Thermal decomposition of fire retardant brominated epoxy resins cured with different nitrogen containing hardeners

Epoxy resins frequently have to meet a flame retardancy grade which can be accomplished by incorporating brominated reactive compounds, like tetrabromobisphenol A (TBBA) cured by a number of hardeners. A few brominated epoxy resins (BERs) have been prepared by curing a mixture of diglycidyl ethers of bisphenol A (DGEBA)/diglycidyl ethers of tertabromobisphenol A (DGETBBA) and different hardeners: dicyandiamide (DICY), 4,4′-diaminodiphenyl sulphone (DDS) and polyethylene polyamine (PEPA). The use of different hardeners strongly affects the thermal degradation behaviour of the BER.The main volatile products of pyrolysis, characterized by Pyrolysis-Gas Chromatography-Mass Spectroscopy (PY-GC-MS) at 423 °C were phenol, isopropyl- and isopropenylphenol, mono- and di-brominated phenols, bisphenol A, mono-, di-, tri- and tetra-brominated bisphenol A. No nitrogen containing volatile products or HBr were evolved whereas SO₂ is formed from BER cured with DDS (BER-DDS) and bromoethylene from BER cured with PEPA (BER-PEPA). Differences of 30-60 °C in thermal stability of epoxy network have been found, depending on the hardener. The experimental evidence suggests a cooperative action of bromine and nitrogen in chain scission of epoxy resins. In particular the ability of the hardener in fixing HBr, evolved from TBBA units, seems to depend on the basicity of the N atom of the hardener: the lower the basicity, the lower the scavenging effectiveness and consequently the higher the thermal stability.     

Interfacial and wetting properties of carbon fiber reinforced epoxy composites with different hardeners by electrical resistance measurement

In this research, interfacial and wetting properties of N,N,N,N-tetraglycidyl-4,4-diaminodiphenylmethane (TGDDM) epoxy resin with two hardeners with different chemical structure were evaluated by electrical resistance (ER) measurement. The heat of reaction of TGDDM epoxy with the two different hardeners, 33 and 44 di-amino di-phenyl sulphone (DDS), was analyzed by differential scanning calorimetry (DSC). The TGDDM epoxy exhibited different mechanical properties with the two different DDS hardeners. Combined ER, wetting measurements and the microdroplet test were used for evaluating the spreading effect and interfacial shear strength (IFSS) of carbon fiber (CF) reinforced TGDDM epoxy composites with these different hardeners. The heat of reaction and mechanical properties of TGDDM/DDS were influenced by the chemical structure and different free volumes of the epoxy resins. The relationships between the ER-wetting results and the IFSS were internally consistent. Ultimately it was demonstrated that ER measurements makes it possible to estimate the interfacial and wetting properties of CF reinforced epoxy composites.     

Origin of epoxies embrittlement during oxidative ageing

Thermal oxidation of three epoxy resins prepared from flexible or rigid prepolymers and hardeners was studied by monitoring epoxy mechanical and physical changes. The physical changes were followed by mass measurements, glass transition temperature using DSC and sub-glass β transition using DMA. It was put in evidence that embrittlement is not directly associated to T_g or mass loss changes since epoxy network based on isophorone diamine (IPDA) hardeners were shown to undergo mainly a chain scission at the beginning of exposure process whereas epoxy network based on trioxatridecane diamine (TTDA) hardeners exhibits a crosslinking process with a significant mass loss. The only common feature for both epoxy systems to understand embrittlement is the drop of amplitude of β transition with oxidation.     

Application of cooling curve analysis in solidification pattern and structure control of grey cast irons

In this article, the composites based on long glass fibre reinforced polypropylene/intumescent flame retardant (LGFPP/IFR) were prepared by melt blending. The influence of thermal oxidative ageing on the LGFPP/IFR composites with different thermal oxidative ageing time at 140 °C was studied by means of oven heating. The thermal stability and flammability of the composites were respectively investigated by thermal gravimetric analysis (TG), limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), scanning electronic microscopy (SEM), mechanical properties test and energy-dispersive X-ray analysis (EDAX). A trend of increase first and then decrease in LOI values was shown in 0–50 days ageing, with the same trend as thermal stability obtained from TG in nitrogen condition. The CCT results indicated that the LGFPP/IFR composites after ageing achieved a higher heat release rate, which means a higher fire risk. The mechanical properties showed a global decrease in just 10 days ageing. Morphologies obtained from SEM showed that both the rupture of PP matrix and fibre interface debonding led to the decrease in mechanical properties. The EDAX proved that IFR particles could emerge and gather on the surface of sample in ageing procedure, which had great effects on the thermal stability and flame retardancy of the composites.     

Formaldehyde-Free Resins for the Wood-Based Panel Industry: Alternatives to Formaldehyde and Novel Hardeners

Due to its carcinogenic properties, the presence of formaldehyde in resins and other industrial products has been a subject of great concern in recent years. The presented review focuses on modern alternatives for the production of wood-based panels; i.e., substitutes for formaldehyde in the production of amino and phenolic resins, as well as novel hardeners for formaldehyde-free wood adhesives. Solutions in which formaldehyde in completely replaced are presented in this review. Recent advances indicate that it is possible to develop new formaldehyde-free systems of resins with compatible hardeners. The formaldehyde substitutes that have primarily been tested are glyoxal, glutaraldehyde, furfural, 5-hydroxymethylfurfural, and dimethoxyethanal. The use of such substitutes eliminates the problem of free formaldehyde emission originating from the resin used in the production of wood-based panels. However, these alternatives are mostly characterized by worse reactivity, and, as a result, the use of formaldehyde-free resins may affect the mechanical and strength properties of wood-based panels. Nonetheless, there are still many substantial challenges for the complete replacement of formaldehyde and further research is needed, especially in the field of transferring the technology to industrial practice.     

Identification of hardeners in solid epoxy resins by high-resolution 13C-NMR

CPMAS ¹³C-NMR spectra at 75 MHz with spinning side band suppression are presented for a series of epoxy resins cured with a variety of commercially important hardeners. The hardeners can be readily identified from the spectra; the high-field is important for distinguishing between related amine hardeners.     

Morphology and dynamic mechanical properties of epoxy/poly(styrene-co-allylalcohol) blends

Blends based on epoxy resins and a random copolymer, poly(styrene-co-allylalcohol) (PS-co-PA) were studied, analysing the effect of epoxy nature. The epoxy cross-linking reaction was carried out by homopolymerisation, using an imidazole as initiator, and by addition of several amine hardeners. The imidazole acts as initiator of anionic epoxy etherification and as catalyser of epoxy-hydroxyl reaction. Important differences were observed on the network structure and phase behaviour of blends depending on the nature of epoxy matrix. These cause that the blends present different morphologies and different dynamic mechanical properties.     

Thermal and water absorption properties of cyanate ester resins modified by fluoride‐containing and silicone‐containing components

In order to enhance the moisture resistance of cyanate ester resins, modifiers containing silicon or fluorine moieties were introduced. The curing behaviors of the obtained resins, as well as thermal, water absorption, and dielectric properties of all cured polymers, were investigated in detail. Results show that properties of fillers in polymer have great influence on the thermal property and of polymer. In all cases, modifier exhibited percolation threshold at 5 wt%. Compared with pristine cyanate ester resins (CE), when the methyl phenyl silicone resin B filler was added, the cured polymer exhibited water absorption as low as 0.39% and excellent thermal oxygen stability at 300°C. The introduction of silicon H improved thermal oxidative stability at 400°C without significant compromise in processability or mechanical properties.     

Properties of polyisocyanurate resins obtained by polymerization of hexamethylene diisocyanate by organotin catalysts

Results are given for the mechanical, thermal and flammability properties of polyisocyanurate resins obtained from hexamethylene diisocyanate by bis-(tributyltin)-oxide catalysis. It is shown that the mechanical properties of the isocyanurate resins and of their glass fibre-reinforced composites are comparable with those of commercial epoxy and polyester resins. The thermal stability and the flame retardance of the isocyanurate resins are far better than of epoxies or polyesters.     

Thermal Oxidative Degradation and Ageing Performance of Silicone Rubber Filled with Attapulgite

The natural attapulgite (NAPT) was disaggregated by high-pressure homogenization technology combined with extrusion process to prepare the attapulgite with disaggregated rod crystal bundles (DAPT) and large specific surface area of 133.7 m²/g. NAPT and DAPT were incorporated into the silicone rubber to obtain the composite NAPT-SR and DAPT-SR by mechanical blending method, respectively. After thermal oxidative ageing at 300 ℃ for 0.5 h, temperature for the 5% weight loss increased greatly from 385 ℃ of the neat silicone rubber to 396℃ - 399 ℃ with addition of NAPT and DAPT. NAPT and DAPT enhanced the interaction between the filler nanoparticles and rubber matrix thus inhibited the nanoparticle agglomeration. The conservation rate of the side methyl group in NAPT-SR and DAPT-SR was greatly improved after ageing. Therefore, the thermal oxidative degradation and ageing performance of the silicone rubber composites was significantly reinforced. Moreover, DAPT could greatly restrain the growth of nanoparticles after ageing. Therefore, DAPT-SR showed the better retention of tensile strength (40.6%), elongation at break (34.9%) and tear strength (30.1%) compared with the corresponding mechanical properties of the neat silicone rubber (10.6%, 7.4%, and 5.0%) after ageing.     

Mechanical Deformation Accelerates Protein Ageing

A hallmark of tissue ageing is the irreversible oxidative modification of its proteins. We show that single proteins, kept unfolded and extended by a mechanical force, undergo accelerated ageing in times scales of minutes to days. A protein forced to be continuously unfolded completely loses its ability to contract by folding, becoming a labile polymer. Ageing rates vary among different proteins, but in all cases they lose their mechanical integrity. Random oxidative modification of cryptic side chains exposed by mechanical unfolding can be slowed by the addition of antioxidants such as ascorbic acid, or accelerated by oxidants. By contrast, proteins kept in the folded state and probed over week‐long experiments show greatly reduced rates of ageing. We demonstrate a novel approach whereby protein ageing can be greatly accelerated: the constant unfolding of a protein for hours to days is equivalent to decades of exposure to free radicals under physiological conditions.     

Epoxy resins from rosin acids: synthesis and characterization

A series of multifunctional cycloaliphatic glycidyl ester and ether epoxy resins were synthesized by reaction of condensed rosin acid‐formaldehyde resins with epichlorohydrin. The chemical structure of the produced resins was determined by IR and ¹H‐NMR analysis. The molecular weight of the produced resins was determined by gel permeation chromatography (GPC). A series of poly‐ (amide‐imide) hardeners were prepared from condensation of Diels–Alder adducts of rosin acid‐maleic anhydride and acrylic acid with triethylene tetramine and pentaethylene hexamine. These amines were also condensed with Diels–Alder adducts of rosin ketones. The curing exotherms of the produced epoxy resins with poly(amide‐imide) hardeners were investigated. The data of mechanical properties, solvent and chemical resistance indicate the superior adhesion of the cured epoxy resins. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis and characterization of novel polythiourethane hardeners for epoxy resins

A novel thiol-terminated polythiourethanes were synthesized from low-molecular-weight di- and multifunctional mercaptans and diisocyanates and employed as curing agent of epoxy resin. The curing reaction of epoxy resin and thermal properties of cured products were investigated with differential scanning calorimetry. Evaluation of climatic ageing resistance was made by the change in mechanical properties. Mechanical studies indicated that the application of polythiourethane has toughening effect and significantly increases ageing resistance of the cured resins. The results of this study indicate that molecular structure and functionality of polythiourethane oligomers are of critical importance in governing the curing mechanism, structure of the network and final properties of epoxy compositions.     

Determination of the thermal degradation rate of polystyrene-divinyl benzene ion exchange resins in ultra-pure water at ambient and service temperature

Polystyrene divinylbenzene resins used for purification in heavy-water moderated nuclear reactors are subject to thermal, oxidative and radiation-induced degradation. The rates (relative or absolute) of these processes are unknown. This work addresses the need to develop a test for the thermal degradation of resins. Resin samples were submitted to temperature bracketing service conditions (25 to 70 °C) in a high purity system. The resin degradation rates were obtained by measuring the Total Organic Carbon (TOC), to obtain rate constants for different nuclear-grade resins, cationic and anionic beds, and also anionic resins converted to different counter-ions. The test showed reproducible results (replicates from a batch, batch-to-batch variations), and the rate constants obeyed the Arrhenius principle. The results indicated that the anionic resins degraded ∼1.6 to 7 times faster than the cationic resins, while the presence of common anions as counter-ions on the resin (chloride, nitrate, sulfate) lowered the degradation rate by up to 2.3 times. Calculations for the full scale of a reactor suggested that thermal degradation alone, producing TOC in a closed-loop circuit, would be a minor factor in saturating a column during normal service. This revised version was published online in July 2006 with corrections to the Cover Date.     

Accelerated ageing due to moisture absorption of thermally cured epoxy resin/polyethersulphone blends. Thermal, mechanical and morphological behaviour

A model epoxy resin/anhydride system, modified with a polyethersulfone (PES) engineering thermoplastic toughening agent, has been studied under hydrothermal ageing in order to investigate the modification of the thermal, morphological and mechanical behaviour through dynamical mechanical thermal analysis, SEM microscopy and fracture toughness test respectively. Two different concentrations of the toughening agent were used in the blends and two ageing conditions have been considered, consisting of the immersion of the samples in distilled water at constant temperature of 70 °C for 1 week and for 1 month. Dynamical mechanical thermal analysis results on hydrothermally aged materials indicated the occurrence of progressive segregation effects with the formation of regions with different cross-linking degrees.Fracture toughness tests showed an increase of the K_IC value with the increase of the toughening agent concentration, revealing both a dramatic decrease of the same parameter after 1 week ageing for all the materials and the tendency to reach an almost constant value after 1 month ageing for all the formulations, with a slight increase with respect to 1 week ageing. These results have been interpreted on the basis of the SEM analysis, showing the presence of a well defined micrometric PES particles distribution in the epoxy/anhydride matrix, and discussed in the light of different water absorption mechanisms at short and long ageing times.     

Hydrothermal ageing of radiation cured epoxy resin-polyether sulfone blends as matrices for structural composites

The hydrothermal ageing of epoxy-thermoplastic blends, used as matrices for carbon fibre composites, cured by electron beam, has been studied. Two different thermoplastic percentages have been adopted. A suitable choice of both curing process and formulation parameters allows to carry out irradiation at mild temperature with several advantages, coming from a “non thermal” process, for both the final properties of the materials and the environment. Nevertheless the occurring of vitrification phenomena needs the use of a short thermal treatment after irradiation on the already solid materials, in order to complete the cure reactions. Radiation cured epoxy based matrices have been subjected to a thermal and moisture absorption ageing treatment and its influence on the thermal and mechanical properties has been investigated through dynamic mechanical thermal analysis and fracture toughness tests. The results have been interpreted on the basis of the different curing degree reached by the investigated systems and in the light of their morphological structures. Plasticization, thermal curing and degradation reactions occur in different extent depending on the kind of the material. In particular, for fracture properties, a better resistance to ageing is shown by the system at higher thermoplastic concentration.     

Characterization of Plukenetia volubilis L. fatty acid-based alkyd resins

Fatty acid-based alkyd resins prepared with different amounts of glycerol and pentaerythritol were characterized. Sacha inchi oil and linseed oil (comparative purposes) were used as fatty acids’ sources. FT-IR and ¹H NMR spectroscopy were done for alkyd structural verification. Alkyd resins were evaluated through physico-chemical (colour, density, viscosity) and thermal characterization. Film coating performance (drying, hardness, chemical resistance) was also studied. The oxidative crosslinking time tendency was corroborated by the quartz crystal microbalance (QCM) technique. Alkyd resins obtained with fatty acids from sacha inchi and linseed oils had similar properties. Results indicated that lighter resins can be obtained from sacha inchi oil, whereas pentaerythritol increases viscosity and thermal stability, and retards drying time of fatty-acid based alkyd resins.     

Curing reaction of biphenyl epoxy resin with different phenolic functional hardeners

The investigation of cure kinetics and relationships between glass transition temperature and conversion of biphenyl epoxy resin (4,4′-diglycidyloxy-3,3′,5,5′-tetramethyl biphenyl) with different phenolic hardeners was performed by differential scanning calorimeter using an isothermal approach over the temperature range 120–150°C. All kinetic parameters of the curing reaction including the reaction order, activation energy, and rate constant were calculated and reported. The results indicate that the curing reaction of formulations using xylok and dicyclopentadiene type phenolic resins (DCPDP) as hardeners proceeds through a first-order kinetic mechanism, whereas the curing reaction of formulations using phenol novolac as a hardener goes through an autocatalytic kinetic mechanism. The differences of curing reaction with the change of hardener in biphenyl epoxy resin systems were explained with the relationships between T_g and reaction conversion using the DiBenedetto equation. A detailed cure mechanism in biphenyl-type epoxy resin with the different hardeners has been suggested. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 773–783, 1998     

热稳定剂对PVC紫外光老化过程中微观结构及宏观性能演变的影响

通过UV-Vis、FTIR、DSC、以及色差、力学性能的测试表征,实时追踪分析了在紫外光老化过程中,含Pb、Sn以及Ca-Zn热稳定剂的PVC体系微观结构和宏观性能的演变过程.结果表明,在相同光老化条件下,PVC/Pb、PVC/Sn和PVC/Ca-Zn体系的微观结构变化规律基本一致,过程中主要的化学反应是,大分子吸收光能后,发生脱HCl生成共轭双键的反应、生成羰基的氧化反应、交联反应和降解反应;不同热稳定剂的作用,主要表现在对于微观结构变化的幅度和动力学过程的影响不同.相应地,3种体系的外观色差和力学性能的变化规律也相似,但色差的变化程度和速度以及老化后力学性能的保持率因所含热稳定剂的不同而不同,其中含Sn体系的颜色稳定性最好,含Pb体系的力学性能保持率最高。     

Synthesis and properties of isosorbide based epoxy resin

Isosorbide based epoxy resin (IS-EPO) of epoxy number: 0.44 mol/100 g was synthesised in the one step reaction from 1,4:3,6-dianhydro-d-glucitol (isosorbide) and epichlorohydrin in the presence of concentrated aqueous NaOH. The product obtained was characterised by means of NMR, FT-IR and ESI MS spectroscopy. Compositions with typical hardeners were prepared and cured. The thermal and mechanical properties of the resulting materials were evaluated. Comparison with commercially available epoxy resin Epidian 5 shows relatively good mechanical performance of IS-EPO which makes isosorbide a promising candidate to replace bisphenol A (BPA).