Novolac Type Epoxy Research Articles

Influence of hydrogen bonding interactions on the properties of ultraviolet‐curable coatings

ABSTRACTPhenolic novolac type epoxy resin has been modified with acrylic acid (AA) and 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) to form ultraviolet‐curable coatings, and integrated performances of the coatings were evaluated. It was found that the hydrogen bonding interactions among the oligomers became stronger along with the increase of AMPS content, thus the oligomer viscosity and a variety of polymer properties were affected. The polar hydrogen bond donors significantly enhanced the adhesion strength and surface wetting behavior of the coatings. Meanwhile, hydrogen bonding interactions can also reinforce the three‐dimensional structure of the film as in polymeric state, which potentially increased its glass transition temperature and mechanical properties. Results of chemical resistance showed that coatings modified with moderate amount of AMPS could be completely removed in several minutes when exposed to alkali solution or anhydrous ethanol. With these attractive features, modified films had prospective applications in temporary protective coatings. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43113.

Optimum mixing ratio of epoxy for glass fiber reinforced composites with high thermal stability

The optimum condition of glass fiber/epoxy composites was investigated according to mixing ratio of two epoxy matrices. Novolac type epoxy and isocyanate modified epoxy were used as composites matrix. Based on chemical composition of mixing matrix, optimum mixing ratio of epoxy resins was obtained through FT-IR instrument. In order to investigate thermal stability and interface of epoxy resin, glass transition temperature was observed by DSC instrument, and static contact angle was measured by reflecting microscope. Change of IR peak and Tg was conformed according to different epoxy mixing ratios. After fabrication of glass fiber/epoxy composites, tensile, compression, and flexural properties were tested by UTM by room and high temperature. The composites exhibited best mechanical properties when epoxy mixing ratio was 1:1.

Effect of epoxy resin properties on the mechanical properties of carbon fiber/epoxy resin composites

Abstract Three kinds of epoxy resins, i.e. tetraglycidyl diaminodiphenyl methane (AG80), difunctional diglycidyl ether of bisphenol-A (E51) and novolac type epoxy resin (F46) were selected as matrices for carbon fiber/epoxy composites. The objective of this work is to study the mechanical properties of fiber/epoxy composites by using these three kinds of epoxy resins with different physical and chemical performance. The results show that the composites fabricated with AG80 present the best stiffness and the composites prepared with E51 have the best toughness. The stiffness and toughness of the composites prepared with F46 are middle values located between those for AG80/epoxy and E51/epoxy composites. Thus, the mixed epoxy resin is a promising approach for industrial production.

Synthesis of Two Novolac Type Epoxy Resin Curing Agents and their Application

Two Novolac Resins Were Synthesized by the Reaction between Bisphenol A and Benzaldehyde (bis-BENR) or Bisphenol A and P-hydroxybenzaldehyde (bis-PHNR). Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR) Were Applied to Characterize the Molecular Structure of Bis-BENR (or Bis-PHNR). then the Two Novolac Resins Were Used as Curing Agent for Bisphenol A Type Epoxy Resin (DGEBA). the Curing Reaction and Curing Kinetics Were Studied by Dynamic FTIR and Differential Scanning Calorimetry (DSC). Dynamic FTIR Showed that the Two Novolac Resins Reacted with Epoxy Resins and Formed a Crosslinking Network Structure. DSC Results Show that the Optimum Mass Ratio between DGEBA and Bis-BENR (or Bis-PHNR) Was 7:3, under which the Curing Reaction Processed Completely. the Mechanical Properties and Sulfide Resistance of DGEBA/bis-BENR (or Bis-PHNR) System Were Also Investigated. the Results Showed that when the Mass Ratio between DGEBA and Bis-BENR (or Bis-PHNR) Was 7:3, the Curing Coatings Had Optimum Mechanical Properties and Sulfide Resistance.

Photocure Kinetics of Thermally Stable Photoreactive Prepolymers with Cinnamate Moiety

New thermally stable photoreactive prepolymers were synthesized by the reaction of t-cinnamic acids (CAs) with different functional groups and two kinds of epoxy resins which are a biphenyl type epoxy resin and a novolac type epoxy resin with furan ring. Their photocure reaction rates and the extent of reaction conversion were measured with Fourier transform infrared spectroscopy, and their photocure reactions were analyzed in terms of nth-order kinetic reaction equation. Their optical and thermal stability were investigated with UV-Visible spectroscopy and thermogravimetric analysis (TGA). Their photocure reaction rates and the extent of reaction conversion increased with the intensity of UV irradiation. The photoreactive cinnamate prepolymers synthesized from FPREP epoxy resin showed a lower reaction conversion rate and a reaction constant than those of the photopolymer systems based on EBPXA epoxy resin. The reaction conversion rates of these photopolymers with hydroxyl group as a functional group of cinnamate were lower than those of only cinnamate moiety. Thermal stability was studied by observing changes in the transmittance of the photocured polymer films upon heating and by measuring weight loss with temperature using TGA. These photoreactive prepolymers with a biphenyl group showed good thermal properties, with almost no transmittance change in the visible range even after they were heated at 250°C for 1 hour, and these cinnamate photopolymer systems exhibited little weight loss up to about 300°C.

Multi-functional Epoxy Resins Performing High Thermal Resistance with Good Flow-ability based on Dimeric Naphthols

Two kinds of naphtols, 2, 7-dihydroxynaphthalene (2,7-DHN) and 2-hydroxy naphthalene (2-HN), were reacted with formaldehyde to produce dimeric naphtols. One of the products, designated as DN-a, was prepared only from 2-DHN and thus possessed tetra-functionality. Two other kinds of dimeric naphtols, DN-b and DN-c were prepared from the mixture of 2-DHN and 2-HN in different ratios providing hydroxyl functionalities of 3.0 and 2.6 for DN-b and DN-c, respectively. The epoxy resins, E-a, E-b, and E-c, were prepared by the reaction of the corresponding dimeric naphtol with epichlorohydrine. The melt viscosity of E-a was comparable with that of cresol novolac type epoxy resin (ECN), and those of E-b and E-c were sufficiently lower so as to provide better flow-ability in comparison with ECN making them potentially more useful. The cured epoxy resins in this report showed higher Tg values in comparison with that of ECN. In particular, the E-a cured resin showed a Tg of 328 °C, which is the highest Tg for epoxy resins reported so far.

Thermal and thermo-oxidative degradation of flame retardant high impact polystyrene with triphenyl phosphate and novolac epoxy resin

Thermal and thermo-oxidative decomposition and decomposition kinetics of flame retardant high impact polystyrene (HIPS) with triphenyl phosphate (TPP) and novolac type epoxy resin (NE) were characterized using thermo-gravimetric experiment. And the flammability was determined by limited oxygen indices (LOI). The LOI results show that TPP and NE had a good synthetic effect on the flame retardancy of HIPS. Compared with pure HIPS, the LOI values of HIPS/NE and HIPS/TPP only increased by about 5%, and the LOI value of HIPS/TPP/NE reached 42.3%, nearly 23% above that of HIPS. All materials showed one main decomposition step, as radical HIPS scission predominated during anaerobic decomposition. TPP increased the activity energy effectively while NE affected the thermal-oxidative degradation more with the help of the char formation. With both TPP and NE, the materials could have a comparable good result of both thermal and thermal-oxidative degradation, which could contribute to their effect on the flame retardancy.

Study on the Polydimethylsiloxane Polyurethane Modified Novolac Type Epoxy Precursor for Manufacturing Carbon–Carbon Composites

The objective of this study is to investigate the feasibility of utilizing the aromatic amine-terminated polydimethylsiloxane polyurethane modified novolac type epoxy to prepare carbon–carbon (C–C) composite with improved mechanical and anti-oxidation properties. The curing kinetics of modified epoxy and the compatibility of polymer blend were investigated. Thermal, physical, and mechanical properties during the post-cure stage and carbonization stage were also examined. The curing kinetic studies show that epoxy matrix modified with polydimethylsiloxane polyurethane decrease the collision factor and increase the total heat of reaction and the active energy of reaction. Polydimethylsiloxane polyurethane is compatible with epoxy resin when the content is below 5 phr (parts per one hundred parts of epoxy resin). Adding polydimethylsiloxane polyurethane can reduce the weight loss of composite during the post-cure process. The volume shrinkage and porosity of carbon fiber reinforced composite and C–C composite decrease with the increase of polydimethylsiloxane polyurethane content. The polydimethylsiloxane polyurethane can increase the mechanical properties after carbonization since polydimethylsiloxane polyurethane releases the internal pressure and protects the fiber surface during the carbonization process. The novolac epoxy, with polydimethylsiloxane polyurethane modified, has better oxygen resistance and lower oxidation rate from the thermogravimetric analysis (TGA) oxidation testing results after the addition of this silicon-containing resin.

Relaxation and Reinforcing Effects of Polyrotaxane in an Epoxy Resin Matrix

Polyrotaxanes with a low threading ratio of α-cyclodextrin (α-CD) on a poly(ethylene glycol) chain effectively acted as both the relaxation and reinforcing reagents in Novolac-type epoxy resin. The polyrotaxanes were incorporated into the epoxy resin during the curing process to produce transparent and rigid epoxy resin/polyrotaxane (E/PR) alloys. From dynamic mechanical analysis (DMA) of the E/PR alloys, it was found that the polyrotaxane contributed not only as a stress-relaxation component but also as a reinforcing modifier in the epoxy resin matrix. The morphology and chemical structures of polyrotaxanes in the epoxy resin matrices were assumed to be in a nanoscale dispersion, forming an interpenetrate network structure with multi cross-linking bonds on threaded α-CDs. This assumption was made based on their transparency, differential scanning calorimetry, small-angle X-ray scattering, and DMA analyses. This is the first report on the unique properties of polyrotaxanes added in a rigid matrix.

Processability, Thermal, Mechanical, and Morphological Properties of Novolac Type-Epoxy Resin-Based Carbon-Carbon Composite

The objectives of this study are to investigate the feasibility of utilizing novolac type-epoxy resin to prepare carbon-carbon(C-C) composite and to study the properties of the composite. Different postcuring times, temperatures, and carbonization heat treatment temperatures were used to treat the novolac type-epoxy resin. The changes in the thermal, physical, and mechanical properties during the carbonization processing are also investigated. The results show that the matrix cured at a higher postcuring time and temperature possesses a significant weight loss on the postcure process and limits the weight loss on carbonization processing. Increasing the postcure time and temperature will improve the mechanical properties of composite after carbonization, however, higher postcure time and temperature will cause additional matrix and fabric damage. In the carbonization process, the mechanical properties and density of C-C composite decrease rapidly after 400 C. When heat treatment temperature is increased to 800 C, mechanical properties and density of composite will remain constant and then increase slightly.

Epoxy resins possessing flame retardant elements from silicon incorporated epoxy compounds cured with phosphorus or nitrogen containing curing agents

New silicon-containing epoxy compounds were obtained by reacting a bisphenol-A type epoxy and an o-cresol–formaldehyde novolac type epoxy with diphenylsilandiol and triphenylsilanol, respectively. The reactions were performed with tin(II) chloride as a catalyst at 140–170 °C. With various feeding ratios of reactants, the epoxy compounds contained various silicon contents. The thermal stability and the flame retardant property of the cured epoxy resins were improved with this incorporation of silicon. Synergistic effects of phosphorus/silicon and nitrogen/silicon on enhancing limited oxygen index values were also observed for the epoxy resins from the silicon-containing epoxy compounds cured with phosphorus- and melamine-containing agents.

Polydimethylsiloxane containing isocyanate group-modified epoxy resin: Curing, characterization, and properties

A synthesized polydimethylsiloxane containing an isocyanate group was used to improve the flexibility and to reduce the internal stress of epoxy resin cured with MDA (4,4′-methylene dianiline). The effect of polysiloxane content on the curing kinetics of a novolac-type epoxy modified with an isocyanate group was investigated. It was found that the modified epoxy resin showed significant improvement in impact strength. The polysiloxane containing isocyanate groups effectively depressed the internal stress of cured epoxy resins by reducing the flexural modulus and the coefficient of thermal expansion, while the glass transition temperature was increased. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2739–2747, 1999

Synthesis and curing behaviour of urethane‐modified epoxy resin having hydroxymethyl group

AbstractSynthesis and curing behaviour of urethane‐modified epoxy resins were studied. The epoxy resins were synthesized by the reaction of 4‐cresol‐type epoxy resin having hydroxymethyl group (EPCDA) with isocyanates. First, as a model compound, EPCDAPI was synthesized by the reaction of EPCDA with phenyl isocyanate (PI). EPCDAPI was heated at 180°C and the reaction products were identified and the reaction mechanism was studied. The following reactions occurred: regeneration of hydroxymethyl group and PI by thermal dissociation of urethane linkage; reaction of epoxide ring and urethane linkage; reaction of epoxide ring and regenerated PI. Urethane‐modified epoxy resin having hydroxymethyl group and urethane linkage (EPCDAMDI) was synthesized by the reaction of EPCDA with 4,4′‐diphenylmethane diisocynate (MDI). The structure was identified by IR, 1H NMR and 13C NMR. The epoxy resin was cured with a mixture of 4,4′‐diaminodiphenylmethane and 1.3‐phenylenediamine (molar ratio 6:4) as a hardener. Curing behaviour of the epoxy resin with hardener was examined by differential scanning calorimetry (DSC). It was found that onset and peak temperatures of the exothermic cure reaction of the EPCDAMDI system were lower than those of the 2‐cresol novolac‐type epoxy resin (EOCN) system, and the rate constant (k) of the cure reaction at 100° C of the former system was about six times larger than that of the latter system and was the same as that of 2‐cresol resol‐type epoxy resin (EOCDA). Viscoelastic properties of the cured resin were studied by dynamic mechanical analysis. It was found that the tan δ of the EPCDAMDI system had two peaks and the lower temperature peak disappeared after further curing over 200° C.

Structure and viscoelastic properties of epoxy resins prepared from o‐cresol novolacs

AbstractThe relation between the structure and viscoelastic properties of the epoxy resins prepared from o‐cresol novolacs was studied. Our model epoxy resins were two kinds of epoxy compounds synthesized from three‐nuclei and four‐nuclei o‐cresol novolacs. In addition to these models, a commercially available o‐cresol novolac‐type epoxy resin was also studied. Each of the three epoxy compounds was cured with one of three kinds of novolacs, which were starting materials of the above‐mentioned epoxy resins. Characteristic properties of the cured resins, such as glass transition temperature (Tg), average molecular weight between crosslinking points (M¯c), and front factor (ϕ) were obtained. It was concluded that the number of functional groups contained in the curing system almost dominated the viscoelastic properties of the cured resins.

酸環境下におけるＢＭＣの劣化に関する研究

The aim of this study was to develop a new BMC (Bulk Molding Compound) with low molding shrinkage and high acid resistance. The resin system used in this study was a novolac type epoxy resin with low shrink additive and the reinforcements used were glass, carbon and aramid fibers.Firstly the mold shrinkage, the heat distortion temperature and the electric resistance of BMC were measured as the functional properties. The immersion test was carried out in a bath with a mixed solution of 25wt%H2SO4 and 7.5wt% HNO3 at 65°C up to 3000hr. The weight change and the reduction of mechanical properties were measured in order to examine the degradation mechanism of BMC.It is concluded that Hybrid BMC which are reinforced by glass, carbon and aramid fibers show the excellent functional properties. The acid resistance of BMC developed in this study is much higher than that of BMC in which the matrix is the epoxy resin with high acid resistance.