Melting Crystallization Temperature Research Articles

Influence of Poly(vinylphenol) Sublayer on the Crystallization Behavior of Poly(3-hydroxybutyrate) Thin Films

The crystallization behavior of poly(3-hydroxybutyrate) (PHB) thin films on poly(vinylphenol) (PVPh) substrate was investigated by surface-sensitive grazing incident X-ray scattering and infrared reflection–absorption spectroscopy techniques. Compared with the crystallization of PHB on a Si wafer, the PVPh sublayer did not significantly affect the crystallization behavior of PHB in solution-cast samples, while significantly inhibited the melt crystallization of PHB. For films thinner than 175 nm, amorphous PHB was always fabricated irrespective of melt crystallization temperature. Only when the film thickness increased to 185 nm, the PHB started to crystallize at temperatures above 53 °C. The PHB crystals preferred to orient with the b-axes perpendicular to substrate. The inhibition of PHB melt crystallization was attributed to the thickness confinement and interdiffusion of PVPh and PHB, which caused a concentration gradient of PVPh in the PHB layer. From the thickness dependence of crystallization behav...

Synthesis, characterization, crystalline morphologies and hydrophilicity of A4 BA4 nonlinear block copolymers

Novel, well-defined A4BA4 nonlinear block copolymers [poly(ϵ-caprolactone)]4-block-poly(propylene oxide)-block-[poly(ϵ-caprolactone)]4 (PCL4-b-PPO-b-PCL4) with eight arms were synthesized by ring-opening polymerization. An investigation of melting and crystallization demonstrated that the values of crystallization temperature, melting temperature and degree of crystallinity of PCL4-b-PPO-b-PCL4 were enhanced with an increase of PCL chain length. At the same time, the crystallizability of PCL segments was influenced by the star-shaped structure of the copolymers and the amorphous PPO segments in the copolymers. Furthermore, PCL4-b-PPO-b-PCL4 showed crystalline morphologies that were different from that of linear PCL according to polarized optical microscopy. Moreover, the hydrophilicity of the copolymers could be improved and adjusted by the star-shaped structure and the alteration of the relative content of the PCL and PPO segments in the copolymers.© 2013 Society of Chemical Industry

Effects of Glass Components Ratio on Structure and Properties of Baiyunebo Tailing Glass-Ceramics

Glass-ceramic in the CaO-MgO-Al2O3-SiO2 quaternary system was prepared using Baiyunebo tailing and fly ash as main raw materials by the method of melting. The processes of producing glass-ceramic included mixture, melting, molding, annealing, heat treatment, etc. The processing schedule for glass melting temperature, nucleation and crystallization temperature were chosen as 1450°C, 720°C and 850°C. The influences of glass components ratio on the structure were investigated by X-ray diffraction (XRD). It can be found that the main crystalline phase of augite, anorthite, magnesioferrite or magnetite mainly depended on glass components ratio. The results of mechanical measurements indicated that the bending strengths, density and chemical durability of glass-ceramics were concerned with the main crystal phase. The glass ceramics with augite phase had higher performance compared with others.

Study on the Preparation and Properties of the Phosphorus-Containing Flame Retardant PET Copolymer

The phosphorus-containing flame retardant PET was synthesized by adding different content CEPPA. The study found that the flame retardant and char formation abilities of PET increased with CEPPA content increasing, but the melting point, glass transition temperature and melt crystallization temperature decrease, and the anti-drip properties got worse and then better. It is attributed to the introduced C-P bond energy of the main chain was much smaller than the C-C bond energy.

The effect of multi-walled carbon nanotubes on morphology, crystallinity and mechanical properties of PBT/MWCNT composite nanofibers

Composite nanofibers of Poly(butylene terephthalate) (PBT)/multiwalled-carbon nanotubes (MWCNTs) were prepared by electrospinning technique in the form of a random fibers web. The effect of MWCNTs on the morphology, crystallinity, and mechanical properties of the electrospun composite nanofibers was investigated by SEM, DSC, and tensile testing, respectively. SEM observations indicated that the presence of MWCNTs resulted in finer nanofibers for lower loading; however, a broader diameter was found for nanofibers with higher amounts of carbon nanotubes.It was also observed that the melt-crystallization temperature (Tc) of PBT nanofibers shifted to a higher temperature (about 8 °C) by the incorporation of MWCNTs which might be due to the nucleating effect of the nanotubes. The mechanical properties (specific strength and modulus) of the PBT nanofibers were significantly enhanced by the incorporation of MWCNTs.

Absorption Coefficient of Molten Aluminum Oxide in Semitransparent Spectral Range

A critical compilation and analysis of all the available experimental data and approximation formulas for the wavelength and temperature dependences of the absorption coefficient of molten aluminum oxide in semitransparent region are presented. The main factors and the influence of physicochemical processes on the value of the absorption coefficient are considered. Special attention is focused on possible reasons for large values of absorption of the alumina melt as compared to the crystal near melting temperature. It is shown that the available data can be divided into two groups, according to the level of absorption. The first group includes the results of the research of optical properties of solid propellant combustion products, and the second group–the results of the research of single crystal melts and some other high-purity molten aluminum oxides. Along with the detailed analysis of the absorption coefficient, also a brief analysis of available data on the refractive index has been done.

Synthesis and Characterizations of Poly(trimethylene terephthalate)-b-poly(tetramethylene glycol) Copolymers

A series of poly(trimethylene terephthalate)-b-poly(tetramethylene glycol) (PTT-PTMEG) copolymers were synthesized by two-step melt-polycondensation. The copolymers were characterized by using Fourier transform infrared spectroscopy (FTIR),1H NMR spectroscopy, rheometer, differential scanning calorimetry (DSC), polarized optical microscopy (POM), thermal gravimetric analysis (TGA), and mechanical properties. The results suggest that by increasing the flexible PTMEG contents from 0% to 60 wt%, the copolymers show decreased glass transition temperatures, melting points, melt-crystallization temperatures, hardness, tensile strength, thermostability, and smaller spherulites dimensions; however it has much increased impact strength and elongation at breaking point. Compared with commercial poly(butylene terephthalate) (PBT)-type TPEE with 25 mol% flexible segments, PTT-type TPEE having 25 mol% flexible segments has a lower glass transition temperature, melting point, crystallization temperature, and much lower tensile strength although it has a much higher impact strength than that of PBT-type TPEE, and it is not suitably used as a commercial TPEE.

Thermal and Mechanical Properties of Polypropylene/Boron Nitride Composites

The purpose of this study is to improve thermal conductivity and properties of polypropylene (PP) by adding functionality fillers. Boron nitride (BN) was used for improving the thermal conductivity of polymers. Two types of BN with different particle sizes were used. In addition, two types of PP with different viscosities were used as the polymer matrix. The thermal conductivity, storage modulus and loss modulus increased with the content of BN. The thermal conductivity of PP can be effectively enhanced by adding BN with large particles. Moreover, the melting temperature and crystallization temperature of PP/BN composites were larger than those of neat PP. The degree of crystallization of PP increased with BN. The effect of BN with small particles on the crystallization of PP was slightly stronger than that of BN with large particles. From the SEM observation, the agglomeration of BN with small particles was locally observed. In contrast, BN with large particles dispersed well in the PP matrix. This study found that BN with large particles effectively enhanced the thermal and properties of PP/BN composites. In addition, the above properties were independent of the matrix viscosity.

Preparation of high-molecular-weight poly(1,4-butylene carbonate-co-terephthalate) and its thermal properties

Condensation copolymerizations of 1,4-butanediol (BD), dimethyl carbonate (DMC), and dimethyl terephthalate (DMT) were conducted by a two-step procedure using sodium alkoxide (0.1–0.2 mol%) as a catalyst with a variable [DMT]/[BD] feed ratio. In the first step, oligomers bearing almost equal numbers of hydroxyl and methoxycarbonyl end-groups were generated, which were polycondensed mostly by the elimination of methanol at 190–210 °C under reduced pressure. By this procedure, high-molecular-weight poly(1,4-butylene carbonate-co-terephthalate)s (PBCTs) were easily prepared with Mw 60 000–200 000 in a reasonably short reaction time (∼8.5 h) and even on a large scale (110 g polymer per batch) in a 250 mL glass reactor. The PBCTs prepared at a high [DMT]/[BD] feed ratio 0.30–0.50 were semi-crystalline polymers with fast crystallization rates and melting temperatures in the range 95–146 °C, which were adjustable by the [DMT]/[BD] feed ratio. The glass transition temperatures were rather high around 0 °C. These thermal properties were comparable to those of commercialized compostable polyesters such as PLA, PHA, PBAT, and PBSA.

Synthesis and thermal behavior of poly(ε-caprolactone) grafted on multiwalled carbon nanotubes with high grafting degrees

Poly(ε-caprolactone) (PCL) was grafted onto multiwalled carbon nanotubes (MWNTs) with high grafting degrees. The surface of MWNTs was first modified by 2-hydroxyethyl benzocyclobutene (BCB-EO) via a [2 + 4] cyclo-addition reaction. Polymerization of ε-caprolactone was conducted in the presence of BCB-EO modified MWNTs and the catalyst stannous octoate. Alternatively, the grafted-BCB-EO first reacted with CpTiCl3 and then the reactant was used to catalyze polymerization of ε-caprolactone. The grafting degrees of PCL prepared from BCB-EO modified MWNTs can reach at least 94%, much higher than those prepared by other two conventional methods. TEM result shows that the morphology and thickness of the grafted PCLs strongly depend on the grafting degree and grafting method. The crystallization and melting behaviors of the MWNTs-grafted PCL were investigated. MWNTs can exert both nucleation and confinement effects on crystallization of the grafted PCL, leading to lower crystallinity but higher crystallization temperature (Tc) and melting temperature (Tm) of the grafted PCLs. It is found that crystallinity of the grafted PCLs increases with the grafting degree, but Tc and Tm also depend on the molecular weight.

Crystallization Behavior of Polypropylene/Syndiotactic1,2-Polybutadiene Blends

The melting and crystallization behaviors of Polypropylene/Syndiotactic1,2-polybutadiene (PP/s-PB) blends and neat PP were studied by using DSC, the results showed that the presence of s-PB in PP would have a strong impact on the crystallization capacity of PP. The presence of s-PB in PP could increase the crystallization temperature(Tc) of PP, and the s-PB could obviously lower supercooling temperature(Tm-Tc) of PP, but the s-PB in PP have a Slightly influence on the melting temperature(Tm) of PP. The proposed reason for those are that the crosslinking s-PB in high temperature is a nucleator for PP’s crystallization and increases PP’s crystalline rate. However, the s-PB lowers PP’s crystallinity. At the same time, the presence of PP in blends lowers s-PB’s crystallinity, but the PP in blends have a Slightly influence on the melting temperature(Tm) and crystallization temperature(Tc) of s-PB.

Stress‐Induced Stabilization of Crystals in Shape Memory Natural Rubber

In contrast to all known shape memory polymers, the melting temperature of crystals in shape memory natural rubber (SMNR) can be greatly manipulated by the application of external mechanical stress. As shown previously, stress perpendicular to the prior programming direction decreases the melting temperature by up to 40 K. In this study, we investigated the influence of mechanical stress parallel to prior stretching direction during programming on the stability of the elongation-stabilizing crystals. It was found that parallel stress stabilizes the crystals, which is indicated by linear increase of the trigger temperature by up to 17 K. The crystal melting temperature can be increased up to 126.5 °C under constrained conditions as shown by X-ray diffraction measurements.

Influence of Rare-earth Coupling Agent on Non-isothermal Crystallization Behaviour of Wood Flour/Polypropylene Composites

The influence of a rare-earth coupling agent (RE) on the non-isothermal crystallization behaviour of PP was studied by differential scanning calorimetry. Experimental results showed that use of RE caused a decrease in the crystallization temperature, melting temperature and crystallinity of PP in WF/RE/PP compared with those in WF/PP. The Avrami, Ozawa and Mo methods were used to describe the crystallization process. The Avrami and Ozawa methods neglected the secondary crystallization and followed primary crystallization. The Mo approach could successfully describe the overall crystallization process. The relation of the half times of crystallization ( t1/2) of the three samples, t1/2(WF/PP) < t1/2(WF/RE/PP) <t1/2 (PP) and the F( T)(WF/PP)< F( T)(WF/RE/PP) <F( T)(PP), suggested that the crystallization rate of WF/RE/PP was slower than that of WF/PP The activation energy was calculated by using the Kissinger method and the results indicated that the incorporation of RE resulted in a compatible effect, which led to a reduction in the crystallization rate and an increase in activation energy compared with WF/PP.

폴리(트리메틸렌 테레프탈레이트-co-트리메틸렌 이소프탈레이트)의 열적 특성

Poly(trimethylene terephthalate-co-trimethylene isophthalate) [P(TT-co-TI)] copolymers with various contents of TI unit were synthesized via a two-step process of transesterification and polycondensation in a high pressure reactor in order to modify the thermal properties of PTT. Effects of TI content on the crystallization and other thermal properties were investigated by DSC, TGA, polarizing microscope, and synchrotron WAXD analysis. DSC analysis indicated that the cold crystallization temperature (<TEX>$T_{cc}$</TEX>) increased and glass transition temperature (<TEX>$T_g$</TEX>) and melting temperature (<TEX>$T_m$</TEX>) decreased with increasing TI content in the copolymer. The radial growth rate of PTT spherulite formed during the decrease of melt-crystallization as TI content increases. The growth and melting of the PTT crystallite were also analyzed in-situ by synchrotron WAXD patterns. A decrease in both <TEX>$T_m$</TEX> during the heating process and melt-crystallization temperature (<TEX>$T_{mc}$</TEX>) during the cooling process for P(TT-co-TI)s were confirmed by WAXD patterns. Although the incorporation of the non-crystallizing comonomer unit of TI into the crystalline body of PTT reduced the crystallization rate of PTT, it did not affect the spherulite formation and crystal structure of PTT. Isothermal TGA analysis revealed that the activation energy for isothermal degradation with weight loss up to 10% of P(TT-co-TI)s was 200~240 kJ/mol, depending on the weight loss and TI content in the copolymer.

Properties of coconut shell powder‐filled polylactic acid ecocomposites: Effect of maleic acid

AbstractEcocomposites were produced by incorporating coconut shell powder (CSP) into polylactic acid (PLA) resin. The effect of filler content and chemical modification on the mechanical properties, thermal properties, and morphology of PLA/CSP ecocomposites were investigated. The addition of filler has decreased the tensile strength and elongation at break of PLA/CSP ecocomposites. However, tensile strength and modulus of elasticity of PLA/CSP ecocomposites were enhanced by maleic acid treatment. Meanwhile, glass transition temperature (Tg) and crystallinity (Xc) of PLA/CSP ecocomposites increased at 30 php of filler content and increased the presence of maleic acid (MA). However, the melting temperature (Tm) and crystallization temperature (Tc) were not significantly changed with the filler content and MA modification The thermal stability of PLA/CSP ecocomposites increased with the CSP content. The MA modification improved the thermal stability of PLA/CSP ecocomposites through better filler–matrix interaction. The improvement was confirmed by scanning electron microscope study. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Electrospun PLA: PCL composites embedded with unmodified and 3-aminopropyltriethoxysilane (ASP) modified halloysite nanotubes (HNT)

Electrospinning is a simple and versatile fiber synthesis technique in which a high-voltage electric field is applied to a stream of polymer melt or polymer solution, resulting in the formation of continuous micro/nanofibers. Halloysite nanotubes (HNT) have been found to achieve improved structural and mechanical properties when embedded into various polymer matrices. This research work focuses on blending poly(e-caprolactone) (PCL) (9 and 15 wt%/v) and poly(lactic acid) (PLA) (fixed at 8 wt%/v) solutions with HNT at two different concentrations 1 and 2 wt%/v. Both unmodified HNT and HNT modified with 3-aminopropyltriethoxysilane (ASP) were utilized in this study. Fiber properties have been shown to be strongly related to the solution viscosity and electrical conductivity. The addition of HNT increased the solution viscosity, thus resulting in the production of uniform fibers. For both PCL concentrations, the average fiber diameter increased with the increasing of HNT concentration. The average fiber diameters with HNT-ASP were reduced considerably in comparison to those with unmodified HNT when using 15 wt%/v PCL. Slightly better dispersion was obtained for PLA: PCL composites embedded with HNT-ASP compared to unmodified HNT. Furthermore, the addition of HNT-ASP to the polymeric blends resulted in a moderate decrease in the degree of crystallinity, as well as slight reductions of glass transition temperature of PCL, the crystallization temperature and melting temperature of PLA within composite materials. The infrared spectra of composites confirmed the successful embedding of HNT-ASP into PLA: PCL nanofibers relative to unmodified HNT due to the premodification using ASP to reduce the agglomeration behavior. This study provides a new material system that could be potentially used in drug delivery, and may facilitate good control of the drug release process.

Development of creatine and arginine-6-oligomer for the ring-opening polymerization of cyclic esters

Natural creatine and arginine-6-oligomer have been effectively engaged as ring-opening polymerization initiators of poly(L-lactide) (PLLA) and poly(ɛ-caprolactone) (PCL) in bulk. The nonlinear structure and thermal properties of the resulted polymers were further elucidated by 1H, 13C nuclear magnetic resonance, and a modulated differencial scanning calorimetry (MDSC). Thermal analysis indicated that the synthesized polymers had lower melting points, glass-transition temperatures, fusion enthalpy, and crystallization temperature than those of linear PCL or PLLA due to the presence of the arginine-6-oligomer in the macromolecule and crystalline imperfections caused by the branched structure. This study provides an efficient and metal-free method for the synthesis of branched biodegradable polymers with incorporated compounds, which exhibit therapeutic properties, adequate for the drug carrier applications. Open image in new window

Inorganic-organic hybrids based on poly (ε-Caprolactone) and silica oxide and characterization by relaxometry applying low-field NMR

®® A200) silica oxide were prepared employing the solution method, using chloroform. The relationships of the amount of nanofillers, organic coating, molecular structure and intermolecular interaction of the hybrid materials were investigated mainly using low-field nuclear magnetic resonance (NMR). The NMR analyses involved the hydrogen spin-lattice relaxation time (T 1 H) and hydrogen spin-lattice relaxation time in the rotating frame (T 1 ρH). The spin-lattice relaxation time measurements revealed that the PCL/silica oxide hybrids were heterogeneous, meaning their components were well dispersed. X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were also employed. The DSC data showed that all the materials had lower crystallization temperature (Tc) and melting temperature (Tm), so the crystallinity degree of the PCL decreased in the hybrids. The TGA analysis demonstrated that the addition of modified and unmodified silica oxide does not cause considerable changes to PCL’s thermal stability, since no significant variations in the maximum temperature (Tmax) were observed in relation to the neat polymer.

Changes in the melting temperature and crystal structure of poly(vinylidene fluoride) by knotting

AbstractA significant increase in the melting temperature of knotted fibers of poly(vinylidene fluoride) (PVDF) was detected by differential scanning calorimetry. The melting peak partially returned to the original peak after the fibers were unknotted. Knotted PVDF fibers were observed with an optical microscope at crossed‐nicol conditions. The knotted portions of the fibers showed birefringence even above the melting temperature of the fibers before knotting. The dependence of the physical properties of PVDF under applied stress was estimated in order to investigate the influence of knotting. The fracture temperature of PVDF fibers increased with applied stress below 1 MPa and decreased above 10 MPa because the applied stress increased the melting temperature of PVDF crystals, but strong stress mechanically broke the fibers. The X‐ray diffraction patterns of the PVDF fibers under different stress were divided into the peaks of α‐ and β‐phase crystals and amorphous. The peak area of the β‐phase crystal increased and that of the amorphous decreased with applied stress. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Anionic nylon 6/TiO2 composite materials: Effects of TiO2 filler on the thermal and mechanical behavior of the composites

AbstractThe nylon 6‐based composite materials containing untreated and surface‐treated TiO2 particles with 3‐aminopropyltriethoxysilane (APTEOS), as coupling agent were prepared by in situ anionic polymerization of ε‐caprolactam in the presence TiO2 as a filler using the rotational molding technique. The thermal behavior and mechanical properties of the neat nylon 6 and its composites were investigated using various techniques such as differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), a tensile and flexural test and impact strength. Experimental results revealed that both untreated and surface‐modified TiO2 had distinct influence on the melting temperature (Tm), crystallization temperature (Tc), and degree of crystallinity (αDSC), thermal stability, storage modulus (E′), and loss factor (tan δ), and mechanical properties of nylon 6 matrix. Dynamical mechanical analysis indicated that addition of TiO2 particles into nylon 6 matrix increased both the storage modulus and the glass transition temperature. The corresponding values of nylon 6 composites with modified filler were higher than that of nylon 6 composite with untreated TiO2 particles. Tensile and flexural characteristics of the nylon 6 composites were found to increase while the elongation at break and impact strength with increase in TiO2 concentration relative to neat nylon 6. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers