the equilibria were retarded while the active surface area was extended to more than double. Observations at different temperatures-15, 25, 35°C, revealed that the extension of the sorptive area took place consistently at the same ammonia content of the specimen. The other mentioned diverging sorption features, however, were intensified variously by raising the temperature. No difference was found between the ammonia sorption properties of cellulose I and III. Bending tests on beech wood laths in ammonia environment displayed a dynamic progression of the plasticization. At the beginning of the exposition to ammonia the bending ability of the specimen was increasingly enhanced. When in course of the plasticization the modulus of elasticity of the laths dropped below 1/3 of the starting value, bendability changed by levelling off progressively. The conclusion thereof that the plasticization of wood can be forced only to given limits was confirmed by destructive bending tests and by porosimetric measurements. To reach a sufficiently softened state of the beech laths with dimensions 25×1×0.6 cm, 15 min appeared to be enough while further alterations could be observed even on the smallest specimen size for considerably longer periods.

Thermal dehydrochlorination of poly(vinyl chloride) models in the liquid phase

Abstract: An investigation was made of the kinetics of thermal dehydrochlorination of 8-chlorohexadecane, 2,4-dichloropentadecane, 4-chloro-2-dodecene, 8-chloro-6-tridecene, 6-chloro-2,4-octadiene, and 7-chloro-3,5-nonadiene in the liquid phase in an inert gas. The course of the reaction is accelerated by the presence of free hydrogen chloride and slowed down by conjugated dienes and trienes. Destruction of the model compounds leads to the formation of oligomers and telomers, some of which were isolated and their elementary composition and molecular weight determined. The reaction occurs much faster in nitrobenzene, compared with the dehydrochlorination of a model without solvent. With respect to its complicated mechanism, the dehydrochlorination reaction was characterized from the kinetic viewpoint by its initial rate kO. Parameters E and A were estimated from the temperature dependence kO = A exp(−E/RT). It follows from the experimental results and from the comparison of thermal dehydrochlorination reactions in the gas and liquid phases and in poly(vinyl chloride) that the reaction under investigation occurs by a ionic mechanism in the liquid phase, and most probably also in the polymer.

Rheological properties of dilute and concentrated solutions of polyvinylchloride branched by irradiation

Abstract: Following a previous study of two commercial poly(vinyl chloride) polymers, with Mw values of 130,000 and 70,000, the influence of γ radiation on the concentrated solutions of two other polymers in tetrahydrofuran was investigated. Their Mw values were 51,000 and 700,000, respectively; the second sample being crosslinked by copolymerization with a polyfunctional monomer. The irradiation-induced changes were investigated by osmometry, light-scattering, gel permeation chromatography and dilute and concentrated solution viscometry. From the experimental data obtained, it can be seen that the viscosity-molecular weight relations are strongly affected by the molecular weight distribtuion and the presence of branching in the samples. By assuming the Stockmayer distribution, and using the equations developed by Kilb, the viscosities of the irradiated samples have been described satisfactorily.

Plasticizing wood with ammonia‐control of color change

Abstract: Recent studies of plasticizing wood with anhydrous ammonia have demonstrated that pronounced changes in the color of wood can occur. These changes are thought to be the result of various oxidation and condensation reactions that are enhanced by ammonia. It was postulated that pretreatment of the wood with sulfur dioxide would effectively block these reactions and thus lead to little, or no, color change in subsequent ammonia treat-ment. A series of tests were run on maple, birch, red oak, and douglas fir specimens that confirm this hypothesis. Reflectance spectra over the range of visible wave lengths show that both liquid ammonia at −35°C and gaseous ammonia at +25°C darken the wood with more darkening occurring at the higher temperature. Pretreatment with sulfur dioxide followed by gaseous ammonia treatment to a highly plastic state results in only slight changes in color while the reverse procedure (NH3 first followed by SO2) results in considerable color change.

Study of the degradation of poly(vinyl chloride) compounds by dielectric spectroscopy

Abstract: A continuously recording dielectric spectrometer was constructed to investigate the effects of degradation on the dielectric spectra and ac conductivities of poly(vinyl chloride) (PVC) compounds. Dielectric spectra were found to be affected by the thermal history of the sample. The elimination-type degradation in hard PVC and in plasticized PVC compounds could be kinetically studied by recording ac conductivity as a function of reaction time. The method was found to be useful for studying the efficiency of stabilizers in a simple way. Changes in the physical structure during the course of degradation could be measured by observing shifts and distortions of the Tg-dispersion signals.

Monomolecular films of poly [methyl(n‐alkyl)siloxanes] on organic liquids

Abstract: A series of poly [methyl(n-alkyl)siloxanes] were studied as insoluble monomolecular films on the following organic substrates: tricresyl phosphate, propylene carbonate, diethyl phthalate, and a highly chlorinated polyphenyl (Aroclor 1242). The siloxanes were discovered to form stable, insoluble, reproducible monomolecular films at each organic liquid/air interface. Film pressure (F) vs. area/molecule (A) isotherms were determined in each instance and were compared with previously determined F-vs.-A isotherms for polydi-methylsiloxanes on the same organic substrates as well as on water. By combining the film balance data with molecular dimensions calculated from ball models, it was possible to make several tentative conclusions regarding the conformation of the adsorbed siloxane molecules as a function of film pressure, n-alkyl chain length and substrate composition. The F-vs.-A curves for the poly(methylethylsiloxane) and polydimethylsiloxane films were consistent with the assumption that they assume a helical configuration when compressed at organic liquid/air interfaces; however, there is little evidence to indicate whether the polymer chains become fully extended at higher areas/molecule or remain in a somewhat coiled configuration.

Preparation and water absorptive capacity of sodium cellulose carboxylate

Abstract: Sodium cellulose carboxylate was prepared by oxidation of cellulose with gaseous nitrogen dioxide followed by treatment with buffer at pH 7.0. The oxidation reaction rate increased with higher initial gas flow rates, higher total weights of nitrogen dioxide and with nitrogen dioxide pressures higher than 1 atmosphere. Moisture acts as a weak catalyst but is also responsible for loss of nitrogen dioxide by formation of nitrogen acids. Sodium cellulose carboxylate absorbs much more water than cellulose. It is formed without loss of fibrous character or gel formation and with high water absorptivity only if an efficient buffer is used at pH 6.5 to 7.0. Higher pH levels lead to gel formation; lower pH levels lead to impaired absorptivity. Salt formation rate appears to be a diffusion controlled process which is highly sensitive to localized depletion of buffer solution. Use of NaOH in place of buffer does not give the highly absorbent salt. Gelation occurs instead. The diameter of 6-carboxy cellulose fibers prepared from softwood pulp increases about 90% during the pH 7.0 buffer treatment.

Application of gpc to studies of the viscose process. III. Effect of various treatments of rayon print cloth on the molecular weight distribution of cellulose

Abstract: Gel permeation chromatography (GPC) has been used to determine the molecular weight distribution of cellulose in rayon print cloths. The fabrics were made from a regular and a high wet modulus rayon with staple length of 1 9/16 inches in an 80 × 80, 31 × 41 singles construction. The effects of various treatments of the print cloths including bleaching exposure to UV and abrading on the yarn properties and the molecular weight distribution were determined. With chemical treatments, the changes in the molecular weight distribution in both warp and fill were similar. The chemical reactions with the fabric immersed in solution were fairly uniform throughout the yarn and in the filaments. In this group, bleaching drastically reduced the average molecular weight. Degradation due to abrasion and flexing was severe. Results indicate that the larger molecules are particularly susceptible to mechanical degradation. The detritus from abrasion of the high wet modulus and the regular rayons had similar, relatively narrow molecular weight distribution. The changes in yarn properties and distribution on washing were primarily the result of mechanical damage. Heating at 400°F for 30 min substantially changed the staining characteristic of cross sections of the yarns. The molecular weight distribution width increased on heating and for these samples, the weight average molecular weight determined from GPC was significantly greater than the value determined viscosimetrically.

Viscosity and the prolate ellipsoid model applied to low molecular weight cellulose triacetate fractions

Abstract: Cellulose triacetate of molecular weight 5,600, obtained by acetolysis, and separated into 15 fractions by preparative permeation chromatography, was analyzed for intrinsic viscosity, number average, and weight average molecular weight. Glucose pentaacetate, cel-lobiose octaacetate, and cellotriose hendecaacetate are also included in the analysis. The axial ratios of a prolate ellipsoid calculated from the viscosity of the low DP CT A fractions, when compared to a molecular model and to the fully extended contour length, confirm the persistence length found by viscosity theory at high molecular weight levels. A long plateau region of slope 0.28 to ca. DP 8, is found in the log-log [n] versus DPn plot. The curve then rises sharply to slope ca. 2.0 at DPn 10 and declines again to slope ca. 0.9 above DP 30. A close correspondence is found with the hydrodynamic predictions of Peterlin [5, 16] for short-chain wormlike or inflexible polymers. Plots of R2/DPn versus DPn for CTA and CA show that coil randomness is apparently not achieved before DP 400. No change in viscosity was detectable for CTA of DP 50, when increasing amounts of nonsolvent isopropyl alcohol were added to 1,2-dichloroethane, short of the precipitation point.

Elementary cellulose fibrils possess an entropic deformation mechanism

Abstract: In order to obtain information on the structure of cellulose elementary fibrils, temperature coefficients of equilibrium tensile forces were determined. A force-temperature coefficient is identical with the negative amount of entropy change during deformation. Thus, data on thermoelasticity can provide insight into the basic mechanism of deformation, hence, into the structure of the deformed specimen. The thermoelastic behavior of native and mercerized ramie fibers was investigated as a function of moisture content. All of the measured force-temperature curves possess positive slopes. The effect of temperature on undeformed length and on moisture content required that temperature coefficients be corrected accordingly. After incorporating the corrections, only moisture-free fibers possess positive slopes. Water-swollen fibers show large negative slopes, whereas air-dried fibers exhibit a behavior between the two extremes. Positive slope implies entropy-elastic deformation. Because dry fibers deform in an entropy-elastic manner, disordered regions within elementary fibrils must exist. The degree of disorder must be higher in the mercerized than in the native fibers. Rearrangement of water molecules during deformation towards higher disorder is evoked to account for the increasing entropy of the water-swollen fibers.

Variations of the dielectric and mechanical characteristics of the poly (vinyl chloride) film: Electric discharges in air

Abstract: One of the principal reasons of the premature failure of the polyvinyl chloride electrical insulation is the action of the discharges in the air voids of the insulation. Therefore, investigation has been carried out of the changes of the dielectrical permittivity e and the loss factor tan δ of a polyvinyl chloride (PVC) film, plastified by dibutyl phthalate, under the effect of the electrical discharges in the air. Since by the discharges in the presence of oxygen a vigorous formation of ozone takes place the changes of the above mentioned characteristics after the exposure of samples in the ozone have been investigated separately. It has been shown that under the effect of the electrical discharges in the air, the temperature dependences of e and tan δ have changed essentially. e is subjected to dispersion over the temperature range from 70 to 100°C; tan δ increases over the whole temperature range, the conductivity losses begin at lower temperatures, and the peak of dipole-segment losses (DSL), which is strongly pronounced in the initial sample, is no more observed. This is due to the fact that under the effect of ozone and owing to the crosslinking of the polymer chains the peak of DSL is shifted to higher temperatures; as a result, both DSL and the conductivity losses are superimposed. The extension of the sample, leading to an additional orientation of macromolecules, weakens considerably the changes of the dielectrical characteristics due to the discharges.

Chemo‐rheology of curing in structural adhesives. II. Polyimide systems

Abstract: Polyimide adhesives are cured through the cyclization of the linear main chain of the polymer, rather than through the formation of a network structure. It was found that the average activation energy E* for the imidization process of the curing is 30.5 ± 5.4 kcal/mole and is substantially higher than that of the epoxy-phenolic adhesive system which we have reported in Part I. The effect of metal filler upon the curing kinetics and mechanical properties of cured material is discussed on the basis of TMA and DSC measurements. In addition, the influence of moisture exposure on the tensile modulus E of the polyimide adhesives are also discussed.