Hydrolytic Removal of Cured Urea–Formaldehyde Resins in Medium-Density Fiberboard for Recycling

This study focused on the removal of cured urea–formaldehyde (UF) resins by hydrolysis of medium-density fiberboard (MDF) at different temperatures and times for MDF recycling. Five aqueous solutions, i.e., two acids, two alkalis, and water, were used for MDF hydrolysis to obtain extract solutions and solid residues for the analysis of mass balance, nitrogen content, and resin removal. As expected, acidic solutions removed the greatest amount of cured resins, followed by water and alkaline. Moreover, temperature had a greater impact on hydrolysis than time. Fourier transform infrared spectra of MDF fibers before and after hydrolysis clearly showed the change in intensity of the amide group in UF resins. Reduction of the amide group was greater with increase in hydrolysis temperature than in time. Statistical analysis results suggested that the hydrolysis of MDF at 80°C for 2 h using oxalic acid solution was optimum condition for the removal of cured UF resins. However, water could be used as hydrolysis agent for the practice of MDF hydrolysis in the future.     

Swelling Behaviour of Cured Urea–Formaldehyde Resin Adhesives with Different Formaldehyde to Urea Mole Ratios

As a part of understanding of the network structure of urea–formaldehyde (UF) resin adhesives, this study examined the swelling behaviour of cured UF resin adhesives with four different formaldehyde–urea (F/U) mole ratios, using Flory–Rehner thermodynamic theory and field emission-scanning electron microscopy (FE-SEM) to relate the swelling behaviour to consequently induce micromorphological changes. Cured UF resin films before and after acetone extraction were exposed to swelling in dimethyl sulphoxide at three different temperatures. For the first time, this study reported the experimentally determined swelling parameters, such as sol fraction (ω_sol), polymer volume fraction (φ_p), polymer–solvent interaction parameter (χ), and the number average molecular weight between cross-links (M_c), for cured UF resin adhesives. Both ω_sol and M_c decreased as the F/U mole ratio increased. But these values increased with an increase in the swelling temperature. The extraction resulted in negative ω_sol values, suggesting the removal of a scattered distribution of ω_sol in the cured UF resins. The micromorphology helped to explain the differences in the molecular integrity of the resins, indicating a close relationship between the swelling behaviour and the morphological changes after the swelling.     

Synthesis,Characterization and Curing of o-Cresol – Furfural Resins

Polycondensation of o-cresol (OC) with furfural (F) was carried out under various reaction conditions. The resultant resin samples designated as OCFs were characterized by elemental analysis, spectral studies, viscometric measurement of solution in 1,4-dioxane and by the estimation of the number – average molecular weight. Thermogravimetric analysis (TGA) of selected resin samples has been carried out. The curing kinetic reaction of selected OCF resin samples was studied by differential scanning calorimetry (DSC). Hexamethylenetetramine (Hexamine) has been used as curing reagent.     

Rheology Study of Sugar Cane Bagasse Lignin-Added Phenol–Formaldehyde Adhesives

The rheological properties of sugar cane bagasse lignin–phenol formaldehyde (PF) (30% lignin – PF) resins were studied using oscillation tests. The bagasse lignin was introduced in the classic adhesive formulation in order to supply a part of PF. Rheological qualities of optimal lignin–PF (30% lignin – PF) resins and commercial PF resin were assessed by using a rotary rheometer (ARES). Dynamic rheological measurements, performed at low strain in the linear range, are useful to characterize the network properties of resins.

The results obtained showed that the time sweep indicates excellent structural stability of optimal lignin–PF (30% lignin–PF) resins and commercial PF resin. The elastic modulus is greater than the viscous one showing a remarkable elastic character of the resins, and the performed frequency sweeps show a typical spectrum of a “weak gels” structure. The time dependence at 125°C shows that the optimum cure time is 7.5 min.     

Bond Strength–Disbonding Behavior and Dimensional Stability of Walnut and Poplar Impregnated with Some Chemicals and Bonded with PVAc,VTKA and Urea Formaldehyde

The aim of this study, is to describe the effects of adhesives (PVAc-Desmodur VTKA and Urea formaldehyde) on wooden materials (walnut and poplar) cut tangentially and radially impregnated with Protim Solignum, CCA and Celcure AC 500 and exposed to: humid–water–heat resistance; heating; and cooling tests. All these tests show a decreased in bonding strength. The conclusion is that poplar wood cut tangentially and impregnated with CCA, bonded with D-VTKA adhesive can be used as a material in damp conditions where good bond strength is required.     

Hydroprocessing of Aromatics Using Sulfide Catalysts Supported on Ordered Mesoporous Phenol–Formaldehyde Polymers

Ni–W sulfide catalysts for the hydroprocessing of aromatic hydrocarbons were synthesized by the in situ decomposition of tetrabutylammonium nickel thiotungstate complex supported on ordered mesoporous phenol–formaldehyde polymer. Catalysts obtained with and without additional sulfidation with dimethyl disulfide were characterized by X-ray photoelectron spectroscopy and transmission electron microscopy. The catalytic activity has been studied using naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, and anthracene as examples. It is shown that the system used in this study proved to be active in hydrogenation and hydrocracking of polyaromatic hydrocarbons.     

Cure rate of Phenol–Formaldehyde (PF) resol resins catalyzed with MgO

One of the main drawbacks that has prevented a wider use of phenol–formaldehyde (PF) resins in the manufacture of impregnated paper and wood composite panels is their relatively slow cure rate. In this study, the curing characteristic of PF resol resins catalyzed with MgO was studied with various formaldehyde (F)/MgO/phenol (P) ratios at various pH values. The results indicated that the pH value, nature of pH regulator and synthesis parameters, including the F/P ratio and MgO content, all influence the rate of cure. The pH value played an important role in affecting both the cure rate and cure time. The cure rate was fast when pH was below 7.5. The cure time decreased as the pH value decreased at all F/MgO/P ratios. The MgO/P ratio had a definite influence on the cure rate, the cure time decreased with the increase of MgO/P molar ratio, and the F/P ratio had no significant influence on the cure rate. Differential scanning calorimetry (DSC) results showed that MgO catalyzed PF resin can cure at a low temperature.     

Investigation of Structure and Oxidation Behavior of Pitch and Resin Resultant Carbon

The structure and oxidation behaviors of pitch carbon,resin carbon and their mixture re-sultant carbon have been investigated.The results indicate that the pitch carbon has relative higher true specific gravity,well developed crystalline and better oxidation resistance than resin carbon,With 20%-35% resin added to pitch,the structure of the resultant carbon can be modified and oxidation resistance will be improved significantly.     

Crystallization Behavior,Mechanical Properties,and Chemical Resistance of Leucite–Fluoroapatite Glass-Ceramic Glazes

The roles of Li₂O and B₂O₃ and heat-treatment condition on crystallization behavior and flowability of leucite–fluoroapatite-based glass-ceramic glazes were investigated. The thermal expansion coefficient, mechanical, and chemical properties of the optimum specimen were determined. Glaze firing was performed in the 650–1100°C interval, in one and two step processes. Based on the results, B₂O₃ was more effective than Li₂O in point of flowability view. Also, the microstructures varied with the adopted firing process, so that the two-step heat-treated sample showed superior mechanical properties than the one-step heat-treated specimens.     

Dry Fractionation of Cupuassu (Theobroma grandiflorum) Fat: Physical–Chemical Properties and Polymorphic Behavior

Physical chemical properties of cupuassu fat were modified by dry fractionation. Stearin and olein fractions were obtained at 29, 26, and 24 °C. Polymorphic behavior of unfractionated cupuassu fat (UCF) and its fractions were studied in situ by small-angle (SAXS) and wide-angle (WAXS) X-ray scattering using synchrotron light. Polymorphic transitions were followed in real time tempering samples with a thermal cycle. For UCF, the main polymorphic form crystallized under selected conditions was the β’₂. α and β’₁-forms appeared in trace amounts. β₂-form was obtained after storage at 25 °C for 3 months. Stearins obtained at 26 (S-26) and 24 °C (S-24) showed a similar polymorphic behavior. However, S-26 with improved physical properties might be more suitable for chocolate production or as a trans-fat alternative than UCF. Stearin fraction obtained at 29 °C (S-29) had a complex polymorphic behavior. The α-form was the first polymorphic form detected followed by β’₂-form. There was a polymorphic transition from α to β’₁-form but no transition between β’-forms. They were independent to each other showing fractionation in two different solid solutions. Increased contents of the triacylglycerols (TAG) SOA and SOB together with lower contents of SOO compared to UCF led to co-crystallization because there was no complete compatibility among all TAG present in S-29. β₁-form crystallized after storage forming crystals with a double-layer arrangement and a characteristic morphology. This form could be useful for accelerating crystallization process in melted liquid systems.     

Structure, Properties and Behavior of Kyanite： Use in Refractory Monolithics

1 Introduction Kyanite is an important naturally occurring in-dustrial mineral and is used in the manufacture of avariety of industrial ceramic products; notable exam-ples include refractories and porcelains. It is a high-pressure polymorph of the aluminosilicates of the ne-sosilicate group, which includes kyanite, sillimanite,and andalusite. These three aluminous or alumina-rich minerals are chemically identical with the compo-sition, Al_2SiO_5, but have different crystal structuresand physical properties. It is, however, their alumina     

Properties and Performances of High Purity Corundum Bricks for Chemical and Petrochemical Industries in China

The properties and performances of high purity corundum bricks for the refractory linings of the gasifiers in the ammonia and ethene synthesis and carbon black reaction furnaces in China are described.The high purity corundum bricks are characterized by high refractoriness,hot strength,dimensional stability and chemical inertness at elevated temperature,Their performances in the gasifiers and carbon black furnaces are very satisfied ,The failure mechansims of the refractory lining are discussed on the basis of the petrographic analysis.     

Chemical Bonding between Phenolic Resins and Polyhedral Oligomeric Silsesquioxanes (POSS) in Inorganic–Organic Hybrid Nanocomposites

Three classes of inorganic–organic hybrid phenolic resin/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were synthesized. Multifunctional dichloromethylsilylethylheptaisobutyl-POSS (POSS-1), trisilanolheptaphenyl-POSS (POSS-2), and poly(phenylsilsesquioxane) uncured POSS (POSS-3) were employed. Nonfunctional POSS-4 (octaisobuty1-POSS) was blended into the uncured phenolic resin and cured under the same conditions used for the other three nanocomposite classes. Weight ratios of 99/1, 97/3, 95/5 and 90/10 were prepared for the POSS-1, 2 and 4 series and 99/1, 97/3 and 95/5 ratios for the POSS-3 nanocomposites. POSS-1 incorporation into this phenolic resin network increases T _g and broadens the tan peak (DMTA) range. T _g and E′ values at T>T _g both increase with higher POSS-1 content. In contrast, incorporating 5 wt% of POSS-2 into the phenolic resin network lowers T _g to 193 from 213°C for the neat phenolic resin. All values of E′ for POSS-2 composites were higher, than those of the phenolic control in both glassy and rubbery regions. The T _g values of the 1 and 10% POSS-2 systems were higher. Incorporating 10 wt% of POSS-1 or POSS-2 improved the heat distorsion temperature and moduli (E′=123 and 201 GPa at 265°C, respectively, versus 56 GPa for the pure phenolic resin). Increases in E′ for T>T _g and T<T _g were also observed for all POSS-3 nanocomposites. However, the E′ at T>T _g and the T _g values of the POSS-4 composites were lower than those of the control resin. Octaisobutyl POSS-4 cannot form chemical bonds to the resin and could be extracted from its composites with THF. POSS derivatives were not present in residues extracted by THF from the phenolic resins containing POSS-1, 2 or 3, because each of these derivatives were chemically bound within the phenolic resin. Subsequent heating cycles produce much larger increases in T _g and E′ values in the rubbery region for the POSS-1, 2 and 3 composites than for the neat phenolic resin or for the POSS-4 systems. An erratum to this article can be found at     

Curing of a tetrafluoroethylene–propylene elastomer with high-vinyl polybutadiene rubber and peroxide

A cocuring agent is necessary for tetrafluoroethylene–propylene elastomer (FEPM), which cannot be cured by peroxide alone. We observed that high-vinyl polybutadiene rubber (HVBR) could be used as a cocuring agent for FEPM. The structure and properties of FEPM–HVBR blend vulcanizates were investigated by ¹³C-NMR, differential scanning calorimetry, swelling tests, tensile tests, dynamic mechanical analysis, and thermogravimetric analysis. This research showed that HVBR significantly improved FEPM by conferring a high crosslink degree to the FEPM–HVBR blends. When the HVBR concentration was 25% without any filler reinforcement, the tensile strength of the FEPM–HVBR blend vulcanizate reached 11.6 MPa, and the crosslinking density reached 171 μmol/cm³. In addition, HVBR improved the thermal stability of FEPM and changed the glass-transition temperature (T _g) of the blend; as the HVBR content increased, the T _g of the blend also increased. ¹³C-NMR analysis confirmed that crosslinks existed between the HVBR and FEPM macromolecules. When the blends contained trace amounts of HVBR, free-radical reaction was more preferred between FEPM and HVBR, whereas when HVBR was 15% or more, crosslinking between HVBR was predominant. These findings expand the choices for the curing of FEPM. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47836.     

Structure and thermal stability of zinc–nickel electrodeposits

ZnNi alloys were electrodeposited from a chloride bath on steel substrates. The effect of nickel bath concentration on chemical composition, structure and microstructure of the deposits is demonstrated. From 0 to 13 nickel, the phases obtained do not correspond to that reported on the thermodynamic phase diagram. It is shown that the substitution of zinc by nickel is responsible for the formation of distorted _d and _d phases corresponding to the supersaturated hexagonal phase of zinc and to the unsaturated cubic phase of Zn–Ni alloy, respectively. Differential scanning calorimetry indicates that the thermal instability of the alloys containing up to 13 wt of nickel, results from the crystallization of the phase from the _d and _d phases at around 200 °C and 250 °C, respectively.     

Structure of NaF–TeO2 glasses and glass-ceramics

The structure of NaF–TeO₂ glasses and glass-ceramics has been studied by XRD, TEM, SEM, Raman and FTIR techniques. The results suggest that, for NaF ≤10 mol%, the entire NaF content enters the structure to convert TeO₄ units into TeO_3/2F and Na⁺[TeO₃₊₁]^– units. It has also been shown that NaF partially forms amorphous and/or crystalline phases for higher NaF content, where the relative concentration of each phase depends on the NaF content. SEM images show agglomerates of different sizes, which are discrete and spread within the structure. XRD revealed formation of crystalline Te₂O₃F₂ for NaF ≤50 mol%, and a dominant phase of crystalline NaF for NaF >50 mol%. Raman and FTIR spectra have been analyzed to calculate the concentrations of the various structural units in glasses and glass-ceramics.     

Mechanical and Bioactive Behavior of Hydroxyapatite–Wollastonite Sintered Composites

The effect of wollastonite amount on the mechanical and bioactive properties of several hydroxyapatite-wollastonite sintered composites was evaluated. The wollastonite reinforcement effect was assessed by measuring hardness and reduced elastic modulus on the materials, using nanoindentation methods. Bioactive properties were analyzed by soaking these materials in a simulated body fluid (SBF) for various periods of time. The analyses reveal an enhancement of hardness and reduced elastic modulus with the addition of wollastonite. In addition, the interaction of these materials with an SBF produces a bone-like apatite layer on their surfaces, which is thicker when the wollastonite is in a higher proportion.     

Effect of Titanium Content and Mechanical Activation on Ni–Al–Ti Combustion

Combustion, Explosion, and Shock Waves - This paper describes the effect of preliminary mechanical activation&nbsp;(MA) and Ti content on maximum temperature, maximum burning rate, composite...