Particleboards from Acetylated Wood Flakes

Summary. Particleboards from acetylated wood flakes with various resins were pressed and compared with untreated control boards with respect to their weathering resistance and mechanical strength. The industrially used melamine, urea, and phenol resins showed a poor adhesion behavior to the acetylated flakes resulting in a high decrease of the mechanical strength of the particleboards. A novel type of apolar resin based on methylmelamines was developed and characterized. Using this resin particleboards with good mechanical strength and weathering stability could be produced.     

Evaluation of the performance of microcrystalline cellulose in retarding degradation of two epoxy resin systems

Accelerated weathering studies are necessary to determine future risks arising from the loss of durability of materials under environmental conditions (e.g. ultraviolet irradiation from the sun, moisture from rainfall, temperature cycling). The influence of different accelerated weathering conditions such as UV light and moisture on the properties of two epoxy resin systems incorporating microcrystalline cellulose (MCC) was evaluated. This study aimed to assess changes in chemical properties (FTIR), mechanical properties (tensile tests), thermal properties (TGA and DSC) and morphology (SEM) before and after accelerated weathering. The samples exposed to different accelerated weathering times (1, 2, 3, 4, and 6?months) were based on the diglycidyl ether of bisphenol A, DGEBA, or hydrogenated diglycidyl ether of bisphenol A, HDGEBA, with amine crosslinker (2,2,4-trimethyl-1,6-hexanediamine, TMDA) and 2% MCC. Incorporation of MCC improved thermal stability, reduced surface oxidation, and gave better retention of mechanical properties after accelerated weathering. Both epoxy resins and epoxy composites exhibited a reduction in the tensile strength upon accelerated weathering with the composites showing less reduction in the tensile strength after 6 months. The glass transition temperatures (T_g) before and after accelerated weathering were also measured. DGEBA-TMDA/2%MCC and HDGEBA-TMDA/2% MCC composites reduced the decrease in the T_g after accelerated weathering, compared to that of DGEBA-TMDA and HDGEBA-TMDA samples. Degradation primarily decreased the mechanical properties of the composites, with some damaged specimens showing on the surfaces of DGEBA-TMDA/2% epoxy composites and HGEBA-TMDA/2%MCC composites. Fewer morphological changes with limited voids were seen on the DGEBA epoxy interface for HDGEBA compared to DGEBA composite samples. Incorporation of 2%MCC in DGEBA-TMDA and HDGEBA-TMDA increased resistance to thermal degradation after accelerated weathering.     

TG-DTA study of melamine-urea-formaldehyde resins

The thermal behaviour of MUF resins from different suppliers with different content of melamine was studied, along with the ¹³C NMR spectroscopic analysis of resin structure and the testing of particleboards in current production at Estonian PB factory Pärnu Plaaditehas AS. The chemical structure of resins from DMSO-d₆ solutions was analysed by ¹³C NMR spectroscopy on a Bruker AMX500 NMR spectrometer. The melamine level in different MUF resins is compared by the ratios of carbonyl carbon of urea and triazine carbon of melamine in ¹³C NMR spectra. Curing behaviour of MUF resins was studied by stimultaneous TG-DTA techniques on the Labsys? instrument Setaram. The shape of DTA curves characterisises the resin synthesis procedure by the extent of polymerisation of UF and MF components and is in accordance with structural data.     

Epoxy-modified, unsaturated polyester hybrid networks

Hybrid polymer networks (HPNs) based on unsaturated polyester resin (UPR) and epoxy resins were synthesized by reactive blending. The epoxy resins used were epoxidised phenolic novolac (EPN), epoxidised cresol novolac (ECN) and diglycidyl ether of bisphenol A (DGEBA). Epoxy novolacs were prepared by glycidylation of the novolacs using epichlorohydrin. The physical, mechanical, and thermal properties of the cured blends were compared with those of the control resin. Epoxy resins show good miscibility and compatibility with the UPR resin on blending and the co-cured resin showed substantial improvement in the toughness and impact resistance. Considerable enhancement of tensile strength and toughness are noticed at very low loading of EPN. Thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) were employed to study the thermal properties of the toughened resin. The EPN/UPR blends showed substantial improvement in thermal stability as evident from TGA and damping data. The fracture behaviour was corroborated by scanning electron microscopy (SEM). The performance of EPN is found to be superior to other epoxy resins.     

Lignocellulose - polymer composites

Water hyacinth and its mechanical pulps were used as lignocellulose to produce composites together with polystyrene or urea-formaldehyde resins. The bending strength of the composites increased with increasing concentration of the resin. The temperatures of the treatment of water hyacinth to obtain the pulps affect the strength and densities of the composites. This may be attributed to the behavior of lignin at temperatures higher than 135°C. The composites produced using urea-formaldehyde resins showed slight increase in bending strengths compared with those produced using polystyrene, which may be attributed to the ability of formaldehyde to make crosslinks with the free OH groups of cellulose and hemicellulose. Contrary to water hyacinth, the use of ground palm leaves together with 10% urea-formaldehyde resin produced composite with high density and low bending strength, while the ground water hyacinth failed. The pulp from palm leaves when processed into composites using 10% urea-formaldehyde resin show bending and densities affected by its preparation and by the amount of the composite mixture to be pressed. Hence the type of the substrate defined the type of the polymers or resin used to obtain composites with proper mechanical properties. The effect of the pressure used to produce composites from ground palm leaves or their pulp together with polystyrene was investigated. Linear relationships between the bending strength and pressure were obtained, the bending strength and densities increasing with increasing pressure. Thus, the increased pressures enhance mechanical properties of the composites.     

The Curing Efficiency and Mechanical Properties of Light-Activated Acrylic Resin

The aim of this investigation was to determine degree of conversion, and flexural and compressive strength of photocurable acrylic resin. The acrylic resins based on bis-phenol A glycidyl dimethacrylate (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) were formulated and then irradiated with red light to form a solid crosslinked polymer. Various post curing conditions were studied to investigate their effects on curing efficiency. Degree of conversion was analyzed by means of Fourier Transform Infrared Spectroscopy (FTIR) to monitor the quantity of remaining acrylic double bond in the cured resin. Three-point bending and compressive strength were tested using Universal Testing Machine (UTM) to evaluate the mechanical performance. Our investigation demonstrated that the formulated acrylic resins were possibly polymerized under irradiation with red light and degree of conversion and mechanical properties were closely correlated.     

Highly efficient multielement flame retardant for multifunctional epoxy resin with satisfactory thermal,flame‐retardant,and mechanical properties

Multifunctional epoxy resins with excellent, thermal, flame‐retardant, and mechanical properties are extremely important for various applications. To solve this challenging problem, a novel highly efficient multielement flame retardant (PMSBA) is synthesized and the flame‐retardant and mechanical properties of modified epoxy resins are greatly enhanced without significantly altering their and thermal properties by applying the as‐synthesized PMSBA. The limiting oxygen index value reaches up to 29.6% and could pass the V‐0 rating in the UL‐94 test with even low P content (0.13%). Furthermore, cone calorimetry results demonstrate that 30.3% reduction in the peak heat release rate for the sample with 10.0 wt% PMSBA is achieved. X‐ray photoelectron spectroscopy and scanning electron microscopy indicate that Si‐C, Si‐N, and phosphoric acid derivative can be transformed into a multihole and intumescent char layer as an effective barrier, preserving the epoxy resin structure from fire. More importantly, mechanical properties such as impact strength, tensile strength, and flexural strength are also increased by 63.86%, 33.54%, and 15.65%, respectively, which show the incorporation of PMSBA do not deteriorate the mechanical properties of modified epoxy resins. All the results show that PMSBA is a promising strategy for epoxy resin with satisfactory, thermal, flame‐retardant, and mechanical properties.     

Curing of urea-formaldehyde resins on awood substrate

TG-DTA analysis method was used to study the curing behaviour of urea-formaldehyde (UF) adhesive resins in the presence of a wood substrate. The cure process was followed using a Setaram labsys^TM instrument in flowing nitrogen atmosphere by varying the ratio of resin and wood. Resin cure was catalysed with 2% of NH₄Cl. Curing tests were performed in the open standard platinum crucibles and in the sealed glass capsules. To characterise the reactivity of curing system, the peak temperatures in DTA curve and the mass loss values in TG curve were taken as the apparent indices. The main attention was paid to phenomena which actually take place in curing of UF resins during manufacturing of particleboards. Reactivity of the curing system depends mostly on methylol content of resin and can be adequetly evaluated by the maximum temperature of exothermic peak. The wood substrate has a substantial influence on the resin and water diffusion in system causing the changes in water/resin separation and water evaporation conditions. The water movement in curing adhesive joint was a confusing parameter in determining the peak positions. The rate of mass loss on a wood substrate is higher as compared to curing UF resin alone.     

Novel propargyl‐substituted azo‐coupled phenolic resins

Novel propargyl that contains phenolic resins via azo‐coupling reaction was synthesized. Peculiarities of curing process were investigated by differential scanning calorimetry analysis. Polymerization of resins with azo groups was estimated to be affected by radicals obtained at resin decomposition causing 10°C peak shift to lower temperatures in comparison with resin containing only propargyl group. At the same time, polymerization of triple propargyl bond was shown to not proceed at radical initiation until Cleisen rearrangement and chromene formation. Thermogravimetric analysis revealed increase of thermal stability by 170–190°C and char yield by up to 20% for modified resins in comparison with original novolac resin. Heat deflection temperature estimated by dynamic mechanical analysis was also shown to be increased by at least 110°C for modified resins in comparison with novolac resin. All the synthesized resins are soluble in acetone and used for preparation of unidirectional glass fiber‐based composites. Flexural strength and modulus for modified resins‐based composites were shown to increase by at least 25% and 10% correspondingly in comparison with novolac‐based composite. Copyright © 2015 John Wiley & Sons, Ltd.     

聚苯乙炔基苯基硅氧硼烷树脂及其复合材料的性能

将双(N-间乙炔基苯基邻苯二甲酰亚胺)醚(DAIE)和双酚A型氰酸酯(CE)分别加到聚苯乙炔基苯基硅氧硼烷(PSOB)和三苯乙炔基苯基硅烷(PTPES)混合体系中进行改性,制得两种纤维增强复合材料PSOB-PTPES-DAIE和PSOB-PTPES-CE.研究了固化后树脂的热稳定性能、力学性能、介电性能和耐水性能.结果...     

A bio-based epoxy resin derived from p-hydroxycinnamic acid with high mechanical properties and flame retardancy

Recent advances in epoxy resins have been forward to achieving high mechanical performance, thermal stability, and flame retardancy. However, seeking sustainable bio-based epoxy precursors and avoiding introduction of additional flame-retardant agents are still of increasing demand. Here we report the synthesis of p-hydroxycinnamic acid-derived epoxy monomer (HCA-EP) via a simple one-step reaction, and the HCA-EP can be cured with 4,4′-diaminodiphenylmethane (DDM) to prepare epoxy resins. Compared with the typical petroleum-based epoxy resin, bisphenol A epoxy resin, the HCA-EP-DDM shows a relatively high glass transition temperature (192.9 °C) and impressive mechanical properties (tensile strength of 98.3 MPa and flexural strength of 158.9 MPa). Furthermore, the HCA-EP-DDM passes the V-1 flammability rating in UL-94 test and presents the limiting oxygen index of 32.6%. Notably, its char yield is as high as 31.6% under N₂, and the peak heat rate release is 60% lower than that of bisphenol A epoxy resin. Such findings provide a simple way of using p-hydroxycinnamic acid instead of bisphenol A to construct high-performance bio-based thermosets.     

丁腈弹性纳米粒子改性酚醛树脂的研究

酚醛树脂具有优异的耐热性、电绝缘性,尺寸稳定性、成型加工性和阻燃性等,广泛地应用在涂料、胶粘剂和复合材料工业上,酚醛树脂由于含有大量苯环以及固化后形成高度交联结构,韧性很差,因此增韧是其高性能化的主要方向之一,橡胶是最广泛使用的增韧剂,几十年来发展了天然橡胶、丁腈橡胶、丁苯橡胶、液体羧基丁腈橡胶、丁吡橡胶等,壬基酚、腰果壳油、桐油、亚麻油、热塑性塑料等也是酚醛树脂有效的增韧剂。     

METHACRYLOYL DERIVITIZED HYPERBRANCHED POLYESTER. 2. PHOTO-POLYMERIZATION AND PROPERTIES FOR DENTAL RESIN SYSTEMS

The purpose of this research is to demonstrate the usefulness of the synthesized hyperbranched multi-methacrylates (H-MMAs) in dental applications. We synthesized three hyperbranched multi-methacrylate oligomers and evaluated them as modifiers for use in the dental resin system: bisphenol A glycidyl dimethacrylate (BisGMA)/tri(ethylene glycol) dimethacrylate (TEGDMA). Their photo-polymerization activities, viscosity, mechanical properties, such as compression, diametral tensile, and flexural strength, were evaluated. H-MMAs (10%) modified dental resins have lower polymerization shrinkage and about 15% increase in mechanical strength compared to the Bis-BisGMA control. For example, H30-MMA has compressive, diametral tensile, and flexural strength of 576, 47, and 85 MPa, compared with the BisGMA control having 497, 43, and 77 MPa. In addition, hyperbranched polymer modified resins have higher glass transition temperature (T_g) and lower thermal expansion coefficient (α) than the control. This research is significant both for increasing our knowledge about hyperbranched multi-functional polymers as well as leading to new dental resin systems with better performance.     

Flame retardancy of fibre-reinforced epoxy resin composites for aerospace applications

The applicability of phosphorus-containing reactive amine, which can be used in epoxy resins both as crosslinking agent and as flame retardant, was compared in an aliphatic and an aromatic epoxy resin system. In order to fulfil the strong requirements on mechanical properties of the aircraft and aerospace applications, where they are mostly supposed to be applied, carbon fibre-reinforced composites were prepared. The flame retardant performance was characterized by relevant tests and mass loss type cone calorimeter. Besides the flame retardancy, the tensile and bending characteristics and interlaminar shear strength were evaluated. The intumescence-hindering effect of the fibre reinforcement was overcome by forming a multilayer composite, consisting of reference composite core and intumescent epoxy resin coating layer, which proved to provide simultaneous amelioration of flame retardancy and mechanical properties of epoxy resins.     

Reactive Core-Shell Bottlebrush Copolymer as Highly Effective Additive for Epoxy Toughening

Herein,we designed a core-shell structured bottlebrush copolymer (BBP),which is composed of rubbery poly(butyl acrylate) (PBA)core and an epoxy miscible/reactive poly(glycidyl methacrylate) (PGMA) shell,as an epoxy toughening agent.The PGMA shell allows BBP to be uniformly dispersed within the epoxy matrix and to react with the epoxy groups,while the rubbery PBA block simultaneously induced nanocavitation effect,leading to improvement of mechanical properties of the epoxy resin.The mechanical properties were measured by the adhesion performance test,and the tensile and fracture test using universal testing machine.When BBP additives were added to the epoxy resin,a significant improvement in the adhesion strength (2-fold increase) and fracture toughness (2-fold increase in Klc and 5-fold increase in Glc)compared to the neat epoxy was observed.In contrast,linear additives exhibited a decrease in adhesion strength and no improvement of fracture toughness over the neat epoxy.Such a difference in mechanical performance was investigated by comparing the morphologies and fracture surfaces of the epoxy resins containing linear and BBP additives,confirming that the nanocavitation effect and void formation play a key role in strengthening the BBP-modified epoxy resins.     

STUDIES ON THE BLEND OF POLYACRYLATE EMULSIONS AND TACKIFIER RESIN EMULSIONS

A series of polyacrylate emulsions were blended with tackifier resin emulsions such asmodified rosin emulsion, C5 resin and C9 resin emulsion. The miscibility of the polyacry-lates and tackifier resins was investigated by means of SEM and visual observation. Thephase diagrams of the miscibility change systematically with the polarity of polyacrylatesand tackifier resins. The influence of the content of the tackifier resins on the adhesionproperties of the polyacrylate emulsions were also studied. The results show that the180℃ peel strength is improved as the amount of the tackifier resin increases and comesto a maximum at a specific content. The ball tack property decreases slightly and the holdstrength changes complicatedly as the tackifier resin increases.     

共聚结构和分子量对热塑性聚酰亚胺树脂熔融与耐热性能的影响

基于具有刚性主链结构的4,4'-(六氟亚异丙基)双邻苯二甲酸酐/对苯二胺(6FDA/p-PDA)树脂体系, 通过共聚引入间苯二胺(m-PDA)、 4,4'-二氨基-2,2'-双三氟甲基联苯(TFDB)和9,9'-双(4-氨基苯基)芴(BAFL)等主链刚性且兼具大自由体积特性的芳香二胺, 以非反应性封端剂邻苯二甲酸酐(PA)对分子量进行调控, 设计制备了系列分子量可控的热塑性聚酰亚胺(TPI)树脂. 系统研究了共聚结构和分子量对TPI树脂熔融性能和耐热性能的影响, 构建了聚合物的聚集态结构与树脂熔融性能的对应关系, 并对树脂的室温和高温力学性能进行了评价. 研究结果表明, 大自由体积的芳香二胺共聚结构的引入可有效降低分子链堆砌密度, 增大聚合物的自由体积, 从而赋予树脂良好的熔融性能. 降低设计分子量可进一步改善树脂的熔融加工性. 这类具有刚性主链结构的TPI树脂兼具优异的耐热性能和力学性能, 树脂的玻璃化转变温度在308~338 ℃之间, 以TFDB和BAFL共聚制备的TPI-C-25K和TPI-D-25K树脂表现出高强高韧的特性, 拉伸和弯曲强度分别超过120 MPa和190 MPa, 断裂伸长率大于8.2%, 并且在250 ℃高温下表现出良好的耐热稳定性.     

Bioinspired Design Provides High‐Strength Benzoxazine Structural Adhesives

A synthetic strategy to incorporate catechol functional groups into benzoxazine thermoset monomers was developed, leading to a family of bioinspired small‐molecule resins and main‐chain polybenzoxazines derived from biologically available phenols. Lap‐shear adhesive testing revealed a polybenzoxazine derivative with greater than 5 times improved shear strength on aluminum substrates compared to a widely studied commercial benzoxazine resin. Derivative synthesis identified the catechol moiety as an important design feature in the adhesive performance and curing behavior of this bioinspired thermoset. Favorable mechanical properties comparable to commercial resin were maintained, and glass transition temperature and char yield under nitrogen were improved. Blending of monomers with bioinspired main‐chain polybenzoxazine derivatives provided formulations with enhanced shear adhesive strengths up to 16 MPa, while alloying with commercial core–shell particle‐toughened epoxy resins led to shear strengths exceeding 20 MPa. These results highlight the utility of bioinspired design and the use of biomolecules in the preparation of high‐performance thermoset resins and adhesives with potential utility in transportation and aerospace industries and applications in advanced composites synthesis.     

Thermal,mechanical, and morphological properties of novolac‐type phenolic resin blended with fullerenol polyurethane and linear polyurethane

Fullerenol polyurethane (C₆₀‐PU) and linear polyurethane (linear‐PU) modified phenolic resins were prepared in this study. Phenolic resin/C₆₀‐PU and phenolic resin/linear‐PU blends show good miscibility as a result of the intermolecular hydrogen bonding existing between phenolic resin and PU modifiers. DSC and thermogravimetric analysis methods were used to study the thermal properties of phenolic resin blended with different types of PUs. The intermolecular hydrogen bonding that existed between phenolic resin and C₆₀‐PU was investigated by Fourier transform infrared spectroscopy. The morphology and mechanical properties of phenolic resin/C₆₀‐PU and phenolic resin/linear‐PU blends were also investigated. The char yield of the modified phenolic resins decreased with increasing PU modifier content. Significant improvement in the toughness of the modified phenolic resins was observed. The improvements of impact strength were 27.4% for the phenolic resin/linear‐PU system and 54.3% for the phenolic resin/C₆₀‐PU system, respectively, both with 3 phr linear‐PU and C₆₀‐PU content. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2436–2443, 2001     

Effect of temperature and volume on the tensile and adhesive properties of photocurable resins

Knowing the mechanical properties of UV‐curable resins at cryogenic conditions is important to ongoing fusion‐energy research and to emerging aerospace applications. The tensile and interfacial shear strengths of two commercially available UV‐curable resins were measured at room‐temperature and cryogenic conditions for both bulk and reduced (subnanoliter) specimen volumes. The tensile properties of cured specimens are remarkably sensitive to both testing temperature and specimen size. For one type of resin, the cold (?150 °C) tensile strength of subnanoliter specimens is ～9× larger (179 ± 19 MPa) than bulk values at room temperature. The interfacial shear strength between SiC fibers and small volumes of resin volumes is comparable to the bulk, room‐temperature tensile strength, but it varies over a wide range at ?150 °C (15–53 MPa). All resins were fully cured, and an analysis of fractured surfaces revealed microstructural features. The enhanced strength in microscopic specimens may be related to inhomogeneous stress fields that develop during cure. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 936–945