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     

Ultradrawing properties of ultrahigh‐ molecular‐weight polyethylene/carbon nanotube fibers prepared at various formation temperatures

The influence of formation temperature on the ultradrawing properties of ultrahigh‐molecular‐weight polyethylene/carbon nanotube (UHMWPE/CNT) fiber specimens is investigated. Gel solutions of UHMWPE/CNT with various CNT contents were gel‐spun at the optimum concentration and temperature but were cooled at varying formation temperatures in order to improve the ultradrawing and tensile properties of the UHMWPE/CNT composite fibers. The achievable draw ratio (D_ra) values of UHMWPE/CNT as‐prepared fibers reach a maximum when they are prepared with the optimum CNT content and formation temperature. The D_ra value of UHMWPE/CNT as‐prepared fibers produced using the optimum CNT content and formation temperature is about 33% higher than that of UHMWPE as‐prepared fibers produced using the optimum concentration and formation temperature. The percentage crystallinity (W_c) and melting temperature (T_m) of UHMWPE/CNT as‐prepared fiber specimens increase significantly as the formation temperature increases. In contrast, W_c increases but T_m decreases significantly as the CNT content increases. Dynamic mechanical analysis of UHMWPE and UHMWPE/CNT fiber specimens exhibits particularly high α‐transition and low β‐transition, wherein the peak temperatures of α‐transition and β‐transition increase dramatically as the formation temperature increases and/or CNT content decreases. In order to understand these interesting drawing, thermal and dynamic mechanical properties of the UHMWPE and UHMWPE/CNT as‐prepared fiber specimens, birefringence, morphological and tensile studies of as‐prepared and drawn fibers were carried out. Possible mechanisms accounting for these interesting properties are proposed. Copyright © 2010 Society of Chemical Industry     

Ultradrawing properties of ultra‐high molecular weight polyethylene/functionalized carbon nanotube fibers

Systemic investigation of the influence of the plain and functionalized carbon nanotube (CNT) contents on the ultradrawing properties of ultrahigh molecular weight polyethylene/carbon nanotubes (UHMWPE/CNTs, FC_y) and UHMWPE/functionalized CNTs (FC_fx‐y) as‐prepared fibers are reported. In a way similar to those found for the orientation factor values, the achievable draw ratios (D_ra) of the FC_y and FC_fx‐y as‐prepared fibers approached a maximum value as their CNT and/or functionalized CNT contents reached their corresponding optimum values. The maximum D_ra values obtained for FC_fx‐0.001 as‐prepared fiber specimens prepared at varying maleic anhydride grafted polyethylene (PE_‐g‐MAH)/modified CNTs weight ratios were significantly higher that of the FC_0.0015 as‐prepared fiber specimen prepared at the optimum plain CNT content. Tensile property analysis further suggested that excellent orientation and tensile properties of the drawn FC_y and FC_fx‐y fibers can be obtained by ultradrawing the fibers prepared at their optimum plain CNT and/or functionalized CNT contents. To understand the interesting orientation, ultradrawing and tensile properties of FC_y and FC_fx‐y fiber specimens, FTIR, specific surface area, and SEM morphology analysis of the plain and functionalized CNTs were performed in this study. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Ultradrawing properties of ultrahigh‐molecular weight polyethylene/functionalized carbon nanotube fibers and transmittance properties of their gel solutions

The influences of the dispersion level of carbon nanotubes (CNTs) and functionalized CNTs on the transmittance properties of ultrahigh‐molecular weight polyethylene (UHMWPE) gel solutions and on ultradrawing properties of their as‐prepared fibers are reported. The transmittance properties suggest that the dispersion level of functionalized CNTs in UHMWPE/functionalized CNTs gel solution is significantly better than plain CNTs in UHMWPE/CNTs gel solutions. The orientation factors, achievable draw ratios, tensile strength (σ_f), and modulus (E) values of UHMWPE/CNTs (F_xC_y) and UHMWPE/functionalized CNTs (F_xC_f‐y) as‐prepared fiber specimens reached a maximum value as their CNT and functionalized CNT contents approached optimum contents at 0.00015 and 0.0001 wt%, respectively. The σ_f and E values of both F_xC_0.0012 and F_xC_f‐0.001 series fiber specimens prepared at their optimum CNT and functionalized CNT contents reached another maximum as their UHMWPE approached optimum UHMWPE concentration of 1.7 wt%. Possible reasons accounting for these interesting properties are proposed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Ultradrawing and ultimate tensile properties of ultrahigh molecular weight polyethylene composite fibers filled with functionalized nanoalumina fillers

Ultradrawing and ultimate tensile properties of ultrahigh molecular weight polyethylene (UHMWPE) composite fibers were successfully improved by the addition of nanoalumina (NAL), acid treated nanoalumina (ATNAL), and/or functionalized nanoalumina (FNAL). As evidenced by FTIR and TEM analyses, maleic anhydride grafted polyethylene (PE_g‐MAH) molecules were successfully grafted onto ATNAL fillers. The specific surface areas of FNAL fillers reached a maximal value at 516 m²/g, as they were modified using an optimal weight ratio of PE_g‐MAH to ATNAL at 8. Achievable draw ratio (D_ra) values of UHMWPE/NAL (F₁₀₀A_y), UHMWPE/ATNAL (F₁₀₀A_x%‐8‐y) and/or UHMWPE/FNAL (F₁₀₀A_x%‐8FPE^z_y) as‐prepared fibers approached a maximal value as NAL, ATNAL, and/or FNAL contents reached an optimal value at 0.1, 0.1, and 0.075 phr, respectively. The maximal D_ra values of F₁₀₀A_x%‐8FPE^z_0.075 as‐prepared fiber specimens were significantly higher than those of F₁₀₀A_0.1 and F₁₀₀A_x%‐8‐0.1 as‐prepared fiber specimens. In which, the maximal D_ra values obtained for F₁₀₀A_x%‐8FPE^z_0.075 as‐prepared fibers reached another maximal value as FNAL fillers were modified using an optimal weight ratio of PE_g‐MAH to ATNAL at 8. The ultimate tensile strength value of F₁₀₀A_2%‐8FPE⁸_0.075 drawn fiber reached 6.4 GPa, which was about 2.4 times of that of the UHMWPE drawn fibers prepared at the same optimal UHMWPE concentration and drawing condition. POLYM. ENG. SCI., 55:2205–2214, 2015. © 2015 Society of Plastics Engineers     

Drawing and ultimate tenacity properties of polyamide 6/attapulgite composite fibers

The drawing and ultimate tenacity properties of the Polyamide 6 (PA6)/Attapulgite (ATP) composite fiber specimens prepared at varying modified ATP (mATP) contents and drawing condition were systematically investigated. As evidenced by Fourier transform infrared (FTIR) and morphological analysis, demarcated translucent resins were found firmly attached on the surfaces of ATP nanofibers. The specific surface areas of the mATP specimens reached a maximum value at 381 m²/g as the weight ratios of silane coupling agents to ATP nanofibers reached an optimum value at 1.0. The percentage crystallinity and melt shear viscosity values measured at varying shear rates of PA6_x(mATP)_y specimens increased consistently as their mATP contents increased. In contrast, melting temperatures of PA6_x(mATP)_y specimens reduced slightly as their mATP contents increased. At a fixed drawing temperature and rate, the achievable draw ratio (D_ra) values of PA6_x(mATP)_y as‐spun fiber specimens approach a maximum value, as their mATP contents are close to the 0.2 wt % optimum value. The maximum D_ra values obtained for PA6_99.8(mATP)_0.2 as‐spun fiber specimens reached another maximum, when their drawing temperatures and rates approached the optimum values at 120°C and 50 mm/min, respectively. At a fixed draw ratio, the tenacity values of PA6_x(mATP)_y drawn fiber specimens drawn at the optimum drawing temperature and rate reached a maximum value, as their mATP contents approached the 0.2 wt % optimum value. Possible reasons accounting for the interesting morphological, specific surface area, drawing, orientation, and ultimate tenacity properties found for the PA6_x(mATP)_y fiber specimens are proposed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Ultrahigh molecular weight polyethylene fibers prepared using conical dies with varying dimensions

Dimensions of conical dies were found to have a significant influence on thermal, morphological, orientation, ultradrawing, and dynamic mechanical properties of the as‐prepared and/or drawn ultrahigh molecular weight polyethylene (UHMWPE) fiber specimens prepared in this study. Many demarcated “micro‐fibrils” were found paralleling to fiber direction of the as‐prepared UHMWPE fiber specimens. The percentage crystallinity, melting temperatures, orientation factor (f_o) and achievable draw ratio (D_ra) values of each as‐prepared UHMWPE fiber specimen prepared at a fixed length of outlet land reach a maximum value, as the entry angles of the conical die approach the optimum value at 75°. The maximum f_o and D_ra values obtained for each F₂₀^75‐y as‐prepared fiber series specimens prepared using the optimum entry angle reach another maximum value as their length of outlet land approach the optimum value of 6.5 mm. The ultimate tensile strengths and moduli of the drawn UHMWPE fibers prepared at the optimum entry angle and length of outlet land are significantly higher than those of fibers prepared at other conditions but stretched to the same draw ratio. Possible reasons accounting for the above interesting properties were discussed in this study. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

Drawing and ultimate tensile properties of modified polyamide 6 fibers

The drawing and ultimate tensile properties of the modified PA 6 (MPA) fiber specimens prepared at varying drawing temperature were systematically investigated, wherein the MPA resins were prepared by reactive extrusion of PA 6 with the compatibilizer precursor (CP). At any fixed drawing temperature, the achievable draw ratio (D_ra) values of MPA as‐spun fiber specimens increase initially with increasing CP contents, and then approach a maximum value, as their CP contents are close to the 5 wt% optimum value. The maximum D_ra values obtained for MPA as‐spun fiber specimens prepared at the optimum CP content reach another maximum as their drawing temperatures approach the optimum drawing temperature at 120°C. The tensile and birefringence values of PA 6 and MPA fiber specimens improve consistently as their draw ratios increase. Similar to those found for their achievable drawing properties, the ultimate tensile and birefringence values of MPA fiber specimens approach a maximum value, as their CP contents and drawing temperatures approach the 5 wt% and 120°C optimum values, respectively. Investigations including Fourier transform infrared, melt shear viscosity, gel content, thermal and wide angle X‐ray diffraction experiments were performed on the MPA resin and/or fiber specimens to clarify the optimum CP content and possible deformation mechanisms accounting for the interesting drawing, birefringence, and ultimate tensile properties found for the MPA fiber specimens prepared in this study. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Drawing and ultimate tensile properties of nylon 6/nylon 6 clay composite fibers

This study systematically investigated the drawing and ultimate tenacity properties of the Nylon 6 (NY6)/nylon 6 clay (NYC) composite fiber specimens prepared at varying NYC contents and drawing temperatures. The achievable draw ratio (D_ra) values of NY6_x(NYC)_y as‐spun fiber specimens initially increase in conjunction with NYC content, and then approach a maximum value, as their NYC contents and drawing temperature approach the 0.5 wt% and 120°C, respectively. The percentage crystallinity (X_c) values of NY6_x(NYC)_y as‐spun fiber specimens increased significantly, as their NYC contents increased from 0 to 2 wt%. As revealed by high power wide angle X‐ray diffraction analysis, α form NY6 crystals grew at the expense of γ form NY6 crystals originally present in NY6_x(NYC)_y as‐spun fiber specimens as their draw ratios increased. The ultimate modulus, tenacity, and orientation factor values of NY6_x(NYC)_y fiber specimens approach a maximum value, as their NYC contents and drawing temperatures approach the 0.5 wt% and 120°C optimum values, respectively. The thermal and melt shear viscosity experiments were performed on NY6_x(NYC)_y resins and/or fiber specimens to determine the optimum NYC content and possible deformation mechanisms accounting for the interesting drawing, orientation, and ultimate tenacity properties found above. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Drawing and tensile properties of polyamide 6/calcium chloride composite fibers

The influence of calcium chloride (CaCl₂) contents on the drawing and tensile properties of polyamide 6 (PA6)/CaCl₂ composite fibers prepared at varying drawing temperatures were investigated. At any fixed drawing temperature, the achievable draw ratio (D_ra) values of PA6_x(CaCl₂)_y as-spun fiber specimens approach a maximum value, as their CaCl₂ contents are close to the 3 wt% optimum value. The maximum D_ra values obtained for PA6_x(CaCl₂)_y as-spun fiber specimens prepared at the optimum CaCl₂ content reach another maximum as their drawing temperatures approach the optimum drawing temperature at 120 °C. The initial modulus, tensile strength and birefringence values of the PA6 and PA6_x(CaCl₂)_y fiber specimens were found to improve consistently with D_ra or with drawing temperatures when they were stretched to a fixed D_ra. Similar to those found for their achievable drawing properties, the ultimate initial modulus, tensile strength and birefringence values of PA6_x(CaCl₂)_y fiber specimens approach a maximum value, as their CaCl₂ contents and drawing temperatures approach the 3 wt% and 120 °C optimum values, respectively. Experiments including thermal, FTIR, melt shear viscosity and wide angle X-ray diffraction experiments were performed on the PA6_x(CaCl₂)_y resin and/or fiber specimens to clarify the possible reasons accounting for the interesting drawing, tensile and birefringence properties found for the PA6_x(CaCl₂)_y fiber specimens.     

Ultradrawing properties of gel films of ultrahigh‐molecular‐weight polyethylene and low‐molecular‐weight polyethylene blends prepared at various formation temperatures

The ultradrawing behavior of ultrahigh‐molecular‐weight polyethylene/low‐molecular‐weight polyethylene film specimens prepared at various concentrations and formation temperatures was studied. The critical draw ratio (D_rc) of UL_?0.7 film specimens was found to depend significantly on the formation temperature used to prepare the film specimens. At any fixed drawing temperature, the D_rc values of UL_?0.7 specimens prepared at various formation temperatures increased significantly as the formation temperatures were reduced. In fact, with an optimum drawing temperature of 95°C, the D_rc values of UL_?0.7 specimens prepared at a formation temperature of 0°C reached 488, about 50% higher than that of UL_?0.7 specimens prepared at a formation temperature of 95°C. These interesting phenomena were investigated in terms of the thermal, birefringence, and tensile properties of these undrawn and drawn UL_?0.7 specimens. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3728–3738, 2003     

Nitroxide‐terminated poly(styrene‐co‐diethyl fumarates) and derived block copolymers

Copolymerization of styrene (S) and diethyl fumarate (DEF) at 125°C in the presence of 2,2,6,6‐ tetramethylpiperidin‐1‐yloxyl radical (TEMPO) and initiated with a thermal initiator, 2,2′‐azobisisobutyronitrile (AIBN), was studied. The molar fraction of DEF in the feed, F_DEF, varied within 0.1–0.9. An azeotropic composition, (F_DEF)_A = 0.38, was found for the copolymerization under study. At F_DEF = 0.1–0.4, a quasi‐living process was observed, transforming to a retarded conventional radical copolymerization at a higher content of DEF in the initial mixtures. The obtained TEMPO‐terminated S‐DEF copolymers were used to initiate polymerization of styrene. Poly(styrene‐ co‐diethyl fumarate)‐block‐polystyrene copolymers were prepared with molecular weight distributions depending on the amount of inactive polymer chains in macroinitiators, as indicated by size‐exclusion chromatography. A limited miscibility of the blocks in the synthesized block copolymers was revealed by using differential scanning calorimetry. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2432–2439, 2002     

Influence of two‐stage drawing conditions on ultradrawing behavior of gel films of ultrahigh‐molecular‐weight polyethylene and low‐molecular‐weight polyethylene blends

The influence of two‐stage drawing conditions on the ultradrawing behavior of the gel films of ultrahigh‐molecular‐weight polyethylene/low‐molecular‐weight polyethylene blends is reported in this article. The critical draw ratios (λ_c) of the gel films prepared near their critical concentrations were found to depend significantly on the draw ratio attained in the first drawing stage (D_1r) and on the temperature utilized in the second drawing stage (T_sec). After drawing the gel films to a fixed draw ratio in the first drawing stage, each two‐stage drawn gel film was made to exhibit a maximum λ_c (λ_cmax) by drawing the drawn gel film at its corresponding optimum T_sec. In addition, the optimum T_sec was found to increase significantly with the D_1r value of the drawn gel films. It is worth noting, on the other hand, that the λ_cmax of two‐stage drawn gel films increased consistently with an increasing D_1r until its value reached an optimum value of 160. These results clearly suggest that, as T_sec and D_1r are increased to their optimum values, the λ_cmax of the two‐stage drawn gel films can be improved further so as to be higher than those of the corresponding one‐stage drawn gel films. These interesting phenomena were investigated in terms of reduced viscosities of the solutions and by an analysis of the thermal, birefringence, and tensile properties of the drawn gel films. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1890–1901, 2001     

Piezoelectric properties of (Na0.5K0.5)(Nb1‐xSbx)O3‐SrTiO3 ceramics with tetragonal‐pseudocubic PPB structure

CuO‐added 0.96(Na_0.5K_0.5)(Nb_1‐xSb_x)O₃‐0.04SrTiO₃ ceramics sintered at the low temperature of 960°C for 10 hours showed dense microstructures and high relative densities. The specimens with 0.0 ≤  x ≤ 0.04 had orthorhombic‐tetragonal polymorphic phase boundary (PPB) structure. Tetragonal‐pseudocubic PPB structure was observed in specimens with 0.05 ≤  x ≤ 0.07, while the specimen with x = 0.08 has a pseudocubic structure. The structural variation in the specimens is explained by the decreases in the orthorhombic‐tetragonal transition temperature and Curie temperature with the addition of Sb⁵⁺ ions. The specimens with 0.05 ≤  x ≤ 0.07, which have tetragonal‐pseudocubic PPB structure, had large electric field‐induced strains of 0.14%‐0.016%. Moreover, these specimens also showed increased d₃₃ values between 280 pC/N and 358 pC/N. In particular, the specimen with x = 0.055 showed particularly enhanced piezoelectric properties: d₃₃ of 358 pC/N, k_p of 0.45, and the electric field‐induced strain of 0.16% at 4.5 kV/mm.     

CuO‐added KNbO3‐BaZrO3 lead‐free piezoelectric ceramics with low loss and large electric field‐induced strain

CuO‐added (1‐x)KNbO₃‐x mol%BaZrO₃ ceramics with 0.0≤x≤7.0 were sintered at 960°C. Large double polarization vs electric field (P‐E) and sprout‐shaped strain vs electric field (S‐E) hysteresis curves were obtained from the specimens with x≤2.0. They exhibited large polarizing electric fields (E_P) owing to the presence of a large number of defect dipoles (P_Ds) that formed between Cu²⁺ ions and oxygen vacancies. Small double P‐E hysteresis curves were observed for the specimens with x≥3.0 with reduced E_P because of the decreased number of P_Ds and the presence of a polymorphic phase structure containing both orthorhombic and pseudocubic structures. In particular, the specimen with x=5.0 exhibited a large strain of 0.16% at 8.0 kV/mm with a small E_P of 1.2 kV/mm and good fatigue property: this specimen maintained a strain of 0.13% at 6.0 kV/mm after 10⁶ cycles of 3.0 kV/mm.     

Synthesis and gelation of novel fluoroalkyl end‐capped N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide copolymers containing triol segments—Interaction of these fluorinated gels with various hydrophilic compounds

Fluoroalkyl end‐capped N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide (DOBAA) copolymers containing triol segments were prepared by the reactions of fluoroalkanoyl peroxide with the corresponding monomer and N‐tris(hydroxymethyl)methylacrylamide (NAT). These obtained fluorinated copolymers [R_F‐(DOBAA)_x‐(NAT)_y‐R_F] were found to cause gelation in water, dimethyl sulfoxide, and N,N‐dimethylformamide under the non‐crosslinked conditions, although the corresponding nonfluorinated DOBAA–NAT copolymer [‐(DOBAA)_x‐(NAT)_y‐] could cause no gelation in these solvents. This gelation is governed by the synergistic interaction of strong aggregations of end‐capped fluoroalkyl segments and intermolecular hydrogen bonding between triol segments. We also studied the uptake and release of a variety of hydrophilic compounds such as methylene blue, methyl orange, 4‐hydroxyazobenzene‐4′‐sulfonic acid sodium salt, 2,4‐dihydroxyazobenzene‐4′‐sulfonic acid sodium salt, acriflavine hydrochloride, acridine hydrochloride, lucigenin, and fluorescein by this fluorinated copolymer gel and fluoroalkyl end‐capped NAT homopolymer gel [R_F‐(NAT)_n‐RF] for comparison. It was demonstrated that the uptake and release ratios of these hydrophilic compounds by R_F‐(DOBAA)_x‐(NAT)_y‐R_F gel become generally lower than those of R_F‐(NAT)_n‐R_F gel. Interestingly, R_F‐(DOBAA)_x‐(NAT)_y‐R_F gel has no releasing power toward methylene blue, acridine hydrochloride, lucigenin, and fluorescein, although R_F‐(NAT)_n‐R_F gel has a good releasing power toward these compounds. Additionally, R_F‐(DOBAA)_x‐(NAT)_y‐R_F gel was applied to the controlled release of anticancer drugs such as methotrexate (MTX), and the releasing ratios of MTX became higher with increasing pH values (from pH 4.3 to 9.1). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88:3212–3217, 2003     

Mn doping effects on electric properties of 0.93(Bi0.5Na0.5)TiO3‐0.07Ba(Ti0.945Zr0.055)O3 ceramics

The validity of Mn element on 0.93(Bi_0.5Na_0.5)TiO₃‐0.07Ba(Ti_0.945Zr_0.055)O₃ ceramics (BNT‐BZT‐xMn) is certified by doping. On account of multiple effects introduced by Mn, the appropriate Mn content facilitates property improvement effectively. Compared with pure BNT‐BZT, d₃₃ of the component x = 0.25 increases about 8% up to 187 pC/N and Q_m of the component x = 1 increases about 84% up to 197. Thermally stimulated depolarization currents (TSDC) measurement reveals Mn additive is helpful to pyroelectric properties as well. The Mn‐doped component x = 0.125 exhibits better pyroelectric performance at room temperature. Corresponding pyroelectric coefficient and the figures of merit reach up to 0.061 μC/(cm² °C), F_i=217 pm/V, F_ν = 0.023 m²/C, and F_d = 12.6 μPa^?1/2, respectively, even superior to lead‐based ceramics. Similar pyroelectric advantage is also observed in the component x = 0.5 near depolarization temperature T_d. Mn doping has slight harmful influence on the ferroelectric‐to‐relaxor transition temperature T_F?R, as well as T_d, but hardly shows restriction on application. These results confirm Mn doping is an available strategy to improve BNT‐based ceramics. Therefore, Mn‐doped BNT‐BZT ceramics will be excellent candidates in area of high‐power piezoelectric application and pyroelectric detectors.     

Part 7. Effects of poly(L‐lactide‐co‐ϵ‐caprolactone) on morphology,structure, crystallization,and physical properties of blends of poly(L‐lactide) and poly(ϵ‐caprolactone)

Blended films of poly(L ‐lactide) [ie poly(L ‐lactic acid)] (PLLA) and poly(?‐caprolactone) (PCL) without or mixed with 10 wt% poly(L ‐lactide‐co‐?‐caprolactone) (PLLA‐CL) were prepared by solution‐casting. The effects of PLLA‐CL on the morphology, phase structure, crystallization, and mechanical properties of films have been investigated using polarization optical microscopy, scanning electron microscopy, differential scanning calorimetry and tensile testing. Addition of PLLA‐CL decreased number densities of spherulites in PLLA and PCL films, and improved the observability of spherulites and the smoothness of cross‐section of the PLLA/PCL blend film. The melting temperatures (T_m) of PLLA and PCL in the films remained unchanged upon addition of PLLA‐CL, while the crystallinities of PLLA and PCL increased at PLLA contents [X_PLLA = weight of PLLA/(weight of PLLA and PCL)] of 0.4–0.7 and at most of the X_PLLA values, respectively. The addition of PLLA‐CL improved the tensile strength and the Young modulus of the films at X_PLLA of 0.5–0.8 and of 0–0.1 and 0.5–0.8, respectively, and the elongation at break of the films at all the X_PLLA values. These findings strongly suggest that PLLA‐CL was miscible with PLLA and PCL, and that the dissolved PLLA‐CL in PLLA‐rich and PCL‐rich phases increased the compatibility between these two phases. © 2003 Society of Chemical Industry     

NaNbO3‐BaTiO3‐NaSbO3 lead and potassium‐free ceramics with thermally stable small‐signal piezoelectric properties

A new lead‐potassium‐free ceramic of (0.9‐x)NaNbO₃‐0.1BaTiO₃‐xNaSbO₃ (NN‐BT‐xNS) was successfully prepared via a solid‐state reaction method. The microstructure, phase structure, dielectric, ferroelectric, and piezoelectric properties were investigated as a function of NS content. The substitution of NS for NN was found to dramatically change the grain morphology from cube‐like grains typical for alkaline niobate‐based ceramics to conventional sphere‐like grains especially for Pb‐based perovskite ceramics. A normal to relaxor ferroelectric phase transformation was accompanied by a tetragonal (T) to rhombohedral (R) phase transition. A composition‐temperature phase diagram demonstrated a vertical morphotropic phase boundary between T and R phases in the composition range of x=0.03‐0.04, where optimum electrical properties of d₃₃=252 pC/N, k_p=36%, Q_m=168, =2063, and T_c=109°C were obtained in the x=0.035 ceramic sintered at 1260°C. Particularly, excellent temperature insensitivity of small‐signal piezoelectric properties suggested large application potentials in various actuators and sensors in comparison with other typical lead‐free materials.     

Compatible and crystallization properties of poly(lactic acid)/poly(butylene adipate‐co‐terephthalate) blends

Differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD) and dynamic mechanical analysis (DMA) properties of poly(lactic acid)/ poly(butylene adipate‐co‐terephthalate) (PLA/PBAT) specimens suggest that only small amounts of poor PLA and/or PBAT crystals are present in their corresponding melt crystallized specimens. In fact, the percentage crystallinity, peak melting temperature and onset re‐crystallization temperature values of PLA/PBAT specimens reduce gradually as their PBAT contents increase. However, the glass transition temperatures of PLA molecules found by DSC and DMA analysis reduce to the minimum value as the PBAT contents of PLA_xPBAT_y specimens reach 2.5 wt %. Further morphological and DMA analysis of PLA/PBAT specimens reveal that PBAT molecules are miscible with PLA molecules at PBAT contents equal to or less than 2.5 wt %, since no distinguished phase‐separated PBAT droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLA/PBAT specimens, respectively. In contrast to PLA, the PBAT specimen exhibits highly deformable properties. After blending proper amounts of PBAT in PLA, the inherent brittle deformation behavior of PLA was successfully improved. Possible reasons accounting for these interesting crystallization, compatible and tensile properties of PLA/PBAT specimens are proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010