Peel Rate Research Articles

Effect of anthraquinones on endwise degradation of hydrocellulose in relation to alkaline pulping

Anthraquinones promote early delignification and stabilisation of cellulose during alkaline pulping. Alkali-catalysed endwise depolymerisation of hydrocellulose was studied at 97°C under nitrogen. In the presence of sodium anthraquinone-2-sulphonate (AQS), the rates of both the chain-propagated unzipping reaction and the competing termination reaction were lowered. Since the former reaction was inhibited to a greater extent than the latter, less dissolution of cellulose occurred at this temperature. These findings are inconsistent with a mechanism that hypothesises coupling of an oxidative stabilisation of cellulosic chain-ends with chemical reduction of an anthraquinone catalyst. The inhibitory action of AQS at 97°C is ascribed to its possible action of diminishing the degree of ionisation of cellulosic reducing chain-ends. As a possible mechanism for the accelerated dissolution of cellulose at pulping temperatures, it is suggested that anthraquinones promote intrachain scissions in cellulose, enhancing the dissolution of chain fragments before unzipping. An anomalously high rate of peeling near neutrality is attributed to an uncatalysed reaction occurring simultaneously with the base-catalysed degradation.

The role of molecular diffusion in the adhesion of EPDM and EPR elastomers

AbstractAdhesion of lightly crosslinked sheets of EPDM (ethylene–propylene–diene terpolymer) to themselves and to a Mylar substrate has been investigated over wide ranges of peel rate and test temperature. The effect of incorporating ethylene–propylene copolymer (EPR) before crosslinking, to yield a loose macromolecular network containing dissolved linear EPR macromolecules, was also studied. The self‐adhesion of these materials was found to be much greater than their adhesion to Mylar, over a wide range of effective peel rates. This is attributed to interdiffusion of EPR and EPDM molecular strands. At extremely low peel rates the enhancement of adhesion was smaller, probably because of back‐diffusion, and at high rates, the strength of adhesion became high in all cases. These results are compared to those obtained previously for polyisobutylene‐co‐ isoprene networks containing linear polyisobutylene molecules. The enhancement of self‐adhesion at intermediate rates of peel was considerably greater for the EPDM‐based materials, probably because of a lower degree of crosslinking and a greater tendency to form molecular entanglements.

End-Wise Degradation of Hydrocellulose in Mildly Alkaline Solutions and Its Retardation By Ammonia

Abstract At pH 11 and 140°C, the rate of end-wise degradation (“peeling”) of hydrocellulose is approximately 27 percent of that in 1 N NaOH. As the pH is reduced further, the rate of peeling declines by a factor of 0.34 per pH-unit. This decline is less than expected on the basis of end-group ionization. Consequently end-wise degradation can be a significant reaction even at neutral pH. The peeling rate is strongly retarded at pH 11 and below by the presence of ammonia and, to a lesser degree, by borate. The retardation is believed to be caused by the formation of Shiff's bases in case of ammonia.

The role of molecular diffusion in the adhesion of elastomers

AbstractButyl rubber (polyisobutylene‐co‐isoprene) mixed with polyisobutylene was crosslinked to yield elastomeric macromolecular networks containing dissolved linear macromolecules. Adhesion of these materials to themselves (self‐adhesion) and to an inert substrate was investigated over a wide range of peel rates and test temperatures. Greatly enhanced self‐adhesion was found when linear polyisobutylene molecules of high molecular weight were present, but the strength of adhesion to a rigid inert substrate was hardly affected. The enhancement of self‐adhesion is attributed to interdiffusion of polyisobutylene molecules. It was greatest at intermediate peel rates and temperatures, becoming insignificant at extremely low rates, probably because the diffusing species can then migrate readily, and at high effective rates of peel when the polymer approaches the glassy state and the strength of adhesion is high in all cases. A transition to somewhat lower levels of adhesion at relatively high rates of peel is tentatively ascribed to the onset of molecular fracture in place of pullout. The presence of large amounts of low‐molecular‐weight polyisobutylene (M̄v = 50,000 g/mol) increased the level of self‐adhesion and of adhesion to an inert substrate to a similar degree, over a broad range of peel rates. This effect is attributed primarily to enhanced viscous losses in the elastomeric layer during separation. Application of these results to crack and weld‐line healing in glassy plastics is discussed.

Some Rheological Aspects of the Peel Strength of Rubbery Adhesives

Abstract The strength of adhesion between two types of SBS triblock elastomer and polyethylene terephthalate (Mylar) has been measured using a peeling geometry. Three aspects of the measured strength have been studied: its dependence upon thickness of the elastomeric adhesive layer, its dependence upon the speed of peeling, and the occurrence in some circumstances of tearing failure of the elastomer, rather than interfacial separation. The bond with the stiffer SBS elastomer (Kraton 1101) had a peel strength that was independent of thickness over the range studied: 0.1–6 mm. However, the peel strength with the softer SBS material (Kraton 3202) increased linearly with thickness before reaching a constant value at thicknesses greater than about 2 mm. This difference in the dependence of the peel strength upon thickness of the adhesive layer for the two elastomers is attributed to the formation of a relatively thin plastically-yielded layer at the peel front in the former case but not in the latter. The dependence of the peel strength of the Kraton 1101-Mylar bond upon the rate of peeling was strongly influenced by the degree to which equilibrium wetting had been achieved before testing. At low levels of interfacial interaction, the peel strength increased markedly with peeling rate, whereas, when the interaction was relatively strong, the strength did not vary much with changes in the rate of peeling. These features are again attributed to the tensile stress-strain behavior of this elastomeric adhesive, and the occurrence of plastic yielding under high local stresses. The adhesion between Kraton 3202 and Mylar underwent a transition in failure mode from rubber failure to interfacial detachment as the peeling rate was increased. The peeling rate at which the transition occurred was found to be proportional to the thickness of the adhesive layer, in accordance with a characteristic rate of straining. This transition is also attributed to ductile processes within the adhesive.

The Role of Chemical Bonding in the Adhesion of Elastomers

Abstract A review is given of several studies of the effect of interfacial bonding upon the mechanical strength of an adhesive joint. In the first, polybutadiene layers were crosslinked by a free radical process while in contact with silane-treated glass. A direct proportionality was found between the minimum peel strength of the joint, at high temperatures and low rates of peeling, and the vinyl content of the silane treatment liquid. Covalent bonding between the diene polymer and vinyl groups on the treated glass was inferred. When radioactively tagged silanes were employed, extensive combination with the glass substrates was demonstrated. Again, the greater the amount of vinyl silane found on the treated glass surface, the greater the mechanical strength of adhesion between the treated glass and a polybutadiene overlayer. In another series of experiments, two partially crosslinked sheets of polybutadiene were pressed together before the crosslinking was taken to completion. The additional crosslinking was determined from measurements of the elastic properties and of the degree of equilibrium swelling by a compatible liquid. Again, the mechanical strength of adhesion between the two sheets under threshold conditions was found to be directly proportional to the inferred degree of interfacial interlinking. Thus, at least at high temperatures and low rates of peel, there is substantial evidence for a direct correlation between the mechanical strength of a joint and the degree of interfacial chemical bonding. Moreover, the relationships established in these studies allow other bonding systems to be diagnosed as chemical or physical in nature. For example, a dramatic increase in the strength of adhesion between two crosslinked polybutadiene layers was observed if they were exposed to air or oxygen for periods of an hour or two before being pressed into contact. It is inferred that interfacial chemical bonds are formed as a consequence of rapid surface oxidation reactions.

Effect of interfacial bonding on the strength of adhesion of elastomers. I. Self‐adhesion

AbstractTwo partially gelled (crosslinked) layers of elastomer were pressed into intimate contact and the gelation reaction was then taken to completion. By varying the extent of initial gelation, the degree of chemical interlinking was varied from zero, when two fully reacted sheets were pressed together, up to a level characteristic of the final density of molecular linking within each layer, when they were brought together before any reaction had occurred. The strength of adhesion between the layers was measured under threshold conditions, i.e., at low rates of peel, at high temperatures, and, in some instances, with the layers swollen with a compatible liquid. Linear relations were obtained between the threshold work of detachment per unit of interfacial area and the amount of chemical interlinking, deduced from the kinetics of molecular linking within each layer. At any degree of interlinking, ranging from zero to the fully interlinked state, the work of detachment was lower for networks composed of shorter molecular chains, in accordance with the Lake–Thomas theory for the threshold strength of elastomer networks. By extrapolation to the fully interlinked state, the strength of adhesion corresponding to cohesive rupture was inferred. These values agreed with measured tear strength for polybutadiene gelled by a free‐radical process. For a sulfur crosslinking system, and for both free‐radical and sulfur crosslinking of poly(ethylene‐co‐propylene), the threshold tear strength of the elastomer was found to be much higher than the extrapolated value from adhesion measurements. This discrepancy is ascribed to roughness of the tear plane in relatively strong elastomers, in contrast to the smooth separation of flat adhering layers. Adhesion of fully crosslinked sheets was generally low, 1–2 J/m2. Higher values, 5–25 J/m2, were found with sulfur crosslinking systems, especially those yielding a high proportion of polysulfidic crosslinks. Interlinking via polysulfide crosslink interchange reactions is suggested in these cases.

The role of chemical bonding in the adhesion of elastomers

A review is given of several studies of the effect of interfacial bonding upon the mechanical strength of an adhesive joint. In the first, polybutadiene layers were crosslinked by a free radical process whilst in contact with silane-treated glass. A direct proportionality was found between the minimum peel strength of the joint, at high temperatures and low rates of peeling, and the vinyl content of the silane treatment liquid. Covalent bonding between the diene polymer and vinyl groups on the treated glass was inferred. When radioactively tagged silanes were employed, extensive combination with the glass substrates was demonstrated. Again, the greater the amount of vinyl silane found on the treated glass surface, the greater the mechanical strength of adhesion between the treated glass and a polybutadiene overlayer. In another series of experiments two partially-crosslinked sheets of polybutadiene were pressed together before the crosslinking was taken to completion. The additional crosslinking was determined from measurements of the elastic properties and of the degree of equilibrium swelling by a compatible liquid. Again, the mechanical strength of adhesion between the two sheets under threshold conditions was found to be directly proportional to the inferred degree of interfacial interlinking. Thus, at least at high temperatures and low rates of peel, there is substantial evidence for a direct correlation between the mechanical strength of a joint and the degree of interfacial chemical bonding. Moreover, the relationships established in these studies allow other bonding systems to be diagnosed as chemical or physical in nature. For example, a dramatic increase in the strength of adhesion between two crosslinked polybutadiene layers was observed if they were exposed to air or oxygen for periods of an hour or two before being pressed into contact. It is inferred that interfacial chemical bonds are formed as a consequence of rapid surface oxidation reactions.

Static Friction of Smooth Clean Vulcanized Rubber

Abstract This picture of the origin of static friction for smooth rubber indicates that it is governed by the purely elastic consideration of the strain necessary to produce surface instability. The interfacial adhesion energy required to detach the rubber, which will be the true thermodynamic value at zero peel rate, does not appear to be the limiting factor. The rate effects observed, which persist to surprisingly low rates, are due to the viscoelastic behavior of the rubber. Once sliding has begun, the energy is lost in the peeling process, and this is then dominated by interfacial peel adhesion scaled by viscoelastic characteristics. At zero rate the value found here of F8/G=0.09 implies a static friction coefficient of about 0.6. However, if the normal load were reduced to zero, a finite contact area would remain, at least for smooth surfaces, due to surface attraction, and to express static friction as a coefficient would be meaningless in this case. It is believed that this investigation demonstrates the existence of a true static friction for smooth clean rubber and suggests that its magnitude is determined by the elastic deformation and consequent instability of the rubber.

果実追熟に対するエチレン効果の機作に関する研究 (第3報)

This study examines the role of glycolysis in respiration of banana fruits stimulated by ethylene.Monoiodoacetate inhibited the respiration of banana peel sections in the absence of ethylene, and the inhibitory effect was strengthened in the presence of the gas (100μl/l). The experiment of incorporation of glucose-1-14C, and glucose-6-14C to carbon dioxide showed a conversion of the pathway from HMP to EMP with the advance of age in peel sections. But the period of alternation of the pathway did not coincide with that of the respiratory increase. However the incorporation rate of each penetrated glucose-14C to carbon dioxide changed with the increase of the respiration rate of peel sections.While the content of reducing sugar increased continuously in pulp and peel, the levels of glycolytic intermediates such as G-1-P, G-6-P, F-6-P, F-1, 6-diP, dihydroxyacetone P and pyruvate corresponded to respiratory changes of climacteric in pulp tissue. Especially, the change of F-1, 6-diP content was remarkable among the intermediates. Although the respiration of peel sections decreased after removal of ethylene, the levels of G-6-P and F-6-P were higher in this tissue than in the tissue in which the respiration was continuously enhanced with ethylene. On the contrary, this tendency was reversed for F-1, 6-diP, dihydroxyacetone P and pyruvate.These results suggest that the respiration climacteric with ethylene may be related to the enhancement of glycolysis and the step between the F-6-P and F-1, 6-diP may be concerned with a regulation of this pathway in pulp and peel of banana fruits.An alternation of temperature caused a change of respiration in green banana fruits. While the respiration was stimulated at 30°C, the levels of G-6-P and F-6-P decreased and other intermediates (F-1, 6-diP, dihydroxyacetone P, phosphoenol-pyruvate, and pyruvate) had no change. This data indicates a difference of metabolism of glycolysis between the respiration climacteric and activated respiration by temperature alternation.

Viscoelastic analysis on peel adhesion of adhesive tape by matrix method

Analysis by means of matrix method is presented on the phenomenon of peel adhesion for 90° peeling of adhesive tape. A model of framed structure was assumed to duplicate the viscoelastic behavior of the tape: The adhesive layer is composed of a network structure made by elastic members for lattice elements and viscous members for diagonal elements. Calculated force distribution near the bond boundary showed good agreement with the experimental results of Kaelble. It was also found that the curve of peel rate versus peel force for the cohesive failure occurred in the adhesive layer was S-shaped; the change of peel force was affected severely by particular range of peel rate. For the interfacial failure at the bound boundary, on the other hand, the peel force possessed a maximum value for medium peel rate. Predicted failure mode for the adhesive tape changed from cohesive failure to interfacial failure with increasing rate of separation. Analytical results for the dependences of thickness of flexible members and adhesive layers on peel forces showed qualitative correlation with the experimental results.

Respiration Rate and Acidity in Parthenocarpic and Seeded Conference Pears

SummaryGibberellin induced parthenocarpic Conference pears started to grow sooner than seeded or naturally parthenocarpic fruits, but their growth rate declined earlier. At harvest the seeded fruits were bigger than GA3-treated and naturally parthenocarpic fruit.Respiration rates in peel and pulp of GA3-treated pears and in the peel of naturally parthenocarpic fruit were higher than in the controls. Respiration rates of peel were always higher than those of pulp or core.Within four weeks of petal fall the titratable acidity of GA3-treated fruits was somewhat higher than that of seeded or naturally parthenocarpic controls. In all treatments acidity fell rapidly after this time and declined further until harvest.

Plasticity in peeling

AbstractContrary to classical theory, a high proportion of bond failures by peeling involve progressive plastic adherend flexural yield. Such yield occurs with adherend thicknesses below a critical value, Tc, which is shown calculable by combining elastic peel mechanics with plastic bending criteria. The geometry of such “peel with yield,” and thence the moment‐controlled peel forces, can be accounted for only if the adhesive is also recognized as behaving essentially plastically. Subsequent plastic adherend unbending is important with highly extensible adhesives. The geometry of “legging” peel in such cases is best described by fully plastic mechanics. These are derived and shown to account for literature data on dependencies of peel force upon peel rate and adhesive thickness. “Stick‐slip” peel phenomena are indicated to be controlled by recurring interacting plastic–elastic transitions, in both adhesive and adherend: adhesive strain rate is critical in such phenomena. Four regimes of peel behavior can therefore apply as adherend thickness (T) increases, with peel forces proportional respectively to T0, T2/3, T3/2 (above Tc) and finally controlled by moment limitations due to joint configurational constraints (“cleavage”).

Determination of Quasiequilibrium Work of Adhesion of Elastic Coatings

Abstract Present methods for the determination of adhesion bonding of elastic polymeric materials entail certain experimental difficulties. In particular, the necessity of strict centering of the test specimen, and the difficulty associated with application of a homogeneously distributed stress over the whole cross-sectional area (homogeneous detachment or shear), or the excessive expenditure of work resulting from polymer deformation (peel).1,2 We are suggesting a method to determine the quasi-equilibrium work of adhesion during the peeling process for elastic polymeric coatings, the value of which, as was demonstrated experimentally, does not depend on the coating thickness, deformation or rate of peeling.

Peel Adhesion of Solid Films-The Surface and Bulk Effects

Abstract The peel strength of rubber and paint films has been measured over a range of peeling velocities using a dead weight method. At low peel rates the peel force is fairly constant but rises rapidly at higher peeling speeds. Experiments show that the peel strength is a function both of the energy of interfacial bonds which must be broken as peeling proceeds and of bulk energy losses in a viscoelastic peeling material. The interfacial effect has two components: an equilibrium surface force which accounts for the peel strength at low velocities, and a viscous peeling force which depends on the peeling rate. This viscous interfacial force explains the increase in peel strength of purely elastic films at higher peeling velocities. The energy loss in the bulk of the peeling film introduces two additional effects: a magnification of the peel strength in steady peeling over a certain velocity range, and a slowing down or stopping of peeling as transient relaxation occurs shortly after the application of the...

RATE LIMITING MECHANISMS IN CAUSTIC POTATO PEELING

The caustic peeling rates of potatoes is considered from an analytical and experimental point of view. The analysis considers the process to be governed by the competing rates of mass transport within the potato (diffusion) and chemical reaction. The chemical reaction between caustic and chlorogenic acid is singled out for analysis since the product of this reaction is a yellow salt which is easily measured by calorimetry. Simplified equations for the concentration of the yellow salt as a function of time is obtained for the two limiting extremes of diffusion controlled rates and reaction controlled rates. Experiments on Idaho Russetts indicate that, over the first 2–3 min of immersion in caustic, the process is diffusion controlled. It is also shown that it is the outer skin which presents the large diffusion resistance. For reasonable times after this initial period the process is reaction controlled and very sensitive to temperature. The implications of these results with respect to processing techniques (e.g., the dry peel process) and sequences is considered and discussed.

Experimental retinal detachment. Biophysical aspects of retinal peeling and stretching.

To simulate traction by organized vitreous, the retina was peeled off pigment epithelium in strips of rabbit eye tissue at rates between 2 and 210 mm/min. At lower peeling rates (2 mm/min) the detachment between retina and pigment epithelium was smooth. At the highest rate (210 mm/min) the detachment was jerky and irregular and sometimes occurred between choroid and sclera. When the release was smooth, the force required to detach the retina was found to increase proportionally to the logarithm of the peeling rate. This relationship indicates that the retina is bonded to the pigment epithelium by a viscoelastic substance, probably mucopolysaccharides, located between the retina and pigment epithelium. The retina stretches during peeling. Elongation is greater at lower peeling rates; at higher rates, the retina stiffens and elongation is less pronounced.

Effect of Wetting Liquids on the Strength of Adhesion of Viscoelastic Material

Abstract The effect of a variety of wetting liquids on the resistance to peeling separation for a lightly crosslinked rubbery adhesive in contact with a Mylar substrate has been studied over a wide range of peeling rates and at two temperatures. Although the magnitude of the peel strength is much greater than the thermodynamic work of detachment, it is reduced by alcohols and alcohol/water mixtures in good agreement with calculated reduction factors. It is concluded that the measured strength is a product of two terms: the thermodynamic work, and a numerical factor, generally large, denoting inefficiency. The latter term is strongly dependent on peel rate and temperature for viscoelastic adhesives. Two anomalies are pointed out: particularly low adhesion is observed at low rates of peel for certain liquids, attributed to swelling of the adhesive, and smaller effects are found for some other liquids than predicted.

Polymer Viscoelasticity: Relation to Peel Strength in Structural Adhesives

Abstract The two tests of most importance in evaluating structural adhesives for metals are (1) lap shear strength and (2) peel strength. Epoxies perform well in the first due to high tensile and shear strength. They are poor in the second unless modified to reduce brittleness. We have developed a urethane modified epoxy for this purpose. By taking climbing drum peel data in which both the temperature and the peel rate are varied, the time-temperature superposition principle can be tested. This principle is most generally applicable to thermoplastic materials between Tθ and Tθ + 100 °C (Tθ = glass transition temperature), and serves as a measure of viscoelastic response in the polymer. First, good agreement was found for a thermoplastic adhesive (PE-AA film). This was done to verify that climbing drum peel data can be used in this manner. Next, data were taken for our urethane modified epoxy. Results showed adherence to the superposition principle only above the heat distortion temperature of the cured po...

Rheology of Peeling

Abstract In this paper, the peeling of an elastic adherend from a rigid substrate is analyzed Theologically. The theoretical relation between peel strength and peeling rate is introduced by the stress distribution over the interlayer at the steady state of peeling and by the assumed mechanical properties of the interlayer. Application of the theoretical relation to the experimental data gives us information about the mechanical properties of the interlayer. It may be concluded that in peeling the mechanical properties of the interlayer can be defined and they are related to the mechanical properties of both materials forming the interlayer.