Structure‐property relationships of LLDPE—highly filled with aluminum hydroxide

The mechanical performance, rheological behavior, and phase morphology of linear low‐density polyethylene (LLDPE) highly loaded with aluminum hydroxide [Al(OH)₃] were investigated. It was found that titanate surface‐active agent and ethylene‐vinyl acetate copolymer (EVA) improve the processing and ductile properties of the composite remarkably but are accompanied by the deterioration of the tensile strength. Addition of vinyl triethoxy silane (VTEO) and dicumyl peroxide (DCP) improves the tensile strength of the composite because of the silane crosslinking structure introduced. A synergistic effect of interface modifying and silane crosslinking method in improving mechanical performance of the composite is presented. Phase morphology of the LLDPE/Al(OH)₃ composites was studied by means of scanning electron microscopy (SEM) technique. SEM micrographs indicate that a core‐shell type with Al(OH)₃ as a core and EVA as a shell is formed in the composite. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2485–2490, 2002     

氢氧化铝高填充聚乙烯材料的界面和力学性能

从Al(OH)3高填充线型低密度聚乙烯（LLDPE）材料的界面性质出发,研究了复合材料界面改性与硅烷交联方法对LLDPE/Al(OH)3复合材料的微观结构,加工流动性及力学性能的影响。钛酸酯和乙烯-醋酸乙烯共聚物能显著改善LLDPE/Al(OH)3复合材料的延伸性能,硅烷交联与界面改性对改善材料的力学性能具有协同作用。     

Carboxymethylation of γ‐irradiated starch

Low viscosity carboxymethyl corn starch was prepared by the reaction of γ‐irradiated starch with monochloroacetic acid in the presence of alkali. It was found that irradiation dose influences the product viscosity remarkably. The viscosity decreases as the irradiation dose level increases; however, the viscosity increases with the increasing dose rate and the degree of substitution (DS). γ‐Irradiation can activate the starch to react with monochloroacetic acid, and the more of the irradiation dose, the higher of the DS and the reaction efficiency. The product has the character of low viscosity at high concentration, and the more of the irradiation dose, the more similar of the rheological behavior to a Newtonian liquid. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2210–2215, 2006     

Oxidation of γ‐irradiated microbial cellulose results in bioresorbable,highly conformable biomaterial

Conformability to tissues and adequate mechanical strength are clinically useful properties of resorbable biomaterials used in soft tissue repair. Microbially derived cellulose is attractive as a high strength, highly conformable, and biocompatible material for tissue repair, but is not naturally resorbable. Here we show that controlled oxidation of microbial cellulose sheets that have been pre‐irradiated with γ‐radiation results in a resorbable and fully conformable membrane that can be rapidly rehydrated in aqueous fluids. In vitro studies showed that degradation of the resorbable membranes occurs in two major phases: (1) initial rapid degradation of about 70–80% of the entire sample followed by (2) slower degradation of an additional 5–10% which eventually levels off leaving a small amount of nonresorbable material. In vivo, prototype materials showed marked degradation at all time points, with the most rapid degradation occurring in the first 2–4 weeks. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39995.     

TGA analysis of γ‐irradiated linear low‐density polyethylene

Linear low‐density polyethylene (LLDPE), based on butene‐1 or hexene‐1, was irradiated with γ‐rays under vacuum or in the presence of air. The study focused on the influence of the dose rate and the γ‐dose on the thermal properties of LLDPE. Differential scanning calorimetry, thermogravimetric analysis (TGA), and TGA/FTIR techniques were used to address the thermal behavior as a result of γ‐irradiation. During this irradiation, competition between crosslinking and scission reactions, subsequent to oxidation reactions, occurred in the polymeric material, which strongly depends on the experimental conditions. A decrease of the crystallinity for γ‐irradiated samples was observed in particular for samples irradiated under vacuum. This observation may be explained by increased hindrance of segment mobility due to crosslinking reactions that prevent crystal growth. TGA investigations revealed an enhancement of the thermal stability for samples irradiated under vacuum but not for those irradiated in air. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2790–2795, 2006     

Physicomechanical properties of α‐cellulose–filled styrene–butadiene rubber composites

In this research, the influence of adding α‐cellulose powder to styrene–butadiene rubber (SBR) compounds was investigated. Physicomechanical properties of SBR–α‐cellulose composites, including tensile strength, elongation, Young's modulus, tear strength, hardness, abrasion, resilience, and compression set, before and after ageing, were determined and analyzed. Young's modulus, hardness, and compression set increased and elongation and resilience decreased with increasing α‐cellulose loading in the composites, whereas tensile strength, tear strength, and abrasion resistance initially increased at low α‐cellulose concentration (5 phr), after which these properties decreased with increasing α‐cellulose content. Lower loadings of α‐cellulose (5 phr) showed better results than higher loadings, given that tensile strength, tear strength, and abrasion resistance increased at low α‐cellulose concentration. Theoretical prediction of elastic modulus was carried out using rule of mixtures, Hashin, Kerner, and Halpin–Tsai equations. Calculated results show that these equations are not suitable for accurate prediction for the work carried out. However, these models can be used with confidence for the prediction of elastic modulus because experimental results are higher than the calculated values. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2203–2211, 2005     

Electrical and thermal properties of γ‐irradiated nitrile rubber/rice husk ash composites

The effects of both the rice husk ash (RHA) loading and fumed silica (FS) loading on the structure, thermal stability, and electrical properties of acrylonitrile–butadiene rubber (NBR) composites were studied. The filler loading were chosen to be 5 and 20 phr for RHA and 5 and 30 phr for silica. Also, the effect of the γ‐irradiation dose (25 kGy) on these parameters was investigated. The structure and thermal stability were studied with X‐ray diffraction and thermogravimetric analysis techniques. Furthermore, some electrical parameters, such as the direct‐current electrical conductivity (σ_dc), activation energy (E_a), dielectric constant (?′), and dielectric loss (?″), were determined. The incorporation of both RHA and FS resulted in improved thermal stability after γ irradiation at 25 kGy. The loading of FS on NBR was shown to decrease σ_dc, ?′, and ?″ and increase E_a. On the other hand, the loading of RHA showed the opposite trend. Finally, γ irradiation of NBR composites filled with both fillers decreased the values of σ_dc, ?′, and ?″ for all the samples, which followed the trend for the unirradiated composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dielectric properties of copolymers based on cyano monomers and methyl α‐acetoxyacrylate

With the aim of developing dielectric polymers containing CN groups with strong dipole moment, alternating and statistical copolymers of the cyano monomers vinylidene cyanide (VCN), acrylonitrile and methacrylonitrile with methyl α‐acetoxyacrylate (MAA) were synthesized and characterized. The copolymer's composition and microstructure were analysed by NMR spectroscopy, SEC and elemental analysis. The reactivity ratios calculated from the Q–e Alfrey–Price parameters for these copolymers indicated the alternating and statistical structures confirmed by NMR analysis. The copolymers have glass transition temperatures T_g in the range 83–146 °C and are stable up to 230 °C. The thermal stability of the copolymers depends on the nature of the cyano monomers. Their molecular dynamics were investigated by dielectric relaxation spectroscopy. We revealed a weak relaxation β at sub‐T_g temperature for poly(VCN‐co‐MAA) usually originating from molecular motions that are restricted to the scale of a few bond lengths. Strong α‐relaxation processes occurred above T_g for these copolymers. This primary relaxation was associated with cooperative movements of the polar groups (CN) at the time of mobility of the principal chains. The activation energy of the α‐relaxation process was also calculated. The values of the dielectric increment Δε for these copolymers were determined by Cole–Cole plots and indicated that the copolymers exhibit interesting dielectric properties compared with similar cyano materials. The polarity–permittivity relationship was also established. © 2012 Society of Chemical Industry     

Crystalline morphology and mechanical properties of isotactic polypropylene composites filled by wollastonite with β‐nucleating surface

Wollastonite‐filled α‐isotactic polypropylene (iPP) and β‐iPP were prepared through introduction of wollastonite (W) and wollastonite with β‐nucleating surface (W_x) in iPP matrix. The α‐ and β‐nucleating ability of wollastonite, crystalline morphology, and mechanical properties of injected iPP filled by wollastonite with different nucleating surface were compared using differential scanning calorimetry, wide‐angle X‐ray diffraction, polarizing optical microscopy, mechanical testing, and scanning electron microscopy. The results indicated that iPP filled by wollastonite with different nucleating surface has different crystalline morphology, melting behavior, and mechanical properties. The W and W_x filled iPP mainly formed α‐ and β‐phase iPP, respectively. The tensile and flexural modulus of iPP/W and iPP/W_x increased with increasing wollastonite content, and the tensile and flexural modulus of iPP/W_x were lower than that of iPP/W. The tensile property, flexural property, and impact strength of iPP/W_x were higher than that of iPP/W and β‐iPP. The synergistic effect of reinforcing of wollastonite and toughening of β‐phase leads to higher mechanical properties. POLYM. COMPOS., 35:1445–1452, 2014. © 2013 Society of Plastics Engineers     

Characterization of degradation of polypropylene nonwovens irradiated by γ‐ray

Polypropylene is a leading commercial, fiber‐forming polymer due to its low cost and potential for making high strength fibers. As the polymer of choice in the biomedical field, polypropylene contains only two elements, namely carbon and hydrogen. As a result, it is very hydrophobic and bio‐inert lacking biodegradability in the landfill. Meltblown and spunbond polypropylene nonwovens were exposed to γ‐radiation doses up to 25 kGy. The changes in morphology, chemical, thermal, and tensile properties were characterized by various analytical techniques. Following γ‐radiation, the FTIR spectrum illustrated an increase in carbonyl groups suggesting radio‐oxidation. Additionally, there was a decrease in thermal and tensile properties indicating deterioration of the polymer. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39917.     

Synthesis and characterization of thermoplastic composites filled with γ‐boehmite for fire resistance

This paper explores the use of boehmite as a fire retardant in low‐density polyethylene and polyamide 6. The structure and morphology of the filler are characterized by X‐ray diffraction and scanning electron microscopy. The water content of our boehmite is estimated about 30% by thermogravimetric analysis. The filler/matrix interactions in nanocomposites are investigated by means of thermo‐physical measurements: differential scanning calorimeter and thermogravimetry. The resulting morphology shows particles individually dispersed in the matrix. The fire tests present a fire‐resistance effect at low filler content despite a different behavior as a function of the matrix. For instance, with only 2% volume of boehmite, the burning time of LDPE composite is significantly increased by 15%. At the same filler content in PA6, the burning time is solely increased by 4.5%. On the other hand, the limiting oxygen index is increased by +7.0% (only 2.6% with LDPE composites). Copyright © 2010 John Wiley & Sons, Ltd.     

Modification of properties of CaCO3‐polymerization‐filled polyethylene

CaCO₃–polyethylene (PE) compositions, containing an ultrahigh molecular polyethylene (UHMPE) interlayer between the filler surface and the PE matrix, were synthesized by two‐step polymerization of ethylene on a filler surface activated with a suitable catalyst. The properties of the compositions were studied depending on the molecular weight of the PE matrix and the thickness of the UHMPE intermediate layer at the filler particles. It was shown that the presence of UHMPE as an interlayer in chalk–UHMPE–PE compositions leads to an increase of plastic deformation of the materials as long as the M_w value of the PE matrix is higher than is the brittleness threshold for PE. Chalk–UHMPE–PE compositions exhibit a higher ability for plastic deformation compared to chalk–PE compositions based on a PE matrix of a molecular weight equal to the molecular weight of the total polymer phase (UHMPE–PE) in the first case. There is no improvment of the mechanical properties when the UHMPE is dispersed in the compositions and not as an interlayer between a filler and a matrix. This means that the method of polymerization filling allows one to incorporate the polymer interlayer with a desired nature and properties between a filler surface and polymer matrix in filled polyolefin compositions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 577–583, 2003     

HIPS/γ‐irradiated UHMWPE/carbon black blends: Structuring and enhancement of mechanical properties

CB‐containing HIPS/UHMWPE and HIPS/XL‐UHMWPE are unique systems, in which structuring takes place, affecting the electrical (to be described in a future article), rheological, mechanical, and dynamical‐mechanical properties. The XL‐UHMWPE particles have undergone structural fixation due to the crosslinking, maintaining their porosity and internal intricate structure even after high‐temperature melt processing, as opposed to the UHMWPE particles. Differences in the flow mechanisms of HIPS/UHMWPE and HIPS/XL‐UHMWPE blends have been attributed to polymer viscous flow in the former case vs. particle slippage in the latter. The mechanical properties of HIPS/UHMWPE are enhanced when utilizing XL‐UHMWPE as a dispersed phase, especially the strength, because of changes in the inherent properties of the UHMWPE following irradiation, and in particular, the nature of the HIPS/XL‐UHMWPE interface. The results for the CB‐containing 70HIPS/30XL‐UHMWPE blend are especially surprising and of practical importance, due to the fact that no degradation of the mechanical properties has occurred as a result of the CB incorporation. The dynamical mechanical properties reflect the differences between the UHMWPE and XL‐UHMWPE‐containing blends as well. The presence of either type of UHMWPE, CB content, and blend composition affect the dissipation, but have only a minor influence on the transition temperatures of the components. Of special interest is the increased damping of XL‐UHMWPE–containing compositions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1731–1744, 1999     

Dielectric properties of highly filled thermoplastics for printed circuit boards

In this study, highly filled high‐temperature thermoplastics (polyethersulfone [PES], polyphenylensulfide, polyetherimide [PEI], and polyetheretherketone [PEEK]) are used as insulating substrate for printed circuit boards (PCBs). Talc has been added to the thermoplastics to adjust their coefficient of thermal expansion (CTE) to the CTE of the copper circuits, thus reducing the possibility of failure of the PCB owing to thermal stress. The dielectric properties of the substrates were analyzed between 10 MHz and 1 GHz, depending on filler fraction and water absorption. An increase of filler fraction resulted in an increase of dielectric constant ε′. As expected, the absorption of water molecules led to an increase of both tan δ and ε′. Moreover, the combination of filler and absorbed water resulted in a strong increase of the dielectric loss factor at low frequencies. Finally, theoretical approaches with fitting parameters could be employed to precisely describe the measured properties between 0.8 and 1 GHz. This study shows that most of the materials investigated here, namely highly filled PPS, PEI, and PEEK, are suitable for high‐frequency PCB applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

One‐Pot Quinine‐Catalyzed Synthesis of α‐Chiral γ‐Keto Esters: Enantioenriched Precursors of cis‐α,γ‐Substituted‐γ‐Butyrolactones

A highly enantioselective one‐pot synthesis of important building blocks, α‐chiral γ‐keto esters, has been developed by combining a quinine‐catalyzed Michael addition of malononitrile to trans‐enones followed by magnesium monoperoxyphthalate (MMPP) oxidation. These synthons proved to be useful reagents for a simple access to challenging cis‐α,γ‐disubstituted γ‐butyrolactones in good diastereoselectivity and high enantiocontrol.

     

Study on mechanical properties of perlite‐filled gamma‐irradiated polypropylene

This study covers the preparation and characterization of perlite‐filled polypropylene (PP). The compositions of 15, 30, and 50 % by weight perlite–PP composites were prepared by melt‐mixing. The PP used in this study was either applied in the virgin form or γ‐irradiated in air at the doses of 10, 25, 50, and 100 kGy to determine the effect of oxidative degradation in composite properties. Furthermore, the active sites containing oxygen produced by γ‐irradiation in PP may provide a possible enhancement by the interfacial interaction between perlite and PP. An initial sharp drop in torque readings during the melt‐mixing of perlite–PP composite preparation indicated an extensive chain scission and degradation by γ‐irradiation. The thermal properties of the composites were characterized by DSC. The ultimate tensile strength and elongation and also impact strength decreased in all composites with γ‐irradiation. Yet, these changes appeared not to be faster than was the change in unfilled PP upon irradiation. Scanning electron microscopy revealed an interfacial adhesion between perlite and irradiated PP while virgin PP did not show any evidence of adhesion. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2670–2678, 2001     

Synthesis of γ‐Fluoro‐α, β‐unsaturated Carboxylic Esters from Saturated α‐Fluoro Aldehydes

γ‐Fluoro‐α, β‐unsaturated carboxylic esters 7a, 7b and 7d and 4‐fluoro‐4‐phenylbut‐3‐enoic ester ( 8 ) are obtained by two alternative pathways from 2‐fluoro aldehydes 5a—d , either by Horner—Wadsworth—Emmons reaction or by Wittig reaction. The aldehydes 5a—d are prepared by Swern oxidation of the corresponding fluorohydrins 4a—d . These are available from α‐olefins by bromofluorination, bromineby‐acetate replacement and subsequent hydrolysis.     

Nanostructured α- and β-cobalt hydroxide thin films

A new perspective in the use of electrochemical methods to deposit cobalt hydroxide thin films is presented. Ordered arrays of α-Co(OH)₂ (hydrotalcite-like (Co-HT)) and β-Co(OH)₂ nanoparticles were synthesized on transparent conductive oxide (TCO) substrates by localized cathodic electrogeneration of hydroxyl via the reduction of NO₂⁻ (or NO₃⁻) ion precursors in solution containing Co²⁺ in very low concentration. The thin films, analyzed by X-ray diffraction and scanning electron microscopy were found to be composed of vertically oriented platelets with the crystallographic c-axis parallel to the substrate surface. Turbostratic disorder was not observed in the films. UV/Vis spectra and thermal gravimetric analyses (TGA) indicated distinct variation between the Co-HT structures. Films deposited at 60 °C using a nitrite precursor generated uniform, vibrant-green mixed-valence Co-HT (Co²⁺/Co³⁺). Nitrate precursors yielded a “hydroxyl-deficient” Co-HT (Co²⁺ only). Films deposited at 95 °C in nitrate solution yielded β-Co(OH)₂. The films obtained in presence of nitrite were thicker than those obtained in nitrate. They were formed of β-Co(OH)₂ and contained traces of Co-HT.     

Preparation and characterization of γ‐irradiated crosslinked silicone rubber/organoattapulgite composites

Silicone rubber (SR)/organoattapulgite (OAT) composites were prepared with γ‐irradiation crosslinking at a dose range varied from 30 to 300 kGy. Natural fibrillar silicate attapulgite (AT) was modified by silane coupling agent, and the obtained OAT was used as reinforcing fillers in SR. The effect of irradiation doses on the degree of crosslinking of SR/OAT composites was determined by solvent swelling method. It was found that the molecular weight between crosslinks (M_c) reduced with the increase in irradiation doses. Moreover, the addition of OAT to SR matrix promoted an increase in the crosslinking density of the composites because of the presence of the active crosslinking sites of OAT. The mechanical properties of the SR/OAT composites including tensile strength, elongation at break, and Shore A hardness subjected to various irradiation doses were studied. The experimental results showed that the tensile strength, elongation at break, and Shore A hardness were all improved significantly in the presence of OAT, which indicated that OAT was an alternative reinforcing filler of SR. In addition, the effect of various irradiation doses on the mechanical properties of SR and SR/OAT composites was also investigated. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers