Adhesive Failure and Deformation Behaviour of Polymers

An instrument has been developed to determine the adhesive fracture energy as a function of the most important parameters such as temperature, contact time etc. and to study the stress-strain behaviour during bond separation. Additionally, the deformation processes during debonding were observed by high speed photography. Investigations of two high molecular weight polymers, polyisobutylene (PIB) and polyethylhexylacrylate (PEHA), showed two different types of bond separation: “brittle” behaviour with low adhesive failure energy for PIB and the formation and deformation of fibrillar structures for PEHA leading to much higher strains at break and adhesive failure energies. It follows from mechanical measurements that both polymers differ mainly by their entanglement networks. The much longer entanglement spacing for PEHA leads to the formation of fibrillar structures which, in accordance with a theory of Good, seem to be the reason for strong adhesion.     

Adhesive Failure and Deformation Behaviour of Polymers

An instrument has been developed to determine the adhesive fracture energy as a function of the most important parameters such as temperature, contact time etc. and to study the stress–strain behaviour during bond separation. Additionally, the deformation processes during debonding were observed by high speed photography. Investigations of two high molecular weight polymers, polyisobutylene (PIB) and polyethylhexylacrylate (PEHA), showed two different types of bond separation: “brittle” behaviour with low adhesive failure energy for PIB and the formation and deformation of fibrillar structures for PEHA leading to much higher strains at break and adhesive failure energies. It follows from mechanical measurements that both polymers differ mainly by their entanglement networks. The much longer entanglement spacing for PEHA leads to the formation of fibrillar structures which, in accordance with a theory of Good, seem to be the reason for strong adhesion.     

The effect of varied monomer composition on adhesive performance and peeling master curves for acrylic pressure‐sensitive adhesives

A group of pressure‐sensitive adhesives were prepared with constant glass transition temperature, using emulsion polymerization. The monomers chosen were butyl acrylate, 2‐ethylhexyl acrylate, and methyl methacrylate, along with a small amount of acrylic acid. The proportion of acrylic acid monomer was held constant for each polymer preparation but acrylic ester monomer levels were varied. The glass transition temperatures of the acrylate copolymers were measured by using differential scanning calorimetry. Drying and weighing the tetrahydrofuran‐insoluble polymer fractions were used to determine the polymer gel fractions. Films of constant coating thickness were applied to poly(ethylene terephthalate) film and adhesive properties (tack and shear) were examined. Peel was examined through the construction of master curves derived from peel tests conducted over a range of temperatures and peel rates. As the 2‐ethylhexyl acrylate content increased, the latex gel fractions were found to increase. With increasing EHA and gel fraction, peel shear was found to increase. When peel force master curves were compared, divergence in peel master curves occurred as peel rates increased where polymers with higher butyl acrylate contents reached greater peel stress values. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2909–2917, 2004     

Relationship between dynamic response of surface to environmental changes and adhesive property of polyacrylate

Acrylate copolymer composed of octadecyl acrylate (OA), 2-ethyl hexyl acrylate (2-EHA), hydroxythyl acrylate (HEA), and vinyl acetate (VA) was synthesized. The copolymer was used to adhere polyethylene (PE) with T-type peel, strength 4.4 N/cm. The interfacial characteristics of copolymer and PE were investigated via ATR-FTIR, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and dynamic contact angle (DCA). Results show that apolar moieties of the adhesive enrich on the interface. Moreover, the time dependence of peel strength coincides with that of enrichment in nonpolar moieties on the interface. © 1995 John Wiley & Sons, Inc.     

Sequential interpenetrating polymer networks of novolac resin and poly(2‐ethyl hexyl acrylate)—thermal,mechanical, and morphological study

Interpenetrating polymer networks (IPN) of novolac/poly (2‐ ethyl hexyl acrylate) (PEHA) have been prepared via in situ sequential technique of IPN formation. Full and semi‐IPNs were prepared with different blend ratios (w/w) e.g., 90 : 10, 80 : 20, and 70 : 30 in which the major constituent was novolac resin. A gradual decrease in specific gravity and hardness values was observed with increase in PEHA incorporation. A steady decrease in crosslink density with increase in PEHA fraction in the IPNs was quite evident. The IPNs were characterized with respect to their mechanical properties, e.g., ultimate tensile strength, percentage elongation at break, modulus, and toughness. Thermal behavior was studied by differential scanning calorimetry and thermogravimetric analysis. A plasticizing influence of PEHA on the rigid, brittle, and hard matrix of crosslinked phenolic resin is evidenced from the mechanical and thermal properties. The two‐phase surface morphology is revealed by scanning electron microscope. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Adhesion Between Hydrated Aluminium and Ethylene Copolymers Containing Methoxy Silane Groups

The peel strength between ethylene copolymers and aluminium has been investigated. The polymers were ordinary LDPE, copolymer with butyl acrylate (EBA), copolymer with vinyltrimethoxysilane (EVS), and copolymer with both comonomers (EVSBA). The aluminium was modified by hydration in boiling water up to 120 s. The strength of melt-pressed laminates was tested with a T-peel test and the failure mechanism was evaluated by FTIR and SEM. The hydration leads to a porous pseudoboehmite with an increased content of Al-OH groups, which causes considerable increases in peel strength for all polymers, in particular for EVS and EVSBA. The mode of failure varied between adhesive and cohesive depending on the surfaces. The introduced porosity contributes with mechanical keying while the Al-OH groups enable polar interactions for EBA and the formation of interfacial covalent bonds for EVS and EVSBA.     

Adhesion Between Hydrated Aluminium and Ethylene Copolymers Containing Methoxy Silane Groups

The peel strength between ethylene copolymers and aluminium has been investigated. The polymers were ordinary LDPE, copolymer with butyl acrylate (EBA), copolymer with vinyltrimethoxysilane (EVS), and copolymer with both comonomers (EVSBA). The aluminium was modified by hydration in boiling water up to 120 s. The strength of melt-pressed laminates was tested with a T-peel test and the failure mechanism was evaluated by FTIR and SEM. The hydration leads to a porous pseudoboehmite with an increased content of Al-OH groups, which causes considerable increases in peel strength for all polymers, in particular for EVS and EVSBA. The mode of failure varied between adhesive and cohesive depending on the surfaces. The introduced porosity contributes with mechanical keying while the Al-OH groups enable polar interactions for EBA and the formation of interfacial covalent bonds for EVS and EVSBA.     

Effect of trifunctional cross-linker triallyl isocyanurate (TAIC) on the surface morphology and viscoelasticity of the acrylic emulsion pressure-sensitive adhesives

Acrylic pressure sensitive adhesive (PSA) latexes were synthesized via a starved monomer-seeded semi-continuous emulsion polymerization process with butyl acrylate (BA), methyl methacrylate, acrylic acid (AA), 2-hydroxyethyl acrylate and trifunctional cross-linker, triallyl isocyanurate (TAIC). Influences of TAIC on the resultant latex and PSA properties were comprehensively investigated. The results indicated that latex particle size was independent of the amount of TAIC in the pre-emulsion feed, while the viscosity of the latex increased remarkably with TAIC content increased. Thermal gravimetric analysis result showed that the thermal stability of the polymers was improved significantly with the addition of TAIC. Besides, with the increase in TAIC content, gel content of the polymer increased significantly, while molecular weight between cross link points (M_c) and sol molecular weight (M_w, M_n) of the polymer decreased remarkably. Moreover, for the cross-linked adhesive film, the shear strength was improved greatly while at the sacrifice of loop tack and peel strength, when compared with the uncrosslinked counterparts. Finally, dynamic mechanical analysis and atomic force microscopy were also used to evaluate the viscoelastic properties and surface morphology of the acrylic emulsion PSA film, respectively.     

Eco-friendly UV-curable pressure sensitive adhesives containing acryloyl derivatives of monosaccharides and their adhesive performances

Two different monosaccharide acrylate monomers were designed and synthesized from glucose and galactose, and were then used to prepare transparent acrylic pressure sensitive adhesives (PSAs) comprised of semi-interpenetrated structured polymer networks. The effects of the monosaccharide architecture in the acrylate monomers on the adhesive performance of the acrylic PSAs were investigated. Prepared UV-curable acrylic PSA syrups were characterized and the optical properties of the acrylic PSAs were also examined. All of the acrylic PSAs exhibited high transparency in the visible wavelength region. With increasing monosaccharide acrylate concentration in the acrylic PSAs, adhesive performances such as the peel strength, cohesion strength, and probe tack were increased. However, there was no difference in their adhesive performances regardless of the different chemical structures of monosaccharide acrylate monomers.     

Effect of adhesive thickness on the stringiness of crosslinked polyacrylic pressure‐sensitive adhesives

The effect of adhesive thickness on stringiness behavior during 90° peel testing was investigated for crosslinked poly(n‐butyl acrylate‐acrylic acid) (A) and poly(2‐ethylhexyl acrylate‐acrylic acid) (B) with a constant crosslinker content. The adhesive thickness was varied over the range from 15 to 60 μm. All adhesive thicknesses exhibited sawtooth‐type peeling with a front frame for B, but only the 30‐μm thickness generated a front frame‐type for A. The peel rate decreased from 15 to 45 μm and plateaued above 45 μm under a constant load test. These results indicate that the adhesion strength increases with adhesive thickness, but reaches a constant value at high thicknesses. The stringiness was also analysed for B and the sawtooth interval observed to increase with increasing thickness. This means the sawtooth number decreased. As a result, the concentrated stress per sawtooth induces easier peeling and so this factor tend to increase the peel rate. Conversely, the stringiness width increased with increasing thickness. The stress load over the stringiness region decreased with an increase in thickness, meaning that a decrease in the concentrated stress decreases the peel rate. The actual peel rate is influenced by the contributions of these two factors. The strain rates during constant peel rate tests decreased slightly with increasing thickness, due to a reduction in the apparent modulus. The molecular mobilities near the adherend and the backing surfaces were evidently restrained by these surfaces, and the relative rates of motion of such restrained molecules decrease with increased thickness. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42210.     

用SPG膜乳化法制造再剥离性压敏胶的研究

以丙烯酸酯类为单体 ,用SPG膜制成乳化液 ,再经悬浮聚合制成粒度均匀的黏性微球体 ,其单分散性可达到 9 3%～ 11 93% ,并且 ,单分散性不受SPG膜孔径尺寸的影响。加入增稠剂等配成再剥离性压敏胶并涂布成试片 ,其粘合性能为 :初粘力 8# 球 ,持粘力 10 0min ,180°剥离强度 0 0 71kN/m ,重复粘贴 10 0次 180°剥离强度 0 0 5 9kN/m。SEM照片显示胶粒分布均匀 ,胶层表面平整     

Acrylic ABA triblock copolymer bearing pendant reactive bicycloalkenyl functionality via ATRP and tuning its properties using thiol-ene chemistry

This investigation reports the preparation of tailor-made ABA triblock copolymers (BCP) of 2-ethylhexyl acrylate (PEHA) and dicyclopentenyloxyethyl methacrylate (PDCPMA) bearing pendant reactive cycloalkenyl functionality via atom transfer radical polymerization (ATRP) and thiol-ene modification of the pendant reactive bicycloalkenyl functionality. The chemical structure and molar composition of the polymers were determined by ¹H NMR spectroscopy and molecular weights of the polymers were determined by gel permeation chromatography. AFM as well as DSC analysis showed nanophase-separated morphology in the block copolymers. The pendant reactive bicycloalkenyl group of PDCPMA in the BCPs was successfully modified by thiol-ene reaction and the mechanical properties of the modified BCPs were studied. The thiol modified BCP showed much greater adhesion strength compared to pristine BCP as determined by lap shear test using a UTM. Hardness of the BCP film and UV-cured thiolated BCP film was studied and compared by using a nanoindenter.     

Tailoring new architectures for polyurethanes using dendritic and hyper-branched polymers and their adhesion behavior. Part 1

Polyurethane adhesives and coatings are used for a variety of applications. The emerging dendritic and hyper-branched (HB) polymers, having three-dimensional (3D) morphology, have opened new avenues to tailor the architecture of polyurethane adhesives and coatings. The methodology followed in this study was based on partial replacement of the polyol in the isocyanate/polyol mixture with HB or dendrimer moieties having reactive functional groups. The resulting formulations were characterized and optimized with respect to adhesion properties (shear and peel strengths) using various HB and dendritic polymers. The results have shown that the incorporation of 1 to 2% (by weight) of hyper-branched polyamidoamine (PAMAM) results in shear strength increase (46 to 78%) compared to a reference formulation (no HB), following curing at room temperature. This was attributed to an increase in cross-link density. Higher concentrations of the hyper-branched polymer resulted in reduced shear strength due to plasticization. When the polyurethane was post-cured (80 °C for 5 h) to enhance diffusion of the HB, both shear and peel strengths increased by 64% and 100%, respectively, compared to the reference formulation. The simultaneous increase of shear and peel strengths is very unique to this adhesive system. This unique phenomenon is attributed to the incorporation of the 3D HB PAMAM which imparted a 3D cross-linked network architecture, as well as an energy-absorbing structure. In the case of PAMAM dendrimer, an optimum was exhibited in the concentration range of 0.05-0.1% (by weight). When the samples were post-cured a less significant increase in shear strength was observed (12-31%), compared to the HB-containing formulation. When the concentration was increased beyond the optimum a reduction in shear strength was obtained as a result of plasticization, as in the case of HB-containing formulations. It was concluded that the 3D architecture obtained by the introduction of 3D dendritic and HB polymers should lead to new directions for enhancing simultaneously the shear and peel strengths of polyurethane adhesives and coatings.     

Preparation and properties of environment-friendly acrylic latex laminating adhesives applied in plastic/plastic composite films

Acrylic latex laminating adhesives (ALLAs) were successfully prepared via a monomer-starved seeded semi-continuous emulsion polymerization with butyl acrylate (BA), methyl methacrylate (MMA), styrene (St), acrylamide (Am), and methacrylate glycidyl ether (GMA) as monomers. Impacts of GMA on the final latex, the dried latex films and the adhesive properties of ALLAs were investigated, respectively. The results indicated that the increase of GMA contents in the pre-emulsion feed has no apparent effect on the final latex average particle size and size distribution, while the gel contents, glass transition temperature (T_g) and water contact angle of the ALLAs gradually increased, and the molecular weight (M_n, M_w) obviously increased. Additionally, as the amount of GMA increased from 0 to 10?wt%, the maximum peel strength of the composite films reached 3.72 N/15mm with 5?wt% GMA contents. When heated to 65?°C, the peel strength of the composite films with 5?wt% of GMA can still maintain an acceptable peel strength (2.51 N/15mm) for application, showing excellent adhesive performance and heat resistance properties.     

Mechanical property enhancement of non‐bonding electrospun mats via adhesive

In the present study, the effect of adhesive on the morphology of different electrospun polymeric mats was investigated. The modification of two polymers, poly(methyl methacrylate) and poly(vinyl chloride), was carried out by blending the polymers with different amounts of poly(butyl acrylate) (PBA) adhesive to investigate the effect of different amounts of adhesive with heat hardener in hybrid mats. The introduction of various concentrations of PBA into different polymer solutions led to the formation of point‐bonded electrospun fibrous mats. Scanning electron microscopy images indicated that point‐bonded polymer/adhesive fibers were uniformly distributed throughout the mats. Fourier transform infrared spectrometry, contact angle measurements and thermogravimetric analysis were used to study the different properties of the hybrid mats. The tensile strength of the blended fibrous electrospun mats was increased effectively. This enhancement of the mechanical properties of the mats due to the presence of adhesive increases the number of potential applications of the electrospun mats, especially for mechanically weak polymers. Copyright © 2012 Society of Chemical Industry     

Structure-Property Relationships in Acrylic Adhesives

Three series of non-polar acrylic copolymers based on 2-ethyl hexyl acrylate and four series of polar copolymers based on ethyl acrylate were synthesised. Their adhesion performance was assessed by measurement of the force required to detach a probe (tack strength), that required to peel a strip (peel strength) and the resistance to a shear force (cold-flow time). The effect of test conditions on these measurements was also surveyed.

With non-polar copolymers the adhesion test values, which are strongly composition-dependent, may be placed on a common basis by relation to the glass transition temperature of the adhesive, provided samples of approximately equal molecular weight are compared. This is not possible with polar copolymers which thereby show the influence of specific interfacial interactions.     

Evaluation of adhesion properties of blends of cottonseed protein and anionic water-soluble polymers

There is increasing interest in agro-based, biodegradable and eco-friendly wood adhesives as partial replacements for petroleum-based adhesives. In this work, we studied the adhesion of cottonseed protein isolate (CPI) blended with several anionic water-soluble polymers. Anionic vinyl polymers studied included poly(acrylate), poly(acrylate-co-acrylamide), poly(vinyl sulfate), poly(vinyl sulfonate), and poly(vinyl phosphonate). Anionic polysaccharides studied included three types of carrageenan, carboxymethyl cellulose (CMC), low-methoxy pectin, alginate, and chondroitin sulfate. In general, the adhesive strength of CPI increased with the addition of anionic polymer up to a certain level and then decreased with further polymer addition. Different anionic polymers showed different enhancements. The best result for vinyl polymers was observed for the CPI/poly(vinyl sulfate) blend, which exhibited a 30% improved dry strength over CPI alone. The best results for the polysaccharides were obtained for the CPI/CMC and CPI/pectin blends, with improvements in dry adhesive strength over the CPI control of 66% and 50%, respectively. The CPI/CMC and CPI/pectin blends also showed improved hot water resistance. These findings suggest that the CPI/anionic polymer blends might be useful components in biobased wood adhesive formulations.     

Influence of Dioctyl Maleate Concentration on Performance Behavior of Water Based Pressure-sensitive Adhesives via Reversible Addition–Fragmentation Chain Transfer Emulsion Polymerization

Reversible addition–fragmentation chain transfer (RAFT)-mediated polymerization was successfully applied for the synthesis of pressure-sensitive adhesives (PSAs) of predetermined molar mass and of low polydispersity index (PDI). The performances of the adhesives were investigated by testing tack, peel, and shear resistance on seven different substrates (coated paper, uncoated paper, polyethylene terephthalate (PET), biaxially oriented polyethylene terephthalate (BOPP), aluminum strip, low linear density polyethylene (LLDPE), and low density polyethylene (LDPE). The influence of monomer composition on the adhesive performance was evaluated by varying the molar ratio of butyl acrylate (BA)/dioctyl maleate (DOM) while keeping the molar ratio of acrylic acid (AA) and 2-hydroxy ethyl acrylate (2-HEA) constant. As the DOM content increased, shear, peel strength, and loop tack were found to increase. It was noted that the adhesive properties of PSAs can be tailored by incorporating small amounts of hydrophobic DOM into the PSAs, which significantly increases the peel and shear strength of the resulting PSAs. Carboxyl terminated bifunctional trithiocarbonate RAFT agent possess the strong potential to polymerize hydrophobic DOM in aqueous phase and exhibit better living character with PDI less than 1.5.     

三元共聚丙烯酸酯压敏胶粘剂的合成

以丙烯酸丁酯 (BA)、苯乙烯 (St)、甲基丙烯酸甲酯 (MMA)为原料 ,用过氧化二苯甲酰 (BPO)为引发剂 ,在甲苯溶剂中 ,三元共聚合成了丙烯酸压敏胶粘剂 ;考察了St、MMA用量及共聚温度对压敏胶剥离强度与固体含量的影响 ,发现在c(BPO) =4× 10 -2 mol/L ,共聚温度为 70℃ ,各单体用量为 :n(MMA) =0 .3mol、n(St) =0 .2mol、n(BA) =0 .5mol时 ,合成的压敏胶粘剂具有高剥离强度 ( 13 .9N/ 2 5mm)与高固含量 ( 64% ) ,这些性能指标均优于商品压敏胶。     

Effect of Molecular Weight on Performance Properties of Pressure-Sensitive Adhesive of Poly (2-ethylhexyl acrylate) Synthesized by RAFT-Mediated Miniemulsion Polymerization

Reversible addition-fragmentation chain transfer (RAFT) polymerization has been applied in the synthesis of controlled molecular weights and dispersity of poly (2-ethylhexyl acrylate) (PEHA) by the miniemulsion technique. The RAFT agent (2-cyanoethyl morpholine-4-carbodithioate) was synthesized and used for 2-ethylhexyl acrylate (2-EHA) polymerization at molecular weights of 2 × 10⁵, 7 × 10, 14 × 10⁵, and 20 × 10⁵ Da and polymerization reaction kinetics were studied. The RAFT agent was characterized by Fourier transform infrared (FTIR) spectroscopy, ¹H-nuclear magnetic resonance (¹H-NMR) spectroscopy, and mass spectroscopy. The synthesized emulsions were characterized by gel permeation chromatography, particle-size analysis, x-ray diffraction (XRD) analysis, and rheological characterization. The PEHAs were used as adhesives for coated and uncoated laminates with low and high surface energies and materials, and their properties such as tack, lap shear strength, peel strength, and shear holding strength were assessed.