The shear strength of Calabrian pine (Pinus brutia Ten.) bonded with polyurethane and polyvinyl acetate adhesives

In this study, the change in shear strength on radial and tangential surfaces of Calabrian Pine (Pinus brutia Ten.) wood having different roughness values as the result of sawing with a circular ripsaw, planing and sanding, and bonded with polyurethane (PU) and polyvinyl acetate (PVAc) adhesives at the pressure levels of 3, 6, and 9 kgf/cm², was studied. Each of the 360 specimens prepared to determine the effect of the variables on bond performance were subjected to shear test in an universal test machine in accordance with the ASTM D 905–98 standards. The values obtained were analyzed statistically and the results were interpreted. The highest shear strength (11.83 N/mm²) for plane of cut was obtained on the tangential surface after sanding and applying PVAc adhesive with a pressing pressure of 9 kgf/cm². The lowest shear strength (6.01 N/mm²) was obtained in the joinings made on the planed surfaces by using PU adhesive and a pressing pressure of 3 kgf/cm². The highest shear strength (9.10 N/mm²) on the radial surface was obtained after sanding and applying PVAc adhesive and pressing with a pressure of 6 kgf/cm². The lowest shear strength (3.76 N/mm²) was obtained in the specimens whose surfaces were sanded and glued with PU adhesive with a pressing pressure of 3 kgf/cm². In general, in the radial surfaces, just like in the tangential surfaces, the specimens bonded with PVAc exhibited a higher shear strength compared with those glued with PU. According to these results, it is definitely necessary to sand the surfaces prior to the bonding process to have a higher shear strength. The bonding process should be made on the tangential surfaces with higher pressures. The PVAc adhesive should be preferred instead of the PU adhesive. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3050–3061, 2006     

Thermoreactive compaction of an alumina — Polymethylsiloxane composition

Conclusions An investigation was carried out of the thermoreactive compaction of a composition of alumina with polymethylsiloxane, the technological parameters being varied. Before a heat treatment the open porosity of specimens containing 20% PMS is 0.8%, the bending strength 260 kgf/cm², and the cold-crushing strength 1070 kgf/cm².Firing at 1700°C gave a high-alumina composition ceramic with an open porosity of 2%, a bending strength of 1000 kgf/cm², a cold-crushing strength up to 5000 kgf/cm², and a thermal-shock resistance of 14–20 reversals from 1300°C into water (in tests with specimens).Translated from Ogneupory, No. 5, pp. 47–50, May, 1978.     

Effects of hydrocarbon tackifiers on the adhesive properties of contact adhesives based on polychloroprene - III. The effect of the molecular weight of the tackifier

Aromatic hydrocarbon resins with different molecular weights (M_w = 1300-50400 daltons) were added to a solvent-based polychloroprene adhesive. The hydrocarbon resins were characterized using infra-red (IR) and differential scanning calorimetry (DSC) measurements. The properties and compatibility of the polychloroprene/resin blends were studied using mechanical tests, DSC measurements, scanning electron microscopy (SEM), and stress-controlled rheology. Tack measurements were also carried out and the adhesion strength was obtained from T-peel tests on roughened styrene-butadiene rubber/polychloroprene adhesive joints. The addition of low-molecular-weight tackifiers produced a compatible polychloroprene/tackifier system (only one T_g was found in DSC measurements), while the addition of a high-molecular-weight (and broad molecular weight distribution) tackifier produced a partially incompatible system (two Tg's were found in DSC measurements). The compatibility of polychloroprene/tackifier blends was also assessed with stress-controlled rheology and SEM. An increase in the T-peel strength and tack were produced when the molecular weight of the tackifier increased, although the addition of a hydrocarbon resin with a M_w higher than about 50 000 reduced the tack. A broad molecular weight distribution in the tackifier favoured incompatibility with the polychloroprene, resulting in a reduction in the tack and rheological properties.     

Metal adhesive properties of polyamides having the 2,3‐bis(1,4‐phenylene)quinoxalinediyl structure

Polyamides were synthesized by interfacial polycondensation of 2,3‐bis(4‐chloroformylphenyl)quinoxaline (BCFPQ) and several aliphatic diamines using a phase transfer catalyst, and their adhesive property for stainless steel was investigated. The inherent viscosity of the obtained polyamides ranged from 0.37 to 1.24 dL g⁻¹. The glass transition temperatures of the polyamides ranged between 154 and 201°C, and their thermal decomposition temperatures were above 450°C. The polyamides were soluble in several organic solvents, including m‐cresol, N‐methyl‐2‐pyrrolidone (NMP), and formic acid. The adhesive property for stainless steel was examined by a standard tensile test. One member of the series, polyamide P8, derived from BCFPQ and 1,8‐octanediamine, displayed high tensile strength with values of 232 kgf cm⁻² at 20°C, 173 kgf cm⁻² at 120°C, and 137 kgf cm⁻² at 180°C. Thus, the tensile strength of P8 decreased at 180°C, but the decrease was much smaller than that of an epoxy resin in wide use as a metal adhesive. Heat distortion temperature, measured by thermal mechanical analysis, of P8 was 191°C. This suggested that P8 possessed high thermal resistance in metal adhesives. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1366–1370, 1999     

The effect of surface properties on the adhesion of modified polychloroprene used as adhesive

The adhesion properties of polychloroprene can be improved by addition of such materials as piperylene–styrene co-polymer (PSC), VeoVa-10 polymer, VeoVa-11/methyl methacrylate/2ethylhexyl acrylate co-polymer (VeoVa-11/MMA/2EHA) and poly(vinyl acetate) waste (wPVAc). Here, the relationship between adhesion properties and surface tension of polychloroprene was investigated. Contact angle measurements have been used to study the effects of nature and content of polymeric additives on the adhesion and surface properties of polychloroprene. Low-surface-tension VeoVa-10 polymer has the tendency to migrate to the surface of polychloroprene; thus, adhesion is determined mainly by this additive property. Enrichment of polychloroprene film bottom layer by the additive was observed using high-surface-tension PSC and wPVAc. In this case, the adhesion properties of polychloroprene depend on the interactions at the interface. Adhesion properties of polychloroprene were found to depend not only on compatibility between adhesive components, but also on compatibility between the adherend and the adhesive.     

Increasing adhesion of a fluoropolymer coating to terlon fabrics

The weave type and density of Terlon fabrics have no effect on the level of their adhesive reaction with a fl uoropolymer coating. Treating Terlon fabric in glow-discharge plasma increases the strength of the bond of the fluoropolymer coating with the fabric by 3-4 times. Use of an adhesive based on urethane rubber and a cross-linking agent — polyisocyanate — increases adhesion of the polymer coating to the Terlon fabric to 1.0 kgf/cm.     

Adhesion characteristics of magnesite dust

Conclusions It was established that the temperature dependence of the adhesion characteristics of magnesite dust is similar to that of its specific electrical resistance. The specific tensile adhesion strength of the dust is at maximum, viz., 16·10^–3 kgf/cm², at 200°C.The temperature dependence of the adhesion characteristics of the dust must be taken into account when designing dust precipitators and their cleaning devices.Translated from Ogneupory, No. 2, pp. 18–20, February, 1978.     

Adhesive potential of marama bean protein

Marama bean is an underutilised indigenous Southern African oilseed legume with protein content similar to soya bean. In this study, the adhesive potential of marama protein was explored. At 45% moisture content, marama protein was very sticky with a force of adhesion (6.5 N), which was about twice that of soya and 5 times that of gluten. Marama protein adhesive prepared using a standard procedure described for soya, had better adhesive properties when applied on a wooden substrate than did soya in terms of strength and resistance to delamination in water. The shear strength of marama protein (36–173 kg/cm²) was about 1.5 times higher than that of soya over the protein concentrations: 1.2–3.6 mg protein/cm². When 2.4 mg protein/cm² was applied on the wood, about 47% of glued wood pieces were delaminated for marama compared to 90% for soya after 2 cycles of 48 h soaking. Marama protein contained more β-sheet structure (54%) than soya (47% β-sheet), which was increased by approx. 12% in marama protein adhesive compared to 3% in soya protein adhesive. By AFM, marama protein adhesive presented a rough surface without holes compared to soya, which was rough but with many holes within its structure. Thus, the high β-sheet conformation and surface structure of marama protein are most likely responsible for its better adhesive behaviour compared to soya.     

Improved adhesion of EVAs with different vinyl acetate contents treated with sulphuric acid

Four ethylene vinyl acetate copolymers (EVAs) containing 9, 12, 18 and 20 wt% vinyl acetate (VA) were treated with concentrated sulphuric acid to improve their adhesion to polychloroprene (PCP) adhesive. The tensile strength and Young's modulus of EVAs decreased as the VA content increased, due to the reduction in crystallinity of the polyethylene blocks in the copolymer. The modifications produced in the EVAs by treatment with sulphuric acid were followed using contact angle measurements (water, 25 °C), ATR-IR spectroscopy and scanning electron microscopy (SEM). Adhesive-bond strength was obtained by T-peel tests on treated EVA/polychloroprene adhesive joints. The vinyl acetate content in the EVA affected the extent, but not the nature, of the surface modification produced by treatment with sulphuric acid. The treatment produced both sulfonation and oxidation on the EVA surfaces. The higher the vinyl acetate content in the EVA, the more significant the modifications produced. Increased T-peel strengths of EVA/polychloroprene adhesive + 5 wt% polyisocyanate joints were obtained and a mixed failure (adhesion failure + cohesive failure in the adhesive) was produced. It was found that, to be effective, the treatment of EVAs must be carried out with 96 wt% sulphuric acid.     

Kinetic study of the solid-state reaction between phthalic anhydride and P-nitroaniline

The addition reaction between the compacted powders of phthalic anhydride and p-nitroaniline was studied. Both the reactants of equal particle size, were mixed in 1-to-1 molar ratio and compacted. Three particle sizes — 0.0065 cm, 0.0178 cm and 0.0376 cm and three compaction pressures — 302.0 kgf/cm², 785.0 kgf/cm² and 1208.0 kgf/cm² were used for the study. Conversions were measured at 80°, 90°, 100°, 110° and 120°C for 1/2, 1, 2, 4, 8, 12, 16, 20 and 24 hours. The reaction rate changed to a constant value, after an initial phase boundary process. The mole percentage conversions increased with decrease in particle size, increase in compaction pressure corresponding to a decrease in the initial porosity of the compact. It was also observed that the final porosity of the compact increased with increase in reaction temperature. Combination of Jander's model and parabolic rate law was used to calculate the values of the reaction rate constant equivalent. The activation energy was calculated to be 14 to 34 kilocalories per gram mole.     

Surface properties of vertically aligned carbon nanotube arrays

This study focuses on the structural changes of vertically aligned carbon nanotube (CNT) arrays while measuring their adhesive properties and wetting behaviour. CNT forests grown by chemical vapor deposition with a height of ~ 100 µm, an outer CNT diameter of ~ 10 nm and a density of the order of ~ 10¹⁰ CNTs/cm² show an average adhesion of 4 N/cm² when pressed against a glass surface. The applied forces lead to the collapse of the regular CNT arrays which limits their reusability as functional dry adhesives. Goniometric water contact angle (CA) measurements on CNT forests show a systematic decrease from an initial value of ~ 126° to a final CA similar to highly orientated graphite. Environmental scanning electron microscopy shows that this loss of hydrophobicity is due to an evaporation induced compaction of CNTs together with the loss of their vertical alignment. We observe the formation of cellular patterns for controlled drying.     

New epoxy-imide resins cured with bis(hydroxyphthalimide)s

New epoxy-imide resins were synthesized using bis(hydroxyphthalimide)s (BHPIs). Among these resins, that cured with BHPI(DDS), synthesized from 4,4′-diaminodiphenylsulfone, exhibits the best thermal resistance, reaching a tan δ maximum temperature of 230°C. This resin also features a tensile lap shear adhesive strength of 320 kgf/cm² when applied to steel test pieces. The cure reaction was followed by infrared spectroscopy and dynamic mechanical analysis. The ring-opening reaction between the phenolic hydroxyl group of BHPI and the epoxy group is observed, and accelerated by a tertiary amine catalyst, triethylamine.     

Preparation and Properties of a Waterborne Contact Adhesive Based on Polychloroprene Latex and Styrene-Acrylate Emulsion Blend

Environmental protection and legislative pressure to eliminate the use of solvents in the adhesive industry have inspired the search for safer alternatives. In the area of contact adhesives, the waterborne route has proved to be of particular interest. Based on the synergistic effect of polychloroprene latex and styreneacrylate emulsion, a waterborne contact adhesive consisting of polychloroprene latex (PCL) and styreneacrylate emulsion (SAE) blend has been developed. In order to blend PCL with SAE easily and to accelerate the drying rate of the adhesive, boric acid was chosen for use in the PCL/SAE blend system. Effects of boric acid and SAE content on the properties of PCL/SAE blends, such as pH value, storage stability and set time, were investigated. At the same time, the effect of SAE content on the mechanical properties of PCL/SAE blend films was studied. The morphology of blend films was characterized by Atomic Force Microscopy. The adhesive performance of the waterborne contact adhesive was evaluated by peel and shear tests. The results showed that when the waterborne contact adhesive formulation contained 40 wt% styrene-acrylate emulsion (dry weight) and 1.25 wt% boric acid, it had a good shelf-stability, its set time was 5 min, and the blend film with this formulation was ductile and flexible with reasonably good tensile strength and very high elongation at break. And the blend films showed structure with a sea–island morphology. The waterborne contact adhesives derived from PCL/SAE blends were found to be comparable to the commercially available solvent-based contact adhesives. The synergistic effect of polychloroprene latex and styrene-acrylate copolymer emulsion was also discussed.     

Improvement of mechanical properties of polylactic acid adhesion joints with bio‐based adhesives by using air atmospheric plasma treatment

The packaging industry generates a high volume of wastes; so that, there is a high demand of biodegradable materials, which do not damage the environment. Nowadays, there is an interesting consumption of polylactic acid (PLA) due to its biodegradable features. This work focuses on the improvement of mechanical properties of PLA adhesion joints for uses in the packaging industry. In order to achieve that purpose, atmospheric plasma treatment is used to selectively modify PLA surface properties. The obtained experimental results show that the atmospheric plasma treatment is suitable to increase the mechanical performance of PLA–PLA adhesive joints. Optimum conditions for the atmospheric plasma treatment were obtained with a nozzle–substrate distance of 10 mm and an advance rate in the 100–300 mm s^?1 range; for these particular conditions, the effectiveness of the surface modification is the highest. The main plasma‐acting mechanisms are microetching together with the insertion of polar groups which lead to an interesting synergy that causes a remarkable increase in mechanical properties of adhesion joints. In particular, the shear strength of untreated PLA–PLA adhesion joints is close to 50 N cm^?2 and this value is increased up to values of about 168.7 N cm^?2 with optimum plasma treatment conditions. This indicates that atmospheric plasma treatment is both a technical and an environmental friendly technique to improve mechanical performance of PLA adhesive joints. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42391.     

Surface modification of polytetrafluoroethylene by Ar+ irradiation for improved adhesion to other materials

A surface of thin square polytetrafluoroethylene (PTFE) samples (1 × 1 × 0.2 cm³) was irradiated with Ar⁺ at 1 keV with varying ion dose from 5 × 10¹⁴ to 1 × 10¹⁷ ions/cm² with and without an oxygen environment. The irradiated surface of the samples was examined by scanning electron microscopy (SEM) for surface textural changes and x-ray photoelectron spectrometry (XPS) for changes in chemical structure. A wettability test was conducted on the irradiated surface of PTFE samples by water droplets. A Scotch ™ tape adhesion test, after a thin film of Cu or Al was evaporated on the irradiated surface, and a tensile test after irradiated samples were glued to sample holders by an adhesive glue (Crystal Bond) was also run. The SEM micrographs showed increasing roughness with fiber forest-like texture with increasing ion dose. The Ar⁺ with an O₂ environment produced finer and denser fiber forest-like texture than that without O₂. The high-resolution XPS spectra showed decreased intensity of the F1s peak and formation of the O1s peak when irradiated with the O₂ environment. The increase of the O1s peak may be attributed to the reaction of oxygen atoms and the free radicals created by Ar⁺ bombardment. The wettability of water droplets on the irradiated surfaces was found to be inversely proportional to the surface roughness. Adhesion tests were conducted on 2000 Å thick Al or Cu film. Full detachment of the metal films was observed when PTFE samples were not modified. Partial detachment of the Al film occurred when PTFE was irradiated without the O₂ environment, regardless of ion dose. No detachment of the film occurred when PTFE was irradiated with the O₂ environment with the ion dose exceeding 1 × 10¹⁶ ions/cm². Partial detachment of Cu film was observed with or without the O₂ environment when the ion dose was 5 × 10¹⁴ ions/cm². No detachment occurred with or without the O₂ environment when the ion dose was 1 × 10¹⁵ ions/cm² or greater. The tensile test showed that adhesion of an adhesive cement (Crystal Bond) to the irradiated PTFE samples increased significantly with increasing ion dose up to 1 × 10¹⁶ ions/cm². Possible mechanisms for the improved adhesion are given. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1913–1921, 1997     

Adhesive tack and green strength of EPDM rubber

Measurement of tack of EPDM (ethylene-propylenediene terpolymer) rubber with natural rubber (NR) of four different molecular weights, styrene-butadiene rubber (SBR), butadiene rubber (BR), bromobutyl rubber (BIIR), and polychloroprene rubber (CR) was done over a range of rates of testing, contact times, and temperatures of contact. The effect of different additives, namely carbon black, phenol-formaldehyde resin, coumarone-indene resin, and methyl methacrylate is also reported. Green strength of all the rubbers was measured. Tack strength increases with increase in contact time for all the rubbers. Adhesive tack between EPDM and low-molecular-weight NR is much higher than that between EPDM and NR of high molecular weight. Tack strength of EPDM with BIIR is the highest among the tack values obtained for synthetic rubbers. The adhesive tack between EPDM and natural/ synthetic rubber passes through a maximum when plotted against temperature of contact. It increases with testing rate. All these phenomena could be explained in terms of interdiffusion of rubber chains under different conditions and solubility parameter of two contacting rubbers. It was observed that tack strength varies with (contact time)^1/2 and (rate)^1/2 in accordance with the reptation theory. Phenol-formaldehyde resin (PF) or coumarone-indene (CI) resin in EPDM improves the tack strength quite significantly. The resin in the NR phase does not have a marked effect. The presence of carbon black decreases adhesive tack strength between EPDM and NR. The surface of EPDM, however, becomes smoother with the addition of the additives. Peel tests and commercial tack tests give similar results in the tack strength between EPDM/NR and EPDM/SBR.     

A simplified approach to achieve gecko-mimic nano-structural adhesives by a simple polymer

In this work, we graft polyacrylate with 3,4-dihydroxyphenylalanine, a functionality alike adhesive protein in mussels, to obtain a mussel-mimic polyacrylate with good adhesive property and interesting nano-patterns during adhesion. The chemical structure of the product is confirmed by ¹H NMR that dopamine is grafted onto the polymer. The analysis of the tensile strength test reveals that the adhesive is improved more than 2 times, from 53 to 124 KPa, when polyacrylate grafted by dopamine. The analysis of the static water contact angle suggests that the hydrophilic of the as-synthesized final polymer is enhanced. It is very interesting to observe that such an adhesive material can form nano-patterns on the adhesion interface during bonding, at about 100 nm in diameter each contact point, which something look like the gecko foot structure. This structural feature maybe related to the increasing adhesive properties of such materials.     

Al2O3 coated glass by aerosol deposition with excellent mechanical properties for mobile electronic displays

Al₂O₃ thin film was deposited on Gorilla glass using an aerosol deposition method to improve the mechanical property of cover glass for mobile electronic device. The deposited Al₂O₃ film (approximately 1 μm thick) was a polycrystalline structure and showed a high light transmittance of approximately 90% in the visible light region. The CIE color space (L*a*b) measurement also showed a characteristic corresponding to the acceptable optical range of the cover glass. Further, it was confirmed that the bending strength improved by 10 %, as compared with bare Gorilla glass (from 6970 kgf/cm² to 7704 kgf/cm²), and the Vickers hardness increased to approximately 1700–2000 HV, as compared with that of Gorilla glass (<700 HV). Owing to the improved mechanical properties, the Al₂O₃ thin film exhibited good anti-scratch properties and is expected to be applied to the cover glass of various display products.     

An investigation on the modification of polypropylene by grafting of maleic anhydride based on the aspect of adhesion

Isotactic polypropylene was modified by a chemical grafting of maleic anhydride in a molten state. The degree of grafting, ranged from 0.078–0.368%, was determined by a titration method. Isotactic polypropylene modified by chemical grafting of maleic anhydride was used as an adhesive in bonding the cold-rolled steel sheets for the correlation of its bondability. It was found that the maximum adhesive strength 159 kg/cm² was obtained from a degree of grafting 0.217%. A higher degree of grafting was detrimental not only to the initial adhesive strength, but also to the durability aged in a wet environment. Electron spectroscopy for chemical analysis was used to analyze the failure loci, because the joint was separated by shearing. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 383–387, 1998     

Status and prospects for production of carbon fibres based on polyacrylonitrile

Production of PAN-based carbon fibres (CF) is a rapidly developing sector. Production in 2006 was 28,000 tons. The production capacities in 2007 increased to 55,500 tons and will attain 66,000 tons in 2008. The Japanese companies Toray, Toho, and Mitsubishi are the leaders and are responsible for 77% of total production. Toray is the leader with respect to fibre quality. The CF manufactured by the company basically have a strength of 500–560 kgf/mm². The properties of the PAN precursor are of decisive importance for the quality of the CF. Each company has its own PAN precursor plant for successfully competing. The fibre manufactured in the RF has a strength of 300–350 kgf/mm². Uglekhimvolokno NlTs has developed technology for production of CF with a strength of 450 kgf/mm². Economy in production of CF is attained by creating units (flow production lines) with individual capacity of 150–200 and even 400 tons/year (the capacity of existing domestic units is 10–20 tons/year). This increase in capacity is attained by using primarily new technical solutions, including conductive tempering of oxidized tows, separate air-oxidant and air-heat carrier circulation, making the PAN tow compact by selecting an appropriate oiling agent, and vertically positioning the carbonization furnace stack. The maximum modulus of elasticity of PAN CF is 60,000 kgf/mm². To attain high orientation and a high degree of crystallinity, boron, which decreases the temperature of transition of the fibre into the highly elastic state and thus facilitates the occurrence of orientation drawing and crystallite growth, should be used as a plasticizer. In semi-industrial conditions, when boron is added in the stage of oxidation in the form of boric acid, CF with a modulus of elasticity of 47,700 kgf/mm² are obtained. To prolong the lifetime of the graphite heaters, it is recommended that they be given a shape that allows focusing radiation on the processed fibre. Thin carbon fillers in the form of prepregs 0.04–0.17 mm thick and fabrics 0.11–0.15 mm thick are manufactured to increase the uniformity of the properties of multilayer composites. Prepregs made of “thick” PAN tow with a linear density of 3.2 ktex which are processed into CF with a strength of 500 kgf/mm², elongation of 2%, and modulus of elasticity of 23,000 kgf/mm², are the most economical. In the RF, unidirectional slivers of the Elur type 0.08 mm thick are manufactured for these purposes, but they have lower strength and due to the low processing speeds, high cost. These drawbacks have been eliminated in the semicontinuous method for manufacturing thin PAN fibres. __________ Translated from Khimicheskie Volokna, No. 1, pp. 20–26, January–February, 2008.