Effects of vacuum ultraviolet on the structure and optical properties of poly(tetrafluoroethylene) films

The effects of vacuum ultraviolet (VUV) at wavelengths of 5–200 nm on the microscopic structure and optical properties of poly(tetrafluoroethylene) (PTFE) films were investigated. X‐ray photoelectron spectroscopy analysis showed that the C_1s spectra changed from a single peak at 292.8 eV to multiplex peaks with binding energies of 284.6, 286.6, 288.6, 290.5, and 293.0 eV after VUV irradiation at 680 esh. With an increasing irradiation dose, the C_1s peaks at 290.5 and 293.0 eV disappeared. After the PTFE film specimens irradiated at 1600 esh were sputtered with argon ions for 3 min, the C_1s peaks at 290.5 and 293.0 eV appeared again, and the height of the peaks at 286.6 and 288.6 eV increased. The content of fluorine decreased after VUV irradiation. The content of fluorine in the film surface layer decreased significantly with the increase in the VUV intensity, but it did not change with the irradiation dose. Fourier transform infrared (FTIR) analysis results indicated that some conjugated bonds, such as ? FC?CF? , were formed during VUV irradiation, but no CH absorption bands were observed in the FTIR spectra; this indicated that the increase in the height of the C_1s peak at 284.6 eV arose mainly from the carbon–carbon bonds, that is, from carbonification. The spectral transmittance of the PTFE film decreased gradually with an increasing VUV irradiation dose, and at a given dose, the lower the intensity was of the VUV irradiation, the greater the change was in the spectral transmittance. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 115–121, 2003     

The effect of 60Co γ‐rays on the crystal structure,melting and crystallization behavior of poly(butylene succinate)

The results obtained for poly(butylene succinate) (PBS) after ⁶⁰Co γ‐ray irradiation, studied by wide‐angle X‐ray diffraction (WAXD), differential scanning calorimeter (DSC) and polarizing optical microscopy (POM), revealed that the degree of crystallinity, melting temperature and enthalpy decreased with increasing irradiation dose, but that the crystal structure of PBS did not vary when compared to non‐irradiated PBS. By using Scherrer equation, small changes occurred in the crystal sizes of L₀₂₀, L₁₁₀ and L₁₁₁. The spherulitic morphology of PBS was strongly dependent on irradiation dose and changed significantly at higher irradiation dosages. The crystallization kinetics of PBS indicated that the Avrami exponent (n) for irradiated PBS was reduced to 2.3, when compared to non‐irradiated PBS (3.3). Copyright © 2004 Society of Chemical Industry     

Formation of an interconnected lamellar structure in PVDF membranes with nanoparticles addition via solid‐liquid thermally induced phase separation

Novel microporous membranes were prepared via thermally induced solid‐liquid (S‐L) phase separation of mixtures containing poly(vinylidene fluoride) (PVDF)/diphenyl ketone (DPK)/nanoparticles [such as montmorillonite (MMT) and polytetrafluoroethylene (PTFE)] in diluted systems with a mass ratio of 29.7/70/0.3 wt %. The crystallization and melting characteristics of these diluted systems were investigated by polarizing optical microscopy (POM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and wide angle X‐ray diffraction (WAXD). The nanoparticle structure and the interaction between PVDF chains and nanoparticle surfaces determined the crystallization behavior and morphology of the PVDF membrane. The addition of MMT and PTFE had a significant nucleation enhancement on the crystallization of PVDF accompanied by S‐L phase separation during the thermally induced phase separation (TIPS) process. It was observed that an interconnected lamellar structure was formed in these two membranes, leading to a higher tensile strength compared with that of the reference membrane without nanoparticles addition. Additionally, addition of MMT facilitates the fiber‐like β phase crystal formation, resulting in the highest elongation at break. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of γ irradiation on the properties of polyacrylonitrile films

In this study, we examined the effects of γ irradiation on the mechanical, thermal, structural, and electrical properties of polyacrylonitrile (PAN). Irradiation doses of 20, 40, 60, 80, and 100 kGy were used, with nonirradiated PAN films serving as control samples. Microhardness measurements, mechanical tests, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry analysis, color determination, X‐ray diffraction, and electrical properties were investigated to evaluate the effects of the irradiation treatments on the PAN films. A fair consistency was observed between the microhardness results. Irradiation caused a significant deterioration in the mechanical properties of the samples. The tensile strength and percentage elongation at break decreased with increasing irradiation dose. Similarly, Young's modulus and toughness also decreased with increasing irradiation dose. The melting and crystallization temperatures decreased, whereas the degree of yellowness increased with increasing irradiation dose. The percentage crystallinity of the PAN film increased with increasing irradiation dose. The FTIR spectra showed that there was a tendency toward a greater effect of γ irradiation on the structure of PAN at higher irradiation doses. The values of the electrical parameters, such as capacitance in parallel, dielectric constant, dielectric loss, resistance in series, resistance in parallel, reactance, and quality factor, increased, whereas the values of capacitance in series, impedance, conductance, susceptance, admittance, and phase angle decreased because of the γ irradiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical and thermal properties of wood‐plastic composites reinforced with hexagonal boron nitride

Mechanical, thermal, and morphological properties of injection molded wood‐plastic composites (WPCs) prepared from poplar wood flour (50 wt%), thermoplastics (high density polyethlyne or polypropylene) with coupling agent (3 wt%), and hexagonal boron nitride (h‐BN) (2, 4, or 6 wt%) nanopowder were investigated. The flexural and tensile properties of WPCs significantly improved with increasing content of the h‐BN. Unlike the tensile and flexural properties, the notched izod impact strength of WPCs decreased with increasing content of h‐BN but it was higher than that of WPCs without the h‐BN. The WPCs containing h‐BN were stiffer than those without h‐BN. The tensile elongation at break values of WPCs increased with the addition of h‐BN. The differential scanning calorimetry (DSC) analysis showed that the crystallinity, melting enthalpy, and crystallization enthalpy of the WPCs increased with increasing content of the h‐BN. The increase in the crystallization peak temperature of WPCs indicated that h‐BN was the efficient nucleating agent for the thermoplastic composites to increase the crystallization rate. POLYM. COMPOS., 35:194–200, 2014. © 2013 Society of Plastics Engineers     

Thermal and wide angle X‐ray analysis of chemically and radiation‐crosslinked low and high density polyethylenes

Low and high density polyethylenes (PE) were crosslinked by two methods, namely, chemically by use of different amounts of tert‐butyl cumyl peroxide (BCUP) and by irradiation with different doses of electron beam. A comparison between the effects of these two types of crosslinking on crystalline structure, crystallinity, crystallization, and melting behaviors of PE was made by wide angle X‐ray diffraction and DSC techniques. Analysis of the DSC first heating cycle revealed that the chemically induced crosslinking, which took place at melt state, hindered the crystallization process and decreased the degree of crystallinity, as well as the size of crystals. Although the radiation‐induced crosslinking, which took place at solid state, had no significant influence on crystalline region, rather, it only increased the melting temperature to some extent. However, during DSC cooling cycle, the crystallization temperature showed a prominent decrease with increasing irradiation dose. The wide angle X‐ray scattering analysis supported these findings. The crystallinity and crystallite size of chemically crosslinked PE decreased with increasing peroxide content, whereas the irradiation‐crosslinked PE did not show any change in these parameters. As compared with HDPE, LDPE was more prone to crosslinking (more gel content) owing to the presence of tertiary carbon atoms and branching as well as owing to its being more amorphous in nature. HDPE, with its higher crystalline content, showed relatively less tendency toward crosslinking especially by way of irradiation at solid state. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3264–3271, 2006     

Long‐chain branching of polypropylene by electron‐beam irradiation in the molten state

The electron‐beam irradiation of polymers generates modification effects in the macromolecular structure and material properties. Therefore, irradiation processing is mostly realized in the polymer solid state. In this way, the modification of linear polypropylene may result in long‐chain branching of polypropylene macromolecules. The objective of this article is to investigate the effect of a polymer in the molten state during electron‐beam irradiation on the macromolecular structure and material properties of polypropylene. For this procedure, a special irradiation vessel (BG3) has been developed in which a rapid transfer of polymer films from the solid state to the molten state and a defined temperature during electron‐beam irradiation are realizable. The irradiated samples have been analyzed by high‐temperature size exclusion chromatography coupled with a multi‐angle laser light scattering detector and differential scanning calorimetry (DSC) measurements. With an increasing irradiation dose, a high reduction of the molar mass and an increasing amount of long‐chain branching are found. Compared with irradiation in the solid state, the modification in the molten state leads to a higher degree of branching. The rheological experiments in elongation flow clearly exhibit the existence of long‐chain branching. Furthermore, DSC measurements show that the glass‐transition temperature and peak temperatures of melting and crystallization decrease. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 260–265, 2006     

FEP熔体流动性能和结晶性能的研究

应用熔体流动速率仪考察了口模半径、载荷及温度对聚全氟乙丙烯(FEP)流动性能的影响。结果表明:FEP熔体的表观黏度随着剪切速率、温度、载荷和口模半径的增加而降低,表现出假塑性流体行为。应用差示扫描量热法测定FEP的熔融和结晶温度及热焓,发现:与聚四氟乙烯(PTFE)相比,FEP熔点较低,熔融热较低,结晶度较小,而且熔融峰较宽。     

Mechanical and thermal properties of potassium salts of poly(ethylene‐co‐ethylacrylate): Polyolefin ionomers in the absence of acid groups

The thermal and mechanical properties of ionomers prepared by partial saponification of poly(ethylene‐co‐ethylacrylate) (EEA) with potassium were investigated by using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The Vicat softening temperature (VST) and bending modulus were also evaluated. Molecular design of the present EEA‐based ionomers eliminates acid groups, which affect ionic aggregates for conventional ionomers. The DSC results showed that the melting enthalpy and main crystallization temperature decreased as the ion content increased, whereas on the other hand, the crystal melting temperature at about 360 K did not depend on the ion content, and a secondary exothermal peak was observed in the cooling process. The variance of the VST increased as the crystallinity decreased. The temperature‐dependent curves of DMA data of the EEA‐based potassium ionomers with a higher ion content showed elastic plateau even at temperatures above their crystal melting points. Our results indicate the existence of strong cross‐linking mediated by ion aggregates. The quadratic increase of stiffness as a function of ion content, increasing VST with decreasing crystallinity, and elastic plateau of temperature‐dependent moduli above crystal melting temperature are significant characteristics of the EEA‐based potassium ionomers, which contain ionic aggregations without acid group presence. POLYM. ENG. SCI., 55:1843–1848, 2015. © 2014 Society of Plastics Engineers     

组成及MPEG用量对PPC/PBS共混物性能的影响

考察了组成和MPEG-2000的质量分数对PBS/PPC力学性能及热性能的影响。结果显示,PPC的引入使得共混物的冲击/拉伸强度明显降低;MPEG质量分数为5%时(PBS/PPC=80/20),拉伸强度和冲击强度分别达到18.9 MPa和20.3 kJ/m2。SEM对断裂面的观察表明:MPEG的引入能引发基体材料的塑性形变,冲击断面具有明显的脆韧转变特征。示差扫描量热分析(DSC)的结果表明:PPC的质量分数从0增加到30%,共混物结晶峰温度从79.3℃降低到61.3℃,结晶焓减小且过冷度增大。     

硬段含量对水性聚氨酯软段结晶性能的影响

以异佛尔酮二异氰酸酯、六亚甲基二异氰酸酯、聚己二酸丁二醇酯为主要原料合成了水性聚氨酯(WPU),通过FT-IR、DSC、XRD、SEM表征手段,研究了硬段含量对软段结晶性及WPU粘结性能的影响。研究表明,随着硬段含量的增加,WPU分子链上氨基甲酸酯键之间的氢键化程度提高,软硬两相相混严重,WPU软段结晶熔融焓变小,熔融温度变低;结晶衍射峰变弱,软段结晶性变差;粘结性能测试表明,在硬段含量较低时,聚氨酯体现出良好的结晶性能,初粘性较好。     

冷却温度对聚丙烯薄膜结晶、形态和拉伸性能的影响

采用示差扫描量热法(DSC)、广角X射线衍射(WAXD)和扫描电镜(SEM)对聚丙烯(PP)薄膜的结晶、形态进行了研究,并测试了薄膜的拉伸性能.结果表明:冷却水温度变化对生产PP薄膜的结晶、形态和拉伸性能有很大影响.在冬季,PP薄膜的结晶度更小,晶体尺寸更均一;但在夏季,PP薄膜的拉伸强度、杨氏模量和断裂伸长率分别提高45%、85%和94%.最后,通过数值模拟,得到了给定条件下相关冷却参数的合理数值.     

Effects of silver nanoparticles on the dynamic crystallization and physical properties of syndiotactic polypropylene

The effects of silver (Ag) nanoparticles on the physical properties of syndiotactic PP (sPP) were investigated concentrating on the isothermal melt crystallization behavior under shear. sPP with 5 wt % Ag nanoparticles presented higher crystallization temperature (T_c) and heat of crystallization (ΔH_c) than pure sPP. At 90°C, the Ag nanoparticles had little effect on the induction time of crystallization but a little increased the half‐time (t_1/2) for the crystallization. At 100°C, however, the induction time was decreased with increasing the Ag content and the t_1/2 was decreased up to the Ag content of 0.5 wt %. DSC melting endotherms exhibited double melting peaks when crystallized at 90°C under shear but a single melting peak when crystallized at 100°C. The WAXD patterns exhibited that the presence of Ag nanoparticles did not produce any change in the crystal structure of sPP. The tensile strength of sPP is little changed up to the Ag content of 0.1 wt % but it was decreased with further addition. In addition, the introduction of less than 0.1 wt % Ag increased the elongation at break, but further addition decreased it abruptly. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

In situ small angle X‐ray scattering study on structural evolution of crosslinked polytetrafluoroethylene during deformation

The structural evolution of virgin and crosslinked polytetrafluoroethylene (PTFE) during stretching was studied by in situ synchrotron small‐angle X‐ray scattering (SAXS). Both yield and tensile stress of crosslinked PTFE increased with increasing crosslinking density. During stretching, for virgin PTFE, amorphous chains gradually turned to tensile direction at early stage, perpendicularly arranged lamellar stacks appeared at high strains (>140%). While for crosslinked PTFE, lamellar structure was observed even at lower strains; with increasing irradiation dose, the lamellar structure became obvious and the long period decreased. Four‐point SAXS patterns were observed only in 3000kGy‐dosed PTFE during deformation, which indicated that an alternately tilted lamella arrangement called herringbone structure was formed. Radiation dose induces crosslinked networks formed, which can carry part of local stress during deformation, resulting in the increase of yield and tensile stress. Crosslinking density is an important factor on structural evolution. In addition, a deformation mechanism of different crosslinked PTFE is proposed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39883.     

Radiation‐induced oxygen scavenging activity in EVOH copolymers

Oxygen scavenging capacity has been observed for the first time in an ethylene‐vinyl alcohol (EVOH29, i.e., 29 mol % of ethylene) copolymer as a consequence of electron beam irradiation at doses of 30 and 90 kGy. This oxygen blocking activity is thought to arise from the reaction of oxygen with the free radicals formed during the irradiation process and it has been observed to be dependent of the irradiation dose, i.e., the higher the dose, the longer the time the polymer is able to react with oxygen. The characterization of the irradiated polymeric samples has been carried out through DSC and FT‐IR and the oxygen transmission rate has been measured as a function of time and compared with the properties of the nonirradiated material. A drop in the melting point and in the enthalpy of fusion and broader peaks were observed after irradiation, which indicated changes in the morphology of the copolymer. Through FT‐IR, a slight decrease in the crystallinity of the irradiated EVOH29 was observed at the highest irradiation dose and several bands arise which correspond to the formation of degradation products such as aldehydes and ketones after irradiation. Those radiolysis compounds were identified through gas chromatography coupled to mass spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Oriented crystallization and mechanical properties of polypropylene nucleated on fibrillated polytetrafluoroethylene scaffolds

It is known that friction deposited polytetrafluoroethylene (PTFE) layers are able to nucleate crystallization of thin films of isotactic polypropylene (iPP). In order to investigate the influence of PTFE on the crystallization behavior and morphology of iPP in bulk, PTFE‐particles of two different sizes in various concentrations were melt‐blended with iPP and subsequently processed by injection molding. For one size of particles, high resolution scanning electron microscopy (HR‐SEM) showed the presence of a PTFE scaffold consisting of highly fibrillated PTFE particles. With X‐ray diffraction (WAXD) pole‐figures, it was evidenced that, after melting and recrystallization of the iPP matrix, a strongly oriented crystallization of iPP on this PTFE scaffold takes place (quiescent crystallization conditions). With WAXD it was also shown that under processing conditions, PTFE acts as a nucleating agent for iPP and that PTFE strongly enhances the formation of processing induced morphologies. Impact and tensile performance of the mixtures were measured. Both the strain energy release rate (G_I) and the E‐modulus were found to increase upon introducing PTFE in iPP. POLYM. ENG. SCI., 45:458–468, 2005. © 2005 Society of Plastics Engineers.     

On the triple melting behaviour of poly(ethylene succinate)

The morphology of melt-crystallized poly(ethylene succinate) (PES) was investigated by optical microscopy and scanning electron microscopy, and the melting behaviour of PES was studied by differential scanning calorimetry (DSC). At low crystallization temperature imperfect crystals were formed which could melt and recrystallize during the DSC scan. Triple melting peaks were observed, and the melting behaviour was strongly dependent on crystallization time and scan rate. It was observed that crystallization at high temperature perfected the crystals (dominant and subsidiary lamellae in the spherulitic structure). Increasing the scan rate reduced the chance for reorganization. However, at high crystallization temperature two melting peaks were observed. The material formed was much more perfect, so that the melting process was not dominated by recrystallization. Accordingly, the cause of dual melting is the existence of two kinds of crystal perfection.     

Heat‐sealing properties of soy protein isolate/poly(vinyl alcohol) blend films: Effect of the heat‐sealing temperature

To promote the heat‐sealing properties of soy protein isolate (SPI) films applied in the packaging field, we mixed a synthetic polymer of poly(vinyl alcohol) (PVA) with SPI to fabricate blend films by a solution‐casting method in this study. To clarify the relationship between the heat‐sealing properties and the heat‐sealing temperature, strength, melting process, crystalline structure, and microstructure, variations of the heat‐sealing parts of the films were evaluated by means of differential scanning calorimetry, tensile testing, scanning electron microscopy, X‐ray diffraction, and Fourier transform infrared spectroscopy, respectively. The test results showed that both the PVA and glycerol contents greatly affected the melting behavior and heat of fusion of the SPI/PVA blends; these blend films had a higher melting temperature than the pure SPI films. The peel strength and tensile strength tests indicated that the long molecular chain of PVA had a main function of enhancing the mechanical properties above the melting temperature. With increasing heat‐sealing temperature, all of the mechanical properties were affected by the microstructure of the interface between the laminated films including the chain entanglement, crystallization, and recrystallization. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fully biobased biodegradable poly(l‐lactide)‐b‐poly(ethylene brassylate)‐b‐poly(l‐lactide) triblock copolymers: synthesis and investigation of relationship between crystallization morphology and thermal properties

Well‐defined poly(l ‐lactide‐b‐ethylene brassylate‐b‐l ‐lactide) (PLLA‐b‐PEB‐b‐PLLA) triblock copolymer was synthesized by using double hydroxyl‐terminated PEBs with different molecular weights. Gel permeation chromatography and NMR characterization were employed to confirm the structure and composition of the triblock copolymers. DSC, wide‐angle X‐ray diffraction, TGA and polarized optical microscopy were also employed to demonstrate the relationship between the composition and properties. According to the DSC curves, the cold crystallization peak vanished gradually with decrease of the PLLA block, illustrating that the relatively smaller content of PLLA may lead to the formation of a deficient PLLA type crystal, leading to a decrease of melting enthalpy and melting temperature. Multi‐step thermal decompositions were determined by TGA, and the PEB unit exhibited much better thermal stability than the PLLA unit. Polarized optical microscopy images of all the triblock samples showed that spherulites which develop radially and with an extinction pattern in the form of a Maltese cross exhibit no ring bond. The growth rate of the spherulites of all triblock samples was investigated. The crystallization capacity of PLLA improved with incorporation of PLLA, which accords with the DSC and wide‐angle X‐ray diffraction results. © 2019 Society of Chemical Industry     

Crystallization,melting behavior,and crystal structure of reactive,intumescent, flame‐retardant polypropylene

Polypropylene (PP)/2‐({9‐[(4,6‐diamino‐1,3,5‐triazin‐2‐yl) amino]‐3,9‐dioxido‐2,4,8,10‐tetraoxa‐3,9‐diphosphaspiro [5.5] undecan‐3‐yl} oxy) ethyl methacrylate (EADP) composites were prepared by the blending of PP with EADP as a new flame‐retardant material. The nonisothermal crystallization and melting behaviors of composites were investigated with differential scanning calorimetry (DSC). Their crystal morphologies and structures were studied by polarized optical microscopy (POM) and X‐ray diffraction (XRD), respectively. The DSC results show that the addition of EADP increased the crystallization onset temperature, crystallization peak temperature, and degree of crystallinity of PP in the PP/EADP composites. The melting onset temperature and melting end temperature of the PP/EADP composites decreased slightly, whereas the melting peak temperature of the PP/EADP composites increased. The POM results show that the addition of EADP greatly reduced the crystal size of PP in the composites. When the content of EADP in the PP/EADP composites was increased, the crystal size of PP became smaller. The XRD results indicate that the addition of EADP changed the crystal structure of PP in the PP/EADP composites, which exhibited both α‐form and β‐form crystal structures. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41374.