Recent trends in (ligno)cellulose dissolution using neoteric solvents: switchable,distillable and bio‐based ionic liquids

Recent years have witnessed the use of different ionic liquids for biomass processing, either at the level of lignocellulose pre‐treatment, to fractionate biomass in its main components, separating hemicellulose and lignin from cellulose, or directly in cellulose decrystallization by dissolving it in the ionic liquid and subsequent precipitation by adding anti‐solvents. Yet, most of the ILs employed in these strategies (e.g. imidazolium‐based solvents) are (still) expensive for such applications, and provide discussable ecological footprints. In an attempt to combine the highly useful generated knowledge with novel neoteric solvents with improved properties, economics, availability and ecology, several new trends have appeared in these areas during recent years. They comprise the use of switchable ILs, based on strong organic bases and CO₂, the application of distillable ILs, as well as the use of bio‐based and low‐cost ILs and deep‐eutectic‐solvents (DES), e.g. choline chloride‐based derivatives. Apart from other emerging uses, for all these solvents some preliminary applications in biomass processing involving pretreatments, cellulose dissolution and other applications have been successfully reported. This Minireview contextualizes these recent trends and discusses them with emphasis on future use of them in biorefineries and biomass valorization. © 2013 Society of Chemical Industry     

Trennleistung von Dünnschichtverdampfern

The evaporation process has recently gained new momentum through special applications in chemical engineering and especially in environmental engineering, e.g. in the recovery of materials of value from liquid production residues. Thin‐layer evaporators with rotating wipers are particularly suitable for such tasks if the products of interest are thermally unstable or are prone to crusting. If these applications involve distillation‐type separation then a knowledge of the expected separation effect is important for calculations. This article aims to make a contribution to this topic. It is based on experimental studies performed on a laboratory‐scale thin‐layer evaporator and on earlier treatments of the theory of distillation in thin‐layer evaporators with a mechanically generated liquid film.     

Comparison of disodium octaborate tetrahydrate‐based and tannin‐boron‐based formulations as fire retardant for wood structures

Boron‐based formulations are used to improve the service life of timber. On the one hand, boron‐treated wood increases resistance to biological attacks (e.g. by fungi and insects), and on the other hand, it renders wood more resistant to burning. In the present study, we analyse the fire behaviour of some water‐borne formulations containing boron. A completely inorganic formulation (disodium octaborate tetrahydrate (DOT)) is compared with new‐generation tannin‐based wood preservatives in which the flavonoid network is used to fix the boron to wood. The study of the fire behaviour was carried out according to four specific fire tests: (i) dripping; (ii) short‐term exposure; (iii) long‐term exposure and (iv) the limiting oxygen index. The Scots pine (Pinus sylvestris L.) specimens treated with DOT have shown a complete efficacy against fire after all tests were completed. It should also be noted that very positive results have also been achieved by the tannin‐based solutions. DOT has to be preferred when high performance is required, but exclusively for interior applications. The use of tannin‐based formulations can be suitable for outdoor fire protection and also for indoor applications when specific aesthetic requirements should be fulfilled. Copyright © 2013 John Wiley & Sons, Ltd.     

Biomass as Feedstock in the Chemical Industry – An Examination from an Exergetic Point of View

Crude oil is the most important raw material for the chemical industry. Due to the continually rising price of crude oil, alternative carbon sources are becoming increasingly important. Biomass is basically the only available renewable carbon source. Because the chemical composition of biomass differs from fossil raw materials, the raw‐material change also offers many chances for new product properties and applications. At the same time, the chemical processes have to be redesigned if the feedstock changes to biomass. Here, the effects of a raw‐material change are examined on a rather generic level. The study is based on exergy balances and indicates that it is exergetically advisable to reconsider the previously established system of platform and basic chemicals. In general, exergy losses can be minimized if the synthesis pathways leading to the final products are adapted to the chemical structure of biomass.     

Mixing and Reactions in Microchannels – an Educational Approach Using the Internet

In many fields, microprocess technology is gaining significance and is increasingly finding its way into use in industrial production. However, specialist knowledge regarding reactions of compounds, mixing and downstream processes in microchannels is required, as experience from the ”?macro world”? can only be applied in a limited way. The appropriate level of education required is still lacking. In this study, a number of educational experiments were set up focusing on mixing processes and emphasizing the significance of viscosity in mixing. Additionally liquid‐liquid extraction as an important downstream process was looked into as a student experiment. In order to make the training widely accessible, a web‐based education platform was established.     

Mechanical Assembly of Thermo‐Responsive Polymer‐Based Untethered Shape‐Morphing Structures

Shape‐morphing robotic structures can provide innovative approaches for various applications ranging from soft robotics to flexible electronics. However, the programmed deformation of direct‐3D printed polymer‐based structures cannot be separated from their subsequent conventional shape‐programming process. This work aims to simplify the fabrication process and demonstrates a rapid and adaptable approach for building stimulus‐responsive polymer‐based shape‐morphing structures of any shape. This is accomplished through mechanically assembling a set of identical self‐bending units in different patterns to form morphing structures using auxiliary hard connectors. A self‐bending unit fabricated by a 3D printing method can be actuated upon heating without the need for tethered power sources and is able to transform from a flat shape to a bending shape. This enables the assembled morphing‐structure to achieve the programmed integral shape without the need for a shape‐programming process. Differently assembled morphing structures used as independent robotic mechanisms are sequentially demonstrated with applications in biomimetic morphing structures, grasping mechanisms, and responsive electrical devices. This proposed approach based on a mechanical assembling method paves the way for rapid and simple prototyping of stimulus‐responsive polymer‐based shape‐morphing structures with arbitrary architectures for a variety of applications in deployable structures, bionic mechanisms, robotics, and flexible electronics.     

Impression creep of PMR‐15 resin at elevated temperatures

The polyimides formed from the polymerization of monomeric‐reactants (PMR) approach have been increasingly used as matrix materials in fiber‐reinforced composites on aerospace and space structures for high temperature applications. The performance of PMR‐based structures depends on the mechanical durability of PMR resins at elevated temperatures, including creep and stress relaxation. In this work, the creep behavior of PMR‐15 resin was studied using the impression technique in the temperature range of 563–613 K and the punching stress range of 76–381 MPa. It was found that there existed a steady state creep for the creep tests performed at temperatures of 563 K and higher, from which a constant impression velocity was calculated. The steady state impression velocity increased with temperature and punching stress with the stress exponent in the range of 1.5–2.2. The average of the apparent activation energy of the PMR‐15 was calculated as 122.7 ± 6.1 kJ/mol. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Setting tolerances on color and texture for automotive coatings

In the automotive industry, color quality control is increasingly done by reflection measurements. We discuss how color tolerances are set in specifications to suppliers of add‐on parts and to paint suppliers. We mention several factors that often lead to unrealistically tight settings, and therefore to incorrect rejections and unnecessary high productions costs. We show that this is likely to occur when the dE_ab color difference equation is used, or when a strict criterion separating pass from fail is used instead of specifying a “grey area” where instrumental monitoring needs to be followed by visual assessments. Unrealistically, tight tolerances also result from halving tolerances in the supply‐customer chain in an attempt to compensate color variations due to uncontrolled application conditions. Tolerances should be widened further when a gap separates an add‐on part from the car body, making visual discrimination of color differences less critical. Other common situations where tolerances should be widened are the presence of visual texture in effect coatings, the lightness of metallic coatings becoming very high (L*> 100) and measurement geometries close to the gloss angle. Finally, we address the issue that instrumental color tolerances should not be tighter than what is allowed by instrumental reproducibility, repeatability, and inter‐instrument agreement. Accounting for these factors, we provide a set of reasonable values for tolerances on color and on visual texture parameters, based on our own practical experience. But realistic tolerance values depend very much on actual conditions, and should be agreed in tripartite discussions among automotive industry, suppliers of add‐on parts, and paint supplier. © 2012 Wiley Periodicals, Inc. Col Res Appl, 39, 88–98, 2014     

Polyurethane networks from polyols obtained by hydroformylation of soybean oil

BACKGROUND: Vegetable oil‐based polyols are a new class of renewable materials. The structure of oil‐based polyols is very different from that of petrochemical polyols, and it is closely related to the structure of oils. The objective of this work was to analyze the structural heterogeneity of soy‐based polyols and its effect on the properties of polyols and polyurethanes. RESULTS: A series of polyols with a range of hydroxyl numbers were prepared by hydroformylation and partial esterification of hydroxyls with formic acid. Polyols were reacted with diphenylmethane diisocyanate to obtain polyurethanes of different crosslinking density. Gelation was simulated using the Monte Carlo method with a calculated distribution of functionalities for each polyol. CONCLUSIONS: Most polyols are powerful crosslinkers since weight average functionality varied from 5 to 2.5 resulting in gel points from 53 to 83% conversion. Heterogeneity of polyols had a negative effect on mechanical properties of rubbery polyurethanes and this should be taken in account when designing polyols for flexible applications. This effect was not pronounced in glassy polyurethanes. Copyright © 2007 Society of Chemical Industry     

Recent advances in the conversion of bioglycerol into value‐added products

A versatile platform chemical and energy vector, bioglycerol from biodiesel manufacturing is increasingly finding new commercial applications. We report on some of the main achievements for converting glycerol into high‐value products and energy developed in the last two years, and conclude by providing an outlook on the evolving status of bioglycerol in the chemical industry.     

Preparation and swelling behavior of biodegradable hydrogels based on α,β‐poly(N‐2‐hydroxyethyl‐DL‐aspartamide)

Biodegradable polymers and the hydrogels have been increasingly applied in a variety of biomedical fields and pharmaceutics. α,β‐Poly(N‐2‐hydroxyethyl‐DL ‐aspartamide), PHEA, one of poly(amino acid)s with hydroxyethyl pendants, are known to be biodegradable and biocompatible, and has been studied as an useful biomaterial, especially for drug delivery, via appropriate structural modification. In this work, hydrogels based on PHEA were prepared by two‐step reaction, that is, the crosslinking of polysuccinimide, the precursor polymer, with oligomeric PEG or PEI‐diamines and the following nucleophilic ring‐opening reaction by ethanolamine. Soft hydrogels possessing varying degrees of gel strength could be prepared easily, depending on the amount of different crosslinking reagents. The swelling degrees, which were in the range of 10–40 g–water/dry gel, increased somewhat at higher temperature, and also at alkaline pH of aqueous solution. A typical hydrogel remained almost unchanged for 1 week, at 37°C in phosphate buffer of pH 7.4, and then seemed to degrade slowly as time. A porous scaffold could be fabricated by the freeze drying of water‐swollen gel. The PHEA‐based hydrogels have potential for useful biomaterial applications including current drug delivery system. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3741–3746, 2003     

Synthesis, properties and biomedical applications of poly(glycerol sebacate) (PGS): A review

Poly(glycerol sebacate) (PGS) is a biodegradable polymer increasingly used in a variety of biomedical applications. This polyester is prepared by polycondensation of glycerol and sebacic acid. PGS exhibits biocompatibility and biodegradability, both highly relevant properties in biomedical applications. PGS also involves cost effective production with the possibility of up scaling to industrial production. In addition, the mechanical properties and degradation kinetics of PGS can be tailored to match the requirements of intended applications by controlling curing time, curing temperature, reactants concentration and the degree of acrylation in acrylated PGS. Because of the flexible and elastomeric nature of PGS, its biomedical applications have mainly targeted soft tissue replacement and the engineering of soft tissues, such as cardiac muscle, blood, nerve, cartilage and retina. However, applications of PGS are being expanded to include drug delivery, tissue adhesive and hard tissue (i.e., bone) regeneration. The design and fabrication of PGS based devices for applications that mimic native physiological conditions are also being pursued. Novel designs range from accordion-like honeycomb structures for cardiac patches, gecko-like surfaces for tissue adhesives to PGS (nano) fibers for extra cellular matrix (ECM) like constructs; new design avenues are being investigated to meet the ever growing demand for replacement tissues and organs. In less than a decade PGS has become a material of great scrutiny and interest by the biomedical research community. In this review we consolidate the valuable existing knowledge in the fields of synthesis, properties and biomedical applications of PGS and PGS-related biomaterials and devices.     

The tensile behavior of off‐axis loaded plant fiber composites: An insight on the nonlinear stress–strain response

Composites in load‐bearing applications are often exposed to off‐axis loads. For plant fiber composites (PFCs) to be seriously and readily considered in structural applications, knowledge and reliable prediction of their response to off‐axis loads is critical. This article (i) characterizes the stress–strain response, (ii) investigates the tensile properties, and (iii) analyses the fracture modes, of unidirectional flax‐polyester composites subjected to off‐axis tensile loading. A key finding of this study is that due to the nonlinear stress–strain response of PFCs, the apparent stiffness of the composite reduces by ∼30% in the strain range of 0.05 to 0.25%. In addition, through cyclic tests on the composites, the elastic strain limit is found to be only ∼0.15%. This has major implications on the strain range to be used for the determination of the composite elastic Young's modulus. Consequently, it is proposed that the tensile modulus for PFCs should be measured in the strain range of 0.025 to 0.100%. Through comparison with experimental data, conventional composite micromechanical models are found to be adequate in quantitatively describing the tensile behavior of off‐axis loaded PFCs. The application of such models has also enabled the determination of, otherwise difficult to measure, material properties, such as fiber shear and transverse modulus. Off‐axis loaded PFCs fail by three distinct fracture modes in three different off‐axis ranges; each fracture mode produces a unique fracture surface. POLYM. COMPOS. 2012. © 2012 Society of Plastics Engineers     

A diagnostic expert system for the dyeing of protein fibres

Coloration of protein fibres is characterised by many variables, each with a different effect on the final product. Because the process can be rather complicated, it is often difficult to achieve the right colour in the first dyeing attempt. Determining the root causes of a given problem tends to be even more challenging. While quality requirements in the textile industry have become increasingly rigorous, seasoned coloration experts have become rather scarce. This situation has exacerbated the need for the development and implementation of expert systems to augment available expertise in this domain. In addition, benefits associated with computer‐based diagnostic systems have become increasingly evident over the past few decades, and the field remains an active area of research. Here we report the design and development of a diagnostic expert system for the dyeing of protein fibres. The system is designed to aid in the identification of root causes of problems with a view to enabling users to arrive quickly at remedial solutions. The performance of the system has been tested and evaluated by human experts and deemed to be highly satisfactory. This diagnostic system can be used to teach students, may be utilised by novice colourists as a problem‐solving tool, and may be employed as a supplementary knowledge resource by seasoned dyers.     

Directed Evolution of Hyaluronic Acid Synthase from Pasteurella multocida towards High‐Molecular‐Weight Hyaluronic Acid

Hyaluronic acid (HA), with diverse cosmetic and medical applications, is the natural glycosaminoglycan product of HA synthases. Although process and/or metabolic engineering are used for industrial HA production, the potential of protein engineering has barely been realised. Herein, knowledge‐gaining directed evolution (KnowVolution) was employed to generate an HA synthase variant from Pasteurella multocida (pmHAS) with improved chain‐length specificity and a twofold increase in mass‐based turnover number. Seven improved pmHAS variants out of 1392 generated by error‐prone PCR were identified; eight prospective positions were saturated and the most beneficial amino acid substitutions were recombined. After one round of KnowVolution, the longest HA polymer (<4.7 MDa), through an engineered pmHAS variant in a cell‐free system, was synthesised. Computational studies showed that substitutions from the best variant (T40L, V59M and T104A) are distant from the glycosyltransferase sites and increase the flexibility of the N‐terminal region of pmHAS. Taken together, these findings suggest that the N terminus may be involved in HA synthesis and demonstrate the potential of protein engineering towards improved HA synthase activity.     

Functionalization of the 3′‐Ends of DNA and RNA Strands with N‐ethyl‐N‐coupled Nucleosides: A Promising Approach To Avoid 3′‐Exonuclease‐Catalyzed Hydrolysis of Therapeutic Oligonucleotides

The development of nucleic acid derivatives to generate novel medical treatments has become increasingly popular, but the high vulnerability of oligonucleotides to nucleases limits their practical use. We explored the possibility of increasing the stability against 3′‐exonucleases by replacing the two 3′‐terminal nucleotides by N‐ethyl‐N‐coupled nucleosides. Molecular dynamics simulations of 3′‐N‐ethyl‐N‐modified DNA:Klenow fragment complexes suggested that this kind of alteration has negative effects on the correct positioning of the adjacent scissile phosphodiester bond at the active site of the enzyme, and accordingly was expected to protect the oligonucleotide from degradation. We verified that these modifications conferred complete resistance to 3′‐exonucleases. Furthermore, cellular RNAi experiments with 3′‐N‐ethyl‐N‐modified siRNAs showed that these modifications were compatible with the RNAi machinery. Overall, our experimental and theoretical studies strongly suggest that these modified oligonucleotides could be valuable for therapeutic applications.     

Multicomponent Syntheses based upon Copper‐Catalyzed Alkyne‐Azide Cycloaddition

The copper‐catalyzed alkyne‐azide cycloaddition (CuAAC) is a highly versatile, regioselective synthesis of 1,4‐disubstituted 1,2,3‐triazoles under mild reaction conditions and has found numerous applications in medicinal, bioorganic, and materials chemistry in the past one and a half decades. By virtue of the enormous tolerance for functional groups and the mild reaction conditions, CuAAC has become increasingly important in combination with multicomponent reactions (MCR), either in a domino or in a consecutive fashion. While the majority of CuAAC‐based MCR are founded on the in situ or en route generation of azides, one‐pot generation of alkynes and the concatenation with other MCR are rapidly catching up and novel sequences for efficient one‐pot syntheses of triazole‐based structures in a multicomponent fashion are constantly evolving. This review summarizes important contributions of CuAAC‐based MCR including MCR‐type applications in polymer science.

     

Multilayer,Multimaterial Thermal Barrier Coating Systems: Design,Synthesis, and Performance Assessment

Thermal barrier coatings (TBCs) are increasingly playing a vital role in enhancing efficiency and performance of gas turbine engines. As engine operating temperatures rise, yttria‐stabilized zirconia (YSZ), the currently principal TBC material, reaches its operational limits. Gadolinium Zirconate (GDZ)‐based pyrochlore oxides are now emerging contenders, not only due to their lower thermal conductivity, but also their ability to resist attack by silicate deposits. However, GDZ cannot be directly substituted for YSZ due to its incompatibility with the thermally grown alumina layer, therefore requiring to be a component of multilayer system. Although industry has already adopted these materials in various applications, a number of fundamental issues arise with respect to layered‐coating design, their properties and processing dependence. In this study several multilayer architectures, based on the YSZ–GDZ system, have been developed and tested for durability under furnace thermal cycling conditions. Coating designs considered optimization of microstructure and properties of individual layers based on their location within the top‐coat thickness to address competing interests of thermal conductivity, compliance, and resistance to silicates. A large variance in durability was observed in coatings made with different multilayer designs. The results and the associated failure mechanisms are rationalized through preliminary evaluation of elastic energies at the failure locations and corresponding energy release rates. The results point to new strategies in the design and manufacturing of optimal multilayer coatings.     

Numerical simulations of bioextruded polymer scaffolds for tissue engineering applications

Scaffolds provide a temporary mechanical and vascular support for tissue regeneration while shaping the in‐growth tissues. These scaffolds must be biocompatible, biodegradable, enclose appropriate porosity, pore structure and pore distribution, and have optimal structural and vascular performance, with both surface and structural compatibility. Surface compatibility means a chemical, biological and physical suitability to the host tissue. Structural compatibility corresponds to an optimal adaptation to the mechanical behaviour of the host tissue. Recent advances in the design of tissue engineering scaffolds are increasingly relying on computer‐aided design modelling and numerical simulations. The design of optimized scaffolds based on fundamental knowledge of their macro microstructure is a relevant topic of research. This research work presents a comparison between experimental compressive data and numerical simulations of bioextruded polymer scaffolds with different pore sizes for the elastic and plastic domain. Constitutive behaviour models of cellular structures are used in numerical simulations to compare numerical data with the experimental compressive data. Vascular simulation is also used in the design process of the extrusion‐based scaffolds in order to define an optimized scaffold design. © 2013 Society of Chemical Industry     

Improving the adhesion of thin stainless steel sheets for fibre metal laminate (FML) applications

Thin stainless steel sheets hold considerable promise for improving several properties of aluminium based fibre metal laminates (FMLs). To allow incorporation of such sheets in FMLs their adhesion to epoxies used in aerospace applications should be at a high level. The present work describes the effects of chemical and mechanical pretreatments to regular and molybdenum-enriched AISI 301 steel sheets. Based on an in-depth knowledge of aluminium pretreatment for FML applications, also aluminium-coated stainless-steel sheets are investigated. Gritblasting was found to yield the best properties. The effect of coating the steel surface with aluminium was found to be promising, but the bond strength between the aluminium and the steel substrate proved insufficient for thin (0.1 mm) AISI 301 steel sheet.