The influence of anisotropic phase structure on the properties of crystalline polymers

By combining quantitative molecular, microscopic and macroscopic information from an oriented crystalline polymer, it becomes possible to unify, predict, and explain not only processing behavior but such important material properties as failure, shrinkage, modulus, yielding, melting, and storage and loss moduli. Among the advantages gained by this approach are the ability to: (a) identify the particular phase of the two-phase system which controls a given property-(b) correlate internal structure quantitatively with a large number of seemingly different types of properties; (c) identify quantitative behavioral rules which are generally valid for Very different crystalline polymers; (d) clarify component roles such that new techniques and processes result; and (e) predict the properties of a crystalline polymer for structural states not previously tested. Using two dissimilar crystalline polymers, isotactic polypropylene and poly(ethylene terephthalate), as examples, the general validity and unifying power of the structural approaches is demonstrated.     

Treatment of ramie fiber with different techniques: the influence of diammonium phosphate on interfacial adhesion properties of ramie fiber-reinforced polylactic acid composite

Ramie fiber-reinforced polylactic acid (PLA) composites were successfully prepared by hot compression molding. Different treatment techniques were used to modify the surface of ramie fiber. The influence of diammonium phosphate (DAP) on the interfacial adhesion between ramie fiber and PLA composites was investigated by the contact angle measurements, FTIR and SEM analyses. The contact angle measurement results showed that alkali treatment combined with DAP was very efficient in decreasing the hydrophilicity of fibers. After treatment, the hydrophilicity of untreated ramie fiber from 5.9 ± 1.3 decreased to 2.0 ± 0.8 mJ/m². The wettability of alkali/silane/DAP-treated ramie fiber/PLA composite was higher (95.4° ± 1.3°) than that of pure ramie fiber/PLA composite (87.3° ± 1.9°). The FTIR results were consistent with the wetting measurements as the increment of hydrophilicity. Thermal analysis indicated that DAP-modified ramie fiber/PLA composites exhibited a lower thermal decomposition temperature, unique decomposition behavior and more residual char formation at decomposition temperature. The tensile, flexural and impact properties of DAP-modified ramie fiber composites were comparable to those of untreated ramie fiber composite. Moreover, proper alignment and uniform distribution of ramie fibers within the PLA matrix were found to be excellent. The morphological structures observed by SEM showed that well-modified ramie fibers enhanced the failure of the PLA composites in tensile, flexural and impact tests.     

PAN纤维致密化过程对纤维晶态结构的影响

应用X射线衍射、声速法等研究了在PAN纤维制备中致密化过程对纤维晶态结构、全取向结构的影响规律,结合差示扫描量热法和纤维的拉伸-形变曲线,探讨了纤维致密化程度与纤维密度及纤维拉伸特性间的关系。结果表明,在PAN纤维制备中,高于大分子玻璃化转变温度的致密化处理过程中,随致密化温度的升高,纤维密度增大,拉伸强度降低,全取向结构降低,但对PAN分子侧氰基的热分解环化行为影响不大。     

聚丙烯腈纤维孔隙结构对预氧化的影响

采用湿法纺丝,通过不同的牵伸条件,制备具有相同的化学组分和不同孔隙率(体密度)的聚丙烯腈纤维,然后在相同的条件下预氧化。借助红外吸收光谱(FT-IR)、场发射扫描电子显微镜(FESEM)、差示扫描量热(DSC)等表征手段对原丝和预氧丝的环化度、皮芯结构及预氧丝横截面的氧径向分布进行分析对比。实验结果表明,随着孔隙率降低(体密度增加),纤维径向的氧含量梯度变大,皮芯结构趋于严重。     

UHMWPE纤维的熔融行为和结晶结构的研究

用DSC法研究了超高相对分子质量聚乙烯(UHMWPE)纤维的熔融行为。随着拉伸倍数提高,纤维经松弛状态下热处理后,其熔融峰数目由1个变为2个;而经部分张力和张力状态下热处理后,其熔融峰数目均由1个变为3个。熔融峰出现的位置可分为4个区:131-138℃,141-143℃,150-152℃,155- 157℃。松弛与张力状态下热处理纤维的主熔融峰不同,前者主要是正交晶系的熔融,后者则分别对应于正交晶相向六方晶相的转变和六方晶相的熔融。经热处理的UHMWPE纤维的DSC图谱表明,代表正交晶相向六方晶相转化的熔融峰面积均有所增大,同时纤维的拉伸强度均有提高,提高幅度达31.1%。     

生产工艺对腈纶结构和性能的影响

采用广角X-射线衍射（WAXD）、双折射等方法分析了不同生产工艺所制备的腈纶的超分子结构,通过动态力学分析（DMA）测定了纤维的玻璃化转变温度。结合纤维的力学性能分析发现,通过降低总拉伸倍数的生产工艺,可以有效降低纤维的结晶度、取向度,降低纤维的断裂强度,并进一步通过增加再拉伸（干热拉伸）的工序降低了纤维的断裂伸长率,...     

三赞胶对钻井液性能影响的研究

三赞胶是我国自主开发的一种新型生物胶环保处理剂。重点研究三赞胶在不同条件下（温度、般土含量和含盐量）对钻井液流变性能和滤失性能的影响规律,并与黄原胶进行对比。试验结果表明：在温度低于90℃的条件下,三赞胶钻井液体系比黄原胶钻井液体系具有更高的表观黏度和动切应力,较低的塑性黏度,剪切稀释性能好,而且具有较高的低剪切黏度;当温度高于90℃,特别是在120℃滚动养护条件下,三赞胶钻井液体系的流型调节能力迅速下降,性能不如黄原胶钻井液体系。对三赞胶在不同温度下性能变化的机理进行了分析。三赞胶在抗温性能方面进一步改进后,有望形成复杂结构钻井液体系的一种新型流型调节剂。     

X-ray study of crystallinity and disorder in ramie fiber

The degree of crystallinity and the disorder parameter in ramie fibers treated with various concentrations of aqueous NaOH solutions at room temperature (～ 30°C) and at 0°C, respectively, have been analyzed by the wide-angle x-ray diffraction method of Ruland and Vonk.^9–11 The results appear to suggest the presence of highly distorted crystalline regions that are first affected by lower concentrations of alkali. At higher concentrations of mercerizing strength it is observed that the lattice conversion to cellulose II is accompanied by a decrease in the degree of crystallinity and an increase in the disorder parameter values. The tensile properties of the fibers corroborate the results. © 1994 John Wiley & Sons, Inc.     

Adjustable wettability of methyl methacrylate modified ramie fiber

The surface hydrophobicity/hydrophilicity of ramie fiber was regulated through the atom transfer radical polymerization of methyl methacrylate from initiators immobilized on the fiber. The optimal reaction conditions for preparing the macroinitiated ramie fiber were determined to be a temperature of 60°C and a reaction time of 24 h. The grafted copolymers were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, energy‐dispersive analysis of X‐rays, gel permeation chromatography, and thermogravimetric analysis. The results indicate that poly (methyl methacrylate) was covalently bonded onto the surface of the ramie fiber, and the polymerization of methyl methacrylate was a living/controlled process under the investigated conditions. The results of the contact angle measurements indicate that the wettability of the ramie fiber could be widely regulated by control of the grafted ratios of poly(methyl methacrylate) from 26 to 33 wt %. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of plasma treatment on properties of ramie fiber and the reinforced composites

In this research, 9 series of ramie fibers were treated under low-temperature plasma with diverse output powers and treatment times. By analysis of the surface energy and adhesion power with epoxy resin, 3 groups as well as control group were chosen as reinforced fibers of composites. The influences of these parameters on the ramie fiber and its composites such as topography and mechanical properties were tested by scanning electron microscopy (SEM), atomic force microscopy (AFM), tensile property and fragmentation test of single-fiber composites. Contact angle and surface free energy results indicated that with the increased treatment times and output powers, surface energy and adhesion work with epoxy resin improved. Compared with the untreated fibers, surface energy and adhesion work with epoxy resin grew 124.5 and 59.1% after 3 min-200 w treatment. SEM and AFM showed low temperature plasma treatment etched the surface of ramie fiber to enhance the coherence between fiber and resin, consequently fiber was not easy to pull-out. After 3 min-200 w treatment, tensile strength of ramie fiber was 253.8 MPa, it had about 30.5% more than that of untreated fiber reinforced composite. Interface shear stress was complicated which was affected by properties of fiber, resin and interface. Fragmentation test showed biggest interface shear stress achieved 17.2 MPa, which represented a 54.0% increase over untreated fiber reinforced composites.     

Thermal conductivity of ramie fiber drawn in water in low temperature

To understand the effect of extension of molecular chain in amorphous region in polymer fibers to thermal conductivity, the thermal conductivity, tensile modulus and crystal orientation angle of ramie fibers and those drawn by the stress of 17.4 kg/mm² (water treatment) in the water were investigated. The tensile modulus of ramie fiber in fiber direction increased from 61 to 130 GPa by drawing in the water. The crystal orientation angles of ramie fiber with and without water treatment were measured by X‐ray diffraction. The orientation degrees of ramie fibers without and with water treatment were estimated as 92.9 and 93.6%, respectively. Therefore, the tensile modulus increases two times as that of blank ramie by water treatment although crystal orientation angle does not change distinctly. The increasing of tensile modulus of ramie fiber by water treatment was explained by extension of the molecular chains in the amorphous region. Thermal conductivities of ramie fibers with and without water treatment were measured in the fiber direction in the temperature range from 10 to 150 K. Thermal conductivity of ramie fiber in the fiber direction increased by water treatment. The increasing ratio of thermal conductivity by water treatment agreed to that of sound velocity induced by increasing tensile modulus. Those results suggest that thermal conductivity of polymer fiber increase by the extension of molecular chains in the amorphous region. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2196–2202, 2006     

The influence of processing terms of chitosan membranes made of differently deacetylated chitin on the crystalline structure of membranes

The crystalline structure of chitosan membranes made of a high degree of (90%) and low degree of (60%) deacetylated chitin by various regeneration processes was studied. The results of X-ray and IR spectroscopy investigations testify that the type of crystalline structre, the degree of crystallinity, and the average lateral crystallite size depend basically on the deacetylation degree of the chitin utilized in preparing the membranes. © 1994 John Wiley & Sons, Inc.     

Radial distribution function analysis study on alkali and heat-treated ramie fiber

The radial distribution function (RDF) analysis of wide-angle X-ray diffraction by ramie fibers in untreated condition and after treatment with alkali of mercerizing strength or heat have been carried out. Interatomic distances, coordination numbers, mean square displacements, and coupling constants for different atom pairs have been calculated. The results have been interpreted in terms of a difference in both the conformation and packing of molecular chains in raw and alkali-treated ramie. In general, the coupling constant values have been found to be more in alkali-treated ramie, indicating relatively weak bond strength. Heat-treated ramie shows a marginal decrease in coupling constant values. © 1994 John Wiley & Sons, Inc.     

Benzylated modification and dyeing of ramie fiber in supercritical carbon dioxide

The effects of pretreatment conditions, including the addition of a phase‐transfer catalyst, on the benzylation of ramie fiber were investigated in this study. Raw and benzylated ramie fibers were dyed in supercritical carbon dioxide, and the color strength (K/S) of the ramie fiber was measured by ultraviolet–visible spectroscopy. An obviously improved dyeing capability of the benzylated ramie fiber, that is, a better level‐dyeing property and a higher K/S, was achieved. Moreover, the color strength of the ramie fiber, indexed as the value of K/S, increased significantly with the degree of substitution of the benzylated ramie fiber. The raw and modified ramie fibers were characterized with Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of surface treatment of ramie fiber on the interfacial adhesion of ramie/acetylated epoxidized soybean oil (AESO) green composite

Recently, many researchers have attempted to convert soybean oil into useful polymers. One of the ways to make soybean oil into a matrix of green composites is to modify its triglyceride structure to obtain the acrylated epoxidized soybean oil (AESO) through epoxidization and acrylation. In this study, the effects of ramie fiber surface treatments such as acetylation, silane, and peroxide treatments on the chemical, morphological, and interfacial adhesion properties of a ramie/AESO green composite were studied. Surface-treated fibers were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and dynamic contact angle analysis. The crystallinity and thermal stability of chemically treated fibers were investigated by wide angle X-ray diffraction and thermogravimetric analyzer. It was demonstrated that surface treatments lead to several morphological changes, including the formation of micro-cracks and removal of impurities by acetylation and peroxide treatment as well as surface smoothing by silane treatment. Surface energy of acetylated fiber decreased with treatment time and showed the lowest value for silane treated fiber. The interfacial shear strength (IFSS) of a fiber/AESO composite was investigated through the microbond test. The IFSS of silane treated ramie was higher than that of others. The result indicates that silane treated fibers improve the interfacial property, which is the most important characteristic for the end use of green composites.     

The influence of H-bonding in liquid crystalline polyazomethine ethers

Summary The model compound 1,4-bis(anisylimido)benzene has been characterized by solution and CP/MAS ¹³C NMR to assist in the characterization of liquid crystalline polyazomethines (PAM) based on the same mesogenic structure. Thermal behavior of several homologs of this PAM series have been compared before and after treatment with the end capping agent benzaldehyde. The results suggest that PAM oligomers containing large quantities of amine termination can strongly effect thermal behavior at constant oligomer molecular weight.     

Lamellar crystalline structure of hard elastic HDPE films and its influence on microporous membrane formation

The development of hard elastic high-density polyethylene (HDPE) precursor films and its influence on the microporous membrane formation have been investigated. As a first step, the HDPE precursor films with ‘row-nucleated lamellar crystalline’ structure were prepared by applying elongation stress to the HDPE melt during T-die cast film extrusion and subsequently annealing the extruded films. This unusual crystalline structure was analyzed in terms of lamellar crystalline orientation, long-period lamellar spacing, crystallite size, and degree of crystallinity. The processing (melt extension and annealing temperature)-structure (lamellar crystalline structure)-property (hard elasticity) relationship of HDPE precursor films was also investigated. The uniaxial stretching of hard elastic HDPE precursor films induces the bending of crystalline lamellae, which leads to the formation of micropores between them. The observation of morphology and air permeability for the HDPE microporous membranes have revealed that the well-developed porous structures characterized by superior air permeability were established preferably from the precursor films prepared by the high stress levels and the high annealing temperatures. Finally, the relationship between the hard elasticity of HDPE precursor films and the air permeability of corresponding microporous membranes was discussed.     

Effect of alcohol pretreatment in conjunction with atmospheric pressure plasmas on hydrophobizing ramie fiber surfaces

To improve interfacial adhesion between hydrophilic cellulose fiber and hydrophobic polymer matrix, ramie fibers were pretreated with isopropanol and n-butanol and then plasma treated using an atmospheric pressure plasma apparatus. For the plasma-treated fibers, the scanning electron microscopy shows increased surface roughness and the X-ray photoelectron spectroscopy analysis shows a significant increase of C–C bond in isopropanol-pretreated group, whereas for n-butanol-pretreated group the raise of C=O bonds is most noticeable. For both alcohol-pretreated and plasma-treated groups, the water contact angles increase significantly. Microbond pull-out test shows interfacial shear strengths of fiber/polypropylene (PP) samples increase by 47 and 34%, respectively, for the two groups compared with the control. Therefore, it can be concluded that the reaction between both alcohols and cellulose induced by plasma can indeed create a fiber surface with increased roughness and decreased polarity, and thus is more compatible to PP.     

化学预处理对碳纤维性能的影响

采用化学预处理法改善碳纤维性能的方法,即采用一种还原性的金属盐水溶液对纤维进行预处理。实验结果表明,化学预处理并未破坏预氧丝外观,金属盐水溶液浓度在0.3%～0.4%时预氧丝的皮芯结构较好,处理时间2～4 min后预氧丝密度增加,最终使碳纤维力学性能都有较大的提高,为碳纤维的生产与研制提供了一种新的方法。