Modified Novolac Resin Research Articles

Fast curing phthalonitrile modified novolac resin: Synthesis, curing study and preparation of carbon and glass fibric composites

Phthalonitrile modified novolac (PNN) was synthesized in aim to develop a fast-curing resin for hot-pressing processing and characterized by NMR to confirm a full substitution of hydroxyl groups with phthalonitrile. PNN blended with high amounts (10–50 wt%) of the amine curing agents have been investigated by DSC, FT-IR spectroscopy and TGA, which revealed T5% = 420 °C. Curing times for the compositions were 4–16 min at 240 °C. The 50 min post-curing cycle for FRPs was selected based on DMA. Composites were fabricated via hot-pressing of prepregs including post-curing at 280 °C (providing Tg > 340 °C) in total of 60 min, which is the fastest curing cycle for thermosetting resins developed for applications up to 300 °C. Carbon and glass fabric reinforced polymers (CFRP and GFRP) were obtained by the developed program yielding integral composites with high mechanical properties and great heat resistance. Interlaminar shear strengths of the CFRP were up to 31 MPa and up to 70 MPa for GFRP. The latter which demonstrated retention of 75% of initial ILLS values after dwelling for 200 h at 300 °C. Thus, a new fast-processing phthalonitrile resin was developed for application in electric transport, aerospace and heat-resistant insulation.

Novolac-based microcapsules containing isocyanate reagents for self-healing applications

Microcapsules (MCs) containing isocyanate compounds for use as self-healing materials in waterborne polyurethane coatings have been synthesized, in the presence of modified Novolac resins. With modification of Novolac resin, it is succeeded partial or total protection (Benzylation and Acetylation) of its hydroxyl groups. The idea here is to use a protected Novolac resin as the organic substrate for the encapsulation of the less reactive Isophorone isocyanate (IPDI) while the more reactive one, Methylene diphenyl diisocyanate (MDI), is used for the shell formation. Based on that strategy microcapsules of different morphologies and sizes were obtained, depending on the agitation conditions, as revealed using SEM and optical microscopy. Selective extraction was performed to determine the amount of the less reactive isocyanate (IPDI) stored inside the capsules through FTIR-ATR spectroscopy and isocyanate titration as well as the stability of IPDI inside the capsules over time. As determined, microcapsules based on Acetyl-modified Novolac resin encapsulated 96 wt% of IPDI monomer; this amount is about five and ten times higher than that encapsulated in MCs based on by Benzyl-modified Novolac resin or unprotected Novolac resin, respectively. At the same time, MCs based on Acetyl-modified Novolac resin were stable, maintaining approximately 80 % of the initial isocyanate content after two months of storage under inert conditions. Finally, the self-healing ability of the microcapsules was tested by adding selected IPDI-loaded microcapsules in waterborne polyurethane dispersions. It was proven that the Acetyl-modified Novolac-based MCs showed efficient healing behavior, in the absence of any catalyst, on the polyurethanes’ surfaces when scratched artificially.

Effect of modified novolac resins on the physical properties and friction performance of railway brake blocks

Formulating or designing friction materials is a very complex endeavor because of the difficulty of characterizing all the effects and interactions of each of the various constituents of a given friction product. Within this work the effect of three differently modified phenolic resins on the mechanical properties and the friction performance of the finished brake blocks was studied. The selected modifications altered the B-transformation time, which refers to the time needed for a resin to cure and it is an important parameter regarding productivity and homogeneous resin dispersion throughout the finished product. The characterization work entailed the physical and mechanical analysis of the blocks (hardness, density and compression tests). A full-scale inertia dynamometer was used for the friction performance analysis. Materials based on resins with medium and short B-transformation times showed similar results. Only the material using the resin with longest B-transformation time showed significant differences in average friction level, speed fade and instantaneous friction evolution. Furthermore, this material revealed metallic inclusions on the surface, commonly known as metal pick-up. All variables considered to be constant, the metal pick-up might be linked to this particular resin modification, although no significant differences were found in the plateau microstructure studied by SEM.

Carbon Fabric Reinforced Addition-Cure Phenolic Resins Based on Propargyl and Allyl Ether Functional Novolac Produced

Composites consisting of propargyl- and allyl/propargyl- modified novolac resins and carbon fabric were obtained by the vacuum infusion molding process. It was established that the presence of potassium cations remaining after the synthesis increase the resin melt viscosity, and acid washing is needed to obtain resins suitable for cost-effective injection techniques of composite fabrication. The mechanical properties of all composites such as compressive strength, tensile strength, in plane shear strength, and interlaminar shear strength were determined at 25, 200 and 230 °С. The carbon fiber reinforced plastics (CFRPs) retained their mechanical properties at temperatures up to 200 °C. It was shown that the use of the obtained allyl-containing polymer matrices improved mechanical properties and increased the thermal stability of the CFRPs in comparison with the propargylated novolac matrices. The composite material with novolac matrices modified by 18% propargyl and 23% allyl groups retains only up to 70% of the initial interlaminar shear strength values at 230 °C which corresponds to the data of the dynamic mechanical analysis of neat cured resins.

Fabrication of high thermal stable cured novolac/Cloisite 30B nanocomposites by chemical modification of resin structure

Cloisite 30B as a modified kind of nanoclay was utilized for the formation of 3D network based on novolac resin with high thermal stable properties. Two types of phenolic resins including neat novolac (NR) and modified novolac resin were used to create a compatible matrix with nanoclay. For this purpose, NR modified with (3‐chloropropyl)triethoxysilane (CPTES) to form SiNR. For improvement of thermal behaviors, Cloisite 30B was dispersed in matrix via ultrasonic waves and cured with hexamethylenetetramine (HMTA) to form 3D network. X‐ray diffraction (XRD) analysis was used to measure the d‐spacing in intercalated systems and results indicated the optimum amount of clay for appropriate thermal properties. Investigation of the thermal properties of the samples by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the presence of Cloisite 30B in matrix resulted in much higher thermal stability and char yield with respect to modification of novolac resin originated from formation of 3D Si–O–Si network. Also, cured modified resin and its nanocomposites showed much higher thermal stability than cured NR and its nanocomposites. Such nanocomposite materials with high thermal stability have potential applications in advanced fields such electronic, industrial molds, coatings, adhesives, and aerospace composites.

A new strategy for the synthesis of modified novolac resin and its polymer/clay nanocomposite

A new strategy for the synthesis of modified novolac resin and its polymer/clay nanocomposite

Incorporation of graphene oxide nanolayers into thermally stable hybrid composites of thermosetting resins by combination of curing and sol–gel reactions

Three different hybrid composites with high thermal stability and char residue were prepared from incorporation of tetraethyl orthosilicate (TEOS)-modified epoxy resin (MER), (3-glycidyloxypropyl) trimethoxysilane (GPTMS)-modified novolac resin (MNR), epoxidized novolac resin (ENR), and also furfuryl alcohol- and (3-aminopropyl) trimethoxysilane (APTMS)-modified graphene oxide (GFS) into silica/siloxane network by a sol–gel reaction. The first hybrid was composed from ENR, MNR, and GFS. The second type was prepared from MER, MNR, and GFS. The third type was prepared from MER, novolac resin, and GFS in the presence of triphenylphosphine (TPP). Results of FT-IR and XPS confirmed successful modification of epoxy and novolac resins and also functionalization of GO with furfuryl alcohol and APTMS. Results of TGA showed that GFS reaches to char residue of 37.3% at 600 °C. Char residues of 44.4, 44.0, and 34.2% were obtained for the first, second, and third hybrid composites without GFS loading. Addition of 1 wt% of GFS into the hybrid networks results in increase of char residues to 56.3, 50.0, and 34.7%, respectively. So, the first hybrid composite reaches to the highest char residue at 600 °C. These hybrid composites showed degradation temperature of 416.4, 434.5, and 424.8 °C.

Preparation of organic-inorganic hybrid nanocomposites from chemically modified epoxy and novolac resins and silica-attached carbon nanotubes by sol-gel process: Investigation of thermal degradation and stability

Abstract Hear, three hybrid composites with high char yield and thermal stability were prepared form tetraethyl orthosilicate (TEOS)-modified epoxy resin (MER), (3-glycidyloxypropyl) trimethoxysilane (GPTES)-modified novolac resin (MNR), epoxidized novolac resin (ENR), and silica-grafted carbon nanotube (SFCNT) by a sol-gel method. The first class was prepared from MER and SFCNT. The second class was prepared from MER, MNR, and SFCNT. And the third class was prepared from MNR, ENR, and SFCNT. TEOS was used as covalent coupling agent in the sol-gel process. Results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed successful modification of epoxy and novolac resins, modification of silica nanoparticles with (3-Aminopropyl)triethoxysilane (APTES), and also functionalization of CNT with amine-modified silica nanoparticles. Results of thermogravimetric analysis confirmed that the hybrid composite containing 4 wt% of SFCNT, MNR, and ENR shows the highest char yield of 58.4%. The hybrid composite containing 4 wt% of SFCNT and MER shows the highest degradation temperature of 442.7 °C. Finally, the hybrid composite formed from 4 wt% of SFCNT, MER, and MNR shows degradation temperature of 439.0 °C and char yield of 47.2%. Microscopic images and X-ray diffraction results confirmed attachment of silica particles at the surface of CNT by chemical bonding.

The effects of silicon and ferrocene on the char formation of modified novolac resin with high char yield

Novolac resin (NR) modified with 1, 1’-bis(dimethylsilyl) ferrocene (FeNR) was synthesized. The thermal properties and structural evolution of cured FeNR were studied to analyze the reason for high char yield of cured FeNR. Thermal stability of cured FeNR has been improved, and the char yield of cured FeNR at 800 °C can be increased by 8.82% in comparison to that of cured NR. The results show that silicon atom and ferrocene contribute to the high char yield of cured FeNR. On one hand, the Si-O structure can be kept in the system during the whole pyrolysis process, which could help to reduce the weight loss. On the other hand, introducing ferrocene into novolac resin promotes the graphitization degree and graphite crystallites of pyrolyzed resins. Moreover, the pyrolyzed products possess different magnetic properties owing to the formation of iron nanocrystal at 800 °C and Fe5Si3 nanocrystal at 1200 °C.

Nanohybrids of novolac phenolic resin and carbon nanotube-containing silica network

Two different methods were used for preparation of novolac phenolic resin nanohybrids containing carbon nanotube and silica/siloxane moieties. Oxidized carbon nanotube was modified with furfuryl alcohol and 3-(trimethoxysilyl)propyl methacrylate (MPS) to obtain CNTFASi. Carbon nanotube xerogel (CNTFAX) was then obtained by incorporation of CNTFASi into silica/siloxane network by using tetraethyl orthosilicate (TEOS). The first nanohybrid was prepared by addition of CNTFAX into the novolac phenolic resin matrix. Incorporation of (3-glycidyloxypropyl) trimethoxysilane-modified novolac phenolic resin, CNTFASi, and TEOS into silica/siloxane network results in the second nanohybrid. These two types of nanohybrids were compared from the viewpoint of thermal properties. Successful modification of carbon nanotube and novolac phenolic resin was proved by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis results. Molar ratios of furfuryl alcohol in CNTFA and MPS in CNTFASi are 597 and 108 μmol g−1, respectively. Formation of silica/siloxane xerogel network in CNTFAX was evaluated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results showed that nanotubes with smooth surface are incorporated into the spongy silica/siloxane matrix. Char residue of CR is decreased from 58.2 to 50.6% by the addition of only 4 mass% of CNTFAX. Finally, char residue of 71.1% for the nanohybrid of modified novolac resin with 4 mass% of CNTFASi shows 12.8% increase in char residue with respect to the neat cured resin.

Effect of Novolac Resin and Modified Novolac Resin on Mechanical Properties of Carbon Fiber/Epoxy Composites

ABSTRACTThe effects of novolac resin (NR) and modified novolac resin (MNR) on the stiffness and toughness of the carbon fiber (CF)/epoxy composites were studied when using these two kinds of modifiers with different physical and chemical performance. The results show that both NR and MNR are excellent toughening agents for the CF/epoxy composites, and the composites treated with MNR present better toughness than that of NR. However, the stiffness of the composites is almost unchanged when adding MNR. The mechanisms were analyzed by fracture studies using scanning electron microscopy and the decrease of cross‐link density caused by MNR was deduced to the toughening effects.

Thermal stability and thermal degradation kinetic study of bismaleimide-epoxy modified novolac resin

The thermal stability of bismaleimide and epoxy modified novolac-type phenolic resin is investigated. Fourier transform infrared spectroscopy results confirm that the phenolic resin is interacted with bismaleimide and epoxy groups. The thermo gravimetric analysis results indicate that the modified resin exhibits better thermal stability than the virgin novolac resin. It is also found that the thermal degradation process can be divided into two stages. The nonisothermal degradation behavior of the modified novolac resin is then studied by multi-stage model-fitting kinetic method and Kissinger–Akahira–Sunose (KAS) model-free method. The two-stage model uses two separated peaks to simulate the DTG curve and the final model predicts the mass loss fraction accurately. It is able to describe the two-stage degradation reaction process and produce two equations corresponding to the two-stage degradation mechanism. The KAS model results in the dependence of activation energy of degradation on mass loss. The activation energy history of degradation also indicates the change of reaction mechanisms.

Degradation kinetics of functionalized novolac resins

We report the relationships between the degradation behaviors (i.e. the degradation kinetics, degradation activation energy, weight loss conversion, and char formation) and the structure features in three modified novolac resins bearing different curable functional groups and aromatic units i.e. Carbonyl phenyl azo novolac resin (CPAN) , 4-(4-hydroxyphenyl azo) benzyl ester novolac resin (HPDEN) and Carbonyl phenyl 4-(4-hydroxyphenyl azo) benzyl ester novolac resin (CHABN) . These modifications enhanced the thermal stability of the cured novolac resins by delaying the decomposition temperature up to 30–100 °C and produced prominent residue char yield up to 68% (CPAN), 56% (HPDEN) and 64% (CHABN), respectively. The two heavily cross-linked samples, CPAN and CHABN displayed even higher Ea than HPDEN. All modified novolacs displayed much higher decomposition activation energy (over 237 KJ/mol*K) compared with the generic phenolic (PN).

Preparation and properties of carbon microbeads by pyrolysis of N-phenyl maleimide modified novolac resin

Carbon microbeads were prepared by direct pyrolysis of N-phenyl maleimide modified novolac resin microbeads, and the properties of the carbon microbeads were studied in this paper. Thermal behavior of the resin microbeads was studied by TGA, FTIR and elemental analysis. The carbon microbeads were characterized using SEM, XRD and particle size analyzer. In addition, electrochemical performance of the carbon microbeads was studied. Results show that the resin microbeads possess excellent thermal properties. The pyrolysis products of the resin microbeads are made up of carbon microbeads with an amorphous structure. The carbon microbeads have high sphericity and smooth surface, and possess the properties including high compressive strength, high capacity and good cycling performance.

Structure characteristics contributing to flame retardancy in diazo modified novolac resins

The physical characteristics of two modified novolac resins (carbonyl phenyl azo novolac resin; CPAN and 4-(4-hydroxyphenyl azo) benzyl ester novolac resin; HPDEN) bearing nitrogen and aromatic functional groups by diazo-coupling or esterification in the branch structure of phenol novolac resin were examined. Presence of the modifiers raised the phenolic decomposition temperature (5% weight loss) from 300 °C (pure Phenolic) to 330 °C and 380 °C, while the char residue increased from 45% to 56% and 68%, respectively. The kinetics for thermal degradation energies ( E a) also rose from 151 kJ/mol K to 254 kJ/mol K (CPAN) and 273 kJ/mol K (HPDEN). The retarded decomposition kinetics is attributed both to the increase of crosslink densities and high aromatic content in the derivative resins. On the other hand, the diazo-coupling or phenyl diazenyl ester produces non-combustible gases (N 2, CO 2 and CO) during formation of aromatic char which dilute the ambient oxygen gas. Both the production of gases and the retarded kinetics due to cross-linking are definitive for the improved flame resistance.

Morphology transition of bismaleimide‐modified novolac resin

AbstractThe bismaleimide (BMI)‐modified novolac resin was synthesized by allylation of the novolac resin and its “Ene” reaction with BMI. The reactions were monitored by Fourier transform infrared analysis (FTIR). The morphology of the BMI‐modified novolac resin changed with degree of allylation (i.e., the amount of BMI used). On the basis of the studies done by dynamical mechanical analysis (DMA), differential scanning calorimetry (DSC), and field emission scanning electron microscopy (FE‐SEM), it was found that when the degree of allylation increased from 48 to 59%, the resin changed from a single‐phase structure to a two‐phase structure. From the research by thermogravimetric analysis (TGA) and DMA, it was found that the higher allyl‐content (when > 48%) caused a decrease of the thermal properties and mechanical properties of the resultant resin. The BMI‐modified allyl novolac resin with 48% degree of allylation has the best thermal properties and the highest dynamic modulus in the current research. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 76–83, 2006

Novel phosphorilated flame retardant thermosets: epoxy–benzoxazine–novolac systems

Modified novolac resins with benzoxazine rings were prepared and cured with isobutyl bis(glycidylpropylether) phosphine oxide (IHPOGly) as crosslinking agent. Their curing behaviour using different epoxy/phenol molar ratios and with or without triphenylphosphine as catalyst was studied. Two different phenolic groups react with oxirane ring, those initially free and those generated after benzoxazine ring opening. In absence of catalyst, it is not possible to distinguish between them. However, for the catalyzed curing of the highest modification degree benzoxazine based novolac resin is possible to distinguish both reactions. The thermal, thermomechanical and flame retardant properties of the cured materials were measured. V–O materials were obtained when the resins were tested for ignition resistance with the UL-94 test.

Acetyl‐capped paraformaldehyde as crosslinking agent for BMI‐modified novolac resin for resin transfer molding

AbstractParaformaldehyde was end‐capped with acetyl groups and was applied as a crosslinking agent for a bismaleimide (BMI)‐modified novolac resin system. The processibility of the resin system containing 5 wt % crosslinking agent still met the need for resin transfer molding (RTM), whereas the thermomechanical properties of crosslinked resin improved significantly. The composites based on the resin system and woven glass fabric showed better flexural strength, modulus, and higher retention rates at 200 and 300°C than that based on a resin system without acetyl‐capped paraformaldehyde. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1265–1271, 2002

Friction and wear of friction materials containing two different phenolic resins reinforced with aramid pulp

Friction and wear characteristics of automotive friction materials containing two different phenolic resins (a straight novolac resin and a modified novolac resin) were investigated using a pad-on-disk type friction tester. Six different friction materials with different relative amounts of the phenolic resins and aramid pulp were manufactured and tested. Two different test modes were employed to examine the friction characteristics concerning accumulated thermal history (a constant initial temperature test: test mode I) and friction heat (a constant interval test: test mode II). Friction characteristics such as friction stability and wear resistance were changed significantly according to the type of phenolic resins and to the relative amount of the resin and aramid pulp. Friction materials with the modified novolac resin showed better friction stability than those with the unmodified novolac resin. In particular, the friction materials that were reinforced with 10 vol.% of aramid pulp showed substantial improvement on friction stability regardless of the resin type. However, the friction materials with the modified resin showed significant reduction in wear resistance.

Polymerization of unsaturated novolac ester

THE valuable properties of phenol-formaldehyde resins have been known for a long time and account for their wide application in the various branches of industry. However, certain shortcomings of these resins necessitate their chemical modification and numerous papers deal with this problem (see e.g. [1]). The purpose of this paper was to obtain a modified novolac resin containing double bonds, owing to which the resin should be made capable of hardening during heating without using additives to promote this process. Thus, with resin hardening according to the polymerization mechanism, separation of low-molecular-weight products can be avoided. These form during hardening by the polycondensation mechanism, disturbing the solid structure and reducing the mechanical strength of specimens. I t can be expected at the same time that shrinkage, during polymerization of such modefied resins, will be very low which is characteristic of the polymerization of oligomers [2]. We modified novolae resin by esterification with acid chloride of methacrylic acid (ACMA) of the phenol hydroxyl resin groups according to the scheme: