Thermal behavior of vinyl ester resin matrix composites reinforced with alkali‐treated jute fibers

The thermal behavior of vinyl ester resin matrix composites reinforced with jute fibers treated for 2, 4, 6, and 8 h with 5% NaOH was studied with Thermo‐gravimetric analysis and differential scanning calorimetry. The moisture desorption peak shifted to a higher temperature, from 37 to 58.3°C, for all the treated‐fiber composites because of improved wetting of the fibers by the resin and stronger bonding at the interface. The degradation temperature of the vinyl ester resin in the composites was lowered to 410.3°C from that of the neat resin, 418.8°C. The X‐ray diffraction studies showed increased crystallinity of the treated fibers, which affected the enthalpy of the α‐cellulose and hemicellulose degradation. The hemicellulose degradation temperature remained the same (299.7°C) in all the treated‐fiber composites, but the enthalpy associated with the hemicellulose degradation showed an increasing trend in the treated composites with a small increase in the weight loss. This could be attributed to the increased hydrogen bonding between the more accessible ? OH groups of the hemicellulose in the noncrystalline region of the jute fiber and the resin. The degradation temperature of α‐cellulose was lowered from 364.2 to 356.8°C in the treated composites. The enthalpy of α‐cellulose degradation showed a decreasing trend with a lowering of the weight loss. The crystalline regions of the fiber, consisting of closely packed α‐cellulose chains, were bonded with the resin mainly on the surface through hydrogen bonds and became more resistant to thermal degradation; this reduced the weight loss. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 123–129, 2004     

Thermal and nondestructive analysis of high density polyethylene filled with milled salago fiber

Fillers are utilized for different purposes. In plastic industry, fillers are mainly used to extend the bulk of the compound; however, they can also improve physical properties, materials processing, and reduce cycle time of plastics. In this article, high-density polyethylene was filled with untreated and 5% alkaline-treated salago fiber, and thereafter the thermal and nondestructive properties of the composites were investigated. It was found that the chemical treatment of fiber increased the thermal stability and the mean coefficient value of linear thermal expansion of the treated composites as compared to the untreated ones. Moreover, the increase of fiber content in composites increased the crystallinity level while decreased the thermal capacity and melting temperature of the composites. The zinc, calcium, and phosphorus contents were found to be within the industry-acceptable range for elemental contents in polyolefins. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47873.     

Activation energy and curing behavior of resol‐ and novolac‐type phenolic resins by differential scanning calorimetry and thermogravimetric analysis

The thermal behavior, thermal degradation kinetics, and pyrolysis of resol and novolac phenolic resins with different curing conditions, as a function of the formaldehyde/phenol (F/P) molar ratio (1.3, 1.9, and 2.5 for the resol resins and 0.5, 0.7, and 0.9 for the novolac resins) were investigated. The activation energy of the thermal reaction was studied with differential scanning calorimetry at five different heating rates (2, 5, 10, 20, and 40°C/min) between 50 and 300°C. The activation energy of the thermal decomposition was investigated with thermogravimetric analysis at five different heating rates (2, 5, 10, 20, and 40°C/min) from 30 to 800°C. The low molar ratio resins exhibited a higher activation energy than the high molar ratio resins in the curing process. This meant that less heat was needed to cure the high molar ratio resins. Therefore, the higher the molar ratio was, the lower the activation energy was of the reaction. As the thermal decomposition of the resol resins proceeded, the activation energy sharply decreased at first and then remained almost constant. The activation energy of the thermal decomposition for novolac resins with F/P = 0.5 or F/P = 0.7 was almost identical in all regions, whereas that for novolac resins with F/P = 0.9 gradually decreased as the reaction proceeded. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2589–2596, 2003     

Investigation of alkaline hydrolysis of polyethylene terephthalate by differential scanning calorimetry and thermogravimetric analysis

The hydrolytic depolymerization of polyethylene terephthalate (PET) with alkaline hydroxides was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The reactions of the mixtures were conducted in their solid states under nitrogen atmosphere. The experimental results showed that potassium hydroxide possessed the hydrolytic activity of depolymerizing PET into small molecules such as ethylene glycol; in contrast, sodium hydroxide did not. The production rate of ethylene glycol was enhanced by increasing charge ratio of potassium hydroxide to PET. The presence of water facilitated the alkaline hydrolysis of PET; however, the presence of metal acetates decreased the hydrolysis rate. The activation energy for alkaline hydrolysis of PET determined by the thermograms was in good agreement with the value obtained from the experiments in a batch reactor. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1939–1945, 1998     

Thermal analysis of high‐density polyethylene and low‐density polyethylene with enhanced biodegradability

The thermal properties of high‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) filled with different biodegradable additives (Mater‐Bi AF05H, Cornplast, and Bioefect 72000) were investigated with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The DSC traces of the additives indicated that they did not undergo any significant phase change or transition in the temperature region typically encountered by a commercial composting system. The TGA results showed that the presence of the additive led to a thermally less stable matrix and higher residue percentages. The products obtained during the thermodegradation of these degradable polyolefins were similar to those from pure polyethylenes. The LDPE blends were thermally less stable than the HDPE blends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 764–772, 2002     

Thermal stability of modified end‐capped poly(lactic acid)

The influence of functional end groups on the thermal stability of poly(lactic acid) (PLA) in nitrogen‐ and oxygen‐enriched atmospheres has been investigated in this article using differential scanning calorimetry, thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Functional end groups of PLA were modified by succinic anhydride and l ‐cysteine by the addition–elimination reaction. PLA was synthesized by azeotropic condensation of l ‐lactic acid in xylene and characterized by nuclear magnetic resonance. The values of the activation energies determined by TGA in nitrogen and oxygen atmospheres revealed that the character of functional end groups has remarkable influence on the thermal stability of PLA. Moreover, DMA confirmed the strong influence of functional end groups of PLA on polymer chains motion. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41105.     

The effect of formaldehyde/phenol (F/P) molar ratios on function and curing kinetics of high‐solid resol phenolic resins

A series of high‐solid resol phenolic resins (HSRPRs) were synthesized with different molar ratios (1.6, 1.8, 2.0, 2.2, and 2.4) of formaldehyde to phenol using calcium oxide and sodium hydroxide as catalyst. The effects of F/P molar ratios on physical properties, free formaldehyde and phenol, activity, structure, and thermally resistant properties of HSRPRs were fully investigated by chemical assays, liquid and solid ¹³C‐NMR, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The curing kinetics of different F/P molar ratios were explored with differential scanning calorimeter at four different heating rates (5, 10, 15, 20°C/min) from 35 to 200°C. Overall, HSRPRs with F/P = 2.0 had excellent comprehensive properties. The study was significant in solving the wastewater problem during the process of industry‐scale preparation of HSRPRs. We believed that the experimental findings would provide a new avenue for further study and application of HSRPRs. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and performance of phenolic polybutadiene‐bound stabilizers

An antioxidant derivative, 6‐sulfanylhexyl 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl)propanoate, was synthesized and examined. With a radical initiator, the addition of this compound to pending vinyls of OH‐telechelic, low molecular weight liquid polybutadiene (LBH) was performed to various degrees of conversion to form polymeric antioxidants (PAOs) in which the phenolic moiety was separated from the main chain by a spacer [? CH₂CH₂? S? (CH₂)₆? O? CO? ]. Pure, unstabilized LBH was mixed in several ratios with PAOs, Irganox 1520, and Irganox 1076, and the oxidation stabilities of these mixtures, determined by thermogravimetric analysis and differential scanning calorimetry, were compared. Probably because of their good compatibility with LBH, PAOs exhibited equal or better effectiveness than commercial antioxidants of the Irganox type. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 885–889, 2003     

Fire‐retardant properties of the viscose rayon containing alkoxycyclotriphosphazene

The viscose rayon containing cyclotriphosphazene were prepared by the method of blending spinning. The combustibility and thermal stability of the fire‐retardant viscose rayon were evaluated by 45 ° slope burning method, limit oxygen index (LOI), differential scanning calorimetry, thermogravimetry analysis. The results indicated that the LOI of the modified fiber could reach LOI ≥ 28, and the combustibility of the modified fiber could reach the fire‐retardant standard of Japan industry standard JIS 10 91–77 (times of ignition ≥ 3 times). The analysis of the fiber's thermal degradation suggested that the flame retardant plays a multirole of heat absorption, catalytic dehydration and carbonization, condensation‐phase and gas‐phase flame retardation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 698–702, 2006     

Thermomechanically stable dielectric composites based on poly(ether ketone) and BaTiO3 with improved electromagnetic shielding properties in X‐band

High‐performance barium titanate (BaTiO₃) filled poly(ether ketone) (PEK) composites were prepared by melt compounding with an aim to investigate the effect of BaTiO₃ on thermal, thermomechanical, dielectric, and electromagnetic interference shielding behavior of PEK. The content of BaTiO₃ in the PEK matrix was varied from 0 to 18 vol %. Scanning electron microscopy studies shows that BaTiO₃ particles were uniformly distributed in the PEK matrix up to 13 vol % loading followed by the formation of agglomerates at higher loading (18 vol %). Rockwell hardness increased up to 13 vol % loading followed by a decrease at 18 vol % loading. Dynamic mechanical analysis revealed that storage modulus increases with increase in BaTiO₃ loading with a maximum value of 3192 MPa at 13 vol % compared to 2099 MPa for neat PEK. Dielectric constant of composites measured in the frequency range of 8.2–12.4 GHz increased approximately three times upon incorporation of 18 vol % of BaTiO₃. This increment in dielectric constant is reflected in improved electromagnetic shielding properties as loading of dielectric filler (BaTiO₃) increases. Total shielding effectiveness of ?11 dB (～92% attenuation) at loading of 18 vol % BaTiO₃ justifies the use of these composites for suppression of EM radiations. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46413.     

Development of polyurethanes with azo‐type chromophores for second‐order nonlinear optical applications

Active nonlinear optical nitro‐substituted thiazole, benzothiazole, and thiadiazole chromophores were prepared and condensed with tolylene‐2,4‐diisocyanate (TDI) and 4,4′‐methylenedi(phenyl isocyanate) (MDI) to yield a series of polyurethanes. The resulting polyurethanes were characterized with Fourier transform infrared, proton nuclear magnetic resonance, and ultraviolet–visible spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and gel permeation chromatography. The weight‐average molecular weights of the polyurethanes ranged between 19,500 and 28,000 (weight‐average molecular weight/number‐average molecular weight = 1.71–2.15). All the polyurethanes exhibited excellent solubility in most common organic solvents, and this indicated that these polyurethanes offered good processability. The glass‐transition temperatures (T_g's) of the polyurethanes were in the range of 166–204°C. Among the polyurethanes, chromophores containing the nitrothiazole moiety exhibited lower T_g values in comparison with those of chromophores containing nitrobenzothiazole and nitrothiadiazole moieties. This was attributed to the small size of the nitrothiazole moiety in the polyurethane matrix. The polyurethanes containing a TDI backbone demonstrated relatively high T_g values in comparison with those of the polyurethanes containing an MDI backbone. This was a result of an enhancement of the rigidity caused by the incorporation of a toluene ring into the polyurethane backbone. The second harmonic generation (SHG) coefficients of the poled polyurethane films ranged from 67.29 to 105.45 pm/V at 1064 nm. High thermal endurance of the poled dipoles was observed for all the polyurethanes. This was attributed to the formation of extensive hydrogen bonds between urethane linkages. Furthermore, none of the developed polyurethanes showed SHG decay below 150°C, and this signified their acceptability for nonlinear optical devices. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Improvements in the thermal conductivity and mechanical properties of phase‐change microcapsules with oxygen‐plasma‐modified multiwalled carbon nanotubes

The thermal properties and mechanical properties are the key factors of phase‐change microcapsules (microPCMs) in energy‐storage applications. In this study, microPCMs based on an n‐octadecane (C18) core and a melamine–urea–formaldehyde (MUF) shell supplemented with O₂‐plasma‐modified multiwalled carbon nanotubes (CNTs) were synthesized through in situ polymerization. Meanwhile, two different addition methods, the addition of modified CNTs into the emulsion system or into the polymer system, were compared and examined. Scanning electron microscopy micrographs showed that the microPCMs were spherical and had a broadened size distribution. Fourier transform infrared testing demonstrated that the modified CNTs did not affect C18 coated by MUF resin. The results indicate that the thermal conductivity and mechanical properties of the microPCMs were remarkably improved by the addition of a moderate amount of modified CNTs, but the heat enthalpy and encapsulated efficiency decreased slightly. Moreover, the thermal conductivity and mechanical properties of microPCMs modified with CNTs directly added to the polymer system were superior to those with CNTs added to emulsion system. In particular, when 0.2 g of modified CNTs were added to the polymer system, the thermal conductivity of the microPCMs was improved by 225%, and the breakage rates of the microPCMs at 4000 rpm for 5, 10, and 20 min decreased by 74, 72, and 60%, respectively, compared with that of the microPCMs without modified CNTs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45269.     

Preparation and characterization of low molecular weight silk fibroin by high‐temperature and high‐pressure method

A low molecular weight silk fibroin powder (LMSF) was prepared through high temperature (200°C) and high pressure (20 kgf/cm²), without any addition of chemicals. The carbonized adducts produced during this process were then removed by treatment with activated charcoal. The yield of LMSF by this preparation method was over 60% after the removal of carbonized adducts by using activated charcoal. Amino acid analysis showed an observable decrease in contents of serine and tyrosine in LMSF prepared by this method, as compared to those prepared by neutral salt. The molecular weight of this LMSF was also observably decreased with an increase in the reaction time. From the measurements of differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA), thermal properties of LMSF through high temperature and high pressure were also decreased as compared to those produced by neutral salts. In addition, wide‐angle X‐ray diffraction (WAXD) patterns showed that the crystallinity of LMSF differed from that of the original silk fibroin. It can be said that the preparation method of LMSF in this study is a simple, economical, and environmentally compatible process with many advantages. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2890–2895, 2002     

Chitosan functionalization with a series of sulfur‐containing α‐amino acids for the development of drug‐binding abilities

Chitosan (Chi; 0.5 g) in 69.66 mM aqueous acetic acid was mixed with 312.4 mM methionine (methi) at 0.01 mL/s to disperse and cause optimum collisions for supporting condensation reactions through ? NH₂ of Chi and ? COOH groups of methi. The functionalized chitosan (f‐Chi) product with methi developed an amide bond, which was represented as methi‐functionalized chitosan [Chi–NH? C(?O)–methi]. Both the 1‐Ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide (EDC) and Dean–Stark methods were followed for Chi functionalization. Sulfonation with chlorosulfonic acid in a dimethylformamide medium was conducted at 90 °C and 750 rpm with an approximately 72% yield. The Chi–NH? C(?O)–methi was characterized by ¹H‐NMR spectroscopy and Fourier transform infrared stretching frequencies. The onset temperature of 280 °C recorded by thermogravimetric analysis/differential scanning calorimetry analysis, confirmed the high stability of the covalent bonds in Chi–NH? C(?O)–methi. The synthesis was repeated with other series members of sulfur (S) atoms containing α‐amino acids: homocysteine, ethionine, and propionine. The shielding of terminal ? CH₃ was enhanced on elongation of the terminal alkyl chain in the case of propionine. The peak for the ? NH₂ of Chi at a δ value of 4.73 ppm shifted to 5.36 ppm in Chi–NH? C(?O)–methi because of the involvement of ? NH₂ in ? NH? C(?O)? . Theoretically, the value of ? NH₂ of Chi was 5.11 ppm, with a difference of 0.38 ppm as compared to the experimentally determined value of 4.73 ppm. Additionally, a new peak at a δ value of 3.26 ppm also confirmed Chi functionalization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46000.     

Free‐radical copolymerization of [(4‐isopropyl phenyl) oxycarbonyl] methyl methacrylate with acrylonitrile and methyl methacrylate

The present investigation has been achieved in accordance with the Diels–Alder reaction (1,4 cycloaddition) to produce a new halogenated bicyclic adduct. ortho‐Bromoallylbenzoate is a new dienophile that was prepared in a pure form, and its structure was confirmed. The Diels–Alder syntheses of hexachlorocyclopentadiene and the new dienophile were studied to determine the optimum condensation reaction conditions under a temperature range of 90–160°C, reaction times of 1–8 h, and molar diene/dienophile ratios from 1:1 to 5:1 as a consequence. The optimum conditions reached were a temperature of 140°C, an initial diene/dienophile molar ratio of 3:1, and a duration time of 6 h. The maximum stoichometric yield under these optimum conditions (82.5%) was obtained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2331–2338, 2003     

Cocrystallization behavior of poly(n‐docosyl acrylate) with n‐docosanoic acid by X‐ray and differential scanning calorimetry studies

Cocrystallization behavior of comb‐like poly(n‐docosyl acrylate) (PDA) with n‐docosanoic acid (C₂₂) has been studied by means of differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) methods. The DSC curves of blended samples of neat PDA with C₂₂ show the characteristic melting endotherms that correspond to the melting of the crystallites. DSC measurements of PDA/C₂₂ blends also suggest the existence of another crystalline form induced by the addition of the C₂₂. From the XRD measurements, the existence of hexagonally‐packed crystalline lattice and the phase behavior of PDA/C₂₂ blends at different mole percent are confirmed. Thermal degradation behavior of PDA and its corresponding blends with C₂₂ is studied by thermogravimetric analysis. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2140–2146, 2005     

Preparation of 2‐ethyl‐4‐methylimidazole derivatives as latent curing agents and their application in curing epoxy resin

Three kinds of 2‐ethyl‐4‐methylimidazole (EMI) derivatives (N‐acetyl EMI, N‐benzoyl EMI, and N‐benzenesulfonyl EMI) were synthesized through the reaction of EMI with acetyl chloride, benzoyl chloride, and benzenesulfonyl chloride, respectively. And the structure was confirmed by Fourier transform infrared spectroscopy (FTIR) and ¹H‐nuclear magnetic resonance spectroscopy (¹H NMR) spectra. Furthermore, the synthesized EMI derivatives were applied in diglycidyl ether of bisphenol A epoxy resin (DGEBA) as latent curing agent. Differential scanning calorimeter (DSC) was used to analyze the curing behavior of DGEBA/EMI derivative systems, indicating DGEBA could be efficiently cured by the EMI derivatives at 110～160°C, and the corresponding curing activation energy ranged from 71 to 86 kJ/mol. Viscosity data proves that the storage life of DGEBA with N‐acetyl EMI (NAEMI), N‐benzoyl EMI (NBEMI), and N‐benzenesulfonyl EMI (NBSEMI) at room temperature was 38 d, 50 d, and 80 d, and that at 10°C was 90 d, 115 d, and 170 d, respectively. Besides, thermogravimetry (TG), izod impact strength (IIS), and tensile shear strength (TSS) were tested to characterize the thermal stability and mechanical properties of DGEBA cured by EMI derivatives. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42563.     

Phase behavior of binary and ternary blends of poly(styrene‐co‐methacrylic acid), poly(styrene‐co‐4‐vinylpyridine), and poly(2,6‐dimethyl‐1,4‐phenylene oxide)

Poly(styrene‐co‐methacrylic acid) (PSMA) and poly(styrene‐co‐4‐vinylpyridine) (PS4VP) of different compositions were prepared and characterized. The phase behavior of these copolymers as binary PSMA/PS4VP mixtures or with poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) as PPO/PSMA or PPO/PS4VP and PPO/PSMA/PS4VP ternary blends was investigated by differential scanning calorimetry (DSC). This study showed that PPO was miscible with PS4VP containing up to 15 mol % 4‐vinylpyridine (4VP) but immiscible with PS4VP‐30 (where the number following the hyphen refers to the percentage 4VP in the polymer) and PSMA‐20 (where the number following the hyphen refers to the percentage methacrylic acid in the polymer) over the entire composition range. To examine the morphology of the immiscible blends, scanning electron microscopy was used. Because of the hydrogen‐bonding specific interactions that occurred between the carboxylic groups of PSMA and the pyridine groups of PS4VP, chloroform solutions of PSMA‐20 and PS4VP‐15 formed interpolymer complexes. The obtained glass‐transition temperatures (T_g's) of the PSMA‐20/PS4VP‐15 complexes were found to be higher than those calculated from the additivity rule. Although, depending on the content of 4VP, the shape of the T_g of the PPO/PS4VP blends changed from concave to S‐shaped in the case of the miscible blends, two T_g were observed with each PPO/PS4VP‐30 and PPO/PS4VP‐40 blend. The thermal stability of the PSMA‐20/PS4VP‐15 interpolymer complexes was studied by thermogravimetry. On the basis of the obtained results, the phase behavior of the ternary PPO/PSMA‐20/PS4VP‐15 blends was investigated by DSC. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Morphology and thermal properties of poly(L‐lactic acid)/organoclay nanocomposites

A modified clay was used to prepare poly(L ‐lactic acid)/clay nanocomposite dispersions. X‐ray diffraction and transmission electron microscopy experiments revealed that poly(L ‐lactic acid) was able to intercalate the clay galleries. IR spectra of the poly(L ‐lactic acid)/clay nanocomposites showed the presence of interactions between the exfoliated clay platelets and the poly(L ‐lactic acid). Thermogravimetric analysis and differential scanning calorimetry were performed to study the thermal behavior of the prepared composites. The properties of the poly(L ‐lactic acid)/clay nanocomposites were also examined as functions of the organoclay content. The exfoliated organoclay layers acted as nucleating agents, and as the organoclay content increased, the crystallization temperature increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and nonlinear optical properties of a novel X‐type polyester containing dicyanovinylnitroresorcinoxy groups with enhanced thermal stability of dipole alignment

A novel X‐type polyester (5) containing 4‐(2′,2′‐dicyanovinyl)‐6‐nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyester 5 is soluble in common organic solvents such as N,N‐dimethylformamide and acetone. Polyester 5 shows thermal stability up to 300 °C from thermogravimetric analysis with a glass transition temperature obtained from differential scanning calorimetry of near 108 °C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer films at the 1064 nm fundamental wavelength is 2.99 pm V^?1. The dipole alignment exhibits thermal stability even at 7 °C above the glass transition temperature, and no significant SHG decay is observed below 115 °C due to the partial main‐chain character of the polymer structure, which is acceptable for NLO device applications. © 2013 Society of Chemical Industry