Lignin-based copolymer adhesives for composite wood panels – A review

Lignin is a natural and renewable organic compound that can be easily obtained from spent pulping liquors. It can be used as feedstock for making wood adhesives. Nonetheless, lignins need to be modified to enhance reactivity prior to being used as feedstock for making wood adhesives. Appropriate crosslinkers are also needed to ensure the bonding quality of the lignin-based wood adhesives. In the present review, the drawbacks of using lignins alone as wood adhesives, modifications to enhance the reactivity of lignins and production of lignin-based copolymer adhesives for composite wood panels are reviewed and discussed. The objective of this review is to provide background information about the recent status on the development of lignin-based copolymer adhesives for the production of composite wood panels as well as the future prospects of these adhesives in industry. Several modifications such as demethylation, oxidation, methylolation, phenolation, reduction and hydrolysis have shown promising results for enhancing the reactivity of lignins. Several crosslinkers such as phenolic resin, tannin, polymethylene polyphenyl isocyanate (pMDI), furfural and ethylenimine are capable of copolymerizing with lignins to produce lignin-based wood adhesives. The performance of composite wood panels bonded with modified lignin-based copolymer adhesives have been shown to meet the requirements of relevant standards. The main obstacles for the composite wood panels industry to widely adopt to lignin-based copolymer adhesives are the economic and technical issues. Nevertheless, lignin modification methods are proving to enhance the reactivity of lignins and the optimization in such modification methods would justify the economic issue. Together with the public awareness on the safety, health and environment concerns, the utilization of lignin-based adhesives in the composite wood panels industry is feasible.     

Bonding of resin adhesives to caries-affected dentin – A systematic review

Minimal invasive dentistry aims at preserving the firm, discolored caries affected dentin (CAD), which is remineralizable. Research studies on resin adhesives are usually performed on sound dentin (SD), though CAD is the substrate routinely encountered for bonding in clinical practice. The aim of this paper was to systematically analyze the published literature on resin-dentin bonding to CAD substrate, in order to answer the question: “Does resin adhesive bonding to CAD produce lower bond strength when compared to SD?”. Three electronic databases (Pubmed, Scopus and ISI web of Science) were searched to identify original laboratory studies that evaluated the bond achieved between resin adhesive and natural CAD by measuring their bond strength. Only articles that met the specific inclusion criteria were included in the review. Among the 29 studies included for this review, majority of the studies had tested the simplified etch-and-rinse or self-etch adhesives. 85% of them showed higher bond strength to SD compared to CAD and the remaining 15% of them showed no difference between these two substrates. Among the studies that used 3-step etch-and-rinse adhesives, 40% showed higher and 60% showed no difference, when bond strength was compared between SD and CAD. Resin adhesives produce lower bond strength to caries-affected dentin than sound dentin. Research studies that reported bond strength of resin adhesives to dentin from sound extracted teeth alone cannot be blindly extrapolated to clinically relevant CAD. Hence, the results from such studies should be dealt with caution.     

Multilayered ceramic composites – a review

With the aim of improving the toughness of ceramic materials, laminated composites have been successfully developed since Clegg et al. (1990) inserted weak interfaces using very thin graphite layers between silicon carbide sheets and obtained a composite that exhibited non-catastrophic fracture characteristics. The weak interface must allow the crack to deviate either by deflection or delamination; in other words, the interface must exhibit a fracture resistance that is lower than that of the matrix layer. In parallel, ceramic laminated composites with strong interfaces were developed in which the residual tensile and compressive stresses appeared in alternate layers during cooling after sintering. These composites are prepared by stacking ceramic sheets produced by lamination or tape casting or by the sequential formation of layers by slip casting, centrifugation or electrophoretic deposition. The techniques may be combined to obtain a composite with the most adequate configuration. This work presents a review about the obtainment of multilayered ceramic composites as a toughening mechanism of ceramic plates.     

Aluminosilicate phosphate cements – a critical review

Phosphate cements are formed by the reaction at an environmental temperature between a phosphate solution and a solid precursor. The precursors can be divided into two categories: One contains mono- or divalent cations that are dissolved and form cation-phosphate precipitates acting as a binder. The other category is based on aluminosilicates, and in these cements, covalent Al–O–P and Si–O–P bonds are formed. There is however not yet agreement on the structure and properties of these cements in the limited literature on this last category. Compressive strengths between 40 and 146?MPa were reported, but these high values were only obtained by one group. The mentioned mechanical strengths in literature render the materials promising candidates for construction purposes. More important is that phosphate cements have a neutral pH after hardening. This allows the use of low-cost glass fibers as reinforcement. The production of Textile Reinforced Cements is thus one of the important future applications. Moreover, there is some disagreement on the molecular structure formed. Some state that Al is present in VI-fold coordination. Others state that berlinite-like structures are formed. Thus, Al is in IV-fold coordination. Crystalline berlinite is however only proven to be present after thermal treatment to at least 250°C. The formation of stable crystalline phases at high temperature makes the material also suited for use as a refractory. A drawback is the scarcity of phosphate minerals to produce phosphoric acid. For this reason, the use of phosphate cement should be limited to niche applications. As phosphates can be fast setting cements, one of these applications might be in additive manufacturing.     

Recovery of gold in iodine-iodide system – a review

Gold leaching in iodine-iodide solution has been intensely researched in 1980s; while due to the high cost, it has not been applied in industry. Currently, as the drawbacks of other hydrometallurgies appearing such as aqua regia and cyanidation, mining and exploration companies are shifting their attention to the iodide leaching, because which has low electrode potential, fast leaching kinetics, high leaching rate, mild reaction conditions and the lixiviant is easy to recover. The common gold leaching agents, although considerable researches have been undertaken, most, if not all, of which have been proven to have limitations that hinder their widespread adoption in the gold mining industry. Iodide leaching could serve as an effective mean for recovering gold through the dynamic, thermodynamic and electrochemical assessment. And a series of parameters, such as oxidants selection, the iodine/iodide ratio, solid-to-liquid ratio, acidity (pH) and leaching time, affect the gold leaching efficiency. Through a comparison with several other hydrometallurgical processes, the presenting merits promote iodine-iodide system to be a promising method for gold recovery. The key challenge of industrialization is how to reduce the cost and to recover gold from the lixiviant.     

Catalytic performance of advanced titanosilicate selective oxidation catalysts – a review

This review article aims to cover the state-of-the-art of titanosilicate catalysts for selective oxidations developed within past seven years. Many elaborated materials (e.g., layered and pillared titanosilicates, hierarchical composite materials, and others) have been prepared and thoroughly characterized; however, their catalytic properties have been usually investigated only using a single or few model substrates and compared with a benchmarking material. The main goal of this article is to summarize the novel catalysts and compare their catalytic performance with each other. The comparison is focused on epoxidation. In addition, phenol hydroxylation and sulphide oxidation are briefly covered.     

Rotating reactors – A review

This review-perspective paper describes the current state-of-the-art in the field of rotating reactors. The paper has a focus on rotating reactor technology with applications at lab scale, pilot scale and industrial scale. Rotating reactors are classified and discussed according to their geometry: stirred tanks, tubes, discs and miscellaneous reactors. Their operating characteristics, industrial applications, and their main advantages and disadvantages are discussed including power requirements, residence time distribution, reactor volume, gas–liquid mass transfer rate, and the micromixing time. Finally, the barriers for further industrial implementations are discussed.     

Room temperature ionic liquids as replacements for conventional solvents – A review

Room temperature ionic liquids are salts that are liquids at ambient temperature. They are excellent solvents for a broad range of polar organic compounds and they show partial miscibility with aromatic hydrocarbons. Typical room temperature ionic liquids have a stable liquid range of over 300 K and have a very low vapor pressure at room temperature. Ionic liquids that are not hydrolyzed show a wide range of solubility in water. These unique properties have suggested that they might be useful as environmentally benign solvents that could replace volatile organic compounds (VOC). By varying the length and branching of the alkane chains of the cationic core and the anionic precursor, the solvent properties of ionic liquids should be able to be tailored to meet the requirements of specific applications to create an almost infinitely set of “designer solvents”. A review of recent applications of ionic liquids is presented along with some results of measurements of liquid-liquid equilibria and partition coefficients with alcohols. The results are compared with predictions based on quantum mechanic calculations.     

Mechanical behavior of advanced nano-laminates embedded with carbon nanotubes – a review

Embedding carbon nanotubes (CNTs) in load-bearing composite laminate hosts to turn them into nano-laminates is a rapidly emerging field and has tremendous potential in enhancing the mechanical performance of the host laminates. This state-of-the-art review intends to provide a physical insight into the understanding of the enhancing mechanisms of the processed and controlled CNTs in the nano-laminates. It focuses on four aspects: (1) physical characteristics of CNTs, including CNT length, diameter, weight percentage and surface functionalization; (2) processing and control techniques of CNTs in the fabrication of nano-laminates, including distribution, dispersion and orientation controls of CNTs; (3) mechanical properties along with their testing methods, including tension, in-plane compression, in-plane and interlaminar shear (ILS), flexure, mode I and mode II fracture toughness as well as compression-after-impact (CAI), ballistic protection and fatigue; and (4) CNT–matrix load transfer and enhancing mechanisms along with a few major governing factors. The selective and uniform production of CNTs with specific dimensions and physical properties has yet to be achieved on a consistent basis. Moreover, the processing details of CNTs vary very significantly among different researchers so that the processed CNTs share little common characteristics. There is little control over the CNT orientations in most fabrication processes of the nano-laminates except for some cases associated with chemical vapor deposition (CVD). There are only two reports on in-plane compression and there is only one on in-plane shear. For reinforcement-dominated mechanical properties such as longitudinal tension and flexure, there was little enhancement reported. However, the substantial enhancement in in-plane compression strength was also reported. For matrix-dominated mechanical properties, such as transverse tension, in-plane shear, ILS strength and mode I and mode II fracture toughness, a significant enhancement, albeit with substantially varying degrees, was reported for ILS strength and mode I and mode II fracture toughness values. Meanwhile, the lack of consistent characterization of those properties was also noticeable. There is little established understanding of the enhancing mechanisms in nano-laminates.     

CFD simulation of fluidized bed reactors for polyolefin production – A review

This literature survey focuses on the application of computational fluid dynamics (CFD) in various aspects of the fluidized bed reactor. Although fluidized bed reactors are used in various industrial applications, this first-of-its-kind review highlights the use of CFD on polyolefin production. It is shown that CFD has been utilized for the following mechanisms of polymerization: governing of bubble formation, electrostatic charge effect, gas–solid flow behavior, particle distribution, solid–gas circulation pattern, bed expansion consequence, mixing and segregation, agglomeration and shear forces. Heat and mass transfer in the reactor modeling using CFD principles has also been taken under consideration. A number of softwares are available to interpret the data of the CFD simulation but only few softwares possess the analytical capability to interpret the complex flow behavior of fluidization. In this review, the popular softwares with their framework and application have been discussed. The advantages and feasibility of applying CFD to olefin polymerization in fluidized beds were deliberated and the prospect of future CFD applications was also discussed.     

Nanostructured insulators – A review of nanotechnology concepts for outdoor ceramic insulators

Nanotechnology is rapidly growing as a new technology alternative to create advance materials with unique characteristics and performance for different applications in several industrial sectors. In recent years, many nanotechnology-based products have appeared in our everyday life. On the other hand, industries have also considered nano-concepts to produce high-added value products with superior capacity, reliability and efficiency. Electric insulators are components with high importance in the electricity network system; reliability and high performance are essential characteristics demanded by actual markets. Recent studies have demonstrated the technical feasibility of innovative nano-concepts to improve the final properties of these electrical components. This paper reviews the state-of-the-art of nanotechnology applications for outdoor insulators. Nano-concepts for ceramic insulators are summarized and reported with the aim to provide an overview of applications and opportunities for electric industry. In addition, the future trends and challenges for this field are also considered in this work.     

Eutectic bonding of copper to ceramics for thermal dissipation applications – A review

Metallic copper, which has low electrical resistivity and high thermal conductivity, is widely used as an interconnector or substrate within microelectronic packages. If a small amount of oxygen is introduced to the surface of the copper, a eutectic liquid forms above 1065 °C. The eutectic liquid wets many ceramics well; it is thus possible to bond slightly oxidized copper to many ceramics directly. The present report summarizes previous results on three systems, Al₂O₃/Cu, AlN/Cu, and Si₃N₄/Cu laminates, prepared by the eutectic bonding process. The reported data demonstrate that ceramic/copper interfaces prepared with this technique are strong. Though little attention has been paid to the thermal characteristics of ceramic/copper laminates, the limited data suggest that the thermal conductivity of the laminates is high, the potential for using the laminates for thermal dissipation is thus high. In the present report, the current status for the technique is summarized; critical topics for further improvement are also proposed.     

Soy-based UV-curable thiol–ene coatings

Novel soy-based thiols and enes were synthesized and characterized. Then, soy-based thiol–ene UV-curable coatings were formulated and their coating physiochemical properties were investigated in detail. The use of biorenewable resources, combined with environmentally friendly UV-curable technology, provides a “green + green” solution to the stricter regulations in the coatings industry. Novel soy-based thiols and enes were synthesized through the Lewis acid-catalyzed ring opening reaction of epoxidized soybean oil with multifunctional thiols or hydroxyl functional allyl compounds. FTIR and NMR confirmed the formation of the target compounds. The soy-based thiols and enes were formulated with petrochemical-based enes and thiols, respectively, to make thiol–ene UV-curable coatings. Typical coating film properties, thermal properties, and photopolymerization kinetics of these coatings were studied. Soy-based thiol–ene coatings having lower functionality thiols and enes have poor UV curability and coating properties, which was attributed to the lower crosslink density. Soy-based thiols and enes with higher functionality can be UV-cured in combination with petrochemical-based enes or thiols even without the presence of free radical photoinitiators. Better coating film properties were obtained from these higher functionality thiol–ene systems that were toughened by commercial hyperbranched acrylates.     

Ultra-high molecular weight polyethylene – Evidence for a three-phase morphology

The phase composition of ultra-high molecular weight polyethylene of two different molecular weights has been estimated using Raman spectroscopy. Materials have then been irradiated in air to give a received doses of 3.5 and 10 Mrad, and crystallinity change with time has been monitored by differential scanning calorimetry (DSC), wide and small angle X-ray diffraction (WAX and SAX) and Raman spectroscopy. Analysis by DSC and X-ray diffraction involved melting and re-crystallisation. Raman spectroscopy demonstrated that the material consists of three phases, fully crystalline, fully amorphous and an intermediate all-trans non-crystalline phase. Following irradiation the mass fraction of this latter phase reduces as total crystal content increases. SAX results indicate a refinement of the original lamellae and the emergence of a population of smaller crystals. It is thought that the all-trans material exists as an interfacial phase and that scission within this phase facilitates the observed crystal changes.     

Total Turnover Number – a Key Criterion for Process Evaluation

The dimensionless total turnover number TTN, the average number of turnovers per active site of a catalyst over the catalyst's lifetime, is a universal criterion for the operational stability of a catalyst. If the cost of the catalyst is known, the cost contribution per catalytic cycle can be determined. The present work honors the contributions by Prof. Christian Wandrey and his group on the topic of TTN and describes some recent developments on the subject.     

Development of hot-melt pressure–sensitive adhesives for transdermal drug delivery

Styrene–isoprene–styrene (SIS) copolymer was epoxidized by in situ epoxidation to prepare a series of epoxidized SIS resins (ESIS). Their epoxidation degrees, phase structures, and compatibility with hydrocarbon resin were characterized with ¹H nuclear magnetic resonance spectroscopy, atomic force microscopy, and differential scanning calorimetry, respectively. These ESIS resins were melt-mixed with synthetic hydrocarbon resin, mineral oil, and antioxidants to fabricate a series of ESIS-based hot-melt pressure–sensitive adhesives (HMPSAs), which were used as carriers of transdermal drug delivery system. Their adhesive performances were measured, including holding power and 180^o peel strength. Geniposide and oleanic acid were representatively chosen as hydrophilic and lipophilic drug, respectively. Their in vitro release behaviors in ESIS-based HMPSAs were investigated using a modified Franz-type horizontal diffusion cells. Although the introduction of epoxide groups could alter the compatibility and phase structures between SIS resins and additives, the adhesive performances were slightly affected, as SIS resins had lower epoxidation degree (<15%). It is even more important that the cumulative release rate of both hydrophilic and lipophilic drugs is markedly enhanced with the increase of epoxidation degree in these ESIS-based HMPSAs. Therefore, this kind of HMPSAs has a promising future as a carrier of transdermal drug delivery system as their SIS resins are appropriately epoxidized.     

Studies on adhesives for bonding rubber to rubber: Part 21 – Reclaimed latex product for adhesive,addition of ultra-accelerator,and use of soluble sulphur

Abstract

One process for retreading tyres involves coating the buffed casing with a solution of natural rubber compound (dough), covering it with a thin layer of solid adhesive, and then applying the precured tread, also coated with dough. Reclaimed material from waste latex products has been used to prepare the adhesive. It was also shown that the addition of an ultra-accelerator to the dough just prior to its application can reduce the bonding time, and hence reduce heat aging of the tread. In the adhesive strip, a small fraction of the insoluble sulphur can be replaced with soluble sulphur, without significant reduction in bond strength.