Investigation of processing,thermal, and mechanical properties of a new composite matrix‐benzoxazine containing aldehyde group

A new benzoxazine aldehyde group containing monomer 3‐phenyl‐6‐formyl‐3, 4‐dihydro‐2H‐1, 3‐benzoxazine (Ald‐B) was synthesized via the Mannich reaction of formaldehyde, p‐hydroxybenzaldehyde, and aniline. The viscosities and curing behavior of the resins were studied. The results indicated that Ald‐B has an initial viscosity lower than 0.110 Pa s at 90°C and the maximum temperature of the exotherm was at 196°C. Dynamic mechanical analysis (DMA) of the copolymer of Ald‐B and methylenedianiline‐type bis‐benzoxazine (B‐BOZ) showed only one T_g of 251°C and high crosslink density in the matrix. The thermal stability of the copolymer was improved noticeably and the char yield at 800°C is 68.4%. The tensile strength and flexural strength of this resin cast are 72 and 137 MPa, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Rheological and thermal properties of agarose aqueous solutions and hydrogels

In this article, we report on the rheological properties of agarose aqueous solutions and gels. Viscosity curves were determined for homogeneous agarose aqueous solutions at different temperatures (from 68 to 38 °C) to study the viscosity behavior as the systems undergo gelation. The gelation phenomenon of agarose solutions was also investigated by shear oscillation experiments and differential scanning calorimetry. The gelation and melting temperature as a function of agarose concentration were determined together with the gelation and melting enthalpies. The results obtained were interpreted using the two‐step model describing the gelation of agarose in water. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 322–328, 2008     

Mechanical and thermal properties of green polylactide composites with natural fillers

Green composites of PLA with micropowders derived from agricultural by-products such as oat husks, cocoa shells, and apple solids that remain after pressing have been prepared by melt mixing. The thermal and mechanical properties of the composites, including the effect of matrix crystallization and plasticization with poly(propylene glycol), have been studied. All fillers nucleated PLA crystallization and decreased the cold-crystallization temperature. They also affected the mechanical properties of the compositions, increasing the modulus of elasticity but decreasing the elongation at break and tensile impact strength although with few exceptions. Plasticization of the PLA matrix improved the ductility of the composites.     

Investigation of thermal,mechanical, and electrical properties of novel polyurethanes/high molecular weight polybenzoxazine blends

In order to prepare tough polyurethane (PU) electrical insulator with improved thermal stability and electrical insulating properties, high molecular weight polybenzoxazine precursor was mixed and co‐cured with crosslinkable urethane prepolymers. Polybenzoxazine precursor (Bmda) was synthesized from reaction of bisphenol‐A, methylenedianiline, and paraformaldehyde. Epoxy‐terminated polyurethanes (EPU1‐4) were prepared by the reaction of glycidol with NCO‐terminated urethane oligomers. The oligomers were prepared from different molecular weight versions of polycaprolactone polyol (CAPA) and hexamethylene diisocyanate. Blends were prepared through thermal treatment of equal weights of two precursors dissolved in chloroform. Optimum curing condition was determined by DSC and DMTA analysis and measurement of the gel content for cured samples. Viscoelastic, thermal, mechanical, and electrical properties of cured samples were investigated and structure–property relationship was established. Copyright © 2008 John Wiley & Sons, Ltd.     

Investigation of the dielectric,mechanical, and thermal properties of noncovalent functionalized MWCNTs/polyvinylidene fluoride (PVDF) composites

To improve the dispersion of multi‐walled walled carbon nanotubes (MWCNTs) and investigate the effect of dispersant for MWCNTs functionalization on the dielectric, mechanical, and thermal properties of Polyvinylidene fluoride (PVDF) composites, two different dispersants (Chitosan and TritonX‐100) with different dispersion capability and dielectric properties were used to noncovalently functionalize MWCNTs and prepare PVDF composites via solution blending. Fourier transform infrared, X‐Ray diffraction, and Raman spectroscopy indicated that TritonX‐100 and Chitosan were noncovalent functionalized successfully on the surface of MWCNTs. With the functionalization of Chitosan and TritonX‐100, the dispersion of MWCNTs changed in different extent, which was investigated by dynamic light scattering and confocal laser scan microscopy. The dielectric, mechanical, and thermal properties of PVDF composites were also improved. Meanwhile, it was also found that the dielectric properties of PVDF composites are closely related to the dielectric properties of dispersant. High dielectric constant of dispersant contributes to the grant dielectric constant of PVDF composites. The mechanical and thermal properties of MWCNTs/PVDF composites largely depend on the dispersion of MWCNTs in PVDF, interfacial interactions and the residual solvent. Copyright © 2016 John Wiley & Sons, Ltd.     

Mechanical and thermal properties of modified bismaleimide matrices toughened by polyetherimides and polyimide

Thermal and mechanical properties such as G_IC (critical strain energy release rate), K_IC (critical stress intensity factor), tensile, and flexural strength of bismaleimide (BMI) matrix toughened by commercially available polyetherimides (Ultem 1000P, Siltem STM 1700, and Extem VH1003) and polyimide P84 were investigated. In case of various contents, polyetherimides soluble in BMI phase separation was observed. The influence of the toughener amount on the mechanical properties of the matrices was studied. It was shown that Ultem and Siltem had a more significant influence on the G_IC and K_IC parameters than the more thermally stable P84 and Extem. Copyright © 2015 John Wiley & Sons, Ltd.     

Differential scanning calorimetry and thermogravimetric analysis investigation of the thermal properties and degradation of some radiation‐grafted films and membranes

The influence of irradiation and grafting on the crystallinity of three base polymers has been investigated with differential scanning calorimetry. Grafting has the largest effect on the base polymer crystallinity and results in a reduction of the crystallinity. The thermal degradation of the base polymers and grafted films has been investigated with thermogravimetric analysis. The extent of the fluorination of the base polymer, the irradiation method, and the graft level all influence the thermal degradation and its activation energy. It is proposed that the variation of the chain lengths of the grafted polystyrene chains is actually a primary underlying factor responsible for the influence of these various parameters on the degradation process. The first results of a comparative thermal analysis of some fuel‐cell membranes are also presented, and the promise and shortcomings of this method are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2612–2624, 2004     

Characterization and thermal properties of Ni-exchanged montmorillonite with benzimidazole

Thermal analysis (TG, DTG), powder diffraction analysis (XRD) and infrared (IR) spectra were used to study of composition and release of benzimidazole from Ni(II)-exchanged montmorillonite under heating. Diffraction analysis indicated that benzimidazole molecules are intercalated into the interlayer space of montmorillonite. IR spectra and the analytical characteristics have shown that different type of interactions of benzimidazole is connected with different reaction conditions (acid or neutral solution). The release of benzimidazole from Ni(II)-montmorillonite under heating from studied samples proceeds in three distinct steps. The first step can be assigned to the release of water molecules while the last (third) one corresponds to the lattice dehydroxylation. The second step can be assigned to release of chemically bonded benzimidazole.     

Mechanical and thermal properties of epoxy/silicon carbide nanofiber composites

The silicon carbide (SiC) nanofibers (0.1, 0.25, and 0.5 phr), produced by self‐propagating high‐temperature synthesis (SHS), are used to reinforce the epoxy matrix cured with an anhydride hardener. Morphological studies reveal a better dispersion of SiC nanofibers and a good level of adhesion between nanofiber and the matrix in composites with lower (0.1 and 0.25 phr) nanofiber loading. The flexural studies show that a maximum increase in flexural properties is obtained for composites with 0.25 phr SiC nanofiber. The fracture toughness of epoxy is found to increase with the incorporation of SiC nanofibers, and 0.25 phr SiC nanofiber loading shows maximum fracture toughness value. The possible fracture mechanisms that exist in epoxy/SiC nanofiber composites have been investigated in detail. Thermogravimetric analysis reveals that SiC nanofibers are effective fillers to improve the thermal stability of epoxy matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis,characterization, and thermal properties of piezoelectric polyimides

Three amorphous piezoelectric polyimides have been synthesized and characterized to analyze their utility for high‐temperature applications. The studied polyimides have been prepared from 4,4′‐oxydiphthalic anhydride and the diamines 2,4‐di(3‐aminophenoxy)benzonitrile (poly2‐4), 2,6‐bis(3‐aminophenoxy)benzonitrile (poly2‐6), and 1,3‐bis‐2‐cyano‐3‐(3‐aminophenoxy)phenoxybenzene (poly2CN). These polyimides differ in the position of the dipolar groups ? CN in the aromatic ring (poly2‐4 and poly2‐6) and in the number of these groups in the repetitive unit (poly2‐6 and poly2CN). The imidization degree has been studied by Fourier transform infrared (FTIR) and thermogravimetry‐mass spectrometry (TG‐MS) and thermal properties by differential scanning calorimetry (DSC) and thermogravimetry (TG). The piezoelectric behavior has been analyzed from remnant polarization measurements. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 722–730, 2009     

Synthesis,characterization, and thermal properties of ladderlike polyepoxysiloxanes

Starting from trichlorosilanes and using 1,4‐phenylenediamine as a template, we have synthesized some ladderlike poly(glycidyl‐co‐alkyl/aryl)siloxanes (polyepoxysiloxanes or polyepoxies for short). The structures of copolymers were confirmed through IR, ¹H NMR, elemental analyses, and gel permeation chromatography. Curing behaviors of these polyepoxies in the absence and presence of a curing agent have been studied with DSC. It was shown that these epoxies could be cured without any curing agent. Copolymers having aromatic groups showed higher curing reactivity than those having alkyl groups. The experimental results also demonstrate that the curing reaction occurred solely via epoxy functionality, not via the condensation reaction of the hydroxy groups located at the end of polymer main chains. The thermal stability of the cured polymers was examined by thermogravimetric analysis. The results confirm that polyepoxies with aromatic groups had better thermal stability than those with alkyl groups. It was also found that polyepoxies cured with a diamine have a higher thermal stability than those cured in the absence of a curing agent. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2215–2222, 2001     

Studies on the thermal properties of caprolactam/long chain lactam copolymer

The thermal properties of caprolactam/long chain lactam copolymer were studied with a Perkin-Elmer DSC 7. The melting point (T _m), heat of fusion (δH _m), crystalline degree (X _c), crystallization temperature (T _c) and glass transition temperature (T _g) of the copolymers increase with decrease of the content of the log chain lactam. From the changes in the mechanical properties with corresponding changes in the thermal properties, it is clear that the copolymers are thermal plastic and elastic. In addition, it is found that the results at a heating rate of 10 deg·min^?1 are almost the same as that at 20 deg·min^?1 after thermal history is erased.     

The influence of soft segments on some properties of new transparent segmented polyurethanes

This work describes the synthesis and structure of the new segmented polyurethanes (SPURs) formed from an aliphatic diisocyanate [1,1′‐methanediylbis(4‐isocyanatocyclohexane] (Desmodur W^®) and unconventional sulfur‐containing chain extender [2,2′‐methylenebis([4,1‐phenylene]methylenesulfanediyl)diethanol]. Soft segments were poly(oxytetramethylene)diol of  = 1000 g/mol (PTMO) or poly(hexametylene carbonate)diol of  = 860 g/mol (PHCD). For all the polymers, the structure, physicochemical, thermal, and mechanical properties were determined. In addition, for selected polymers, optical properties (refractive index and transparency), adhesive properties, and antimicrobial activity were also determined. The type and amount of soft segment used for the synthesis of SPURs had a significant effect on the properties of the polymers. SPURs from PHCD are characterized by higher glass transition temperatures, molar masses, hardness (up to 91/50°Sh in scale A/D), and tensile strengths (up to 36.5 MPa) but lower elongations at break compared with the SPURs with PTMO. The tests of adhesion and optical properties showed that the PHCD‐based SPUR was characterized by higher value of refractive index, transparency, and more than three times the adhesive strength than the PTMO‐based SPUR. Antimicrobial activity studies showed that the SPUR presence in the medium inhibited proliferation of both Gram‐positive and Gram‐negative bacteria. Copyright © 2017 John Wiley & Sons, Ltd.     

Non-steady effective thermal properties of semi-infinite unidirectional fiber-reinforced composites using thermal wave method

Photothermal techniques and effective medium method combining with image method are applied to investigate the non-steady effective thermal properties of semi-infinite unidirectional fiber-reinforced composites, and the effect of the semi-infinite surface on the non-steady effective thermal properties is considered. The dispersion relation for the effective wave number in the semi-infinite random composites is derived. The image method is used to satisfy the adiabatic boundary condition at the semi-infinite surface. The numerical solutions of the non-steady effective thermal properties are obtained by using an iterative scheme. Analyses show that the variation of the non-steady effective thermal properties near the semi-infinite surface is significantly different from those of the infinite composite structure. The effects of the circular frequency of thermal waves, the volume fraction of fibers, and the properties contrast ratio on the maximum non-steady effective properties near the surface are examined. Comparison with the steady case is also given.     

Study of the influence of plasticizers on the thermal and mechanical properties of poly(3-hydroxybutyrate) compounds

The influence of four types of plasticizers, dioctyl phthalate (DOP), dioctyl adipate (DOA), triacetyl glycerol (TAG) and polyadipate (PA), in the thermal and mechanical properties of Poly(3-hydroxybutyrate) (PHB), a highly crystalline biodegradable polyester, was evaluated in this work. The plasticizers were introduced alone or mixtures of them, using concentrations that varied from 5 to 30% wt. Their influence in some important polymer parameters as Tg, Tm and degree of crystallinity, and on its mechanical behavior, elongation and tensile strain were investigated. The best results were obtained for the sample with 30% TAG and that one using a binary mixture of plasticizers PA 20% and TAG 10%.     

Preparation,thermal properties,and flame retardance of epoxy–silica hybrid resins

A novel epoxy system was developed through the in situ curing of bisphenol A type epoxy and 4,4′‐diaminodiphenylmethane with the sol–gel reaction of a phosphorus‐containing trimethoxysilane (DOPO–GPTMS), which was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with 3‐glycidoxypropyltrimethoxysilane (GPTMS). The preparation of DOPO–GPTMS was confirmed with Fourier transform infrared, ¹H and ³¹P NMR, and elemental analysis. The resulting organic–inorganic hybrid epoxy resins exhibited a high glass‐transition temperature (167 °C), good thermal stability over 320 °C, and a high limited oxygen index of 28.5. The synergism of phosphorus and silicon on flame retardance was observed. Moreover, the kinetics of the thermal oxidative degradation of the hybrid epoxy resins were studied. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2354–2367, 2003     

Applications of thermal analysis in some solid-state reactions

TG-DTG-DTA has been used to characterize various isomers of CoCl₂·2(CH₃C₆H₄NH₂). Thermal analysis is further used to analyse the binary mixtures of these isomers. DTA recorded after different elapsed times follows the progress of reaction between cobalt chloride and benzocaine where progressively small endotherms are associated with starting materials. The application of thermal analysis to following the solid-solid reactions between metal acetates and 8-hydroxyquinoline was highlighted. The stoichiometry of such reactions was confirmed from the decrease in intensity of an endotherm as one increases the stoichiometry.Thanks are due to Drs. Keshav Chander, K. Kaur, Rajinder Singh and G. S. Chopra for helpful discussions and experimental work.     

Ab-initio study of electronic,optical, thermal,and transport properties of Cr4AlB6

Theoretical investigation of different physical parameters of Cr₄AlB₆ have been done within the framework of density functional theory. Cr₄AlB₆ is a no band gap material. Its Cr-3d states contributes the most at the Fermi level. Thermal properties are investigated using quasi-harmonic Debye model as implemented in Gibbs code for different values of pressure and temperature. Study of transport property suggests that its electrical conductivity increases nonlinearly with increase in temperature but the relative change in its value is very low whereas its thermal conductivity increases linearly with the increase in temperature and relative increase in thermal conductivity is very high. The behavior of Cr₄AlB₆ is anisotropic and property is ceramic. It has potential applications in making ceramic capacitors. Its reflectivity is high in low energy region. It suggests that material can be used as coating material for far-infrared radiation. Study of the transport property suggests that because of very high value of thermal conductivity, it can be used for heat sink applications.     

Improved thermal and mechanical properties of polybenzoxazines based on alkyl‐substituted aromatic amines

The thermal and mechanical properties of polybenzoxazine thermoset networks containing varying amounts of phenolic Mannich bridges, arylamine Mannich bridges, and methylene bridges have been investigated. In materials based on m‐toluidine and 3,5‐xylidine, the onset of thermal degradation is delayed until around 350 °C with no significant effect on the final char yield. The first of the three weight‐loss events usually seen in aromatic amine‐based polybenzoxazines is absent in these two materials. Materials with additional amounts of arylamine Mannich bridges and methylene bridges show improved mechanical properties, including higher crosslink densities and rubbery plateau moduli. Correlations between the observed mechanical properties and network structures are established. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3289–3301, 2000