A study of the crystallinity index of polypropylene fibres

Crystallinity measurements were carried out with the help of X-ray diffraction, differential scanning calorimetry (DSC) and density measurements. The results of this study provide a better understanding of the morphology and complex thermal behaviour of polypropylene fibres. Crystallinity studies show that the crystallinity of PP fibres when measured by X-ray and DSC methods as a function of draw-ratios increases with increasing draw-ratios while the crystallinity of the same samples as derived by density measurements shows an inverse trend. These discrepancies are accounted for by the formation of microvoids within the polypropylene fibres due to drawing. In the DSC scan two endothermic peaks were found to occur in some of the samples. This is explained by the presence of two morphological forms i. e. lamellar and fibrillar morphology in the same sample. The crystallinity values obtained from different methods are correlated with mechanical properties, such as tenacity and elongations.Dedicated to Prof. Dr. H. Janeschitz-Kriegl, a pioneer of Polymer Physics in Austria, in honour of his sixtieth birthday.     

Nanoindentation studies of polyimide thin films with various internal linkages in the diamine component

Polyimide thin films were synthesized from 3,3′,4,4′‐biphenyltetracarboxylic acid dianhydride (BPDA) and four different diamines (p‐phenylene diamine, 4,4′‐oxydiphenylene diamine, 4,4′‐biphenylene diamine, and 4,4′‐sulfonyldiphenylene diamine). The nanoindentation behavior of the resulting polyimides, namely, poly(p‐phenylene biphenyltetracarboximide) (BPDA‐PDA), poly(4,4′‐biphenylene biphenyltetracarboximide) (BPDA‐BZ), poly(4,4′‐oxydiphenylene biphenyltetracarboximide) (BPDA‐ODA), and poly(4,4′‐sulfonyldiphenylene biphenyltetracarboximide) (BPDA‐DDS), were investigated. Also, the morphological properties were characterized with a prism coupler and wide‐angle X‐ray diffraction and were correlated to the nanoindentation studies. The nanoindentation behavior and hardness varied quite significantly, depending on the changes in the chemical and morphological structures. The hardness of the polyimide thin films increased in the following order: BPDA‐DDS < BPDA‐ODA < BPDA‐BZ < BPDA‐PDA. For all the polyimide thin films, except that of BPDA‐BZ, the hardness decreased with an increase in the load. The birefringence, a measure of the molecular in‐plane orientation, increased in the following order: BPDA‐DDS < BPDA‐ODA < BPDA‐PDA < BPDA‐BZ. The X‐ray diffraction studies revealed that the crystallinity of the polyimide thin films varied with the changes in the chemical structure. The studies showed that the indentation response with an applied load and the hardness by nanoindentation for the BPDA‐based polyimides were closely related to the morphological structure. The nanoindentation and birefringence results revealed that the mechanical properties of the polyimide thin films were dependent on the crystallinity, which arose because of the chain order along the chain axis and the molecular packing order. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 861–870, 2004     

The effect of MWCNT on dynamic mechanical properties and crystallinity of in situ polymerized polyamide 12 nanocomposite

This work aims at investigating the dynamic mechanical properties of in situ anionic ring opening polymerized polyamide 12 in the presence of multi‐walled carbon nanotubes (MWCNT). According to the dynamic mechanical thermal analysis results, the addition of only 0.1 wt.% of MWCNTs led to 30% enhancement in modulus at room temperature which exhibited improved mechanical behavior of the nanocomposites. Test results showed that by the presence of 1.2% wt MWCNTs, the modulus is almost doubled, and it did not show any tangible changes by the addition of more nanotubes. Also, the effect of different frequencies on the viscoelastic behavior was investigated in order to determine the thermal transitions occurred in the synthesized nanocomposites. After that, the crystallinity of the samples has been studied using differential scanning calorimetry and X‐ray diffraction data in order to investigate the effect of MWCNT content on the crystals' dimension.     

Interaction of naproxen with α-, β-, and γ-hydroxypropyl cyclodextrins in solution and in the solid state

Solid combinations of naproxen with amorphous hydroxypropyl derivatives of -, -, and -cyclodextrin with an average substitution degree per anhydroglucose unit of 0.6 were investigated for thermal behaviour (differential scanning calorimetry), drug crystallinity (X-ray diffractometry), and dissolution rate (dispersed amount and rotating disc methods). Phase-solubility analysis and computer-aided molecular modelling were carried out to study the inclusion complexation of naproxen with hydroxypropyl cyclodextrins. The cavity size of the host is a selective factor for the solubilizing effect, complexing ability, and dissolution rate enhancement on naproxen, hydroxypropyl -cyclodextrin being markedly the most effective derivative. No relationship was found between the decrease in crystallinity of the drug dispersed in the amorphous carrier matrix and the geometrical features of the cyclodextrin macrocycle.     

差示扫描量热法测定聚乙烯结晶度的不确定度评定

采用差示扫描量热法(DSC)测定聚乙烯(PE)的结晶度，讨论了测定PE熔融焓过程中由测量重复性、称量过程及PE本身结构的不均匀性等因素所带来的不确定度分量，计算了测定PE熔融焓的合成标准不确定度及扩展不确定度和测定PE结晶度的扩展不确定度。采用Dsc法测定高密度聚乙烯(HDPE)和低密度聚乙烯(LDPE)结晶度的扩展不确定度均小于l％。     

Poly（L—lactide）—Poly（ethylene glycol） Multiblock Copolymers：Synthesis and Properties

Poly (L-lactide)-poly (ethylene glycol) multiblock copolymers with predetermined block lengths were synthesized by polycondensation of PLA diols and PEG diacids. These copolymers presented special properties, such as better miscibility between the two components, low crystallinity and better hydrophilicity, which can be modulated by adjusting the block lengths of the two components.     

Heterogeneous aspects of acid hydrolysis of α-cellulose

Hydrolysis of α-cellulose by H₂SO₄ is a heterogeneous reaction. As such the reaction is influenced by physical factors. The hydrolysis reaction is therefore controlled not only by the reaction conditions (acid concentration and temperature) but also by the physical state of the cellulose. As evidence of this, the reaction rates measured at the high-temperature region (above 200°C) exhibited a sudden change in apparent activation energy at a certain temperature, deviating from Arrhenius law. Furthermore, α-cellulose, once it was dissolved into concentrated H₂SO₄ and reprecipitated, showed a reaction rate two orders of magnitude higher than that of untreated cellulose, about the same magnitude as cornstarch. The α-cellulose when treated with a varying level of H₂SO₄ underwent an abrupt change in physical structure (fibrous form to gelatinous form) at about 65% H₂SO₄. The sudden shift of physical structure and reaction pattern in response to acid concentration and temperature indicates that the main factor causing the change in cellulose structure is disruption of hydrogen bonding. Finding effective means of disrupting hydrogen bonding before or during the hydrolysis reaction may lead to a novel biomass saccharification process.     

Synthesis and characterization of novel polyarylates from 2,5-bis(4-hydroxyphenyl)-3,4-diphenylpyrrole and various aromatic dicarboxylic acids

A new tetraphenylated heterocylic diol, 2,5-bis(4-hydroxyphenyl)-3,4-diphenylpyrrole, was synthesized in three steps starting from 4-methoxydeoxybenzoin. The tetraphenylpyrrole-containing polyarylates having inherent viscosities of 0.28–0.88 dL/g were prepared from the diol and various aromatic dicarboxylic acid chlorides by both phase transfer catalyzed two-phase polycondensation and high temperature solution polymerization methods. All the polyarylates were semi-crystalline, and were readily soluble in a variety of solvents including N-methyl-2-pyrrolidone, m cresol, pyridine, and 1,4-dioxane. These polymers had glass transition temperatures in the range of 223–279°C, with no weight loss below 400°C in both air and nitrogen atmospheres. © 1994 John Wiley & Sons, Inc.     

Oxygen transport as a solid‐state structure probe for polymeric materials: A review

In the quest to elucidate the solid‐state structures of polymers, insight into the amorphous phase is particularly elusive. Although the permeability of small molecules is often measured as an important performance property, numerous researchers have found that a deeper analysis of the transport characteristics provides insight into polymer morphology, especially if used in combination with more usual characterization techniques. The transport of small gas molecules senses the permeable amorphous structure and probes the nature of the free volume. In recent years, our interest in the gas barrier of polyesters has resulted in an unusual opportunity to investigate the nature of the free volume in the polymer glassy state. This effort has been aided by access to aromatic polyesters with designed variations in their chemical structure. This review focuses on oxygen transport, supplemented with other methods of physical analysis, as a probe of the excess‐hole free volume. The review addresses the profound effects of orientation and crystallization on the free volume of the glassy state. The discussion also presents a simple odel for the gas permeability of the isotropic glass based on lattice concepts and tests more sophisticated models for the gas permeability of semicrystalline polymers. The final section addresses other opportunities for fruitful applications of oxygen transport as a solid‐state structure probe. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1047–1063, 2005     

煤焦的晶格结构,本征反应活性和密度初探

通过对低变质程度烟煤的镜质组分分别在空气和高纯氧中所得中温焦炭的密度和晶格化程度的初步研究，并作了链条锅炉飞灰炭的本征反应活性和密度关系比较，认为煤在不同气氛中加热其晶各化结构增强的决定性作用是温度，其次是煤在加热中的停留时间，煤焦的密度大小可作为煤焦晶格化程度的一种表征，煤焦的本征反应活性与煤焦密度和晶格化程度具有相关性。