Thermal characterization of three‐component blends for hot‐melt adhesives

Traditional solvent‐based adhesives used in the footwear industry have been demonstrated as harmful to the workers' health and environment. Solvent‐free three‐component adhesives (hot‐melt adhesives or HMAs) for various applications including the leather and footwear industry are becoming more and more attractive. Thus, the formulation of a three‐component HMA was realized in this study. Thermogravimetry, differential scanning calorimetry, and the apparent strength of the adhesive bond were used to investigate the relationship between their properties and the polymer/wax/resin compositions. The thermal stability of HMA formulations was determined and compared with thermal traces based on an additive weight computation of the single components' thermal profiles. All HMA formulations showed a direct relationship between the glass‐transition temperature and the apparent adhesive shear strength at the leather–rubber interface. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2889–2901, 2001     

Preparation and properties of emulsifier/N‐methylpyrrolidone‐free crosslinkable waterborne polyurethane–acrylate emulsions for footwear adhesives. I. Effect of the acrylic monomer content

Stable emulsions of emulsifier/N‐methylpyrrolidone‐free crosslinkable waterborne polyurethane–acrylates (C‐WBPUAs) with various acrylic monomer contents (0, 10, 20, and 30 wt %) for footwear adhesive materials were successfully prepared in this study. The effects of the acrylic monomer content on the shelf stability, mean particle size, and viscosity of the C‐WBPUA emulsions; the tensile properties and dynamic mechanical thermal properties of the C‐WBPUA film samples; and the adhesive strengths between the upper (synthetic leather) and the sole (ethylene vinyl acetate rubber) in both the dry and wet states of the formulated adhesives (C‐WBPUA emulsion–thickener–hardener) were examined. The adhesive strengths of the formulated adhesives for footwear (leather–sole) in both the dry and wet states increased with increasing acrylic monomer content up to 20 wt %; after this, they almost levelled off. Thus, C‐WBPUA20 and C‐WBPUA30, where the number indicates the acrylic monomer content, can be recommended as high‐performance adhesive materials for footwear. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43758.     

Preparation and properties of emulsifier-/solvent-free slightly crosslinked waterborne polyurethane-acrylic hybrid emulsions for footwear adhesives (III)–effect of trimethylol propane (TMP)/ethylene diamine (EDA) content

Stable emulsions of emulsifier-/solvent-free slightly crosslinked waterborne polyurethane-acrylic hybrids (WPU/AC-Ts) with a fixed acrylic monomer content (20 wt.%) and different trimethylol propane (TMP)/ethylene diamine (EDA) (0/0.20, 0.02/0.17, 0.04/0.14, 0.06/0.11, 0.08/0.08, the number indicated the mole% of TMP/EDA) for footwear adhesive materials were successfully prepared in this study. The as-polymerized hybrid emulsion containing 0.10/0.05 mole% of TMP/EDA content was found to be unstable, indicating that near 0.10/0.05 mole% of TMP/EDA content was beyond the limit value of crosslinkable TMP component for self-emulsifing. This study examined the effect of mole% of TMP/EDA on the stability and viscosity of hybrid emulsions, the tensile properties and dynamic mechanical thermal properties of hybrid film samples, and the adhesive strengths of formulated adhesives for footwear at both dry and wet states. As TMP content increased, the tensile strength/modulus/storage modulus/hardness of WPU/AC-Ts film samples increased, however, their elongation at break and water swelling% decreased significantly. The adhesive strength (peel strength) of formulated adhesives was found to be dependent upon the degree of drying, but almost not upon the TMP content in WPU/AC-Ts. The adhesive strength of footwear (EVA/leather) dried at room temperature for 24 h was higher than that of footwear dried for 30 min. However, the adhesive strength at wet state increased significantly with increasing TMP content. The optimum TMP/EDA contents were found to be 0.06/0.11 and 0.08/0.08 mole% to achieve the desired high performance adhesive properties such as high strength in wet state.     

Anionomeric waterborne poly(urethane semicarbazide) dispersions and their adhesive properties

Aqueous polyurethane dispersions were prepared from isocyanate‐terminated ionic polyurethane prepolymers by chain extension with dihydrazides. These water‐borne dispersions had excellent adhesive properties and were used to bond leather and canvas. The base polymers were varied with respect to (1) the ionic content with the same chain extender and (2) the nature of the chain extender with the ionic content kept constant. Studies on the particle size and viscosity revealed that the ionic content had an influence on the aforementioned properties: the particle size decreased and the viscosity increased with increasing ionic content. The polarity of the films cast from the dispersions were determined with contact‐angle measurements: hydrophilic character was exhibited by all the compositions. X‐ray studies revealed that the increase in the ionic content led to increasing intensities of the diffraction peaks due to increased secondary forces of bonding. The tensile strength measurements showed that the films were highly elastomeric and had good mechanical strength, which varied with the composition. A shear strength and peel strength analysis of specimens obtained through the bonding of leather to leather, leather to canvas, and canvas to canvas revealed that the waterborne dispersions were excellent adhesives for bonding leather surfaces. Thus, a very efficient, ecofriendly waterborne dispersion of polyurethane that could find applications in bonding leather in the footwear industry was prepared successfully. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Behaviour of Urethane Adhesives on Rubber Surfaces

The paper presents the results of chemical investigations into some of the bonding problems of the footwear industry and pays particular attention to the importance of the substrate surfaces.

The importance of the presence of metal soaps on rubber surfaces and their detrimental effect on adhesion is pointed out together with the concomitant beneficial effects of solvent soap dispersing treatments on subsequent adhesion.

The special needs of the footwear industry for a single adhesive system capable of adhering strongly to a wide range of substrates led to the requirement of improving the bond of urethane adhesives to rubber surfaces. The role of free isocyanates in promoting this bond is outlined.

The practical advantages of halogenating rubber surfaces in conferring excellent adhesion properties on moulded rubber surfaces when used with solvent urethane adhesives are pointed out. The observed phenomena associated with halogenation are discussed qualitatively in relation to proposed theories of adhesion.     

Adhesion to Polyolefins with Flexible Adhesives

Compounds based on polyolefins may find further use in the footwear industry as solings. However, a significant problem is the poor adhesion obtained with the urethane adhesives currently used. SATRA has recently attempted to develop practical bonding systems for commercial olefinic compounds. The use of flame treatments for polyethylene appeared to be a possible method of improving compatibility between the adhesive and substrate if an isocyanate is present at the interface. Polypropylene does not respond to the flame treatment but reasonable bonds have been obtained after surface oxidation or by using a sensitiser in conjunction with UV irradiation. The use of dual compound moulding is described as a possible alternative means of obtaining adequate adhesion to difficult surfaces.     

Primers for Bonding Polyolefin Substrates with Alkyl Cyanoacrylate Adhesive

Polyolefins, such as polypropylene and polyethylene, are among the most commonly-utilized plastics in the world, but, because of their non-polar surfaces, are among the most difficult to bond with adhesives. A surface treatment is required before adhesive application to achieve good adhesion.

Alkyl cyanoacrylates are widely used instant adhesives, e.g. Super Glue^®, for bonding a variety of substrates, such as metal, plastics, glass, wood, and leather. It would be desirable to bond polyolefins with these adhesives because of their availability and ease of use. Amines and ammonium carboxylates, possessing long alkyl chains, were evaluated as adhesion promoting primers for alkyl cyanoacrylate adhesives on polyolefins.

Among trialkyl amines, trialkylammonium carboxylates, and tetraalkylammonium carboxylates, trialkylammonium carboxylate primers produced an adhesive bond so strong that the failure occurred at the polyolefin substrate. Trialkylammonium carboxylate primers also demonstrated excellent performance retention over prolonged atmospheric exposure prior to application of the adhesive. Trialkyl amines and tetraalkylammonium carboxylates also promoted adhesion but lost maximum effectiveness on exposure to the atmosphere. The cause of the deterioration in amine primer effectiveness over prolonged exposure was identified to be trialkylammonium bicarbonate formation and/or diffusion of the primer into the polyolefin surface.     

超支化聚合物改性明胶胶粘剂的制备及性能

以二乙醇胺、丙烯酸甲酯、三羟甲基丙烷以及环氧氯丙烷为原料,合成不同代数的端环氧基超支化聚（胺-酯）(EHPAE)。其后,以从制革废弃物中提取的明胶为原料,不同代数的EHPAE分别作为交联单体进行改性,制得一种环保型鞋用或包袋用胶粘剂。采用FT-IR光谱,1H-NMR谱图和GPC对超支化聚合物和胶粘剂的结构及相对分子质量分布进行表征,之后对胶粘剂的粘接性能进行测定,结果表明：EHPAE-Ⅲ较其余两者的改性效果更为明显,当EHPAE-Ⅲ用量为明胶用量的30％时,改性后胶粘剂的固含量由11.42%提高到了30.33%,同时剪切强度为2.216 MPa,T-剥离强度为3.375 N/mm,水接触角为100.9o,相较于市售胶粘剂的剪切强度 (1.88 MPa),T-剥离强度 (2.864 N/mm),水接触角(84.8o),制备得到胶粘剂的粘接性能和疏水性均更优。     

Primers for Bonding Polyolefin Substrates with Alkyl Cyanoacrylate Adhesive

Polyolefins, such as polypropylene and polyethylene, are among the most commonly-utilized plastics in the world, but, because of their non-polar surfaces, are among the most difficult to bond with adhesives. A surface treatment is required before adhesive application to achieve good adhesion.

Alkyl cyanoacrylates are widely used instant adhesives, e.g. Super Glue^®, for bonding a variety of substrates, such as metal, plastics, glass, wood, and leather. It would be desirable to bond polyolefins with these adhesives because of their availability and ease of use. Amines and ammonium carboxylates, possessing long alkyl chains, were evaluated as adhesion promoting primers for alkyl cyanoacrylate adhesives on polyolefins.

Among trialkyl amines, trialkylammonium carboxylates, and tetraalkylammonium carboxylates, trialkylammonium carboxylate primers produced an adhesive bond so strong that the failure occurred at the polyolefin substrate. Trialkylammonium carboxylate primers also demonstrated excellent performance retention over prolonged atmospheric exposure prior to application of the adhesive. Trialkyl amines and tetraalkylammonium carboxylates also promoted adhesion but lost maximum effectiveness on exposure to the atmosphere. The cause of the deterioration in amine primer effectiveness over prolonged exposure was identified to be trialkylammonium bicarbonate formation and/or diffusion of the primer into the polyolefin surface.     

A specific distribution and bonding mechanism of emulsified adhesives in granular and fibrous substrates

It is shown both theoretically and experimentally that highly effective bonding of granular and fibrous materials can be realized on the basis of a specific liquid distribution and adhesive linkage mechanism of emulsions during evaporation. The formation of adhesive links was investigated with glass microspheres as a standard substrate and a series of emulsified and dissolved adhesives. In contradistinction to dissolved adhesives, emulsified adhesives of the type oil-in-water could be located almost quantitatively at the contact sites of the substrate material as a result of interfacial retraction during evaporation. Retraction and the selective accumulation of the adhesive at contact sites of the glass microspheres appeared to be governed by the contact angle, the surface tension, and the colloidal stability of the emulsion. Aggregate formation was measured with a given amount of the adhesive in different states of dilution, so as to change the water content of the substrate upon application. These measurements showed that water is involved in the distribution of emulsified adhesives as a carrier: relatively high water contents of the substrate are required in order to incorporate the larger substrate materials into aggregates. The formation of aggregates and their mechanical stability attain a maximum at dilutions corresponding to saturation of the substrate capillary system. This carrier mechanism was confirmed by measurements of the size distributions of the glass particles in aggregates of different size classes. The selective location of adhesives at the contact sites of substrate materials, the high efficiency of aggregate formation, and the high aggregate stability are promising in view of the production of composites with specific perspiration characteristics.     

Fumaric Acid as a Promoter of Adhesion in Vulcanized Synthetic Rubbers

The addition of dicarboxylic acids to polyurethane adhesives, to improve their adhesion to vulcanized synthetic rubbers, may cause the degradation over time of the adhesives. To avoid the degradation of polyurethane adhesives, this study proposes a surface treatment on vulcanized synthetic rubbers with carboxylic acid solutions instead of adding them to the adhesives. In all the styrene-butadiene rubbers studied, a great improvement in adhesion to polyurethane adhesives has been obtained. The nature of the solvent used to disperse the fumaric acid over the surface, as well as the nature of the rubber, determined the effectiveness of the surface treatment. The use of fumaric acid solutions provided optimum results when the surface of the rubber was slightly roughened. The increase in the adhesion properties of styrene-butadiene rubbers, treated with fumaric acid, has been attributed to an increase in the degree of the surface roughness and to an enhancement in the surface energy (due to the elimination of abhesive substances on the surface of the rubber and to the formation of C-O groups by surface oxidation). The effectiveness of the surface treatment on rubbers with fumaric acid in the adhesion of styrene-butadiene rubbers has been compared with those produced by other common treatments, such as halogenation and roughening. In general, T-peel strengths obtained in the rubbers treated with fumaric acid were similar to those obtained through halogenation and were always higher than those obtained through roughening. Therefore, surface treatment of styrene-butadiene rubbers with fumaric acid can be considered as an alternative method to chemical treatments currently used, especially in the footwear industry.     

Utilization of waste leather shavings as filler in paper making

Leather industry generates large amounts of wastes, most of them are burned causing environmental pollution. This study aims to use these wastes as filler in bagasse pulp before sheet formation, as a novel method. Leather shavings were subjected to multistage disintegration to prepare powder, then treated with different monomers and applied in paper sheets. The formed sheets exhibit a considerable improvement in some of their properties such as tear, water resistance, air permeability, and thermal stability. Only breaking length was affected by adding untreated and treated leather shavings. Consequently, the resulting paper sheets have potential for application in wrapping and packaging industries. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

国内各种PVC材料的粘接概况

综述近十余年来国内各种PVC材料粘接的研究进展,分类介绍PVC膜、PVC管材,PVC革、PVC板材和PVC装饰材料等所用胶粘剂的概况,讨论了各种材料所适用的胶粘剂种类,并通过剥离强度,粘接强度等主要性能指标分析了各胶粘剂的主要性能。     

Application of lock-in thermography in nondestructive evaluation of adhesively-bonded aluminum joints

A major problem in industrial applications of structural adhesives is the quality assurance of manufactured joints. At present, for lack of a suitable nondestructive technique, production standards for adhesively-bonded aluminum joints are established on the basis of destructive tests and statistical inference. An experimental study was carried out to assess if lock-in thermography (LT) could be used as a tool for nondestructive evaluation of adhesively-bonded aluminum joints. Several samples were fabricated by varying the governing parameters such as nature of aluminum alloy, substrate thickness, surface treatment, adhesive type and bondline thickness. The effects of surface treatments on the loading capability of lap joints were evaluated through both destructive tensile tests and nondestructive evaluation with infrared LT. Tensile tests showed that the joint performance was not affected by the nature of the aluminum alloy but by the substrate thickness, the adhesive type and the bondline thickness. LT was capable of detecting imperfections such as scratches on substrates and foreign inclusions in the adhesive layer.     

Soy-based adhesives for wood-bonding – a review

Over recent years, the interest in bio-adhesives, including soy-based adhesives, has increased rapidly. Among natural renewable resources suitable for industrial use, soy is a reasonable choice due to its high production volume and the small use of soy meal-based products for human food consumption. Soy flour can be an ideal raw material for the manufacturing of wood adhesives due to its low cost, high protein content and easy processing. There are also more concentrated forms of soy proteins, i.e. concentrates and isolates, which are also suitable raw materials for adhesive production except that their prices are higher. Extensive research has been carried out on improving the cohesive properties, especially water resistance, of soy-based adhesives. However, there is insufficient experimental data available for understanding the influences of modification methods on the structure of soy proteins and therefore for understanding the influences of structural changes on the adhesion. In this paper, some experimental techniques are proposed to be used for analysing soy-based adhesives to enable better understanding of those factors and improve future development. This review of soy-based adhesives is made with the focus on soy proteins’ chemical composition, soy protein product types (raw materials for adhesive production), modification methods for improving the adhesive properties of soy-based adhesives, and commercial soy-based adhesives.     

胶接接头在静态负载条件下的蠕变和松弛行为

Modern high performance adhesives are designed to offer an optimized balance of elasticity,toughness and plastic deformation capacity for the individual fields of application in e.g. the building and construction or transportation and vehicle industry. The long-term life prediction for adhesive joints based on laboratory tests requiring only days,weeks,or months is still a demanding challenge. Testing in practice is carried out with the intention of accelerating time dependent aging effects that may occur in a bonded joint during its service time. Initial strength values of bonded joints,such as shear or peel properties can often be obtained from the adhesive manufacturers or retrieved from literature. They are useful to compare different adhesives and to demonstrate the effect of parameters such as bond line thickness,overlap length or curing conditions,and,in some cases,the surface state. On the other hand only few data are available describing the mechanical long-term properties of adhesives related to creep and relaxation under static load conditions. Due to the nature of the polymer network of organic adhesives their viscoelastic-plastic deformation behavior is strongly time-and temperature dependent. The objective of this paper is to illustrate effective methods for investigating and predicting the creep and relaxation properties of adhesively bonded joints in the long-term region and for creating basic data for the design and engineering with adhesives.     

Technological performance of formaldehyde-free adhesive alternatives for particleboard industry

Due to their high reactivity, chemical versatility and economic competitiveness, formaldehyde-based poly-condensation adhesives are used in huge amounts - in 2010 in the order of 20 million metric tons - around the globe, primarily in the wood-processing industry. Since the 1970s formaldehyde emissions from products made thereof came under pressure and were reduced continuously. The discussion intensified again initiated by the latest European CLP (classification, labelling and packaging) regulation, which came into force in 2016, classifying formaldehyde as a Carcinogen Category 1B compound. In view of potential and even stronger future restrictions of formaldehyde use, appropriate alternatives to substitute formaldehyde-based adhesive systems such as urea formaldehyde would have to be developed and implemented in the wood processing industry. The present review represents a critical appraisal of formaldehyde-free adhesive systems for particulate wood composites production proposed in literature so far. Adhesive systems analyzed here include both synthetic and renewable-based adhesives. The core of the review is an assessment of the individual adhesive systems based on selected technological (product and process) parameters relevant for wood-particleboard production. Based on this data we evaluated their potential to identify suitable alternative adhesives having a certain probability to meet the requirements of a large-scale processing industry sector. As an overall conclusion, there are still many challenges to overcome to replace formaldehyde. Except for pMDI-based systems, most of the alternative adhesives are considerably less reactive, which would result in dramatically higher production costs. Furthermore, the availability of most components proposed to produce alternative adhesives are currently not available in the necessary quantities. Moreover, toxicological investigations on alternative systems are still missing. As several components replacing formaldehyde are also toxic or hazardous to different extents, it cannot be guaranteed that the individual proposed alternative adhesives are safer during processing and service life compared to conventional systems. Due to the nature of the organic material wood, particleboards will always release a certain amount of formaldehyde, even when produced with formaldehyde-free adhesives.     

Effect of reinforcements at different scales on mechanical properties of epoxy adhesives and adhesive joints: a review

Improvement of the mechanical properties of adhesives and adhesive joints has been a subject of great interest in recent years. Up to now, several methods have been presented such as modifying substrate shapes, adding microparticles (MPs) and nanoparticles (NPs), and embedding micro and macrofibers in the adhesive layer. This review aims to investigate how these reinforcements of different scales in the adhesive layer influence the mechanical properties of adhesive joints and adhesives. Characteristics and applications of reinforcements are introduced in the first part. In the second part, the effects of several parameters commonly investigated by researchers on the strength, stiffness and fracture toughness improvement of polymeric materials are reviewed for reinforcements of different scales. Finally, damage mechanisms involved in increasing or decreasing the mechanical properties are reviewed and discussed.     

Adhesives in construction: A contractor's viewpoint

The development of epoxy- and polyester-based adhesives has dramatically widened the scope of adhesive bonding in the civil engineering industry but the technology of the adhesives used has often been more appropriate to the workshop than to the construction site. There is a need for the suppliers of structural adhesives to recognize this and to develop compositions and application techniques more amenable to site use. It is equally necessary for the construction industry to make more effort to understand these materials, to take advantage of their outstanding properties, and hence to use them successfully for the construction and repair of concrete structures.     

Influence of ultrasound on diffusion through skin/leather matrix

Leather is a unique porous material, which is composed of a three-dimensional weave of tanned collagen fibre bundles. Collagen is a fibrous protein well organized in the formation of skin as building block. This paper studies the use of ultrasound in improving the diffusion process through porous skin/leather matrix. A diffusion model for leather processing has been proposed taking into account of pore characteristics in leather. Dye diffusion experiments have been carried out with leather and powdered leather to show the influence of ultrasound under two different diffusion conditions. Apparent diffusion coefficient (D) of dye through leather matrix has been calculated from the experimental dye uptake data. The results indicate that the use of ultrasound could achieve, 16.2 and 8.56 times improvement in D value for leather at 50 °C and 30 °C, respectively as compared to 2.99 and 1.55 times for powdered leather. Scanning electron microscopy (SEM) analysis of leather has also been performed which shows that fibre structure and morphology are not affected by the use of ultrasound. This study throws some light on enhanced transport through porous materials of complex nature such as skin/leather using ultrasound.