Viscoelastic fracture behaviour for different rubber-modified epoxy adhesive formulations

The viscoelastic fracture behaviour of various rubber-modified epoxy formulations was analysed using a time-temperature superposition approach. The shift factors for all of these systems were quite similar. In addition, an equivalent analysis of yield stress data was performed for one of the samples; it gave shift factors similar to those from the fracture experiments thus indicating a close correlation between yield and toughening. A simple empirical equation was found to describe the fracture data for all the materials and, consequently, the parameters in this equation provide a good method to characterize the fracture behaviour and to compare different materials.     

Synthesis and properties of high-solids hybrid materials obtained from epoxy functional urethanes and siloxanes

In this work series of novel high-solids crosslinked hybrid networks based on the epoxy-terminated polyurethane prepolymer and the comb-like structure co-poly(dimethyl)(methyl, 3-glycidoxypropyl)siloxane cured with diethylenetriamine, were obtained. The viscosity lowering of epoxy-terminated polyurethane prepolymer with temperature allowed for the preparation of the hybrid systems without using of any solvent. The structure of the obtained poly(urethane–siloxane) thermosets was confirmed by FT-IR spectroscopy. The DSC studies reveal, that the addition of siloxane resulted in the decrease of the glass transition temperature of the hybrid materials. The synthesized poly(urethane–siloxane) networks are hydrophobic, with the free surface energy of 17–31 mJ/m². An increased amount of siloxane resulted in an increase of water contact angle and decrease of degree of water absorption as well as of FSE, which confirms a hydrophobic nature of the employed siloxane. Some properties of obtained hybrid materials based coatings were also studied.     

Low moisture absorptive epoxy formulations for Gr/Ep laminates

The incorporation of 2-undecyl-imidazole (C₁₁Z) and chromium acetylacetonate (Cr(acac)₃) additives into N, N, N′, N′-tetraglycidyl diaminodiphenylmethane (TGDDM)/diaminodiphenylsulfone (DDS) epoxy formulations was found to significantly decrease the moisture absorption of their prepared graphite/epoxy laminates. However, the same additions did not much affect the moisture absorption of the cured TGDDM/DDS neat resins. Thus, the former case was attributed to the processing effects in view of the fact that C₁₁Z pre-reacting with TGDDM during lay-up process produced the ether-linkage polymer chains in the epoxy networks and raised the viscosity. The following compacting stage of laminates was believed to squeeze the small molecules such as unreacted TGDDM, DDS and Cr(acac)₃, toward the surface of carbon fibers and increase the chance of Cr(acac)₃ to block the hydroxyl groups in the epoxy networks produced by the reactions between TGDDM and DDS. Some evidence was provided to support the above hypothesis in this study.     

Acrylate-based fluorinated copolymers for high-solids coatings

A series of low, medium, and high molecular weight copolymers containing methyl methacrylate, n-butyl acrylate, 2-hydroxyethyl methacrylate, and 2,2,2-trifluoroethyl methacrylate were synthesized by solution polymerization under monomer-starved conditions. The acrylate-based copolymers were characterized by FTIR; ¹H, ¹³C, and ¹⁹F NMR, and MALDI-TOF mass spectrometry. The molecular weights and the glass transition temperatures of the copolymers were determined using Gel Permeation Chromatography (GPC) and Differential Scanning Calorimetry (DSC). The copolymers were crosslinked with a methylated melamine formaldehyde resin in order to obtain thermosetting acrylics. Surface, optical, barrier, mechanical, and viscoelastic properties of the acrylic coatings were investigated. An enrichment of fluorinated units at the acrylic surface was directly verified measuring dynamic contact angles. Lower wettability, higher oxygen permeability, and lower refractive index were observed for higher concentrations of fluorinated monomer in the copolymer composition. High number-average hydroxyl functionality of high molecular weight copolymers increased the crosslink density of the acrylic films, resulting in improved tensile strength and tensile modulus.     

Cure kinetics of neat and graphite-fiber-reinforced epoxy formulations

An investigation was carried out into the cure kinetics of neat and graphite fiber-reinforced epoxy formulation, composed of tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM) resin and diaminodiphenyl sulfone (DDS) curing agent. Two experimental techniques were employed: isothermal differential scanning calorimetry (IDSC) and dynamic differential scanning calorimetry (DDSC). An autocatalytic mechanism with the overall reaction rate order of 2 was found to describe adequately the cure kinetics, of the neat resin and the composite. All kinetic parameters, including reaction rate constants, activation energies and preexponential factors, were calculated and reported. The presence of graphite fibers in the composite had only a very small initial effect on the kinetics of cure.     

低温固化环氧胶粘剂组分配比的优化设计

为改善固化物的脆性，用低分子聚酰胺PA－650作固化增韧剂，选择改性苯二甲胺A－50作固化剂、咪唑改性物作促进剂，开展低温固化环氧树脂胶粘剂的研究。运用计算机辅助二元二次回归正交设计的方法，经9组实验和数据处理，得到树脂性能与组分配比的回归方程，绘制性能一配比的立体曲面图，优化出性能优异的低温固化环氧树脂胶粘剂配方。     

Liquid crystalline acrylic copolymers for high-solids enamel coatings

Carboxyl functional liquid crystalline (LC) acrylic copolymers were synthesized and were compared with carboxyl functional control copolymers of M?_n about 5000–15,000. Both types were crosslinked with a hexakismethoxymethyl melamine (HMMM) resin at 150°C, a temperature below the clearing points of the LC copolymers. Birefringent phases were visible in the crosslinked films made from LC polymers. FT-IR indicated the presence of unreacted COOH in all crosslinked materials. Unreacted COOH groups in crosslinked LC copolymers appeared only slightly higher than those in crosslinked amorphous copolymers. The potential utility of these LC copolymers as binders for thermosetting coatings was assessed. Variables studied were HMMM content, the length of PHBA grafts, T_g and M?_n of the acrylic copolymer backbone, and functionality. Optimum LC copolymers have low backbone T_g (<O°C) and low functionality (< 7.5 mol %). Cured films of such copolymers have both high hardness (> 35 KHN), high impact resistance (> 80 in. ib), excellent adhesion, and good solvent resistance.     

复合溶剂吸收废气中醋酸丁酯的研究

采用散堆填料塔,分别考察了油酸甲酯、油酸乙酯和油酸甲酯-油酸乙酯复合溶剂对废气中醋酸丁酯的吸收性能.分析了醋酸丁酯质量浓度、油酸甲酯体积分数、液气比和空气流量对含醋酸丁酯废气吸收率的影响.结果表明,醋酸丁酯质量浓度ρ =0.535 g/L,复合吸收剂中油酸甲酯体积分数φ=0.5,液气比1.25 L/m3,空气流量v=4 L/min时,废气中醋酸丁酯吸收率可达94.12％.采用普通精馏对含醋酸丁酯的吸收液进行后处理,塔顶回收所得醋酸丁酯质量分数可达99.0％以上,塔釜回收所得油酸甲酯-油酸乙酯复合溶剂对醋酸丁酯废气回收率达91.01％.     

Effect of catalyst on the curing of tetrafunctional epoxy resin formulations

Cure kinetics of tetraglycidyl 4,4′-diaminodiphenyl methane resin formulations with diaminodiphenylsulfone as hardener and borontrifluoride-ethylamine adduct as accelerator has been studied by differential scanning calorimetry (DSC) technique both dynamically and isothermally. The DSC scans show multiple exotherm peaks, indicating the complex nature of reaction. The curing exotherms obtained have been analysed to derive the kinetic parameters associated with the curing process. The heat of reaction shows a decreasing trend with increasing catalyst concentration.     

Toughening of epoxy resin blended with thermotropic hydroxyethyl cellulose acetate

Thermotropic hydroxyethyl cellulose acetate (HECA) was totally miscible with uncured epoxy resin, and the miscibility was not influenced by the degree of substitution (DS) of HECA. When the epoxy resin was cured with diamine (DDA), HECA became immiscible with the epoxy resin matrix, and a heterogeneous system was formed. Epoxy resin existed as a constant phase, and HECA-rich domains were dispersed in the matrix with dimensions of about 0.2–0.5 μm. Epoxy resin could be toughened by HECA, and the impact strength of the epoxy resin blends with 10 wt % HECA was the maximum. HECA exhibited the highest toughening ability when the epoxy resin was cured at the temperature at which the HECA existed as a liquid crystalline state. The toughening ability was also influenced by the degree of substitution for acetyl of HECA, and the impact strength of the epoxy resin blends decreased with increasing the DS for acetyl of HECA. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1159–1163, 1998     

微波辐射下无溶剂催化合成乙酸辛酯

在微波辐射下,以硫酸氢钠为催化剂,不用溶剂,对乙酸与正辛醇之间的酯化反应进行了研究,考察了醇酸物质的量比、催化剂用量、微波辐射功率、微波辐射时间对乙酸辛酯收率的影响。结果表明,硫酸氢钠有着良好的催化活性,在正辛醇用量0.1 mol,n(正辛醇)∶n(乙酸)=1∶2.5,催化剂用量为反应物总质量的0.75%,微波功率450 W,辐射时间16 min条件下,乙酸辛酯收率可达91.2%,催化剂重复使用5次仍保持较高活性。     

In-situ phosphatizing coatings II: A high-solids polyester baking enamel

A single step in-situ phosphatizing coating (ISPC) can be formulated by pre-dispersing an optimal amount of in-situ phosphatizing reagents (ISPRs) into the paint system. The technique of ISPC is applied to a high-solids polyester-malemine baking enamel using a designed “ISPR-2.” The in-can stability of ISPC is verified using rheological measurements. The coating properties and protective performance of the ISPC are compared to those of the multi-step coating of control sample (MCCS). The immersion tests in a 3% NaCl solution and salt spray testings show a significant improvement in paint disbondment from the “X” scribe for ISPC. The observed coating performance enhancement of ISPC over MCCS is confirmed from the multi-functionality of ISPRs. Phosphate chemistry proceeds via an acid-base type of interaction, P-O⁻- Mⁿ⁺, and polymer chemistry generates a covalent P-O-C linkage with the polymer network. Presented at 24th International Waterborne, High-Solids, and Powder Coatings Symposium, February 5–7, 1997, New Orleans, LA. Dept. of Chemistry and Biochemistry, DeKalb, IL 60115-2862.     

Cure kinetics of epoxy formulations of the type used in advanced composites

An analysis of the cure kinetics of three different formulations composed of tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM) epoxy resin and diaminodiphenyl sulfone (DDS) was performed. A series of isothermal tests was run, and the experimentally obtained results were checked against the proposed kinetic model. An autocatalyzed mechanism with the overall reaction order of 2 was found to adequately describe the cure kinetics. An increase in reaction rate was observed at higher temperature and higher DDS concentration. For a given formulation, the extent of reaction corresponding to the maximum reaction rate was independent of temperature. A secondary exotherm was detected, particularly in formulations with low DDS concentration, at approximately 40% conversion. At that point, the rate of primary amine–epoxide reaction decreases, and other reactions dominate the curing process. Such a mechanism is likely to cause a formation of an inhomogeneous thermoset morphology.     

Improving processability for in-mold coating formulations: Part II: Two-reinforcement formulations

The in-mold coating (IMC) process nowadays is well accepted by the sheet molding compound industry. The currently used IMC contains 2.8 wt% carbon black (CB) to provide enough electrical conductivity for maximum paint transfer efficiency (PTE) for electrostatic painting. Due to its relatively large viscosity, this formulation makes use of more than one injection gate for coating some large parts necessary. Our previous research investigated the possibility to replace the CB with higher conductivity carbon-based nanoparticles, namely carbon nanofibers (CNFs), multi-wall carbon nanotubes (MWCNTs), industrial graphene (grapheneblack [G]), and single-wall carbon nanotubes (SWCNTs) and found that the IMC with 11.3 wt% G has the best processability among all IMC formulations. To improve this formulation, herein, we study the use of a second reinforcement in combination with G, i.e., CB, CNF, and MWCNT. Results from this study suggest that most G/CB-reinforced IMC formulations have a better performance than the G-reinforced IMC formulations, and IMC with 1 wt% CB and 6 wt% G is the best among all G/CB-reinforced IMC formulations. To be specific, the new formulation allows parts to be painted to have a 300% increase in size when compared with the standard IMC.     

叔丁醇脱水制备异丁烯新方法

叔丁醇脱水生产异丁烯的关键是如何及时将叔丁醇生产异丁烯过程中的副产水移去。本实验首次采用三元共沸脱水剂的新技术，及时把副产物移走，以保证异丁烯生成速率高且平稳。实际生产表明：运用该新技术生产异丁烯比目前国内其它生产技术生产异丁烯速度提高５～６倍。     

Aluminum compounds as additional crosslinkers for air-drying high-solids alkyd paints

Aluminum compounds, especially complexes of alcohols, are known as additional crosslinkers for air-drying alkyd paints. Particularly, the drying behavior of high-solids alkyd systems applied under adverse conditions may be improved distinctly. Besides the ether- and peroxy-crosslinks resulting from oxidative drying, coordinative crosslinking occurs. However, exterior weathering of paint films containing Al-complexes frequently results in severe embrittlement. In order to cope with these problems, drying and aging of alkyds and Al-complexes were investigated. All ligands in the complex appeared to get lost during drying, a probable cause of poor weathering performance. Using specially developed alkyd paints for Al-compounds, possible ways of controlling embrittlement are discussed. P.O. Box 9300, 6800 SB Arnhem, The Netherlands. P.O. Box 3, 2170 BA Sassenheim, The Netherlands.     

位阻型硅烷保护剂——叔丁基二苯基氯硅烷的研制

以氯代叔丁烷、镁、四氢呋喃为原料,采用格氏法合成叔丁基二苯基氯硅烷。考察反应物料配比、反应温度、反应时间、催化剂种类等对合成反应的影响。结果发现,合成叔丁基二苯基氯硅烷的最佳条件是：催化剂为NaSCN,反应温度为90℃,反应时间为5h,氯代叔丁炕与镁的量之比为1：1．2,目的产物的收率为65％。     

Synthesis of acrylic resins for high-solids coatings by solution and separation polymerization

Conventional solution polymerization under monomer-starved conditions was compared with separation polymerization, also known as monomer-starved, as a method for making acrylic resins with low polydispersity (D=M_w/M_n). Separation polymerization employs aliphatic or cycloaliphatic solvents that are good solvents for the monomers but poor solvents for the resin; thus, the resin separates during polymerization. Various process conditions, initiators, chaintransfer agents, and solvents were studied, focusing mainly on a monomer line-up of methyl methacrylate, styrene, ethyl acrylate, and 2-hydroxy ethyl methacrylate in a 15/15/40/30 weight ratio. Two initiators, t-amyl peroxy 2-ethyl hexanoate and t-butyl peroxy 2-ethyl hexanoate gave about equal, excellent results. 2-Mercapto ethanol was selected as a chain transfer agent. With these ingredients, the separation polymerization method is capable of producing oligomeric acrylic polyol resins with polydispersities (D) of about 1.7 to 1.8 when M_n is in the range 1350 to 1600. These resins have substantially lower solution viscosities than a commercial benchmark resin, which has M_n=1230 and D=2.03. In preliminary tests of 2K polyurethane coatings, the film properties obtained with acrylics made by separation polymerization were, on balance, superior to those obtained with a commercial benchmark resin. 430 W. Forest Avenue, Ypsilanti, MI 48197. Polymer and Coatings Program, Department of Materials Science, Shanghai 200433, P. R. China.     

Photocuring of cycloaliphatic epoxy formulations using polyesters with multiarm star topology as additives

Multiam star polyesters were synthesized by growing poly(ε‐caprolactone) (PCL) arms from hyperbranched polyesters cores of different molecular weight and used as polymeric modifiers in UV‐curable cationic formulations based on a biscycloaliphatic epoxy resin. The effect of the multiarm stars on the curing kinetics has been investigated by real‐time FTIR. The thermal‐mechanical properties of the photocured thermosets have been studied with calorimetry and dynamomechanical and thermogravimetric analysis. Impact strength tests have been performed to assess their effect on the toughness of the cured materials. An accelerative effect of these modifiers has been observed as a consequence of the participation of the hydroxyl groups of the modifiers in the cationic curing of the epoxy resin. A modest increase in toughness accompanied by a decrease in the glass transition are observed, as a consequence of the incorporation of the modifiers into the network structure, leading to homogeneous, in situ reinforced materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40005.