Recent Advances on the Development of Protein-Based Adhesives for Wood Composite Materials—A Review

The industrial market depends intensely on wood-based composites for buildings, furniture, and construction, involving significant developments in wood glues since 80% of wood-based products use adhesives. Although biobased glues have been used for many years, notably proteins, they were replaced by synthetic ones at the beginning of the 20th century, mainly due to their better moisture resistance. Currently, most wood adhesives are based on petroleum-derived products, especially formaldehyde resins commonly used in the particleboard industry due to their high adhesive performance. However, formaldehyde has been subjected to strong regulation, and projections aim for further restrictions within wood-based panels from the European market, due to its harmful emissions. From this perspective, concerns about environmental footprint and the toxicity of these formulations have prompted researchers to re-investigate the utilization of biobased materials to formulate safer alternatives. In this regard, proteins have sparked a new and growing interest in the potential development of industrial adhesives for wood due to their advantages, such as lower toxicity, renewable sourcing, and reduced environmental footprint. This work presents the recent developments in the use of proteins to formulate new wood adhesives. Herein, it includes the historical development of wood adhesives, adhesion mechanism, and the current hotspots and recent progress of potential proteinaceous feedstock resources for adhesive preparation.     

Lignin and Lignin-Derived Compounds for Wood Applications—A Review

Improving the environmental performance of resins in wood treatment by using renewable chemicals has been a topic of interest for a long time. At the same time, lignin, the second most abundant biomass on earth, is produced in large scale as a side product and mainly used energetically. The use of lignin in wood adhesives or for wood modification has received a lot of scientific attention. Despite this, there are only few lignin-derived wood products commercially available. This review provides a summary of the research on lignin application in wood adhesives, as well as for wood modification. The research on the use of uncleaved lignin and of cleavage products of lignin is reviewed. Finally, the current state of the art of commercialization of lignin-derived wood products is presented.     

Adhesives and coatings from phenol-formaldehyde/resorcinol-formaldehyde resins

Resole phenol-formaldehyde resins were prepared and modified with the prepared resorcinol-formaldehyde resins. The optimum conditions of formulation and curing processes were studied to obtain modified wood adhesives characterized by high-tensile shear strength values. This study indicated that the more suitable conditions are equal weight ratios of phenol-formaldehyde to resorcinol-formaldehyde resins in the presence of paraformaldehyde (10 or 15 wt%) of the resin content as a curing agent at 80 or 25°C for 40 min or 100–110 days, respectively. The activation energies of the curing reactions for phenol-formaldehyde/resorcinol-formaldehyde resin samples were determined. Metallic and glass coatings from the previous pure resins and their formulated cured mixtures were prepared and evaluated as varnishes or paints. Copyright © 1998 John Wiley & Sons, Ltd.     

脲醛树脂胶粘剂及其发展状况

脲醛树脂是目前使用量最大的木材用胶粘剂,文章主要从脲醛树脂的合成、改性、应用及固化机理等方面,综述了近年来脲醛树脂的研究进展。讨论了脲醛树脂的合成工艺,分析了pH值对脲醛树脂合成工艺的影响。针对脲醛树脂释放甲醛、耐水性差的缺点,列举了脲醛树脂常用的各种改性物质及它们的改性效果。并讨论了脲醛树脂在使用过程中使用的助剂和固化剂。     

Investigation of artificial resin-based adhesives in works carried out by the all-Russia Scientific Research Institute of Aviation Materials in 1936–1937

The main preconditions for developing principally new (for the examined period of time) adhesives based on artificial resins are presented. The results of application of the combined (casein and resin) adhesives, adhesives based on novolak, karbolit and barite phenol formaldehyde resins are given. It is shown that the phenol-barite resin of VIAM-6 grade was the most suitable for the aviation industry at that time.     

Investigation of the artificial resin-based adhesives in works carried out by the All-Russia Scientific Research Institute of Aviation Materials in 1938–1939

The main preconditions for developing principally new (for the examined period of time) adhesives based on artificial resins are presented. The results of application of the combined (casein and resin) adhesives, adhesives based on novolak, karbolit and barite phenol formaldehyde resins are given. It is shown that the phenol-barite resin of VIAM-6 grade was the most suitable for the aviation industry at that time.     

Adhesives and coatings based on phenolic/epoxy resins

Low molecular weight epoxy resin based on bis (4‐hydroxy phenyl) 1,1 cyclohexane was prepared and modified with various types of the prepared phenolic resins. Phenol–, cresol–, resorcinol–and salicylic acid–formaldehyde resins were used. The optimum conditions of formulation and curing process were studied to obtain modified wood adhesives characterized by high tensile shear strength values. This study indicated that the more suitable conditions are 1:2 weight ratio of phenol–or cresol–formaldehyde to epoxy resin in the presence of phthalic anhydride (20 wt%) of the resin content as a curing agent at 150°C for 80 min. Resorcinol–or salicylic acid–formaldehyde/epoxy resins formulated at 1:2 weight ratio were cured in the presence of paraformaldehyde (20 wt%) at 150°C for 60 min. The effect of the structure of phenolic resins on the tensile shear strength values of formulated resin samples, when mixed with the epoxy resins and cured under the previously mentioned optimum conditions for different times, was investigated. Metallic and glass coatings from the previous resins were also prepared and evaluated as varnishes or paints. Copyright © 1999 John Wiley & Sons, Ltd.     

Introducing flexibility in urea–formaldehyde resins: Copolymerization with polyetheramines

Adhesives obtained by copolymerizing urea, formaldehyde, and difunctional polyetheramine with different molecular weights (230, 600, 900, and 2000 g mol⁻¹) are presented as a more resilient alternative to conventional urea–formaldehyde resins. Urea and polyetheramine contents were varied and the resulting resins characterized by FTIR, ¹³C‐NMR, and TGA. These resins were used for production of agglomerated cork panels, an application that demands that the binder system is flexible. Polyetheramine with molecular weight 900 g mol⁻¹ yielded the most promising agglomerated cork panel, with remarkable flexibility, good tensile strength, and with the E1 formaldehyde content specification for wood‐based panels used in construction, according to European Standard EN 12460‐5. These new thermoset adhesives have demonstrated to be capable of being used in systems where conventional formaldehyde‐based resins do not perform well due to inherent high rigidity. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1834–1843     

New trends in creation of epoxy adhesives

Modern trends in development of production of epoxy adhesives with the purpose of obtaining high-strength, waterproof, and high-temperature adhesives are described. Such adhesives are developed and manufactured at ZAO ENPTs EPITAL based on the epoxy-diane and cycloalphatic epoxy resins. The modified aromatic amines, aromatic polyaminoamides, alkylamino phenols, as well as original curing systems are used as curing agents.     

An uninflammable film adhesive and an adhesive prepreg based on it

The properties of a composition that can be used as a film adhesive and a binding agent for glass-reinforced plastics are presented. The composition is developed based on brominated epoxy resins and is selfextinguishing. It is shown that the use of adhesives and binding agents based on brominated epoxy resins makes it possible to obtain glass-reinforced plastics with hot-performance capabilities coming close to the properties of structural inflammable materials.     

Modification of Phenol- and Carbamide-Formaldehyde Resins by Cellulose By-products

To improve their properties, phenol- and carbamide-formaldehyde adhesives were modified by cellulose by-products. It has been shown that the introduction of pectol into phenol-formaldehyde resin of SFZh-3013 grade and products of sulfite-cellulose production into adhesive compositions based on carbamide-formaldehyde resins increases the plywood gluing strength and curing rate.     

GC-MS characterisation and identification of natural terpenic resins employed in works of art

Natural resins were frequently employed in the past as adhesives or as components of oleo-resinous media in paintings. The identification of vegetable resins is still an open problem. The aim of this paper is to analyse by GC-MS some vegetable resins frequently employed in paintings, such as Venice turpentine, dammar, copal, elemi, in order to identify their main components in samples both raw and aged. Some molecules are proposed as chemical markers to identify these natural resins. Two samples scraped off from XV and XVII century paintings were used to test the reliability of proposed method.     

Thermal study of phenol–formaldehyde resin modified with cashew nut shell liquid

In this study, an experimental phenol–formaldehyde resin with 20% phenol replacement by cashew nut shell liquid (CNSL) was studied and compared with a conventional phenol–formaldehyde resin synthesized totally from petrochemical raw materials. The resins were characterized with standard lab analysis for their physicochemical specifications, while their thermal properties were studied with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). For comparison reasons pure CNSL and wood were also included in the TGA study. A DSC study conducted both for the neat resins and the system wood–resin as to examine the effect of wood on the curing performance of the resins in the real time conditions of their usage at the wood-based panels industry.The adhesion strength of these resins was investigated by their application in plywood production. The plywood panels were tested for their shear strength and wood failure performance while their free formaldehyde emissions were determined with the desiccator method. It was proved that although the neat CNSL modified PF resin (PCF) cures at longer time and higher temperature than a conventional PF resin, wood affects it more significantly, resulting in the evening of their curing performance. This is a novel finding that manifests the possibility of replacing a convention PF resin by a CNSL modified one in the plywood production, without changing any of their production conditions and with improvement to their overall properties.     

Migration of non intentionally added substances from adhesives by UPLC–Q‐TOF/MS and the role of EVOH to avoid migration in multilayer packaging materials

Polyurethane adhesives are commonly used to laminate multilayer packaging materials for food. Since these materials are in direct contact with the food, compounds could migrate from adhesive into it. For this reason, it is important to identify all the potential migrants and verify their migration. Ultra‐high performance liquid chromatography–quadrupole time‐of‐flight–mass spectrometry analyses and ChemSpider database are used to identify the potential migrants from polyurethane adhesives, and these techniques were demonstrated to be very powerful and useful tools for this purpose. Migration tests were carried out using Tenax® as food simulant. Nine out of fifteen non‐volatile compounds, identified in the cured adhesives, migrated. Most of them were identified as cyclic compounds, adipic based, which is the most commonly used monomer to make the polyester/polyol resins for polyurethane bi‐component adhesives. In this work, the use of EvOH layer in several multilayer materials to minimize or avoid migration was evaluated too. Copyright © 2013 John Wiley & Sons, Ltd.     

The Effect of Tackifier on the Properties of Pressure-Sensitive Adhesives Based on Styrene–Butadiene–Styrene Rubber

Russian Journal of Applied Chemistry - Pressure-sensitive polymer adhesives based on styrene–butadiene–styrene rubbers and aromatic petroleum hydrocarbon resins making the block...     

Investigations of the Rheology and Reactivity of Extrudable Wood-Resin Compounds

Summary. The extrusion of wood composites based on thermosetting resins is a new application in the field of wood plastic composites. To enable the extrusion of wood thermosetting compounds, it is necessary to know their reactivity and rheology well beforehand, to prevent the system curing inside the extruder. This study shows the different techniques that were adapted to allow in combination an estimation of the processing behaviour of wood-resin compounds in extrusion.     

Investigations of the Rheology and Reactivity of Extrudable Wood-Resin Compounds

The extrusion of wood composites based on thermosetting resins is a new application in the field of wood plastic composites. To enable the extrusion of wood thermosetting compounds, it is necessary to know their reactivity and rheology well beforehand, to prevent the system curing inside the extruder. This study shows the different techniques that were adapted to allow in combination an estimation of the processing behaviour of wood-resin compounds in extrusion.     

木质素活化及在木材胶粘剂中的应用进展

木质素是相对分子量较高的天然聚合物,由于具有苯酚结构利于制备木材胶粘剂,但是木质素本身反应活性低,一般都将其活化后再利用.而且,除了以往利用最多的造纸工业产生的木质素外,研究发现木材经过褐腐菌降解后残留主要成分是结构部分发生变化的木质素,这种可再生生物质资源以其自身的结构特点在合成胶粘剂上也有很大的优势,本文结合木质素胶粘剂应用中的问题,重点概述了活化木质素的各种方法及褐腐木质素在木材胶粘剂中的应用.     

New polymer‐chemical developments in clinical dental polymer materials: Enamel–dentin adhesives and restorative composites

In the past 10 years, many new components were synthesized and evaluated for an application in enamel–dentin adhesives and direct composite restoratives. New bisacrylamide cross‐linkers with improved hydrolytic stability and new strongly acidic polymerizable phosphonic acids and dihydrogen phosphates, as well as novel photoinitator systems, in combination with the implementation of novel application devices, have significantly improved the performance of the current enamel–dentin adhesives. The currently used resins for direct composite restoratives are mainly based on methacrylate chemistry to this day. A continuous improvement of the properties of current composites was achieved with the use of new tailor‐made methacrylate cross‐linkers, new additives, and photoinitiators as well as tailor‐made fillers. Nowadays, dental adhesives and methacrylate‐based direct restorative materials have found wide‐spread acceptance. Nevertheless, future developments in the field of dental adhesives and direct composite restoratives will focus on improving durability and biocompatibility as well as the development of materials with a broader application spectrum and of smart adhesives or composites. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012