微层共挤出(PP+EVOH)/PP阻隔材料的结构与性能研究

利用微层共挤出技术制备了具有交替层状结构的(PP+EVOH)/PP复合材料,其中PP为聚丙烯,EVOH为乙烯-乙烯醇其聚物.通过扫描电子显微镜观察、气体渗透实验、差示扫描量热仪分析以及力学性能测试研究了微层共挤出复合材料的形态结构及其对复合材料气体阻隔性能、力学性能以及结晶性能的影响.研究结果表明,通过微层共挤出技术,PP层和(PP+EVOH)层沿挤出方向交替排列,EVOH在PP基体中的的分散形态由零维球形变为一维纤维状,进而演变为二维片状.这些形态导致微层共挤出材料的氮气渗透系数和断裂伸长率较普通共混物分别下降了两个数量级和提高了27倍,并且显著影响其结晶行为.当层数超过64层后,由于PP层减薄,界面增多,EVOH不仅对(PP+EVOH)层中PP相存在结晶成核作用,而且对PP层也有结晶成核作用.     

Confined crystallization of PVDF and a PVDF‐TFE copolymer in nanolayered films

Layer‐multiplying coextrusion was used in conjunction with isothermal recrystallization to study the confined crystallization of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride‐tetrafluoroethylene (PVDF‐TFE) using polycarbonate (PC) and polysulfone (PSF) as confining materials. Three layered systems were produced (PC/PVDF, PSF/PVDF, and PC/PVDF‐TFE) with layer thicknesses ranging from 525 to 28 nm. The crystal morphology was affected by both layer thickness and recrystallization temperature. Specifically, increased recrystallization temperature and decreased layer thickness facilitated the formation of high aspect ratio in‐plane crystals in both PVDF based polymers. On the other side of the spectrum, thicker layers and lower recrystallization temperatures produced on‐edge PVDF crystals and isotropic PVDF‐TFE crystals. The morphology was correlated with oxygen permeability, which decreased by almost two orders of magnitude compared with the bulk. A variety of crystal structures were obtained and explained with nucleation and diffusion theory. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Enhanced electrical properties of highly oriented poly(vinylidene fluoride) films prepared by solid‐state coextrusion

Oriented poly(vinylidene fluoride) (PVDF) films with β‐form crystals have been commonly prepared by cold drawing of a melt‐quenched film consisting of α‐form crystals. In this study, we have successfully produced highly oriented PVDF thin films (20 µm thick) with β‐crystals and a high crystallinity (55–76%), by solid‐state coextrusion of a gel film to eight times the original length at an established optimum extrusion temperature of 160°C, some 10°C below the melting temperature. The resultant drawn films had a highly oriented (orientation function f_c = 0.993) fibrous structure, showing high mechanical properties of an extensional elastic modulus of 8.3 GPa and tensile strength of 0.84 GPa, along the draw direction. Such highly oriented and crystalline films exhibited excellent ferroelectric and piezoelectric properties. The square hysteresis loop was significantly sharper than that of a conventional sample. The sharp switching transient yielded the remnant polarization P_r of 90 mC/m², and the electromechanical coupling factor k_t was 0.24 at room temperature. These values are about 1.5 times greater than those of a conventional β‐PVDF film. Thus, solid‐state coextrusion near the melting point was found to be a useful technique for the preparation of highly oriented and highly crystalline β‐PVDF films with superior mechanical and electrical properties. The morphology of the extrudate relevant to such properties is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2549–2556, 1999     

Oxygen barrier properties of crystallized and talc‐filled poly(ethylene terephthalate)

The improvement in oxygen barrier properties of poly(ethylene terephthalate) (PET) by incorporation of an impermeable phase such as crystallinity or talc platelets was examined. Crystallinity was induced by crystallization from the glassy state (cold crystallization). Microlayering was used to create talc‐filled structures with controlled layer architecture. The reduction of permeability in crystallized and talc‐filled PET was well described by Nielsen's model. Changes in permeability of crystalline PET could not be ascribed to the filler effect of crystallites only. Our data on solubility, obtained on the basis of measurements of the oxygen transport coefficients, confirmed a previous finding that the amorphous phase density of PET decreases upon crystallization. The data were amenable to interpretation by free volume theory. Talc‐filled materials processed by different methods showed the same permeability; however, much better mechanical properties were achieved by microlayering. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 847–857, 1999     

Polymeric One‐Dimensional Photonic Crystals by Continuous Coextrusion

It is shown that narrowband one‐dimensional photonic crystals can be fabricated from polymeric materials using laboratory scale layer‐multiplying coextrusion technology. The tuning of the photonic bandgap is demonstrated with films that selectively filter different regions of the visible electromagnetic spectrum. The layer uniformity of the photonic crystals is evaluated by comparing the measured UV‐vis transmission spectra with model simulations, and is independently confirmed with atomic force microscopy. Assemblies of alternating polystyrene and poly(methyl methacrylate) layers exhibit a narrow reflection band with close to 100% reflection in good agreement with the prediction for uniform layers. The flexibility of the process is demonstrated by the fabrication of elastomeric one‐dimensional photonic crystals. It is anticipated that this technology will enable the rapid and facile realization of new polymeric optical devices.

     

Multilayered polycarbonate/poly(vinylidene fluoride‐co‐hexafluoropropylene) for high energy density capacitors with enhanced lifetime

The dielectric lifetime and corresponding damage morphology of polycarbonate/poly(vinylidene fluoride‐co‐hexafluoropropylene) (PC/P(VDF‐HFP)) layered systems are studied under constant direct current (DC) field. Melt blends of the two polymers are also considered for comparison. The dielectric lifetimes of the latter are systematically much shorter than the layered systems. The interfaces between the polymers act as flaws that induce up to two orders of magnitude difference between the layered and blend systems. The capacitance values versus time during breakdown progression exhibit an inversed S‐shape pattern. The three regimes in the S‐shape pattern are consecutively attributed to randomly isolated breakdowns, interconnecting breakdowns, and wearing‐out of the capacitor film. The film breakdown images during dielectric lifetime test confirmed the transition from randomly isolated breakdowns to interconnecting breakdowns. This transition was further evidenced by a bimodal distribution in the Weibull analysis. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Melt-processed polymer multilayer distributed feedback lasers: Progress and prospects

Reflecting recent progress in the functionalization of roll-to-roll processed polymer multilayers, this review describes the development and characterization of versatile large-area multilayer distributed feedback (DFB) lasers. These developments are reviewed in the broader context of microresonator lasers, with a brief tutorial on the theory and experiment needed to understand their unique features. Of particular interest is the broad tunability of these DFB lasers by simple modification of their structure, mechanical stretching, and temperature. Prospects for commercialization of polymer multilayer DFB lasers are also discussed. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 251–271     

聚合物在受限层空间中的形态结构演变及相关性能研究进展

自然界中的层状有序结构如强韧的贝壳、树木等,往往带来优异的性能或特殊的功能。作为仿生材料学在高分子加工成型技术中的应用,聚合物微纳层共挤出技术是通过特殊的流道设计对聚合物熔体进行多次强制分割叠加,来制备高性能交替多层聚合物材料的新方法。层倍增器单元对熔体的多重力场作用,为多相多组分体系形态的原位调控提供了可能。而通过两相交替层状排布形成的受限层空间和丰富的层界面不仅赋予了材料独特的力学、光电、阻隔等性能,还为聚合物结晶调控提供了理想的研究模型。本文简要综述了近年来在层倍增过程中聚合物的形态结构演变及其对相关性能影响方面的研究进展。     

Progress in low‐loss and high‐bandwidth plastic optical fibers

Plastic optical fibers (POFs) are highly promising transmission media for future home networking.In comparison to glass optical fibers (GOFs), which are commonly used in core and metropolitan networks, POFs offer many advantages such as great flexibility and easy handling. This review begins with the basic concepts of optical fibers and moves on to the early history of loss reduction in POFs. What drastically changed the status of POFs in the communications field was a graded‐index technology that improved the bandwidth to over 1 gigabits per second. However, even after the loss and bandwidth were enhanced to their limits, the performances of POFs were insufficient for market demand when using conventional optical polymer materials such as poly(methyl methacrylate). Recently, this problem has been solved by several lines of material research using fluorinated polymers. As a result, high‐speed optical home networking by POFs has become more realistic. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Simulation of mechanical properties of multilayered propylene–ethylene copolymer/ethylene 1-octene copolymer composites by equivalent box model and its experimental verification

Multilayered propylene–ethylene copolymer (PPE)/ethylene 1-octene copolymer (POE) composites were prepared by a microlayered coextrusion system. Static and dynamic tensile results showed that yield strengths and storage moduli of the multilayered samples were distinctly larger than those of conventional blends. The equivalent box model (EBM) proposed by Kolarik was used to explain the effect of morphology on mechanical properties. Experimental and theoretical results indicated that the excellent mechanical properties of multilayered composites were ascribed to the phase continuity. The effects of interfacial layers in multilayered composites on mechanical properties were also discussed. The existence of interfaces between POE and PPE layers not only led to the invalidation of EBM for prediction of mechanical properties of multilayered composites with larger number of layers, but also induced a new absorbing peak in loss modulus-temperature spectrum because of the shearing friction between POE and PPE layers through interfaces.