Benzoxazine monomers based on aromatic diamines and investigation of their polymerization by rheological and thermal methods

In the present article with the aim to find new polybenzoxazines with improved thermal properties, new benzoxazine monomers based on phenol and the following aromatic diamines were synthesized: 3,4′-oxydianiline (P-3,4′oda); o-tolidine (P-ot); m-tolidine (P-mt) and 4,4′-(1,3-phenylenedioxy)dianiline (P-tper) and their comparison with the previously known benzoxazines based on 4,4′-diaminodiphenylmethane (P-ddm); 4,4′-oxydianiline (P-4,4′-oda) and 2,2-Bis[4-(4-aminophenoxy)phenyl]propane (P-bapp). The dependence of the thermal and rheological characteristics on the structure of benzoxazine monomers based on various diamines was estimated and possible methods for their processing were identified. All the polybenzoxazines obtained in this work have high char yield and reduced flammability. It was found that the structure of the diamine can have a fundamental effect on both the rheological properties and heat resistance of polybenzoxazines. The benzoxazine monomers P-ddm, P-tper and P-4,4′oda retain viscosity up to 1 Pa s. at 110°C for 2 h, the P-tper monomer with a resorcinol bridge has about five times lower viscosity compared to the P-bapp monomer with a bisphenol A bridge. Polybenzoxazines based on the monomers P-ddm, P-mt, P-bapp and P-tper show excellent thermal stability with a temperature of 10% weight loss above 400°C. In particular, T_g of P-3,4′oda and P-mt monomers is relatively high (202 and 239°C, respectively), while P-ot's is unusually low (115°C), which may be caused by the specific effect of the substituents in the aromatic ring of the amine and their position.     

Synthesis of a novel phosphorus‐containing dicyclopentadiene novolac hardener and its cured epoxy resin with improved thermal stability and flame retardancy

A novel phosphorus‐containing dicyclopentadiene novolac (DCPD‐DOPO) curing agent for epoxy resins, was prepared from 9,10‐dihydro‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and n‐butylated dicyclopentadiene phenolic resin (DCPD‐E). The chemical structure of the obtained DCPD‐DOPO was characterized with FTIR, ¹H NMR and ³¹P NMR, and its molecular weight was determined by gel permeation chromatography. The flame retardancy and thermal properties of diglycidyl ether bisphenol A (DGEBA) epoxy resin cured with DCPD‐DOPO or the mixture of DCPD‐DOPO and bisphenol A‐formaldehyde Novolac resin 720 (NPEH720) were studied by limiting oxygen index (LOI), UL 94 vertical test and cone calorimeter (CCT), and differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. It is found that the DCPD‐DOPO cured epoxy resin possess a LOI value of 31.6% and achieves the UL 94 V‐0 rating, while its glass transition temperature (T_g) is a bit lower (133 °C). The T_g of epoxy resin cured by the mixture of DCPD‐DOPO and NPEH720 increases to 137 °C or above, and the UL 94 V‐0 rating can still be maintained although the LOI decreases slightly. The CCT test results demonstrated that the peak heat release rate and total heat release of the epoxy resin cured by the mixture of DCPD‐DOPO and NPEH720 decrease significantly compared with the values of the epoxy resin cured by NPEH720. Moreover, the curing reaction kinetics of the epoxy resin cured by DCPD‐DOPO, NPEH720 or their mixture was studied by DSC. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44599.     

Influence of methacryl polyhedral oligomeric silsesquioxane on the thermal and mechanical properties of methylsilicone resin

A methacryl polyhedral oligomeric silsesquioxane (POSS)‐reinforced methylsilicone resin was prepared in this work. The structures of the obtained products were confirmed with Fourier transform infrared and atomic force microscopy. The influence of methacryl‐POSS on the thermal behavior of the methylsilicone resin was studied by thermogravimetric analysis and isothermal thermogravimetric analysis. The results showed that the thermal stability of the methylsilicone resin was improved, and the degree of thermooxidative degradation was lowered; this was due to the retardation of polymer chain motion and the formation of a protective layer of SiO₂. The interlaminar shear strength and flexural strength of quartz fiber/methylsilicone resin composites were tested to determine the effects of methacryl‐POSS on the mechanical properties of methylsilicone resin. The results revealed that the mechanical properties of the methylsilicone composites also increased obviously after the incorporation of methacryl‐POSS because of the increase in the cure degree and rigidity of the resin. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Welding and reprocessing of disulfide-containing thermoset epoxy resin exhibiting behavior reminiscent of a thermoplastic

Thermoset resins generally lack the ability to be welded or reprocessed like thermoplastics because of their cross-links. Increasing use of fiber-reinforced composites in large structures, such as rail and aircraft parts, as well as wind blades, calls for better ways to repair damages and be compliant with recycling and environmental regulations. In this article, an epoxy resin containing disulfide bonds was prepared and characterized by Fourier transform infrared, ¹H-NMR, and ¹³C-NMR. The dynamic nature of the disulfide bonds allowed the cured epoxy resin to be welded like thermoplastics, and the welded joints had strength that matched the resin's cohesive strength. It could also be reprocessed with 90% tensile strength retention after three reprocessing cycles, allowing the parts to be repaired instead of being replaced. In addition, the cured resin was chemically degradable in a thiol-based solvent, allowing it to be recycled in closed-loop processes. Moreover, the cured epoxy resin showed a glass transition temperature of 116°C, demonstrating its potential for advanced composite applications.     

Development of high Tg epoxy resin and mechanical properties of its fiber‐reinforced composites

A new epoxy resin with high glass transition temperature (T_g) (～ 180°C) and a viscosity low enough for infiltration into dry reinforcements at 40°C was developed for the vacuum‐assisted resin transfer molding process. To study the curing behavior and viscosity, several blends were formulated using multifunctional resin, aromatic hardener, and reactive diluents. Effects of these components on the viscosity and T_g were investigated by thermomechanical analysis, dynamic scanning calorimetry, and rheometer. Experimental results showed that a liquid aromatic hardener and multifunctional epoxy resin should be used to decrease the viscosity to <1 Pa·s at 40°C. Moreover, the addition of a proper reactive diluent decreased the viscosity and simultaneously minimized the deterioration of T_g. Mechanical properties of the composite produced with the optimized blend were evaluated at both room‐temperature and high‐temperature conditions. According to the results, the composite showed comparable mechanical properties with that of the current commercial resin. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal degradation analysis of the isocyanate polyhedral oligomeric silsequioxanes (POSS)/sulfone epoxy nanocomposite

The sulfone epoxy (SEP)/polyhedral oligomeric silsesquioxane (POSS) nanocomposite contains bulky POSS side chains was studied in this research. Its glass transition temperature (T_g) decreases with the bulky POSS content, indicating that the bulky POSS side chains could not only generate the oligomers but also interrupt the network architectures of SEP. Homogeneous and uniform dispersion of POSS in SEP matrix can be obtained through the carbamate/oxazolidon covalent linkage, which is evidenced by scanning electron microscopy. The increasing concentration of POSS into SEP exhibits an increase of char yield in the nanocomposites, indicating that the POSS segments provide the antithermal‐oxidation effect for SEP/POSS, thereby inhibiting thermal degradation under open air at high temperatures. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A new Schiff base epoxy oligomer resin: Synthesis,characterization, and thermal decomposition kinetics

Oligo{2,2′‐{1,4‐phenylenebis[nitrilomethylylidene]}bis(6‐methoxyphenol)} (OPNMMP) was synthesized from o‐vanillin and p‐phenylene diamine by oxidative polycondensation with NaOCl in an aqueous alkaline. Then, a new Schiff Base epoxy oligomer resin, OPNMMP–epichlorohydrine (EPC), was produced with EPC. The structures of the resulting compounds were confirmed by Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, ¹H‐NMR, and ¹³C‐NMR. Further characterization processes were preformed by thermogravimetry (TG)–differential thermal analysis, gel permeation chromatography, and solubility testing. Also, the kinetics of the thermal decomposition of OPNMMP–EPC were investigated by thermogravimetric analysis. The TG curves showed that the thermal decomposition of OPNMMP–EPC occurred in one stage. The kinetic parameters related to the decomposition kinetics of OPNMMP–EPC were obtained from TG curves with the following methods: Friedman, Flynn–Wall–Ozawa, Kissinger, invariant kinetic parameter, and Coats–Redfern (CR), under an N₂ dynamic atmosphere and different heating rates (5, 10, 15, and 20°C/min). The mechanism function and pre‐exponential factor were also determined by a master plots method. The apparent activation energies of the thermal decomposition were calculated from these methods for OPNMMP–EPC. The analysis of the results obtained by the CR and master plots methods showed that the decomposition mechanism of OPNMMP–EPC in N₂ was a deceleration‐type mechanism. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and properties of methyl hexahydrophthalic anhydride‐cured fluorinated epoxy resin 2,2‐bisphenol hexafluoropropane diglycidyl ether

The fluorinated epoxy resin, 2,2‐bisphenol hexafluoropropane diglycidyl ether (DGEBHF) was synthesized through a two‐step procedure, and the chemical structure was confirmed by ¹H n uclear magnetic resonance (NMR), ¹³C NMR, and Fourier transform infrared (FTIR) spectra. Moreover, DGEBHF was thermally cured with methyl hexahydrophthalic anhydride (MHHPA). The results clearly indicated that the cured DGEBHF/MHHPA exhibited higher glass transition temperature (T_g 147°C) and thermal decomposition temperature at 5% weight loss (T₅ 372°C) than those (T_g 131.2°C; T₅ 362°C) of diglycidyl ether of bisphenol A (DGEBA)/MHHPA. In addition, the incorporation of bis‐trifluoromethyl groups led to enhanced dielectric properties with lower dielectric constant (D_k 2.93) of DGEBHF/MHHPA compared with cured DGEBA resins (D_k 3.25). The cured fluorinated epoxy resin also gave lower water absorption measured in two methods relative to its nonfluorinated counterparts. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2801–2808, 2013     

Synthesis and characterization of diamide–diimide–diamines based on p‐amino benzoic acid and their curing and thermal behavior with epoxy blends containing phosphorus/silicon in the main chain

Diimide–diacid ( I ) having an imide group in its rigid structure was synthesized by the refluxing of 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride [4,4′‐carbonyldiphthalic anhydride (BTDA)] and p‐amino benzoic acid in a mixture of acetic acid and pyridine (3 : 2 v/v). The chloroderivative of the diacid ( I ) was synthesized by its reaction with thionyl chloride, this was followed by condensation with different diamines with phenyl, naphthyl, ether, sulfide, and cardo groups to generate a series of diamide–diimide–diamines (DADIDAs). The resultant DADIDAs were characterized by elemental analysis and spectroscopic techniques, namely, Fourier transform infrared spectroscopy and NMR spectroscopy, and were used as epoxy curing agents to impart flame retardancy to the epoxy system. Two epoxy blends (designated as ES and EP) were prepared by the homogeneous mixing of diglycidyl ether of bisphenol A (DGEBA) with 1,3‐bis(3‐glycidyloxypropyl)tetramethyl disiloxane and DGEBA with tris(glycidyloxy)phosphine oxide: each in a ratio of 3 : 2 respectively. The synergistic effect of phosphorus/silicon with nitrogen on the thermal properties of the modified epoxy system was studied. The curing behavior of the epoxy resins formulated by the reaction of stoichiometric amounts of ES/EP with the synthesized DADIDAs were determined by differential scanning calorimetry, and the thermal stabilities of the cured epoxies were evaluated by thermogravimetric analyses (TGAs) under nitrogen and air. TGA indicated that the residual weight percentage of polymers at 800°C was in the range 36.4–60.0 in nitrogen, and in air, it was up to 6.5. However, the major loss in weight in air occurred at elevated temperature; this demonstrated their potential use as flame‐retardant epoxy systems for electronic/electrical encapsulants. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of a novel curing agent containing organophosphorus and its application in flame‐retarded epoxy resins

A novel amine‐terminated and organophosphorus‐containing compound m‐aminophenylene phenyl phosphine oxide oligomer (APPPOO) was synthesized and used as curing and flame‐retarding agent for epoxy resins. Its chemical structure was characterized by Fourier transform infrared (FTIR) spectroscopy, ¹H nuclear magnetic resonance (¹H NMR), ¹³C nuclear magnetic resonance, and ³¹P nuclear magnetic resonance. The flame‐retardant properties, combusting performances, and thermal degradation behaviors of the cured epoxy resins were investigated by limiting oxygen index (LOI), vertical burning test (UL‐94), cone calorimeter test, and thermogravimetric analysis. The EPO/APPPOO thermosets passed V‐1 rating with the thickness of 3.0 mm and the LOI value reached 34.8%. The thermosets could pass V‐2 rating when the thickness of the samples was 1.6 mm. The cone calorimeter test demonstrated that the parameters of EPO/APPPOO thermosets including heat release rate and total heat release significantly decreased compared with EPO/PDA thermosets. Scanning electron microscopy revealed that the incorporation of APPPOO into epoxy resins obviously accelerated the formation of the compact and stronger char layer to improve flame‐retardant properties of the cured epoxy resins during combustion. The mechanical properties and water resistance of the cured epoxy resins were also measured. After the water‐resistance test, EPO/APPPOO thermosets still remained excellent flame retardant and the water uptake was only 0.4%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41159.     

Synthesis and properties of phthalonitrile terminated polyaryl ether nitrile containing fluorene group

A series of phthalonitrile terminated polyaryl ether nitrile oligomers containing fluorene group (BPPENs) were synthesized and cured in the presence of bis[4‐(4‐aminophenoxy)phenyl]sulfone. Additionally, the quartz fiber reinforced composites were prepared by hot‐pressing process. The structure of oligomers was characterized by ¹H‐NMR and GPC. The curing behavior of BPPENs was studied by DSC, IR, and rheological tests in detail. Thermal stability and mechanical properties were also investigated. The results showed that the oligomers showed excellent solubility. BPPENs could be dissolved in common solvents at ambient temperature. TGA and DMA results showed that the cured polymer and composites possessed excellent thermal properties with high residual weight of 72.4% at 1000 °C and 5% thermal degradation temperature (T_5%) of 548 °C under inert atmosphere. The bending strength of quartz fiber reinforced composites was about 500 MPa, exhibiting good mechanical property. The products could be used as high performance polymers or a modifier for heat‐resistant resins. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46606.     

Synthesis of restorative microcapsules having vinyl ester healing medicine for hybrid resin/modified carbon fiber self-healing composites

In this study, we aimed to synthesize restorative microcapsules using aminopropyl triethoxy silane through a combination of both microemulsions with a sol–gel technique and vinyl ester resin used as a healing component. The characteristic features of the microcapsules were analyzed by FTIR, XRD, and SEM and confirmed by the formation of core-shell microspheres with desired properties. The fabricated core-shell microspheres were reinforced into a hybrid resin (vinyl ester (80): epoxy (20)/silane modified carbon fiber composites) using the hand lay-up method. The effect of the microspheres on the mechanical and self-healing properties of composites was investigated. The mechanical test results showed a significant improvement in the flexural and impact strength by approximately 23% and 30%, respectively. The healing property was observed using the flexural test and the results indicated that the recovered strength almost 74% of the composites after initial damage was due to the healing medicine released from the broken portion of the core-shell microspheres that filled and cured the cracked area of the composites.     

Cure behavior and thermal stability analysis of multiwalled carbon nanotube/epoxy resin nanocomposites

As‐received multiwalled carbon nanotubes (MWCNTs) were first treated by a 3 : 1 (v/v) mixture of concentrated H₂SO₄/HNO₃ and further functionalized by ethylenediamine/dicyclohexylcarbodiimide/tetrahydrofuran solution. MWCNT/epoxy nanocomposites were prepared. Their cure behaviors were investigated by dynamic differential scanning calorimetry. Quantitative analysis of the activation energy as a function of the degree of curing was carried out by the Flynn‐Wall‐Ozawa method. The fitted multiple regression equations for values of the activation energy of different systems were obtained. MWCNTs have the retardation effect on the cure reaction of epoxy resin, while the functional groups on the surface of amine‐modified MWCNTs could accelerate the cure reactions. Thermal stability was studied by thermogravimetric analysis. The filling of amine‐modified MWCNTs is beneficial to lower the cure activation energy and improve thermal stability of the nanocomposite. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and performance of a thermosetting resin: Acrylated epoxidized soybean oil curing with a rosin‐based acrylamide

A synthesized rosin‐based polymeric monomer, N‐dehydroabietic acrylamide (DHA‐AM), was introduced into an acrylated epoxidized soybean oil (AESO)/DHA‐AM system to afford a thermosetting resin through thermocuring. Different molar ratios of the thermosetting AESO/DHA‐AM samples were obtained through curing in the presence of an initiator, and the curing processes of the AESO/DHA‐AM systems were evaluated by differential scanning calorimetry. The structures and performances of the resulting thermosets were characterized by Fourier transform infrared spectroscopy, dynamic mechanical analysis, elemental analysis, thermogravimetric analysis, and contact angle (θ) analysis. The analyses showed that with increasing content of DHA‐AM introduced into the copolymer, the storage modulus, glass‐transition temperature, thermal stability, and θ values of the cured samples all increased. Moreover, the copolymers changed from hydrophilic materials to hydrophobic materials. The results also demonstrate that the rosin acid derivatives showed comparable properties to those of reported petroleum‐based rigid compounds for the preparation of soybean‐oil‐based thermosets. The presence of DHA‐AM moieties in the composite structures could expand the use of AESO into the development of heat‐resistant and hydrophobic materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44545.     

Epoxidized natural rubber/epoxy blends: Phase morphology and thermomechanical properties

Epoxidized natural rubbers (ENRs) were prepared. ENRs with different concentrations of up to 20 wt % were used as modifiers for epoxy resin. The epoxy monomer was cured with nadic methyl anhydride as a hardener in the presence of N,N‐dimethyl benzyl amine as an accelerator. The addition of ENR to an anhydride hardener/epoxy monomer mixture gave rise to the formation of a phase‐separated structure consisting of rubber domains dispersed in the epoxy‐rich phase. The particle size increased with increasing ENR content. The phase separation was investigated by scanning electron microscopy and dynamic mechanical analysis. The viscoelastic behavior of the liquid‐rubber‐modified epoxy resin was also evaluated with dynamic mechanical analysis. The storage moduli, loss moduli, and tan δ values were determined for the blends of the epoxy resin with ENR. The effect of the addition of rubber on the glass‐transition temperature of the epoxy matrix was followed. The thermal stability of the ENR‐modified epoxy resin was studied with thermogravimetric analysis. Parameters such as the onset of degradation, maximum degradation temperature, and final degradation were not affected by the addition of ENR. The mechanical properties of the liquid‐natural‐rubber‐modified epoxy resin were measured in terms of the fracture toughness and impact strength. The maximum impact strength and fracture toughness were observed with 10 wt % ENR modified epoxy blends. Various toughening mechanisms responsible for the enhancement in toughness of the diglycidyl ether of the bisphenol A/ENR blends were investigated. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39906.     

Effect of Quasi‐nanometer zirconium carbide on the physical characterization of zirconium carbide/polyurethane composite films irradiated under ultraviolet light

We used quasi‐nanometer zirconium carbide (ZrC) and a polyurethane (PU) resin under roller pressure to form a composite film and found that the tensile strength at break, elongation at break, and modulus gradually decreased with increasing ultraviolet (UV)‐irradiation time for films of both PU and the PU/ZrC composite. However, this phenomenon was significantly higher for the PU film than for the ZrC/PU composite film. The construction of the PU film changed after UV irradiation, but that of the PU/ZrC composite film was almost unchanged. The degradation of PU molecules occurred in the absence of ZrC particles after irradiation with UV light but almost did not occur in the presence of ZrC particles. This was confirmed with Fourier transform infrared spectroscopy and gel permeation chromatography analyses. It was suggested that polymer radicals which formed through the photooxidation of UV irradiation and free radicals which formed through the photoreduction of nanometer ZrC/UV irradiation interacted to form a dead polymer to stop the degradation; simultaneously, the chemical bonding between polymer molecules could be re‐formed from free radicals created by photooxidation and photoreduction and thus reduce the mobility of PU molecules, thereby raising the glass‐transition and melting temperatures of the soft segment. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4842–4849, 2006     

Preparation and characterization of silicone oil modified polyurethane damping materials

A series of polyurethane (PU) composites, which could be used as damping materials, with different contents of hydroxyl silicone oil were successfully prepared in this study. The damping and mechanical properties, thermal stability, and molecular groups of the PU composites were characterized by dynamic mechanical analysis, electronic tensile analysis, thermogravimetric analysis, and Fourier transform infrared (FTIR) spectroscopy, respectively. The surface morphology was also observed via scanning electron microscopy (SEM). FTIR spectroscopy showed that the hydroxyl silicone oil was embedded in the PU. The soft and hard segments of the PU composites appeared thermodynamically incompatible and showed microphase separation, as shown by the SEM pictures. The PU composite with 8% hydroxyl silicone oil was found to possess the best synthetic properties among these composites. The maximum values of tan δ were 0.376, 0.561, and 0.573 at 1, 10, and 20 Hz, respectively. The temperature range for the use of damping materials becomes wider at 1 Hz. Frequencies of 10 and 20 Hz might suitable surroundings for the application of damping materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47579.     

Synthesis and architecture study of a reactive polybutadiene polyamine as a toughening agent for epoxy resin

In this study, a novel reactive toughener for the epoxy resin was developed and compared with traditional hydroxyl‐terminated polybutadiene (HTPB). For this purpose, the highly reactive aliphatic amine‐terminated polybutadiene (ATPB) was synthesized at ambient conditions by nucleophilic substitution amination. The characterizations of the product were provided by Fourier transform infrared and ¹H NMR spectroscopy. According to the mechanical test results, incorporation of ATPB into epoxy networks can significantly toughen the epoxy matrix. The addition of 10 phr ATPB increased the critical stress intensity factor (K_IC) and critical strain energy release rate (G_IC) of the epoxy from 0.85 to 2.16 MPa m^1/2 and from 0.38 to 3.02 kJ m^?2, respectively. Furthermore, unlike HTPB, the presence of the ATPB did not deteriorate the tensile strength of the matrix. The toughening and failure mechanisms were discussed based on the epoxy network morphological characteristics. The reduction in cross‐linking density and glass transition temperature of the epoxy system upon modification with liquid rubbers was confirmed by dynamic mechanical analysis. This article opens up the possibility of utilizing reactive flexible diamines with polybutadiene backbone as effective toughening agents for thermoset polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44061.     

The flame retardant and thermal performances of polypropylene with a novel intumescent flame retardant

A novel mono-component intumescent flame retardant(m-IFR), called poly-(spirocyclic pentaerythritol bisphosphonate-1,3,5-triazine-O-bicyclic pentaerythritol phosphate) (PSTBP) was synthesized and characterized. PSTBP was used in polypropylene (PP) to obtain PP/PSTBP mixture whose flame retardancy, thermostability, and water resistance were studied by limiting oxygen index (LOI), vertical burning test (UL-94 V) and thermogravimetric analysis (TGA). In addition, flame-retardant mechanism of the PSTBP was investigated. The results showed that the residue of PSTBP reached 34.58% at 800°C and the volume of the PSTBP increased by dozens of times. When the content of PSTBP was 30.0 wt%, the PP/PSTBP mixture could achieve an LOI value of 32.5% and an UL-94 V-0 rating. Compared with PP/APP/PER system, PP/PSTBP mixture showed better water resistance. The TGA and Fourier transform infrared spectroscopy (FTIR) results showed that PSTBP could generate free radicals and capture the free radicals of the thermal decomposition of PP, and form a dense, strong, and thick intumescent char on the substrate, thus effectively retard the degradation and combustion of PP.     

Eco‐friendly cardanol‐based phenalkamine cured epoxy‐cenosphere syntactic foams: Fabrication and characterisation

The performance of epoxy/cenosphere syntactic foams cured using phenalkamine (PA) were analyzed and characterized. The PA system was found to cure faster at room temperature, had lower density, and lower water absorption values. The thermogravimetric analysis result implied higher thermal stability. The cure studies using DSC inferred faster cure reaction in the ambient temperature conditions. The compression studies confirmed that unlike the epoxy system based on conventional triethylenetetramine curative, PA‐based system did not undergo brittle failure. This was also confirmed with the scanning electron microscope images. Dynamic mechanical analysis inferred the glass transition temperatures (T_g) as 81.4°C. The specific modulus and specific strength were higher for 40% cenosphere loading in PA‐based syntactic foams. As the need for light weight core materials is continually increasing, there is a great possibility for the utilization of this novel bio‐based curing agent to produce sustainable products. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44189.