Enhancement of dimensional stability and mechanical properties of light MDF by adding melamine resin impregnated paper waste

This study investigated the utilization of resin impregnated decorative and overlay paper wastes obtained from the edge trimming of partially cured, dried papers as a binder in the manufacture of the light medium density fiberboard (MDF). The light MDF panels were prepared from various mixtures of the softwood fiber and hammer-milled impregnated paper waste, 95/5, 90/10, and 80/20 wt%. The results of the experiments showed that the dimensional stability and mechanical properties of the light MDF panels were improved by adding hammer-milled melamine impregnated paper waste. The resin impregnated paper waste could be evaluated as a binder for the manufacturing of the light MDF panels having better dimensional stability and mechanical properties than standard light MDF panels used in interior applications.     

Drying and curing behaviour of melamine formaldehyde resin impregnated papers

Melamine formaldehyde (MF) resins are widely used for the gluing and surface coating of wood‐based consumer products in the interior design of living environments. MF resins are especially relevant in decorative laminate applications because of their good performance‐to‐price ratio. In their industrial processing, an important intermediate state is the liquid MF prepolymer that is used for decorative paper impregnation. Here, the drying of impregnated papers is investigated with respect to premature curing. A new method to quantify water release upon drying that allows estimation of the degree of undesired precuring is described. Since curing proceeds via polycondensation, crosslinking brings about the release of water molecules. By thermogravimetric analysis (TGA), drying was studied in terms of water release due to physical drying (elimination of “dilution water”) and chemical crosslinking of the prepolymer to a three‐dimensional MF network (elimination of chemically liberated water). The results obtained by TGA/IR spectroscopic analysis of the liberated volatiles show that the emission of water from b‐stage MF can be clearly analytically separated into a physical (evaporation of dilution water) and a chemical (liberation via condensation) sequence. TGA experiments were correlated with curing experiments performed with differential scanning calorimetry (DSC) to estimate the residual crosslinking capacities of the impregnated papers. The drying conditions used during the preparation of impregnated decorative papers seemed to significantly affect their remaining reactivity only when harsh drying conditions were used. Upon heat exposure for prolonged time, precuring of the oligomer units results in a shift of the temperature maxima in TGA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39860.     

Classification of reaction-to-fire of decorative high-pressure laminates (HPL)

Decorative high-pressure laminates (HPL) are used in many applications where their reaction-to-fire is of particular interest. They form finishes of walls and ceilings in buildings, ships and vehicles. Due to the different specifications and regulations in these fields, different grades of this largely standardized material have been tested worldwide with similar results. As a consequence, German and French building regulations state decorative high-pressure laminates to be generally admissible on a minimum level without individual testing. This survey indicates their generic suitability in other fields, e.g. to have ‘low flame-spread characteristics’ according to the International Convention for the Safety of Life at Sea.     

A comparative study of vacuum‐assisted resin transfer molding (VARTM) for sandwich panels

Vacuum‐assisted resin transfer molding (VARTM) of sandwich panels can be facilitated by using high permeability layers (HPL) over the skins or adding channels in the surfaces of the core (CIC). The present paper investigates the advantages and disadvantages of both methods in terms of manufacturing cost and time through simulations and experimental observations. A cost model is developed, and the resin infusion time for each method was minimized through simulations. The design parameters are the number of high‐permeability layers and the number and size of channels. A penalty function with equal weight on cost and time is used to find the optimum values of the design parameters. Under the conditions studied, the optimal HPL method is found to be better than the optimal CIC method. While the conclusion is limited to the present study, the proposed approach can be used to optimize manufacturing processes for larger sandwich panels under different conditions.     

Flash IR pre-curing of the decorative layer in metal-flake powder coatings

Metal-flake powder coatings are a special class of metallic paint finishes composed of two superimposed layers: a pigmented decorative base coat and an overlaying transparent protective top coat. In the present investigation, a novel curing procedure for such bilayer coatings is proposed. Flash IR pre-curing of the base coat promotes the formation of a surface diffusion barrier and limits movement of the decorative pigments and metal flakes around their initial positions. Oven baking after deposition of the top coat then completes curing of the bilayer coating. The influence of the IR intensity and irradiation time on the final properties of bilayer coatings was investigated. The visual appearance, surface morphology and scratch resistance were evaluated. Experimental findings revealed that the hybrid IR/oven baking curing procedure is a viable method for obtaining bilayer powder coatings with outstanding properties in a shorter processing time and with considerable energy savings.     

Lignins for phenol replacement in novolac‐type phenolic formulations,part I: Lignophenolic resins synthesis and characterization

Several lignin (L)‐based novolac‐type phenolic prepolymers with two phenol (P) substitution degrees have been synthesized using three L from different origin (kraft pine L, soda/anthraquinone (AQ) flax L, and sulfonated kraft softwood L). These lignophenolic (LPF) resins have been characterized by means of free P and formaldehyde (F) analysis, viscosity, chemical structure (FTIR), and thermal behavior (DSC). Temperature at which curing reaction begins (DSC), hardening time at several curing temperatures (rheology) and volumetric changes (PVT) have also been determined for the curing process with 10 wt % hexamethylenetetraamine (HMTA). All the results have been compared to those obtained for a commercial novolac. Depending on the L type employed a homogeneous material with lower curing onset temperature and gelation time than reference PF can be obtained even at high P substitution level (45 wt %). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Electroplated bright aluminium coatings for anticorrosion and decorative purposes

This paper is dedicated to the study of electrodeposited aluminium layers as anticorrosion protective coatings on metallic substrates. The aim of this approach is to propose a non-toxic alternative to the traditional nickel–chromium coating, for anticorrosive and decorative purposes. Aluminium was electrodeposited on carbon steel substrates from chloroaluminate based ionic liquids with and without the addition of 1,10-phenantroline. In the first case, the Al deposits are dense but dull, while in the latter homogeneous and bright coatings suitable for decorative purposes were achieved.     

紫砂壶中纹饰的设计与创新

从追溯紫砂的发展历史入手,探讨紫砂艺术发展中纹饰的重要地位,并且区分了纹饰的确切定义及不同种类——定型纹饰与象形纹饰。此外,本文厘清了纹饰与线条的关系,并以笔者的作品为例对纹饰在紫砂中的应用做了详尽而独到的分析,为学界进一步讨论纹饰相关主题打下了良好的基础。     

Lignins for phenol replacement in novolac‐type phenolic formulations. II. Flexural and compressive mechanical properties

Several hexamethylenetetraamine‐cured novolac‐type lignophenolic resins have been subjected to mechanical analysis to check the influence of the addition of different types of lignins (kraft pine lignin, soda/anthraquinone flax lignin, and sulfonated kraft lignin from mixed softwoods) and the influence of different phenol substitution levels. Both flexural and compression tests have been performed to evaluate the influence of the curing temperature and pressure. The results have been compared with those from a commercial novolac system. Flexural tests show that lignin incorporation leads to systems with increased rigidity, whereas up to 82% of the maximum strength can be retained with respect to a commercial phenolic (phenol–formaldehyde) at a 45 wt % substitution degree. Compression analyses show that modified prepolymers are not significantly affected by the presence of lignin at a medium curing pressure (150 bar), but their deformability results considerably increase at high curing pressures (400 or 600 bar). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Self-stratifying coatings: a review

A self-stratifying coating is an economical coating containing multiresinous components with different functional groups, which spontaneously stratify after application to the substrate. These coating systems could be composed of two or more different layers to protect substrates against corrosion, by first layer, and simultaneously to create a desirable appearance, by second layer, with decorative properties. Conventional multilayer coating systems encounter some problems such as poor interfacial adhesion, application, and labor costs and also lengthy processing time. The concentration gradient of two layers would eliminate the inter-coating boundary which can be the point of failure in conventional coatings. In this paper, the surface tension and solubility theory regarding these coatings are discussed. In addition, the effects of different factors on the pigment location into the coating systems are studied. The main factors, including curing mechanisms, substrate effects, thickness, viscosity, kinetics of reaction, evaporation rate of solvents, dispersing agents, and surface properties of pigments have been reviewed. The models for prediction of self-stratifying coatings such as UNIFAC and computer simulation have also been addressed and taken into consideration. The prospect of these coatings and their application in different industries is presented.     

Preparation and Characterization of Demethylated Lignin-Polyethylenimine Adhesives

Petrochemical-based adhesives such as urea-formaldehyde and phenol-formaldehyde resins are predominant wood adhesives. In this study, a new wood adhesive from lignin was developed and characterized. The new adhesive consisted of demethylated kraft lignin (DKL), a byproduct in the production of dimethyl sulfoxide from kraft lignin, and a polyethylenimine (PEI). Lap-shear specimens bonded with this new DKL-PEI adhesive system had very high shear strength and were very water-resistant. The effects of the preparation time, the curing conditions, the total solids content of the adhesive, the DKL/PEI weight ratio and the molecular weight of PEI on the shear strength and water-resistance of the resulting lap-shear specimens were studied in detail. Investigation on the curing chemistry of this new adhesive revealed that phenolic hydroxyl groups were oxidized to form quinones that further reacted with PEI. It was proposed that the curing mechanisms of this DKL-PEI adhesive were similar to the quinone-tanning processes in nature.     

Use of Superheated Steam Drying to Increase Strength and Bulk of Papers Produced from Diverse Commercial Furnishes

Studies from this laboratory have documented significant changes in properties when paper is dried in superheated steam rather than, as in all current processes, in air. Extending these investigations to additional important pulp types, to recycled pulps and to filled papers, using commercial furnishes from mills, has identified further grades of paper for which drying in superheated steam enhances key properties. For bleached chemithermomechanical pulps and blends with kraft pulp as used for tissue and toweling, strong paper resulted, with 10% higher bulk. Linerboard from 100% recycled old corrugated containers (OCC) is obtained with various strength properties increased by up to 21% with no densification, actually a 4% increase in bulk. Linerboard from high-yield (55-67%) virgin kraft pulps show 23 to 37% increase in strength and toughness. Filled papers containing 0-10% clay can be produced with the same brightness but about 23% higher tensile index when dried in superheated steam.     

Preparation and Characterization of Demethylated Lignin-Polyethylenimine Adhesives

Petrochemical-based adhesives such as urea-formaldehyde and phenol-formaldehyde resins are predominant wood adhesives. In this study, a new wood adhesive from lignin was developed and characterized. The new adhesive consisted of demethylated kraft lignin (DKL), a byproduct in the production of dimethyl sulfoxide from kraft lignin, and a polyethylenimine (PEI). Lap-shear specimens bonded with this new DKL-PEI adhesive system had very high shear strength and were very water-resistant. The effects of the preparation time, the curing conditions, the total solids content of the adhesive, the DKL/PEI weight ratio and the molecular weight of PEI on the shear strength and water-resistance of the resulting lap-shear specimens were studied in detail. Investigation on the curing chemistry of this new adhesive revealed that phenolic hydroxyl groups were oxidized to form quinones that further reacted with PEI. It was proposed that the curing mechanisms of this DKL-PEI adhesive were similar to the quinone-tanning processes in nature.     

Methodology of the assessment of the interlayer bond in concrete composites using NDT methods

The paper presents multivariate methodology of assessing the interlayer bond in concrete composites using non-destructive testing (NDT) methods. This methodology eliminates the shortcomings of the pull-off method, which is used for this purpose in practice. Methodology of searching for the delamination of layers together with methodology of assessing the value of the pull-off adhesion between layers in existing composites with a constant thickness of the overlay has been shown. Also the methodology of evaluating the pull-off adhesion value between the overlay and the existing concrete substrate in newly made or existing composites which were repaired by applying a repair overlay has been presented. It has been indicated which NDT methods and also the aid of which specific parameters can be helpful to achieve this. Furthermore, an example of practical use of one of the methodologies, which confirms its usefulness in the evaluation of the pull-off adhesion, was also provided. It should be expected that the use of the proposed methodology could contribute to a more precise assessment of the interlayer bond in concrete composites, which could be useful for the acceptance of construction works.     

Enhancement of Properties of Diverse Grades of Paper by Superheated Steam Drying

Abstract:

Studies from this laboratory have documented significant changes in properties when paper is dried in superheated steam rather than, as in all current processes, in air. Extending these investigations to additional important pulp types, recycled pulps, and filled papers, and using commercial furnishes from mills, has identified further grades of paper for which drying in superheated steam enhances key properties. For bleached chemithermomechanical pulps and blends with kraft pulp, as used for tissue and toweling, strong paper resulted with 10% higher bulk. Linerboard from 100% recycled old corrugated containers (OCC) is obtained with various strength properties increased by up to 21% with no densification, actually a 4% increase in bulk. Linerboard from high-yield (55–67%) virgin kraft pulps shows a 23 to 37% increase in strength and toughness. Filled papers containing 0–10% clay can be produced with the same brightness but 23% higher tensile index when dried in superheated steam.     

Use of Superheated Steam Drying to Increase Strength and Bulk of Papers Produced from Diverse Commercial Furnishes

ABSTRACT

Studies from this laboratory have documented significant changes in properties when paper is dried in superheated steam rather than, as in all current processes, in air. Extending these investigations to additional important pulp types, to recycled pulps and to filled papers, using commercial furnishes from mills, has identified further grades of paper for which drying in superheated steam enhances key properties. For bleached chemithermomechanical pulps and blends with kraft pulp as used for tissue and toweling, strong paper resulted, with 10% higher bulk. Linerboard from 100% recycled old corrugated containers (OCC) is obtained with various strength properties increased by up to 21% with no densification, actually a 4% increase in bulk. Linerboard from high-yield (55–67%) virgin kraft pulps show 23 to 37% increase in strength and toughness. Filled papers containing 0–10% clay can be produced with the same brightness but about 23% higher tensile index when dried in superheated steam.     

Lipoxygenase and hydroperoxide lyase activities in two olive varieties from Northern Italy

Lipoxygenase (LOX) and hydroperoxide lyase (HPL) activities were characterised in olive pulp microsomes from two cultivars (Ghiacciolo and Nostrana di Brisighella) from Northern Italy. LOX activity exhibited a maximum at pH 5.5 in both cultivars, and the highest value was found in cv Ghiacciolo. This was correlated with the higher total antioxidant capacity detected in cv Nostrana, rather than by a different LOX expression, as demonstrated by immunoblotting assay. Furthermore, isomer characterisation showed the predominance of 13‐hydroperoxides of linoleic acid (HPOD) in both cultivars, suggesting the occurrence of a 13‐LOX. HPL activity exhibited an optimum at pH 7.5 in the two cultivars, but was higher in cv Nostrana, as confirmed by the increased amount of hexanal production after 13‐HPOD addition. In addition, the constitutive aldehyde profile in cv Nostrana fruits were shown to be enriched in aldehydes too when compared to cv Ghiacciolo. These results suggest that the different features in the two olive cultivars are mainly due to genetic rather than environmental factors. Practical applications: In this paper we studied the lipoxygenase (LOX) and hydroperoxide lyase (HPL) activities, and the formation of their products (hydroperoxides and aldehydes) in microsomes extracted from olive pulp of two Italian cultivars. The study of LOX and HPL, belonging to the so‐called ‘oxylipin pathway’, has important implications on the aroma development in both fruit and oil. Thus, a better knowledge of the properties of these enzymes can be useful to improve the organoleptic features of the oil. In fact, ‘LOX pathway’ may play a positive role in the formation of pleasant flavours during the technological processes. The preliminary study of the activity of the LOX/HPL enzymes could represent an important tool to facilitate the varietal choice in order to improve oil quality.     

Mechanism of crosslinking of papers with polyfunctional carboxylic acids

Brief thermal curing of papers treated with an aqueous solution of polyfunctional carboxylic acids and NaH₂PO₄ imparts substantial wet strength to the papers. The effectiveness of such carboxylic acids increases with their functionality in the order 1,2,3,4-butanetetracarboxylic acid (BTCA) > tricarballylic acid (TCA) ? succinic acid. The two main stages of the curing reaction of papers, i.e., pendant attachment of the polyfunctional carboxylic acids via esterification with cellulosic hydroxyl groups, and its further reaction with another cellulose hydroxyl group producing crosslinks of the cellulose fibers were analyzed separately using a combination of acid-base and conductometric titrations. The extent of reaction of the polyfunctional carboxylic acids with paper was followed by pH titration, which shows the total decrease in acid functions as the curing progresses and is directly related to the total consumption of carboxylic acids groups by ester attachment and ester crosslinking steps. The conductometric titration, on the other hand, measures the increase in carboxylic acids bound to cellulose units of the paper as a direct result of previous esterification steps. Our studies reveal that the reaction of BTCA with papers is essentially quantitative after 15 min of curing. The amount of once-reacted BTCA increases in the initial phases of the curing reaction and then decreases as more and more carboxylic acid units are converted into crosslinking sites, while the amount of crosslinked BTCA increases throughout the curing reaction. The reaction profile of papers with TCA differs from that of BTCA in that the curing reaction is initially dominated by the formation of ester appendages; crosslinking becomes the main reaction only after extended curing times. We attribute this difference to the ability of BTCA to form an highly reactive difunctional crosslinking reagent at the outset of the curing reaction, while TCA is initially monofunctional in its reaction with cellulosic hydroxyl groups (formation of a monoanhydride). The relationship between the wet tensile strength of the treated papers and their degree of crosslinking is also discussed. © 1995 John Wiley & Sons, Inc.     

Preparation of Cellulose Insulating Paper with Low Dielectric Constant by BTCA Esterification Crosslinking

This study aims to decrease the dielectric constant of kraft paper by 1,2,3,4‐butanetetracarboxylic acid (BTCA) esterification crosslinking. Kraft paper samples are treated with various concentrations of BTCA to prepare modified paper with different reaction degrees. Morphology and surface chemical composition are characterized. The dielectric constant and loss of the plain and modified paper are also investigated. Results show that esterification occurs successfully between cellulose molecular chain and BTCA. The intrinsic dielectric constant and loss of 6 g L^?1 BTCA‐treated paper decrease by 23.5% and 36.3%, respectively, at 50 Hz. The esterification can reduce the hydroxyl amounts on cellulose. The formed crosslinking network between the cellulose chains restricts the cellulose orientation polarization, thereby reducing cellulose polarizability. The electrical strength, mechanical properties, and thermal behavior of the samples are explored to evaluate comprehensively the modifying effect. BTCA esterification crosslinking proves to be a promising method for decreasing the dielectric constant of kraft paper.     

新型水性非异氰酸酯聚氨酯涂料的开发应用

合成了一系列水性环碳酸酯树脂及其配套使用的固化剂,制备成具有一定装饰效果和优异机械性能的新型水性非异氰酸酯聚氨酯涂料,考察了其在不同基材上的基本性能及在木器涂料中的应用。结果表明,其不仅具有传统聚氨酯耐磨、抗拉、弹性好等优点,又具有更好的耐化学品性能及抗渗透性。