Viscoelastic and thermal properties of woven‐sisal‐fabric‐reinforced natural‐rubber biocomposites

Textile–rubber biocomposites were prepared by the reinforcement of natural rubber with woven sisal fabric. The viscoelastic properties of the composites were analyzed at different frequencies. Sisal fabric was subjected to different chemical modifications, such as mercerization, silanation, and thermal treatment, and the influences of the modifications on the dynamic mechanical properties were analyzed. The storage modulus was found to increase with reinforcement of natural rubber with woven sisal fabric. The chemical modification of the sisal fabric resulted in a decrease in the storage modulus. The damping factor was found to decrease with chemical treatment, and the gum compound exhibited maximum damping characteristics. The thermal stabilities of the composites were also analyzed by thermogravimetric studies. Scanning electron microscopy studies were performed to evaluate the morphology of the fabric–matrix interface.© 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermal decomposition studies of Schiff‐base‐substitute polyphenol–metal complexes

The thermal behaviors of 2,3‐bis[(2‐hydroxyphenyl)methylene] diaminopyridine, oligo‐2,3‐bis[(2‐hydroxyphenyl)methylene] diaminopyridine, and some oligo‐2,3‐bis[(2‐hydroxyphenyl) methylene] diaminopyridine–metal complexes were studied in a nitrogen atmosphere with thermogravimetric analysis, derivative thermogravimetric analysis, and differential thermal analysis techniques. The decompositions of oligo‐2,3‐bis[(2‐hydroxyphenyl) methylene] diamino pyridine–metal complexes occurred in multiple steps. The values of the activation energy (E) and reaction order of the thermal decomposition were calculated by means of several methods, including Coats–Redfern, Horowitz–Metzger, Madhusudanan–Krishnan–Ninan, van Krevelen, Wanjun–Yuwen–Hen–Cunxin, and MacCallum–Tanner on the basis of a single heating rate. The most appropriate method was determined for each decomposition step according to a least‐squares linear regression. The E values obtained by each method were in good agreement with each other. It was found that the E values of the complexes for the first decomposition stage followed the order E_OHPMDAP–Ni > E_OHPMDAP–Cd > E_OHPMDAP–Cu > E_OHPMDAP–Fe > E_OHPMDAP–Zn > E_OHPMDAP–Co > E_OHPMDAP–Cr > E_HPMDAP > E_OHPMDAP. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal degradation kinetics of poly(N‐adamantyl‐exo‐nadimide) synthesized by addition polymerization

The thermal decomposition behavior and degradation kinetics of poly(N‐adamantyl‐exo‐nadimide) were investigated with thermogravimetric analysis under dynamic conditions at five different heating rates: 10, 15, 20, 25, and 30°C/min. The derivative thermogravimetry curves of poly(N‐adamantyl‐exo‐nadimide) showed that its thermal degradation process had one weight‐loss step. The apparent activation energy of poly(N‐adamantyl‐exo‐nadimide) was estimated to be about 214.4 kJ/mol with the Ozawa–Flynn–Wall method. The most likely decomposition process was an F1 deceleration type in terms of the Coats–Redfern and Phadnis–Deshpande results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3003–3009, 2007     

A Novel Intumescent Flame‐Retardant Polyethylene System

Summary: A novel carbonization agent was synthesized and characterized. The flame retardancy and thermal behavior of a new IFR system with and without metal chelates for LDPE were investigated by LOI, UL‐94 test, and TGA. Metal chelates can remarkably improve the flame retardant performance of intumescent systems according to the tested results of LOI values and UL‐94 ratings because they can act both as inhibitors of radicals and as promoters of carbonization. The TG curves show that the amounts of residue of IFR‐PE/metal chelate systems increase compared to those of PE and IFR‐PE at temperatures ranging from 400 to 650 °C. The IFR‐PE/metal chelate system can obviously reduce the amounts of decomposing products at higher temperatures and promotes the formation of carbonaceous charred layers. A LOI value of 29.8 and UL‐94 V‐0 rating could be achieved when the synthesized carbonization agent, APP, MP, and CoOSA were added into LDPE.

TG curves of PE, IFR‐PE, and IFR‐PE/metal chelate systems.     

Effects of polyethylene‐grafted maleic anhydride (PE‐g‐MA) on thermal properties,morphology, and tensile properties of low‐density polyethylene (LDPE) and corn starch blends

The effects of polyethylene‐grafted maleic anhydride (PE‐g‐MA) on the thermal properties, morphology, and tensile properties of blends of low‐density polyethylene (LDPE) and corn starch were studied with a differential scanning calorimeter (DSC), scanning electron microscope (SEM), and Instron Universal Testing Machine, respectively. Corn starch–LDPE blends with different starch content and with or without the addition of PE‐g‐MA were prepared with a lab‐scale twin‐screw extruder. The crystallization temperature of LDPE–corn starch–PE‐g‐MA blends was similar to that of pure LDPE but higher than that of LDPE–corn starch blends. The interfacial properties between corn starch and LDPE were improved after PE‐g‐MA addition, as evidenced by the structure morphology revealed by SEM. The tensile strength and elongation at break of corn starch–LDPE–PE‐g‐MA blends were greater than those of LDPE–corn starch blends, and their differences became more pronounced at higher starch contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2904–2911, 2003     

聚乙烯的热降解动力学研究

采用三种不同的动力学分析方法,即Freeman方法、Flynn-Wall-Ozawa以及Kissinger方法对不同类型聚乙烯的热分解动力学进行了探讨。结果表明,Flynn-Wall-Ozawa法I、Friedman法的测试结果与三者聚乙烯的结构特征较吻合,不同聚乙烯降解活化能的大小顺序为HDPE>LLDPE>LDPE。     

Thermal decomposition kinetics of poly(nButMA‐b‐St) diblock copolymer synthesized by ATRP

The reaction mechanism of decomposition process and the kinetic parameters of the poly(n‐butyl methacrylate‐b‐styrene), poly(nButMA‐b‐St), diblock copolymer synthesized by atom transfer radical polymerization (ATRP) were investigated by thermogravimetric analysis (TGA) at different heating rates. TGA curves showed that the thermal decomposition occurred in one stage. The apparent activation energies of thermal decomposition for copolymer, as determined by the Kissinger's, Flynn–Wall–Ozawa and Tang methods, which does not require knowledge of the reaction mechanism (RM), were 112.52, 116.54, and 113.41 kJ/mol, respectively. The experimental results were compared with master plots, in the range of the Doyle approximation. Analysis of experimental results suggests that in the conversion range studied, 3–18%, the actual RM is an A₂ sigmoidal type. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Transparent,Lightweight, and High Strength Polyethylene Films by a Scalable Continuous Extrusion and Solid‐State Drawing Process

The continuous production of transparent high strength ultra‐drawn high‐density polyethylene films or tapes is explored using a cast film extrusion and solid‐state drawing line. Two methodologies are explored to achieve such high strength transparent polyethylene films; i) the use of suitable additives like 2‐(2H‐benzotriazol‐2‐yl)‐4,6‐ditertpentylphenol (BZT) and ii) solid‐state drawing at an optimal temperature of 105 °C (without additives). Both methodologies result in highly oriented films of high transparency (≈91%) in the far field. Maximum attainable modulus (≈33 GPa) and tensile strength (≈900 MPa) of both types of solid‐state drawn films are similar and are an order of magnitude higher than traditional transparent plastics such as polycarbonate (PC) and poly(methyl methacrylate). Special emphasis is devoted to the effect of draw down and pre‐orientation in the as‐extruded films prior to solid‐state drawing. It is shown that pre‐orientation is beneficial in improving mechanical properties of the films at equal draw ratios. However, pre‐orientation lowers the maximum attainable draw ratio and as such the ultimate modulus and tensile strength of the films. Potential applications of these high strength transparent flexible films lie in composite laminates, automotive or aircraft glazing, high impact windows, safety glass, and displays.     

不同类型聚乙烯光氧老化特性比较研究

利用热重分析法、热分解动力学Coats-Redfern方法和力学性能测试研究了不同类型聚乙烯[高密度聚乙烯(PE-HD)、线型低密度聚乙烯(PE-LLD)、低密度聚乙烯(PE-LD)]在氙灯光氧老化条件下的热稳定性、动力学参数和力学性能的变化规律。结果表明,随着老化时间的延长,PE-LD的热稳定性下降幅度最大,且主要集中于老化后期;老化初期PE-HD,PE-LLD和PE-LD的活化能均下降较快,表明此时三者均发生了较为严重的老化现象,分子链断裂较为强烈,而老化后期活化能下降幅度顺序为PE-LDPE-LLDPE-HD,表明这个期间PE-LD的老化最为强烈;PE-LD比PE-HD和PE-LLD的弯曲强度和冲击强度下降更为显著,且主要集中于老化后期,PE-LLD的力学性能下降幅度次于PE-HD。3种聚乙烯光氧老化容易顺序依次为PE-LDPE-LLDPE-HD。     

Synthesis,characterization, and catalytic study of polymeric metal complexes derived from divalent transition metal ions with 2,4‐dihydroxy benzophenone and 2,4‐dihydroxy acetophenone

The polymeric metal complexes of poly (3‐hydroxy‐4‐((Z)‐1‐(phenylimino)ethyl)phenyl‐3‐methylbut‐2‐enoate) designated as [poly(3H4‐1PEPMB)] and poly (3‐hydroxy‐4‐((Z)‐phenyl(phenylimino)methyl)phenyl‐3‐methylbut‐2‐enoate designated as [poly(3H4‐PPMPMB)] containing Cu(II), Ni(II), Co(II), Cd(II), Mn(II), Ca(II), and Zn(II) ions were synthesized. The ploymer ligands and metal complexes were charcterized by Fourier transform infrared, nuclear magnetic resonance (NMR), thermogravimetric analysis, differential scanning calorimeter (DSC), and X‐ray diffraction (XRD) techniques. The XRD study of the complexes revealed highly crystalline nature of polychelates. The polymeric complexes were active for the oxidation of aldehyde group. The oxidation activity of Cu (II) complex of poly (3H4‐1PEPMB) was studied for the oxidation of benzaldehyde and its derivaties to corresponding carboxylic acids. The oxidation products were confirmed by GC‐MS analysis. The oxidation of aldehydes was quantitative with 100% selectivity for benzioc acid. Thermal analysis of complexes indicated reasonably good thermal stability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis,characterization, and thermal properties of alternate copolymers containing N,N′‐bis(diphenylsilyl)tetraphenylcyclodisilazane

Hexamethyldisilazane was used as the starting material to synthesize N,N′‐bis(hydroxydiphenylsilanyl)tetraphenylcyclodisilazane (BHPTPC). By condensation polymerization of BHPTPC with α,ω‐bis(dialkylamino)dimethylsiloxane, a series of alternate copolymers containing N,N′‐bis(diphenylsilyl)tetraphenylcyclodisilazane was synthesized. GPC studies show that the highest molecular weight was obtained at a ratio of 1.005 : 1 (BHPTPC: α,ω‐bis(dimethyl amino)dimethylsiloxane). Data of DSC indicate that the temperature of glass transition (T_g) and temperature of melting point (T_m) decreased with the increasing of dimethylsiloxane segments units. Three stages of degradation were found in the thermogravimetric analysis curves. The activation energy of the copolymer (with m = 2, 3, and 7) was calculated by using Flynn–Wall–Ozawa method. The activation energy of the copolymer with m = 2, 3, and 7 at second stage is 214, 211, and 184 kJ/mol, respectively. Isothermal gravimetric analysis shows that for the same temperature and the same time, the weight loss of the alternate copolymer was greatly less than that of common polydimethylsiloxane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 611–617, 2007     

Preparation of granular crosslinkable medium‐density polyethylene

Granular crosslinkable medium‐density polyethylene (XLPE) without scorch inhibitor was prepared adding organic peroxide [2, 5‐dimethyl‐ 2, 5‐ di‐ (t‐butyl‐peroxy) hexyne‐3] through extrution process, in industrial scale. Twin screw extruder was used to mix the polyethylene and the peroxide. The temperature zones of the extruder were controlled very carefully to prevent unwanted crosslinking during extrusion. Compression molding, rotational molding, and injection molding of XLPE at 155°C made no crosslinking in PE, and then they were exposed to higher temperatures at which the organic peroxide decomposed to provide free radicals which led to the crosslinking of the MDPE. The thermal properties (using dynamic mechanical analysis, DMA, differential scanning calorimetric analysis, DSC, and thermogravimetric analysis, TGA, techniques) and mechanical properties (including strain at break and stress at break) of virgin PE, crosslinkable PE, and crosslinked PE have been compared. The crossliked PE and virgin PE were also studied by X‐ray diffraction (XRD) technique. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1873–1879, 2007     

Thermal,dielectric, and mechanical properties of SiC particles filled linear low‐density polyethylene composites

A thermally conductive linear low‐density polyethylene (LLDPE) composite with silicon carbide (SiC) as filler was prepared in a heat press molding. The SiC particles distributions were found to be rather uniform in matrix at both low and high filler content due to a powder mixing process employed. Differential scanning calorimeter results indicated that the SiC filler decreases the degree of crystallinity of LLDPE, and has no obvious influence on the melting temperature of LLDPE. Experimental results demonstrated that the LLDPE composites displays a high thermal conductivity of 1.48 Wm^?1 K^?1 and improved thermal stability at 55 wt % SiC content as compared to pure LLDPE. The surface treatment of SiC particles has a beneficial effect on improving the thermal conductivity. The dielectric constant and loss increased with SiC content, however, they still remained at relatively low levels (<10² Hz); whereas, the composites showed poorer mechanical properties as compared to pure LLDPE. In addition, combined use of small amount of alumina short fiber and SiC gave rise to improved overall properties of LLDPE composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A novel method for the preparation of monocarboxyl‐end‐grouped polycaprolactam with an adjustable molecular weight

A novel method was used to synthesize adjustable‐molecular‐weight polycaprolactams with monocarboxyl end groups. The reaction device and conditions are discussed. The products were characterized by Fourier transform infrared spectroscopy, ¹H‐NMR spectroscopy, high‐resolution pyrolysis gas chromatography–mass spectrometry, and wide‐angle X‐ray diffraction. The thermal properties were studied by differential scanning calorimetry and thermogravimetric analysis. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 722–727, 2004     

Polyethylene‐collagen hydrolizate thermoplastic blends: Thermal and mechanical properties

Collagen, a natural macromolecular protein from renewable resources, is widely used in many industrial applications. Mixtures of low‐density polyethylene (LDPE) with collagen hydrolizate derived from the tannery industry were investigated to assess the feasibility of producing polymeric materials suitable for production of thermoplastic items for applications in packaging and agricultural segments. Different grades of polyethylenes and collagen hydrolizates characterized by different molecular weight and salinity were investigated to develop optimal blends. The physical–chemical properties of the obtained blends were assessed by thermal–mechanical, spectroscopical analysis. Following the ongoing research activity, the reutilization of collagen hydrolizate derived from the leather industry for the production of environmental degradable polyethylene‐based thermoplastic films appears feasible and promising. Blends of collagen hydrolizate and LDPE up to 20–30 wt % of collagen hydrolizate allow obtaining slightly opaque, cohesive and flexible films that show satisfactory thermal–mechanical responses. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermostability and esterification of a polyethylene‐immobilized lipase from Bacillus coagulans BTS‐3

Extracellular lipase from Bacillus coagulans BTS‐3 was immobilized on activated (alkylated, 2.5% glutaraldehyde) and native (nonactivated) polyethylene powder, and its thermostability and esterification efficiency were studied. Immobilization on activated support was found to enhance thermostability as well as esterification efficiency. The optimum time for immobilization on activated (AS) and nonactivated (NS) polyethylene support was found to be 10 min, and the binding of the lipase was markedly higher on AS. Lipase was more efficiently bound to AS (64%) than to NS (30%) at an optimum temperature of 37°C. The pH and temperature optima for AS‐ and NS‐bound lipase were 9.0 and 55°C and 8.5 and 55°C respectively. At 55°C the free lipase, which had a half‐life of 2 h, lost most of its activity at elevated temperatures. In contrast, AS‐bound lipase retained 60%–80% of its original activity at 55°C, 60°C, 65°C, and 70°C for 2 h. Exposure to organic solvents resulted in enhanced lipase activity in n‐hexane (45%) and ethanol (30%). Both AS‐ and NS‐bound biocatalysts were recyclable and retained more than 85% of their initial activity up to the fourth cycle of hydrolysis of p‐nitrophenyl palmitate. The AS‐bound lipase efficiently performed maximum esterification (98%) of ethanol and propionic acid (300 mM each, 1 : 1) in n‐hexane at 55°C. With free or NS‐bound lipase in similar conditions, the conversion of reactants into ester was relatively low (40%). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3986–3993, 2006     

Thermal properties of hydrophobically modified methacrylic acid–ethyl acrylate copolymer solutions

The thermal behavior of a water‐soluble associating polymer system, hydrophobically modified alkali‐soluble emulsion (HASE) polymer, was investigated. This polymer contains a methacrylic acid–ethyl acrylate copolymer backbone with 1 mol % of pendant hydrophobic groups grafted to it. The thermal behavior of the HASE polymer exhibits different trends compared to the hydrophobic ethoxylated urethane (HEUR) system. The lifetime of the hydrophobic junction of the HASE polymer increases with temperature due to the increase in the entropy of the system. However, the structural relaxation time decreases with temperature, caused by the enhanced Brownian dynamics of polymer chains. The relaxation behavior of HASE polymers is either governed by the lifetime of the hydrophobic junction, the structural relaxation time, or a combination of both, depending on the degree of network formation and temperature. Temperature studies indicated that the transient network theory proposed by Tanaka and Edwards is inadequate for describing the activation process of hydrophobic junctions in the HASE associative polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 604–612, 2004     

Nanocomposites Based on Polyethylene and Polyhedral Oligomeric Silsesquioxanes, 1 – Microstructure,Thermal and Thermomechanical Properties

Nanocomposites of linear low‐density polyethylene (LLDPE), with three different amounts of polyhedral oligomeric silsesquioxanes (POSS), were prepared through melt‐mixing in a batch‐mixer at 150 °C. The structure of the prepared nanocomposites was studied by X‐ray scattering and optical microscopy. The surface morphology of the nanocomposites was investigated through field‐emission SEM. The thermal properties of the pure LLDPE and nanocomposites were studied by differential scanning calorimeter (DSC). Thermomechanical properties were assessed on a Paar‐Physics MCR501 rheometer using a solid‐state rectangular fixture. Results exhibited a significant improvement in both the storage and loss moduli of the neat LLDPE upon the incorporation of the POSS particles. A substantial improvement in thermal stability was also observed in the high‐temperature region.

     

Evaluation of the tensile properties and thermal stability of ultrahigh‐molecular‐weight polyethylene fibers

The thermal stability of ultrahigh‐molecular‐weight polyethylene (UHMWPE) should be paid attention in its applications, although the fiber has excellent flexible tensile properties. The measurements for two kinds of UHMWPE fibers, Dyneema SK65 (The Netherlands) and ZHF (Beijing, China), were carried out at different annealing temperatures and for different aging times. Experimental and regression analysis results showed that the aging behavior of the fibers followed an exponential attenuation with the annealing temperature and aging time. The critical temperature for the safe use of the fibers was equal to or lower than 70°C and depended on the glass‐transition temperature; this was validated by tensile tests. The difference between the two fibers in the thermal properties resulted from the intrinsic supermolecular structures of the two fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 310–315, 2005     

Microstructure and physical properties of open‐cell polyolefin foams

The cellular structure, physical properties, and structure–property relationships of novel open‐cell polyolefin foams produced by compression molding and based on blends of an ethylene/vinyl acetate copolymer and a low‐density polyethylene have been studied and compared with those of closed‐cell polyolefin foams of similar chemical compositions and densities and with those of open‐cell polyurethane foams. Properties such as the elastic modulus, collapse stress, energy absorbed in mechanical tests, thermal expansion, dynamic mechanical response, and acoustic absorption have been measured. The experimental results show that the cellular structure of the analyzed materials has interconnected cells due to the presence of large and small holes in the cell walls, and this structure is clearly different from the typical structure of open‐cell polyurethane foams. The open‐cell polyolefin foams under study, in comparison with closed‐cell foams of similar densities and chemical compositions, are good acoustic absorbers; they have a significant loss factor and lower compressive strength and thermal stability. The physical reasons for this macroscopic behavior are analyzed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009