Nonisothermal cure kinetics of diglycidylether of bisphenol‐A/amine system reinforced with nanosilica particles

Epoxy‐silica nanocomposites were obtained from directly blending diglycidylether of bisphenol‐A (DGEBA)‐based epoxy and nanoscale silica (NS) and then curing with 4,4′‐diaminodiphenylamine (DDA). The effect of amount of nanosilica (NS) particles as catalyst on the mechanism and kinetic parameters of cure reaction of DGEBA/DDA system was studied. The kinetics parameters were obtained from nonisothermal differential scanning calorimeter (DSC) data using the Kissinger and Ozawa equations. The exothermic peak was shifted toward lower temperatures in DGEBA/DDA/NS system with increasing the amount of nanoslica particles. However, the existence of NS particles with hydroxyl groups in the structure in the mixture of DGEBA/DDA catalyzes the cure reaction and increases the rate constant. The activation energy of cure reaction of DGEBA/DDA system obtained from two methods were in good agreement, and showed a decrease when NS particles were present in the mixture. The mechanism of reaction of DGEBA with DDA was carried out by isothermal curing in the oven at 130°C and measuring the disappearance peak of epoxide group at 916 cm^?1 using FTIR. The diffusive behavior of two systems was investigated during water sorption at 25°C and the experimental results fitted well to Fick's law. Diffusion coefficient of cured sample from DGEBA/DDA/10% NS blend decreased in comparison with the sample without NS particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3855–3863, 2007     

Experimental characterization of a curing thermoset epoxy‐anhydride system—Isothermal and nonisothermal cure kinetics

This work describes in detail the kinetic model for the cure of an epoxy‐anhydride thermoset matrix resin system. The cure kinetics in both nonisothermal and isothermal modes has been characterized using differential scanning calorimetry. The Sestak–Berggren two‐parameter autocatalytic model was used to describe the nonisothermal cure behavior of the resin satisfactorily. The isothermal cure data was fitted with Kamal's four‐parameter autocatalytic model, coupled with a diffusion factor. These characterization data will form material property inputs for a multiscale modeling framework for the estimation of cure‐induced residual stresses in thick thermoset matrix composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of surface area of nanosilica particles on the cure kinetics parameters of an epoxy resin system

Knowing of thermoset curing kinetics is essential for process development, quality control, and achieving desirable products. Hence, in this article, cure kinetics of an EPON 828 epoxy resin/dicyandiamide curing agent/diuron accelerator system is investigated. This resin system is usually used for the production of epoxy/glass fiber prepregs used in wind turbine blades. For this, differential scanning calorimetry analysis is used and the effect of temperature, weight percentage, and size of nanosilica is studied by conducting isothermal tests at several temperatures for samples with and without nanoparticles. An autocatalytic curing model is applied to describe the cure kinetic of system and then the variations in model parameters calculated by curve fitting using the MATLAB software. The results show that the increase in temperature, weight percentage of nanosilica from 0 to 6%, and surface area of nanosilica particles lead to the increase in curing rate, whereas the increase in the percentage and surface area of nanosilica particles significantly decreases total heat of reaction. At the end, the relation between each of model parameters and the total surface area of nanosilica particles, calculated by mathematical equations, is obtained. The allowable maximum surface area of nanosilica used in the mathematical equations is 12 m² g⁻¹. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47958.     

Novel observations on kinetics of nonisothermal crystallization in fly ash filled isotactic‐polypropylene composites

A study on nonisothermal crystallization kinetics in fly ash (FA) filled isotactic‐polypropylene (PP) composites has revealed some interesting phenomena. Composites made by injection moulding of PP with 0, 20, 45, and 60 wt % of FA were nonisothermally studied using differential scanning calorimetry at cooling rates 10°C, 15°C, and 20°C per min from a melt temperature of 200°C cooled to ?30 °C. Whilst neat PP showed a mono modal α crystalline phase‐ only structure, presence of FA led to bimodal thermographs revealing partial transcrystallisation of α into β, to maximum 14%. The onset and peak crystallization temperatures of all samples decreased by ～ 3°C with each 5°C/min increase in cooling rate. Parameters such as crystal growth rate, dimensions, and activation energy were determined using a series of established models. The Avrami graphs showed that contrary to the published data, there are two sets of straight lines (a) with a lower slope at low cooling rate and (b) with a distinctly higher slope for high cooling rate. Activation energy of the materials reached a maximum at 45% FA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Isothermal and nonisothermal melt‐crystallization kinetics of syndiotactic polystyrene

Analyses of the isothermal and nonisothermal melt kinetics for syndiotactic polystyrene have been performed with differential scanning calorimetry, and several kinetic analyses have been used to describe the crystallization process. The regime II→III transition, at a crystallization temperature of 239°, is found. The values of the nucleation parameter K_g for regimes II and III are estimated. The lateral‐surface free energy, σ = 3.24 erg cm^?2, the fold‐surface free energy, σ_e = 52.3 ± 4.2 erg cm^?2, and the average work of chain folding, q = 4.49 ± 0.38 kcal/mol, are determined with the (040) plane assumed to be the growth plane. The observed crystallization characteristics of syndiotactic polystyrene are compared with those of isotactic polystyrene. The activation energies of isothermal and nonisothermal melt crystallization are determined to be ΔE = ?830.7 kJ/mol and ΔE = ?315.9 kJ/mol, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2528–2538, 2002     

Preparation and characterization of novel ultra‐high molecular weight polyethylene composite fibers filled with nanosilica particles

Ultrahigh molecular weight polyethylene (UHMWPE)/nanosilica (F₂S_y) and UHMWPE/modified nanosilica (F₂S_mx‐y) as‐prepared fibers were prepared by spinning of F₂S_y and F₂S_mx‐y gel solutions, respectively. Modified nanosilica particles were prepared by grafting maleic anhydride grafted polyethylenes onto nanosilica particles. The achievable draw ratios (D_ra) of F₂S_y and F₂S_mx‐y as‐prepared fibers approached a maximal value as the original and modified nanosilica contents reached corresponding optimum values; the maximal D_ra value obtained for F₂S_mx‐y as‐prepared fiber specimens was significantly higher than that of the F₂S_y as‐prepared fiber specimens prepared at the optimum nanosilica content. The melting temperature and evaluated lamellar thickness values of F₂S_y and F₂S_mx‐y as‐prepared fiber series specimens decrease, but crystallinity values increase significantly, as their original and modified nanosilica contents respectively increase. Similar to the achievable drawing properties of the as‐prepared fibers, the orientation factor, tensile strength (σ_f) and initial modulus (E) values of both drawn F₂S_y and F₂S_mx‐y fiber series specimens with a fixed draw ratio reach a maximal value as the original and/or modified nanosilica contents approach the optimum values; the σ_f and E values of the drawn F₂S_mx‐y fiber specimens are significantly higher than those of the corresponding drawn F₂S_y fiber specimens prepared at the same draw ratios and nanosilica contents but without being modified. To understand the interesting ultradrawing, thermal, orientation and tensile properties of F₂S_y and F₂S_mx‐y fiber specimens, Fourier transform infrared, specific surface area and transmission electron microscopy analyses of the original and modified nanosilica were performed in this study. © 2012 Society of Chemical Industry     

Isothermal and nonisothermal crystallization kinetics of poly(ε‐caprolactone)/multi‐walled carbon nanotube composites

Differential scanning calorimeter (DSC) and polarized optical microscopy (POM) have been used to investigate the isothermal and nonisothermal crystallization behavior of poly(ε‐caprolactone) (PCL)/multi‐walled carbon nanotube (MWNT) composites. PCL/MWNT composites have been prepared by mixing the PCL polymer with carboxylic groups containing multi‐walled carbon nanotubes (c‐MWNTs) in tetrahydrofuran solution. Raman spectrum of c‐MWNT indicated the possible presence of carboxylic acid groups at both ends and on the sidewalls of the MWNTs. The TEM micrograph showed that the c‐MWNT is well separated and uniformly dispersed in the PCL matrix. DSC isothermal results showed that the introduction of c‐MWNT into the PCL initiates strongly heterogeneous nucleation, which induced a change of the crystal growth process. The activation energy of PCL significantly decreases by adding 0.25 wt% c‐MWNT into PCL/c‐MWNT composites and then increases as c‐MWNT content increases. The result demonstrates that the addition of c‐MWNT into PCL induces the heterogeneous nucleation at lower c‐MWNT content and then inhibits the polymer chain transportation ability during crystallization at higher c‐MWNT content. In this study, we have also studied the nonisothermal crystallization kinetics and melting behavior of PCL/c‐MWNT composites at various cooling rates. The correlation among isothermal and nonisothermal crystallization kinetics and melting behavior of PCL/c‐MWNT composites can be also discussed. POLYM. ENG. SCI., 46:1309–1317, 2006. © 2006 Society of Plastics Engineers     

Isothermal and nonisothermal crystallization kinetics of fully bio‐based polyamides

We studied the crystallization behaviors of bio‐based BDIS polyamides synthesized from the following biomass monomers: 1,4‐butanediamine (BD), 1,10‐decanediamine (DD), itaconic acid (IA), and sebacic acid (SA). Isothermal crystallization, melting behavior, and nonisothermal crystallization of BDIS polyamides were investigated by differential scanning calorimetry (DSC). The Avrami equation was used to describe the isothermal crystallization of BDIS polyamides. The modified Avrami equation, the Ozawa equation, the modified Ozawa equation, and an equation combining the Avrami and Ozawa equations were used to describe the nonisothermal crystallization. The equilibrium melting point temperature of BDIS polyamide was determined to be 163.0°C. The Avrami exponent n was found to be in the range of 2.21–2.79 for isothermal crystallization and 4.10–5.52 for nonisothermal crystallization. POLYM. ENG. SCI., 56:829–836, 2016. © 2016 Society of Plastics Engineers     

Influence of nanosilica particles on the cure and physical properties of an epoxy thermoset resin

Measurements are reported on the cure and physical properties of an epoxy resin created using a functionalised nanosilica filler. The filled bisphenol A epoxy (Nanopox A410) contained 40 wt% silica nanoparticles and was blended with two bisphenol A resins of molecular weights of 355 and 1075 g mol^?1, respectively. Cure was achieved using 3,3‐diaminodiphenylsulfone. The functionality of the mixture containing the epoxy nanoparticles was determined using NMR analysis. Cure times showed a progressive decrease with increasing silica level. Dynamic mechanical thermal analysis showed a decrease in the value of the glass transition temperature (T_g) with increasing silica level. T_g was further studied using differential scanning calorimetry. The ability of the nanosilica to create a stable network structure was demonstrated by the variation of the high‐temperature modulus with silica composition. Thermomechanical analysis carried out below and above T_g showed a progressive decrease in the expansion coefficients with increasing silica level, indicating the effectiveness of the functionalised silica nanoparticles in forming a network. The network formed during cure in the nano‐modified epoxy is unable to undergo the densification possible in the pure resin material and explains the observed lowering of T_g with increasing nanosilica content. Copyright © 2009 Society of Chemical Industry     

Mechanical performance of woven carbon fabric reinforced pCBT composites with nanosilica particles

The effect of nanosilica content (0, 0.5, and 2 wt%) on mechanical performance of carbon fabric woven cloth reinforced polymerized poly(butylene terephthalate) resin composites (CF/pCBT) is investigated. The catalyst and nanosilica particles are added on the prepreg surface, and hot‐press processing is adopted in order to manufacture CF/pCBT composites. The experimental results reveal that nanosilica could enhance the mechanical performance of CF/pCBT composites. After adding nanosilica in the composites, elastic modulus enhances 23.96%, and Mode‐II fracture toughness increases 380.43%. Scanning electron microscope observation shows that dispersity of nanoparticles in composites plays an important role on the overall mechanical performance of the obtained composites. Furthermore, failure mechanism has been analyzed according to the damage morphology. POLYM. COMPOS., 38:2528–2535, 2017. © 2015 Society of Plastics Engineers     

Preparation and characterization of nano/micro‐calcium carbonate particles/polypropylene composites

A new kind of polypropylene (PP)/CaCO₃ composites was prepared on a twin screw extruder with the nanoparticle content of 5 wt % and the 2500 mesh microparticle content of 15 wt %. The mechanical property of four different samples [pure PP (1) , PP filled with 15 wt % microCaCO₃ particle composites (2) , PP filled with 5 wt % nanoCaCO₃ particle composites (3) and PP filled with micro/nano‐CaCO₃ complex size particle composites (4) ] was investigated through tensile tests, notched Izod impact tests and SEM. The results indicated that the sample 4 had the best mechanical property. The proofs of SEM showed that the high impact energy could lead to debonding and creating microcavitation between the nanoparticle and polymer interface if the polymer was filled with the nanoparticles. This process could absorb a lot of mechanical failure energy, but too much mechanical failure energy would lead to the enlargement of microcavitation and the destruction of the composites in sample 3 . In sample 4 , the microparticle could be used to prevent the enlargement of microcavitation in the matrix polymer under the higher impact failure energy. In this article, the model of the impacting failure process of micro/nanoCaCO₃/PP composites was established. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of conductive polyaniline/nanosilica particle composites through ultrasonic irradiation

Polyaniline/nano‐SiO₂ particle composites were prepared through ultrasonic irradiation. Polymerization of aniline was conducted under ultrasonic irradiation in the presence of two types of nano‐SiO₂: porous nanosilica and spherical nanosilica. The stability of the colloid dispersion, UV–vis spectra, composition, interaction, conductivity, and other characteristics of the composites were examined. It was found that the aggregation of nano‐SiO₂ could be reduced under ultrasonic irradiation and that nanoparticles were redispersed in the aqueous solution. The formed polyaniline deposited on the surface of the nanoparticle, which led to a core–shell structure. Two particle morphologies, threadlike aggregates with a few spherical nanoparticles for porous nanosilica and spherical particles with a few sandwichlike particles for spherical nanosilica, were observed. X‐ray photoelectron spectroscopy showed that for two types of composites the ratio of Si atoms to N atoms (Si:N) on the surface was much higher than that in the bulk. The UV–vis spectra of the diluted colloid dispersion of polyaniline/nano‐SiO₂ composite particles were similar to those of the polyaniline system. Fourier transform infrared spectroscopy suggested strong interaction between polyaniline and nano‐SiO₂. The conductivity of the polyaniline/porous nanosilica (23.1 wt % polyaniline) and polyaniline/spherical nanosilica (20.6 wt % polyaniline) composites was 2.9 and 0.2 S/cm, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1811–1817, 2003     

Isothermal and nonisothermal crystallization kinetics of novel even‐odd nylon 10 11

Isothermal and nonisothermal crystallization kinetics of even‐odd nylon 10 11 were investigated by differential scanning calorimetry (DSC). Equilibrium melting point was determined to be 195.20°C. Avarmi equation was adopted to describe isothermal and nonisothermal crystallization. A new relation suggested by Mo was used to analyze nonisothermal crystallization and gave a good result. The crystallization activation energies have been obtained to be ?583.75 and ?270.06 KJ/mol for isothermal and nonisothermal crystallization, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1637–1643, 2005     

Effects of UV‐irradiation on the nonisothermal crystallization kinetics of polypropylene

The influences of UV‐induced photodegradation on the nonisothermal crystallization kinetics of polypropylene (PP) were investigated by differential scanning calorimetry. The Avrami analysis modified by Jeziorny, Ozawa method, and a method modified by Liu were employed to describe the nonisothermal crystallization process of unexposed and photodegraded PP samples. Kinetics studies reveal that the rates of nucleation and growth may be affected differently by photodegradation. A short‐term UV‐irradiation may accelerate the overall nonisothermal crystallization process of PP, but a long‐term UV‐irradiation should impede it. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Adhesive properties of DGEBA–acid homopolymer and DGEBA–acid copolymer systems

Adhesive properties of high molecular weight acid copolymers used as hardeners for a commercial epoxy resin are investigated. For comparative purposes, physical blends of poly(acrylic acid)–polystyrene are used as hardeners. Joints prepared from physical blends exhibit lower lap shear strength than do those prepared form synthesis products. The use of copolymers is more adequate. Thermodynamic work of adhesion using wettability criteria is explored to explain the differences. The apparent energies of rupture determined by lap shear tests are 10³ higher than those of the thermodynamic work of adhesion. © 1995 John Wiley & Sons, Inc.     

Interphase‐layer effect on deformation of silicone rubber filled with nanosilica particles

The viscoelastic and statically tensile deformation properties of silicone rubber composites filled with nanosilica (300 nm in diameter) and microsilica particles (1.5 μm in diameter) were investigated on the basis of experimental results to clarify the interphase‐layer effect on these properties. The interphase layers formed around the nanoparticles without chemical coating were found to be glassy, even though the composites were in the rubbery state. The interphase layer thickness was determined to be approximately 20 nm using Guth and Gold's mixture law with the viscoelastic properties of the nanoparticle‐filled rubber in the rubbery state. The determined thickness of the interphase layer was confirmed by comparing the maximum strains at fracture for the nanoparticle‐filled rubber, which decreased for higher volume fraction of the nanoparticles. Therefore, the deformation properties were clarified to depend on the volume fraction of the apparent particles composed of the nanoparticles and interphase layers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45880.     

Preparation and characterization of water‐absorbing polyurethane foam composites with microsized sodium polyacrylate particles

This article introduces the preparation of rigid polyurethane foam (PUF) and studies the effect of various mass percentages of sodium polyacrylate (PAAS, microsized) on PUF hydrophilicity. The characterization of PUF (with 0–5.5 wt % PAAS) was conducted via scanning electron microscopy, contact angle analysis, differential scanning calorimetry, and pore size distribution. All modified foams showed an improvement in their water sorption and water maintenance capacities, and the PU foam content of 5.5 wt % PAAS showed a water absorption of 891%, and the water retention performance was 408% (96 h) compared to the pure PU foam. Through contact angle measurements, the relationship between the hydrophilicity of the modified foams and PAAS content was investigated. The compression strength of the samples was also tested. When the PAAS is 2.6 wt %, the compression strength of the composites decreased about 50% compared with the pure PU foam. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46702.     

Preparation and properties of thermosensitive organic‐inorganic hybrid gels containing modified nanosilica

A series of thermosensitive organic–inorganic hybrid gels containing nanosilica or modified nanosilica were prepared from N‐isopropylacrylamide (NIPAAm), and N,N′‐methylene‐bis‐acrylamide (NMBA) and nanosilica (AE200) or modified AE200 (mAE200); and NIPAAm, NMBA, 3‐(trimethoxysilyl) propyl methacrylate (TMSPMA) as coupling agent and AE200 or mAE200 in this study. The effect of inorganic nanosilica on the swelling behaviors and mechanical properties were investigated by adding different amount of nanosilica and modified nanosilica. Results showed that the swelling ratios of the hybrid gels decrease with increasing nanosilica content. Existence of silane coupling agent would also reduce the swelling ratios of the hybrid gels. Adding coupling agent or nanosilica would improve the gel strength. Modification of nanosilica by grafting amino‐silane via sol–gel process was carried out and the effect of addition of modified silica on gel properties was also investigated. Results showed that the hybrid gels containing modified silica would have higher swelling ratios and moduli than those containing unmodified silica. Gels containing both silane coupling agent and silica would have higher crosslinking density because the silica would be better crosslinked with coupling agent. POLYM. COMPOS., 31:1712–1721, 2010. © 2010 Society of Plastics Engineers.     

Isothermal and nonisothermal crystallization kinetics of MC nylon and polyazomethine/MC nylon composites

Crystallization kinetics of MC nylon (PA6) and polyazomethine (PAM)/MC nylon (PAM/PA6) both have been isothermally and nonisothermally investigated by different scanning calorimetry (DSC). Two stages of crystallization are observed, including primary crystallization and secondary crystallization. The Avrami equation and Mo's modified method can describe the primary stage of isothermal and nonisothermal crystallization of PA6 and PAM/PA6 composite, respectively. In the isothermal crystallization process, the values of the Avrami exponent are obtained, which range from 1.70 to 3.28, indicating an average contribution of simultaneous occurrence of various types of nucleation and growth of crystallization. The equilibrium melting point of PA6 is enhanced with the addition of a small amount of rigid rod polymer chains (PAM). In the nonisothermal crystallization process, we obtain a convenient method to analyze the nonisothermal crystallization kinetics of PA6 and PAM/PA6 composites by using Mo's method combined with the Avrami and Ozawa equations. In the meanwhile, the activation energies are determined to be ?306.62 and ?414.81 KJ/mol for PA6 and PAM/PA6 (5 wt %) composite in nonisothermal crystallization process from the Kissinger method. Analyzing the crystallization half‐time of isothermal and nonisothermal conditions, the over rate of crystallization is increased significantly in samples with a small content of PAM, which seems to result from the increased nucleation density due to the presence of PAM rigid rod chain polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2844–2855, 2004     

Synthesis and characterization of nanosilica ball—PMMA hybrid composites

Organic–inorganic hybrid materials are one of the most attractive topics, which deals from fundamental researches to practical applications. In the present research, we have studied the polymerization of methyl methacrylate (MMA) on the surface of γ‐methacryloxy propyl trimethoxy silane (γ‐MPS) modified nanosilica ball (NSB). The polymeric materials were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and thermo gravimetric analysis (TGA). The results show that new core‐shell structured materials, NSB core‐PMMA shell composites, have been synthesized. The core‐shell hybrid materials can be adjusted to form only a single spherical phase. The addition of the core‐shell hybrid materials to the clearcoat enhances the surface hardness and antiscratch property. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013