Low Peel Rates Research Articles

Adherence within biological multilayered systems: Development and application of a peel test on wheat grain peripheral tissues

The wheat grain is surrounded by a multilayered system composed of different tissues differing in their composition and mechanical properties. Up to now, these properties have been determined using classical tensile tests. However no methodology exists to evaluate the inter-tissular adherence. With this purpose, a micromechanical device adapted to wheat tissue (5 tissues with thickness varying from 2 to 55 μm) was built in order to investigate an interface of industrial interest for wheat processing (between the aleurone layer and the nucellar epidermis). Taking into account the complexity of the peel force measured, the stored elastic energy on the peel arms was estimated using tensile tests of peel arms and was found to approximate 0.15% of the total peel force at low peel rates. The energy dissipated was investigated as a function of peel test parameters (angle, curvature radius and rate), and seems to have a minimal influence when low peel rates were applied (20 μm s −1). The peel test was finally used to investigate the adherence distribution around the wheat grain using samples dissected in different directions. The bottom of the grain was the least adherent region, whereas the top of the grain towards the brush was the most adherent region. Even though the interpretation of the peel force was complex, this technique could be appropriate to evaluate the adherence within natural biological tissues.

Paper properties affecting pressure-sensitive tape adhesion

The interaction between paper and pressure-sensitive adhesive was investigated by peel adhesion testing. The paper/adhesive peel curves were analyzed by plotting the logarithm of the peak peel force (i.e. the maximum value) against the logarithm of the peel rate, yielding two linear segments: a peel-rate-dependent interfacial failure domain and a rate-independent paper failure domain. Three independent parameters were extracted from these plots, namely, the interfacial peel force (F in) at a low peel rate of 1 mm/min, the maximum peel force (F c) and the slope (S p) in the plot of log (interfacial peel force) versus log (peel rate). The linkages between paper and its peel responses were analyzed using the multivariate statistical methods. The paper properties influencing peel force in interfacial failure domain were found to be primarily the paper surface chemistry, characterized by oxygen/carbon ratio (determined by XPS), and secondarily paper surface roughness. The peel force increased with oxygen/carbon ratio and with the surface roughness. The log–log slope in the interfacial failure domain was found to be independent of paper properties; it is determined by the adhesive rheology. The governing paper property in the paper failure domain was found to be the paper internal bond strength as measured by an internal (Scott) bond tester.

New analysis of peeling data from paper

Peel force measurements are used routinely in the adhesive industry to characterize the performance of pressure sensitive adhesive (PSA) tapes. Indeed the art of PSA formulation involves balancing “the peel,” a measure of adhesion, with shear tests, a measure of the cohesive strength of the PSA [1]. In many cases peeling is done from stainless steel, silicon, or glass and one usually observes either separation at the PSA/solid interface or cohesive failure within the adhesive layer. There had been many experimental and theoretical analyses of peeling from hard surfaces. Simple semi-empirical models can account for peel angle [2], peel rate and the contribution of thermodynamic work of adhesion [3, 4]. On the other hand, there are no fundamental models relating PSA material properties to peeling behavior because of the complexity of PSA deformation at the peel front. Our interests have focused on PSA peeling from paper. This is a more complicated system because paper surfaces are not uniform and because failure often occurs within the paper substrate. The overall goal of our work is to understand the links between paper properties and peeling behavior. The objective of this note is to introduce a new method of analysis of peeling data from paper. We anticipate that this analysis would also be relevant to peeling from skin and other weak substrates. Fig. 1 shows the peeling behavior for a PSA tape (3M No. 9974B) on newsprint. The peel angle was 180 degrees and the other experimental details were described previously [5]. At a low peel rate the tape cleanly separates from the paper (i.e. interfacial failure) and the peel force quickly achieves a steady-state value. The higher peel rate experiment shows more complicated behavior. After climbing to a peak value, the peel

Development of local patches containing melilot extract and ex vivo–in vivo evaluation of skin permeation

Melilot extract could be effective in treating localised varicose syndrome or capillary fragility. The monolayer patch was selected to obtain a prolonged release of coumarin contained in the phytocomplex. Two types of methacrylic patches (patch 1 based on a blend of Eudragit E100 and Eudragit NE; patch 2 based on Eudragit L100) were prepared. Both patches were equivalent in terms of coumarin release and ex vivo skin permeation profiles. The two patches differed significantly as regards respective adhesive properties. At low peel rate only patch 1 showed adhesive failure as confirmed by the in vivo performance. When comparing the behaviour of the patches containing melilot extract with analogous patches containing synthetic coumarin, no melilot phytocomplex enhancer effect was shown. The data of the ex vivo coumarin skin permeation and those obtained by the in vivo stripping technique showed a good correlation ( r 2=0.9727 for patch 1, r 2=0.9835 for patch 2).

The Influence of Surfactants on the Peel Strength of Water-based Pressure Sensitive Adhesives

In order to study the effect of surfactants on the adhesive properties, peel measurements were performed with two series of model polymers of ethylhexylmethacrylate (PEHMA), the first prepared by emulsion polymerization with four anionic surfactants, and the second by post-adding the same surfactants to a surfactant-free latex. Cohesive fracture is observed at low peel rates; the peel strength depends on the bulk mechanical properties and is independent of the emulsifier. A transition to another type of separation occurs at higher peel rates, which seems to be an interfacial failure by visual inspection. Surface analytical studies, however, give evidence that this “interfacial” failure is, in fact, a mixed failure, leaving traces of the polymer on the substrate surface. The peel rate at this transition as well as the peel strength at mixed fracture are influenced by the surfactants. Large differences were observed between the four surfactants as well as between both series of polymers, leading to the conclusion that the surfactants have a different mobility within the film. This is also reflected by a different aging behaviour of the films.

Effect of peel rate and temperature on delamination toughness of PC–SAN microlayers

The effect of peel rate and temperature on peel toughness and delamination failure mode of coextruded microlayer sheet consisting of alternating layers of polycarbonate (PC) and poly(styrene-co-acrylonitrile) (SAN) was studied with the T-peel test. Microlayers with thin (<1.5μm) SAN layers always failed by interfacial delamination and consequently the interfacial toughness was independent of rate and temperature. In microlayers with thicker SAN layers, the crack alternately propagated through crazes in the SAN and along a PC–SAN interface at intermediate peel rates. The length of the crack-tip zone, the number of crazes and the amount of craze fracture increased with increasing peel rate; the peel toughness increased accordingly. Extending the tests through eight decades in peel rate revealed a transition from craze-dominated cohesive fracture at intermediate rates to predominately interfacial fracture at either very high or very low peel rates. Transitional peel behaviour resulted from the rate sensitivity of yielding and crazing in SAN as determined from tensile tests of bulk polymer.

Adhesion and Failure Mechanisms of a Model Hot Melt Adhesive Bonded to Polypropylene

A model hot melt adhesive (HMA) based on an ethylene/vinyl acetate copolymer (EVA), an Escorez® hydrocarbon tackifier, and a wax has been used to bond together polypropylene (PP) films to give equilibrium bonding. Peel strengths were determined over a broad range of peel rates and test temperatures. Contrary to the peel behavior of joints with simple rubbery adhesives [1], peel strengths with this semi-crystalline adhesive are not rate-temperature superposable, and multiple transitions in failure locus occur. The semi-crystalline structure of the HMA also prevents rate-temperature superposition of its dynamic moduli. At different test temperatures, the dependence of peel strength on peel rate shows some resemblance to the dependence of the loss tangent of the bulk adhesive on frequency. This is consistent with a previous result [2] that the HMA debonding term. D, varies with the loss tangent of a HMA at the T-peel debonding frequency. This model HMA, similar to block copolymer/tackifier blends [3], consists of two phases: an EVA-rich and a tackifier-rich phase, in its amorphous region. At a low peel rate of 8.33 × 10−5 m/s, the peel strength shows a maximum at a temperature that corresponds to the transition temperature of the tackifier-rich phase (T 1). At a higher peel rate of 8.33 × 10−3 m/s, the peel strength rises with increasing test temperature, but becomes essentially constant at temperature T 1'. It is believed that, to optimize the peel strength of a HMA at ambient temperature, it is advantageous to formulate the EVA polymer (or other semi-crystalline polyolefins) with a compatible tackifier that yields a tackifier-rich phase with a transition temperature (T 1') in the vicinity of room temperature.

Adhesion of Pure and CaCO3Filled Latex Films on Poly(ethylene terephthalate)

Abstract Adhesion to poly(ethylene terephthalate) of carboxylated styrene-butadiene latex films, filled with calcium carbonate particles, was studied in this work. The acid content (2, 4 or 6 wt%) the degree of crosslinking (25, 50 or 75 wt% of insoluble polymer) of the latex particles, and the percentage of filler (0, 20, 40, 60, 80 or 90wt%) were varied. A peel test at 180° was used. It was shown that, for the lowest filler percentages (up to 60 wt%), the films were non-porous and adhesion decreased when the peel rate, the percentage of filler, the degree of crosslinking and the acid content increased. Failure was always localized at the film-support interface (except at very low peel rate). At low peel rate, stick-slip was observed. The adhesion lowering can be explained by a decrease of the energy dissipation during peeling due to a reduced mobility of the polymeric chains. At high filler percentage (80 or 90 wt%), the films became porous and the level of adhesion very low. Failure occurred in the bul...

Peel Adhesion of Poly(Vinyl Chloride) to Nitrile Rubbers

Abstract In addition to molecular interaction and physical entanglement of the molecular chains across the interface in poly (vinyl chloride)-nitrile rubber joints, at high temperatures and long contact times interfacial chemical bonds may be formed which seem to couple the two adherends thereby resulting in cohesive failure of the rubber matrix on peeling. This is verified by performing the peel tests at high temperatures, low peel rates and under swollen conditions. Infrared spectroscopic studies of the PVC/NBR blend reveal the formation of chemical bonds at the contact temperatures studied. The peel fracture energy is found to depend on the acrylonitrile content and presence of carboxylic content in the NBR, and the presence of stabilizer and plasticizer in the PVC phase, in addition to the molding and testing conditions.

Peel Strength of Aluminium-Aluminium Joints Bonded by Adhesive Based on Carboxylated Nitrile Rubber-Chlorobutyl Rubber Blend

Abstract The peel strength of aluminium-aluminium joints bonded by an adhesive based on carboxylated nitrile rubber and chlorobutyl rubber was found to depend on surface topography and use of a silane primer. Anodization causes a marginal increase in bond strength while the silane primer improves the adhesive joint strength remarkably. The peel strength was also found to be dependent on test conditions (test rate and temperature). The threshold peel strength value obtained by measurements at low peel rate and high test temperature was found to depend on the type of failure during peeling (cohesive or interfacial) which, in turn, is controlled by the presence of silica filler in the adhesive. Two different threshold values of peel strength were obtained: 60 N/m for interfacial failure (in silica-filled adhesive), 140 N/m for cohesive failure (in unfilled adhesive).

Temperature and humidity effects on adhesion of polyimide film to a silicon substrate

A 90° peel tester with substrate heating capability was built to evaluate the adhesion strength of polyimide films to a silicon substrate. The effects of polyimide film thickness and peel rate on polyimide adhesion to a silicon substrate under high or low humidity, and at elevated temperatures, have been evaluated. In a high humidity environment, a low peel strength was measured. The influence of moisture on the peel strength increases with decreasing peel rate. Peeling at elevated temperature reduces the moisture effect even under high humidity conditions. Using a low peel rate in a high humidity environment, the measured peel strength showed a maximum as the polyimide film thickness increased. No striations in peeled polyimide films were observed for peeling in a high humidity environment.

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.

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...