聚乳酸的非等温结晶行为

用差示扫描量热法(DSC)研究聚乳酸(PLA)从熔体及玻璃态为初始条件下的非等温结晶行为,采用Ozawa方程、Mo法、Khanna法和Kissinger法对结晶动力学参数进行计算处理。 实验结果表明,这几种方法均适合处理PLA的非等温结晶过程,而Khanna法提出的结晶速率系数(CRC)能够方便地评价PLA相对结晶速率的大小。 PLA从玻璃态升温结晶比从熔体降温结晶容易得多,升温过程有利于晶核生成,而降温有利于晶体生长。 升温结晶时,升温速率2.0 ℃/min时,结晶焓(ΔH_c)达到最大为27.1 J/g。 从熔体等速降温过程中,随着冷却速率的降低ΔH_c单调增加,冷却速率为0.25 ℃/min时ΔH_c增加到28.3 J/g。 在较低温度下从玻璃态结晶,主要表现为异相成核的二维生长方式。 在较高的温度下从玻璃态升温结晶及从熔体冷却结晶时,以均相成核的三维生长方式结晶为主。 与升温过程相比,冷却不利于晶核的生成,所以导致冷却过程总体ΔH_c偏低,扩散活化能偏大。     

Influence of PEG‐ran‐PPG Surfactant on Vapour Phase Polymerised PEDOT Thin Films

The oxidant, Fe(III) tosylate, was used in the vapour phase polymerisation (VPP) of PEDOT. The amphiphilic co‐polymer poly(ethylene glycol‐ran‐propylene glycol) was added and its influence examined. Both the PEDOT conductivity and optical contrast range increased with the inclusion of the co‐polymer, with the maximum being recorded at 4 wt.‐%. Loadings higher than this resulted in a systematic decrease in both conductivity and optical contrast. Evidence indicates that in addition to the beneficial anti‐crystallisation effect to the oxidant layer, the co‐polymer also reduces the effective reactivity of the oxidant, as demonstrated by slower polymerisation rates. Confirmation of the change in polymerisation rate was obtained using a quartz crystal microbalance (QCM). The slower polymerisation rate results in higher conductivity and optical contrast; however, XPS data confirmed that the co‐polymer remained within the PEDOT film post‐washing and this result explains why the performance decreases at high surfactant loadings.

     

Annealing of Polypropylene/Polyethylene Blends Near to the Melting Points in TMDSC

Annealing experiments have been carried out just below the melting temperature of both polyethylene (LLDPE) and polypropylene (PP) and their blends. The total melting enthalpy measured after the annealing cycle was greater by 10-15% with respect to the value having been measured before it. During the annealing period the heat capacity decreases to a lower value within the first 2-3 min. Heat capacities of PP (either in pure form or in the blends) measured during the heating cycle following the annealing cycle have the same value as during the cooling section. The heat capacities of the LLDPE in the heating cycle following the annealing were those of the preceding heating cycle. The total heat flows in the cooling section following the annealing cycle were greater than those in another cooling cycle at the same temperatures indicating that the crystallisation takes place during the cooling rather than during the annealing periods. The presence of LLDPE decreases the crystallisation temperature of PP. The presence of SEBS in the blend results in a greater crystallisation temperature than that of pure PP. The crystallisation temperature of LLDPE increases with increasing levels of PP. This revised version was published online in July 2006 with corrections to the Cover Date.     

Crystallisation kinetics of some archetypal ionic liquids: isothermal and non-isothermal determination of the Avrami exponent

The properties of ionic liquids give rise to applications in diverse technology areas including mechanical engineering, mining, aerospace and defence. The arbitrary physical property that defines an ionic liquid is a melting point below 100 °C, and as such, an understanding of crystallisation phenomena is extremely important. This is the first report dealing with the mechanism of crystallisation in ionic liquids. Assuming crystallisation of the ionic liquids is a thermal or mass diffusion-controlled process, the values of the isothermal Avrami exponent obtained from three different ionic liquids with three different anions and cations all indicate that growth occurs with a decreasing nucleation rate (n=1.8-2.2). For one of the ionic liquids it was possible to avoid crystallisation by fast cooling and then observe a devitrification upon heating through the glass transition. The isothermal Avrami exponent of devitrification suggested growth with an increasing nucleating rate (n=4.1), compared to a decreasing nucleation rate when crystallisation occurs on cooling from the melt (n=2.0). Two non-isothermal methods were employed to determine the Avrami exponent of devitrification. Both non-isothermal Avrami exponents were in agreement with the isothermal case (n=4.0-4.15). The applicability of JMAK theory suggests that the nucleation event in the ionic liquids selected is a random stochastic process in the volume of the material. Agreement between the isothermal and non-isothermal techniques for determining the Avrami exponent of devitrification suggests that the pre-exponential factor and the activation energy are independent of thermal history. The heating rate dependence of the glass transition enabled the calculation of the fragility index, which suggests that the ionic liquid is a "strong" glass former. This suggests that the temperature dependence of the rate constant could be close to Arrhenius, as assumed by JMAK theory. More generally, therefore, it can be concluded that there is nothing unusual about the crystallisation mechanism of the ionic liquids studied here.     

Transfer of contaminant during the processing of thick bi-layer food packages made of recycled and virgin polymer layers

A new route of recycling old polymers consists of using them as new food packages. Because of the potential contamination of the old polymer resulting from its previous use, the new packages are made of the old polymer layer bound to a virgin polymer layer. As it takes some time for the contaminant to diffuse through the bi-layer packaging, the food is protected over a period of time. The process of binding the two polymer layers is studied, when the two layers are heated at around the melted temperature and then cooled down at room temperature. Heat transfer by conduction through the polymer and the mould during the heating stage is considered as well as the cooling period in air. During this heating and cooling period, the process of contaminant diffusion through the two polymer layers is evaluated by considering a temperature-dependent diffusivity. The results are expressed in terms of profiles of temperature and of profiles of concentration of contaminant developed through the polymer layers. The kinetics of contaminant transfer from the recycled layer to the virgin polymer layer are also determined, for various thicknesses of the package. Dimensionless numbers are used, as well as various thicknesses of the package.     

‘Weak links’ in polystyrene

A first step in the thermal degradation of polystyrene prepared by radical polymerisation has been isolated by heating the polymer in the temperature range 199–280°C. In this step a chain scission process occurs without formation of volatile products, involving, on average, about one bond between structural units in every 10 000. This gives more direct evidence than hitherto of the presence of ‘weak links’ in polystyrene which are shown to be randomly distributed in the polymer chains, their scission resulting in a single break in the molecule of polystyrene to which they belong.The very low energy of activation for chain scission suggests that more than one rate determining step is involved in the process.     

A Comparison of the use of FTIR spectroscopy with DSC in the characterisation of melting and crystallisation in polycaprolactone

The infrared spectrum of polycaprolactone has been recorded as a function of temperature in the range where melting and crystallisation of the polymer can occur. Examination of the carbonyl band of the spectra reveals a clear morphological sensitivity; heating the semi-crystalline polymer through the melting region results in a decrease in the intensity of the crystalline component of the carbonyl band. Accordingly, there was a subsequent increase in intensity of the crystalline carbonyl band on cooling. To enable comparison of these findings with a more conventional method of thermal analysis, similar experiments were conducted using a differential scanning calorimeter. The heated ATR accessory adopted for use in the FTIR spectrometer imposed significant limitations in the range of possible heating and cooling rates, but when these rates were carefully matched between FTIR and DSC, close correlation between the melting point and onset of re-crystallisation was observed. The results confirm that FTIR can be used as an alternative, if more laborious, way of investigating melting and re-crystallisation.     

Temperature modulated dynamic mechanical analysis

Temperature modulated dynamic mechanical analysis (TMDMA) was performed in the same way as temperature modulated DSC (TMDSC) measurements. Temperature modulation with amplitude 0.5 K and period 20 min was realised by a series of linear heating and cooling cycles (saw-tooth modulation). As in TMDSC TMDMA allows for the investigation of reversible and non-reversible phenomena in the melting and crystallisation region of polymers. The advantage of TMDMA compared to TMDSC is the high sensitivity for small and slow changes in crystallinity, e.g. during re-crystallisation. The combination of TMDMA and TMDSC yields new information about local processes at the surface of polymer crystallites. It is shown that during and after isothermal crystallisation the surface of the individual crystallites is in equilibrium with the surrounding melt.     

Optimization of Processing Parameters for Minimizing Warpage of Large Thin-walled Parts in Whole Stages of Injection Molding

This study investigated total warpage of a type of motorcycle seat support made of polypropylene（PP） during the entire process of injection molding and free-cooling after demolding. Finite element modeling（FEM） analysis for injection molding and its associated thermal deformation was carried out in the study. The effects of processing parameters on warpage occurring in different stages were analyzed by Taguchi optimization method. It was found that packing pressure is the major factor that affects warpage in the injection stage, whereas cooling time is the major factor in free-cooling stage. From an overall evaluation, melt temperature affects the total warpage most, followed by cooling time, packing pressure, packing time and mold temperature. The result proved that optimum parameters for minimizing final warpage of the injected parts can be obtained only when the deformation in the entire manufacturing process is addressed in both molding and demolding stages.     

Processing-induced chromism in thin films of polythiophene derivatives

Langmuir-Blodgett films of amphiphilic poly[3-oligo(oxyethylene)-4-methylthiophene] have been obtained. The resulting thin films are poorly conjugated, with a maximum of absorption at 405 nm which remains almost constant upon heating or cooling. In contrast, cast thin films of this polymer exhibit a maximum of absorption at 550 nm and show interesting thermochromic effects. These results to indicate that the method of preparation of thin films can have a significant influence on the conformational structure of the polymer at room temperature and, consequently, on its thermochromic behaviour.     

透明导电玻璃(ITO)基材自加热传感静态芯片聚合酶链反应(PCR)

利用商品化ITO玻璃导电层的温阻效应, 无需任何微加工手段, 实现了自加热和传感的芯片温度自动程序控制, 最大程度地减小了传感滞后对温度控制稳定性的影响, 温度控制的稳定性达到了0.2 ℃, 升温速度最快可达20 ℃/s以上, 在冷却风扇辅助下降温速度最快达到了8 ℃/s. 芯片温控单元的引线从传统的两对(一对用于传感, 一对用于加热)减少为一对. 通过在该芯片上直接构建多个开放微池反应器的方法成功地实现了λDNA 157 bp片段的并行扩增. 将该芯片置于倒置荧光显微镜样品台上, 以蓝色(575 nm)发光二极管为光源, 以光电倍增管为检测手段检测了dsDNA和SYBR Green Ⅰ嵌合物的荧光强度随温度的实时变化曲线.     

Process dependence of pressure-specific volume-temperature measurement for amorphous polymer: Acrylonitrile-butadiene-styrene

The process dependence of pressure-specific volume-temperature (pvT) measurement for an amorphous polymer, acrylonitrile-butadiene-styrene (ABS), was investigated. The influences of different measurement processes (heating, cooling, compression, and decompression with different rates) were considered in the pvT measurements. The pvT measurements of isobaric cooling and heating with different cooling and heating rates (2, 5, and 10 °C/min) and isothermal compression and decompression with different compression and decompression rates (up to 920 bar/s) were conducted. The testing temperature ranged between 40 and 230 °C and the pressure ranged between 20 and 2200 bar. The obtained results demonstrated that the pvT diagram will be significantly different depending on the direction in which the pressure or temperature is changing and also on the rate of the change. Isobaric pvT diagrams are different between cooling and heating. Fast cooling accelerates phase transitions, while fast heating reverses. Specific volume at the same pressure and temperature in decompression process is lower than that in compression. Compression and decompression leads to different pvT curves. Compression and decompression rates have different effects on specific volume in different states.     

Precision and control in polymer synthesis why it's important and some recent examples of how to do it

This paper discusses some of the reasons why precision and control in polymer synthesis is of importance. By way of illustration it describes in outline recent results from the authors' laboratories in three areas. Namely; the controlled syntheses of poly(arylene vinylene)s and the influence of cis/trans vinylene content on luminescence in such polymers; the living polymerisation of highly functionalised polymers in water and the regulation of the crystallisation of calcium carbonate from water by the resultant well-defined water soluble polymers; and a simple route to hyperbranched polymers and the influence of the structure and topology of the products on solution properties. In each case the influence of control of architecture on properties will be discussed.     

Organogelators and Polymer Crystallisation

The specific impact of low molecular weight organic gels on polymer crystallisation is examined. Conventional nucleating agents (NA) influence the polyolefins crystallisation and improve their mechanical properties, via an epitaxial mechanism. In the particular case where the pair NA/polymer form a gel at intermediate temperatures on cooling, optical properties (clarity) are significantly improved. This improvement is linked with the ability of organic gels to develop 3-D fibrillar network. The fibres morphology offers a large specific area, thus produces a high density of nuclei, homogeneously dispersed. Gelling organic molecules are certainly a promising route towards the design of efficient additives in polymer processing.     

DSC测试中样品内部的温度分布及其对比热测试的影响

由傅里叶导热定律结合Tools-Narayanaswamy-Moynihan(TNM)松弛模型提出了一种计算聚合物样品内温度分布的方法.对PS的计算结果表明温度梯度随样品厚度、升温速率增大而增大,对于1.0 mm的PS以1 K/min降温后再以10 K/min升温时样品内部最大温差为0.882 K.在此基础上提出了不同样品厚度、不同热处理条件下聚合物测定比热的计算方法,结果表明计算结果与实测数据基本一致.     

Isothermal crystallisation kinetics of poly(3-hydroxybutyrate) using step-scan DSC

The crystallisation kinetics, melting behaviour and morphology, of bacterial poly(3-hydoxybutyrate) (PHB) have been investigated by using differential scanning calorimetry (DSC), step-scan DSC (SDSC), wide angle X-ray diffraction (WAXRD) and hot stage polarised optical microscopy (HSPOM). DSC imparted isothermal crystallisation thermal history. The subsequent melting behaviour revealed that all PHB materials experienced secondary crystallisation during heating and the extent of secondary crystallisation varied depending on the crystallisation temperature. PHB samples were found to exhibit double melting behaviour due to melting of SDSC scan-induced secondary crystals, while considerable secondary crystallisation or annealing took place under the modulated heating conditions. The overall melting behaviour was rationalised in terms of recrystallisation and/or annealing of crystals. Interestingly, the PHB materials analysed by SDSC showed a broad exotherm before the melting peak in the non-reversing curve and a multiple melting peak reversing curve, verifying that the melting-recrystallisation and remelting process was operative. HSOM studies supported the conclusions from DSC that the radial growth rate of the PHB spherulites was significantly varied upon the crystallisation conditions. One form of crystals was shown by WAXRD from isothermally crystallised PHB.     

聚合物基微纳米功能复合材料3D打印加工的研究

高分子材料3D打印加工可制备传统加工不能制备的形状复杂的高分子制件,是近年来发展很快的先进制造技术。但适用于3D打印加工的高分子材料种类少,结构功能单一,难以制备高分子功能器件。本文介绍了我们在聚合物基微纳米功能复合材料3D打印加工方面的研究工作:通过有机/无机杂化、固相剪切碾磨、超声辐照、分子复合等技术制备适合于选择性激光烧结(SLS)和熔融沉积成型(FDM)的聚合物基微纳米功能复合材料;实现了聚合物基微纳米功能复合粉体的SLS加工和功能复合丝条的FDM加工;研究了3D打印低维构建、层层叠加、自由界面成型、复杂固-液-固转变过程;建立了功能复合粉体球形化技术,发明了直接熔融挤出新型FDM打印机;制备了常规加工方法不能制备的数种形状复杂的功能器件,如尼龙11/钛酸钡压电器件、柔性聚氨酯/碳纳米管传感器、个性化人颌骨模型等,突破了传统加工难以制备复杂形状制品和目前3D打印难以制备功能制品的局限。     

Microstructural origin of physical and mechanical properties of polyamide 12 processed by laser sintering

The microstructure and properties of plastic parts made by laser sintering are known to be affected by a number of process and material parameters, whose influences are not totally elucidated yet. This study addresses the influence of the energy supplied to the powder on the microstructure and on the physical properties of sintered parts. Two different polyamide 12 powders were used. The energy density, which is derived from the laser characteristics, was shown to have a great impact on the residual porosity and on the amount of nascent particles in parts.The study of the pore size and of the porosity distribution was carried out by X-ray tomography. It is shown that the particles size distribution and the crystallisation temperature are the key parameters in the porosity formation. Finally, the influence of the microstructure and crystalline features on the mechanical properties of sintered parts is discussed.     

Study on mechanical properties of co-injection self-reinforced single polymer composites based on micro-morphology under different molding parameters

Self-reinforced single polymer composites (SRCs), which are fabricated by combining the same type of polymer with different properties into one body, have high specific strength, no interfacial heterogeneity, and ease of recycling. To better understand the relationship between the micro-morphology and mechanical properties of SRCs, the co-injection molding process was used in this study to process SRCs parts with different molding parameters and obtain the co-injection self-reinforced single polymer composites parts(CI-SRCs parts). Further, the micro-morphology of CI-SRCs parts were observed by polarizing microscope (PLM), scanning electron microscope (SEM), differential scanning calorimetry (DSC) and wide Angle X-ray diffraction (WAXD). From the results, it was found that the tensile properties of CI-SRCs parts with different molding parameters were improved by up to 23.94% compared with the conventional parts. Through PLM observation, it is found that the section shape of CI-SRCs parts perpendicular to the flow direction shows a double ‘skin-core’ structure, and the area ratio of skin layer was higher than that of conventional parts, with a maximum increase of 68%. The low-temperature and low-speed environment were conducive to the formation of skin layer, and the tensile property of CI-SRCs parts were positively correlated with the area ratio of skin layer. SEM was carried out on the skin layer near the fusion position of the interface, and the highly oriented ‘shish-kebab’ structure was observed. The 1D-WAXD pattern analysis shows that the crystallinity of CI-SRCs parts were lower than that of conventional parts, with a maximum reduction of 19.32%. The crystallinity of CI-SRCs parts were positively correlated with melt temperature gradient, and its tensile properties were negatively correlated with the change of crystallinity. The 2D-WAXD pattern analysis shows that the molecular orientation of CI-SRCs parts were higher than conventional parts, with the maximum increase of 37.44%. Low temperature and low speed can improve the molecular orientation of CI-SRCs parts, and the change of molecular orientations were positively correlated with the tensile properties of CI-SRCs parts. By means of response surface method, the molecular orientation obtained was the decisive factor affecting the performance of CI-SRCs parts. Furthermore, by means of the least squares minimization program, the dimensionless equations among molding parameters, micro-morphologies and mechanical properties were established. The prediction of mechanical properties of CI-SRCs parts based on micro-morphologies were realized, providing theoretical support for the ‘adjustability’ of CI-SRCs parts properties.     

Study on the electro-optical properties of polyimide-based polymer-dispersed liquid crystal films

The reflectivity control device, initially developed for attitude control, is utilised to control the solar sail orbit by switching the states between absorption and specular reflection. Actually, the major parts of the device are the polymer-dispersed liquid crystal (PDLC) films. Here, PDLC films based on polyimide (PI) as polymer matrix and a low molecular weight LC can be prepared by the thermally induced phase separation (TIPS) method. The influences of cooling rate and the content of LC on the size and uniformity of LC droplets dispersed in a polymer matrix by a TIPS process were investigated. It was found that a fast cooling rate gave smaller droplet sizes and hence a more uniform distribution as compared to the ones produced under a slow cooling rate. If the LC content was increased, the droplet size would be increased. Furthermore, the effect of LC droplet size on the electro-optical properties of the PI-based PDLC films was discussed, such as transmittance, threshold voltage, driving voltage and contrast ratio (CR).