The microstructure of poly(vinyl chloride) as revealed by x-ray and light scattering

Small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS) as well as small-angle light-scattering (SALS) techniques have been applied to investigate the microstructure of a number of commercial poly(vinyl chloride) (PVC) samples. From the wide-angle x-ray scattering, crystallinity and crystal size parameters have been determined. The crystallinity of the samples investigated range from 5% to 10%. Superstructure parameters such as crystallite thickness, distribution functions of crystallite and amorphous thicknesses, and size of ordered regions have been obtained by an analysis of the SAXS curves using the cluster model. The crystallinity agrees well with the WAXS crystallinities indicating that most of the crystals are lamellar shaped, though some rodlike entities are present in the sample as is shown by the small-angle light scattering. From the SAXS analysis, the microstructure is described as clusters of lamella stacks which are identical with the subprimary particles. Their size is determined to be 220–240 Å. Emulsion type PVC also contains lamellar-shaped crystals. The superstructure, however, of this type of PVC is different from that of mass or suspension-polymerized material. The SAXS curve does not reveal any correlation between the crystals.     

Structural aspects of suspension poly(vinyl chloride): Influence of temperature on the macro- and microstructure

The structural aspects of rigid suspension poly(vinyl chloride), PVC, have been investigated on the basis of two independent series of suspension PVC samples, polymerized at temperatures between 26 and 84°C. The reproducibility of the suspension polymerization process and the importance of the polymerization temperature with respect to the macro- and microstructure is demonstrated. Quantitative examination of the grain structure by small angle neutron scattering, Brunauer-Emmett-Teller absorption technique, and mercury porosimetry clarifies the gradual increase of the specific surface on lowering the polymerization temperature. A detailed WAXS study shows an increasing degree of crystallinity on lowering the polymerization temperature, which can be associated with the corresponding increase of the syndiotacticity. Furthermore, the presence of a polymerization history in the PVC powders with respect to the crystallinity is evidenced. This effect seems to be related to chain mobility restrictions during the polymerization process and is determined by the difference between the polymerization temperature and the glass-transition temperature (T_g) of rigid PVC. This so-called T_g effect is indicative of the fact that no appreciable swelling of PVC by its monomer occurs. © 1994 John Wiley & Sons, Inc.     

X-ray diffraction and infrared studies on annealed highly syndiotactic poly(vinyl chloride)

X-ray diffraction scans and infrared absorption spectra for the C-CI stretching region were obtained for a highly syndiotactic poly(vinyl chloride) (PVC) sample made by the urea clathrate method. When the polymer was annealed at a series of increasing temperatures up to 180°C, x-ray diffraction measurements showed that the crystallinity increases steadily with annealing temperature. Even at 50°C an increase above the original value of 63% was detectable and by 180°C it had reached 70% with a further increase to 78% after cooling to ambient temperature. There is a concurrent significant increase in the lateral crystallite dimensions. However, the infrared spectrum did not change, in agreement with the recent prediction of Moore and Krimm that there is no observable band splitting from interchain interaction in crystalline regions, thus indicating that these C-CI bands cannot be used as a measure of crystallinity. The results from computer curve fitting of the spectra suggest that at least 85% of the polymer consists of long planar syndiotactic sequences and there is therefore substantial order along the chain direction. A mechanism for the increase in crystallinity on annealing, involving the lateral ordering of these regular chains, is discussed. Furthermore, as the temperature is raised some amorphous material is converted to a nematic phase, and this may crystallize during the subsequent cooling.     

Effect of the microstructure on the dye diffusion and mechanical properties of polyamide‐6 fibers

The morphology, mechanical properties, and dye diffusion of drawn and heat‐set polyamide‐6 (PA6) yarns were examined. Correlations between the microstructure of PA6 yarns and the dye diffusion coefficients and mechanical properties were established. The crystallinity of PA6 yarns was estimated with density and Fourier transform infrared spectroscopy measurements. A decrease in the γ crystallinity and an increase in the γ‐crystallite size with the draw ratio were observed and attributed to the disappearance of small crystallites and an increase in the average γ‐crystallite size population during the deformation process. The scouring treatment increased the total crystallinity, almost entirely as a result of an increase in the α fraction. Thermally induced crystallization involved increases in both crystalline phases (α and γ) and did not involve crystal‐to‐crystal transformation, whereas drawing PA6 yarns involved both crystallization of the amorphous phase in the α form and γ→α transformation. A sharp decrease in the diffusion coefficient with an increasing draw ratio of PA6 yarns was correlated with an increasing amorphous orientation. The influence of thermally induced crystallinity on the diffusion coefficient seemed exceptionally strong. The mechanical properties of PA6 yarns were examined and correlated with structural changes. It was demonstrated that the crystallinity had a direct correlation with the terminal modulus and extension at break, whereas there was no correlation with the initial modulus. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 349–357, 2007     

Strain‐induced crystallization of natural rubber with high strain rates

Strain‐induced crystallization (SIC) of natural rubber (NR) samples with different strain rates at a fixed strain was investigated by synchrotron radiation X‐ray diffraction measurements, which provided the evolution trends of crystal sizes and crystallinity during the SIC process. It was found that the Avrami index was about 1 during the crystallization of NR after the cessation of stretch, which demonstrated that sporadic nucleation occurred during SIC process. The increase of the crystallinity was attributed to the increase of the number of new crystallites rather than the growth of the crystal size. An unexpected relationship between the final crystallinity and the strain rates was observed. The increase of physical crosslink points originated from either entanglement or crystallite was considered as the reason that leads to the nonmonotonic variation of the final crystallinity with strain rates. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

热处理对聚醚醚酮晶体结构参数及结晶度的影响

采用广角Ｘ射线衍射（ＷＡＸＤ）方法研究了不同热处理温度下聚醚醚酮（ＰＥＥＫ）的晶胞参数、微晶尺寸及结晶度的变化。根据Ｘ射线散射强度理论，运用图解多重峰方法导出了以ＷＡＸＤ方法计算ＰＥＥＫ结晶度的公式；用此公式对经不同热处理的ＰＥＥＫ样品进行计算，结果与由密度法及量热法测定的结果具有较好的可比性。     

热处理对聚芳醚腈的结晶行为及熔融的影响

利用广角X射线衍射 (WAXD)方法和示差扫描量热法 (DSC)研究了不同热处理温度 (Th)下聚芳醚腈(PCE)的微晶尺寸、结晶度及热性能的变化 .结果表明 ,淬火样品在熔融温度以下 ,热处理对微晶尺寸、结晶度、Tg 及Tm 均有不同程度的影响 ,且都随Th 的升高 ,其Dhkl、Xc 和Tm 也升高 .实验还发现 ,结晶样品的结晶度与原粉试样相比较均下降 ,说明PCE聚合物在熔融过程中出现了交联 ,导致了结晶度的下降     

乙烯-α-烯烃共聚物的结晶性能及其临界序列结晶长度的研究

本文用DSC、WAXD及偏光显微镜(PLM)方法,研究了化学反应法催化剂合成的乙烯-α-烯烃共聚物的结晶性能及其临界序列结晶长度。结果表明,随共聚物中α-烯烃含量增大,共聚物的微晶尺寸、结晶度及熔点均逐渐减小,而晶胞参数增大。变化的辐度戊烯>辛烯。共聚物的临界结晶序列长度(n)和k值均戊烯<辛烯。上述结果表明影响支链进入晶格的主要因素是α-烯烃支链长度和结构。     

聚-3,4异戊二烯的x-射线研究

对聚异戊二烯的研究一直很活跃。含3,4-链节70%左右的晶性聚3,4-异戊二烯(3,4-PⅠ),是适用于室温下较理想的吸振材料,其晶体结构尚未见报导。     

Poly(ethylene oxide) irradiated in the solid state,melt and aqueous solution—a DSC and WAXD study

Interactions of the aggregate state of poly(ethylene oxide), PEO, and γ-irradiation conditions (total dose, atmosphere) on its thermal and crystalline properties were investigated by DSC and WAXD taking into account sample molecular mass and form. In PEO irradiated in the solid state and in the presence of oxygen, chain scission dominated over concurrent crosslinking up to 200 kGy, particularly in PEO powders, due to a large surface being in contact with air. In solid samples the degree of crystallinity and crystallite size increased with the dose up to 50 kGy, probably not just due to partial crystallization upon degradation of amorphous phase, but to recrystallization of broken tie molecules. The least changes in crystallinity and phase transformation temperatures occurred in solid films. A substantial decrease in crystallinity and transformation temperatures without the initial crystallinity increase was achieved in samples that were amorphous on irradiation, at temperatures above the PEO melting temperature and in aqueous solutions. Radiation crosslinking of the PEO aqueous solution in an inert atmosphere is the most suitable way to obtain a lower degree of crystallinity and phase transformation temperatures while preserving mechanical properties.     

Probing the effect of high energy ball milling on PVC through a multitechnique approach

The effects induced by ball milling treatment on PVC features and properties were deeply investigated through a multitechnique approach. SEM analysis showed a drastic change in PVC morphology; the hierarchical structure of PVC grains was partially destroyed as well as the domain size strongly reduced. A X-ray diffraction and DSC comparative study proved a structural modification in the PVC crystalline phase. Moreover, it was found that these morphological and structural changes strongly affected the gelation behavior, the microstructure and the mechanical parameters of PVC. In particular, the gelation time increased with increasing the ball milling time; the residual primary crystallite content doubled with respect to neat PVC and the toughness improved up to 25% as a function of the resulting microstructure.     

Effect of Characteristics of Magnesium Oxide Powder on Composition and Strength of Magnesium Potassium Phosphate Compound for Solidifying Radioactive Waste

Phase composition, particle morphology, and granulometric composition of commercial samples of MgO powders of various chemical purities (classification from technical grade to chemical grade) prepared by heat treatment at 1300°C for 3 h were studied for the subsequent synthesis of a compound based on magnesium potassium phosphate matrix MgKPO₄·6H₂O, promising for solidifying liquid radioactive waste. It has been established that to obtain a homogeneous mineral-like compound with compressive strength of about 15 MPa, which meets the regulatory requirements for solidified forms of liquid radioactive waste, it is necessary to use magnesium oxide powder with a particle size of not more than 50 μm, which have a high degree of crystallinity (the average crystallite size is not less than 40 nm). It was noted that the impurities of metal compounds, primarily silicon, calcium, and iron in the MgO powder, do not affect the synthesis conditions and the mechanical strength of the compound.

     

聚合温度对聚氯乙烯树脂结构和性能的影响

采用凝胶渗透色谱法、¹³H NMR和DSC法测定了悬浮聚合PVC树脂的平均分子量、间规度、结晶度和玻璃化温度.结果表明:聚合温度下降,PVC的平均分子量上升,分子量的对数值与聚合温度的倒数成正比;PVC的间规度和结晶度均增大,在形成结晶的间规链段的最短长度(ξ_min)为6时,由间规度计算的结晶度理论值与测定值接近;分子量和结晶度增加的共同作用,使PVC的玻璃化转变温度上升.     

振磨降解制备的低分子量聚氯乙烯形态结构的研究

本文首次通过ＦＴＩＲ和扫描电镜等手段研究了振磨作用对聚氯乙烯（ＰＶＣ）颗粒尺寸、微晶结构、表现密度和增塑剂吸收量的影响。结果表明，该聚合物位于６３５ｃｍ＾－１处结晶吸收谱带的强度随振磨时间的增加而降低，逐步趋于消失。随振磨时间的增加，ＰＶＣ的颗粒尺寸减小，比表面积增加，增塑剂的吸收量增加。通过振磨可以制得用一般化学方法难于制得的超细、低微量含量、易于加工的较低分子量ＰＶＣ。     

Synthesis of ZnO Nanoparticles Based on Zn Complex Achieved from L‐leucine

In the present study, ZnO nanoparticle preparation in a water‐base medium without using toxic chemicals was investigated. Zinc (II) acetate dehydrate, L? leucine and 5? sulfosalicylaldehyde sodium salt were utilized as the starting materials. X? ray diffraction analyses proved that ZnO was achieved as a unique phase. The highest value of crystallinity was obtained at 600 °C and the minimum values of crystallite size and lattice strain were reported at 400 and 500 °C, respectively. The photoluminescence spectroscopy showed that firing at 500 °C leads to decrease the point defects in ZnO structure. SEM and TEM images confirmed the relation between the firing temperature, the degree of crystallinity and the crystallite size. Firing at 400 °C leads to form ZnO nanoparticles with a size distribution ranging from 15 to 50 nm with cubic, circle and hexagonal shapes. By increasing the temperature to 500 °C, the nanoparticles dimensions increase to 30–60 nm. The particle size of sample ‘c’ is more than 50 nm. The optimum temperature to achieve the goal of this research, namely a high crystallinity and low structure defects, was found to be 500 °C.     

X-ray Diffraction Study of the Structure of Gamma-Irradiated Low-Density Polyethylene

High Energy Chemistry - Gamma irradiation leads to a change in the crystallite size and crystallinity of low-density polyethylene. Under irradiation with a dose of 100 kGy, the crystallinity and...     

Comparison of sample crystallinity determination methods by X-ray diffraction for challenging cellulose I materials

Cellulose crystallinity assessment is important for optimizing the yield of cellulose products, such as bioethanol. X-ray diffraction is often used for this purpose for its perceived robustness and availability. In this work, the five most common analysis methods (the Segal peak height method and those based on peak fitting and/or amorphous standards) are critically reviewed and compared to two-dimensional Rietveld refinement. A larger (\(n=16\)) and more varied collection of samples than previous studies have presented is used. In particular, samples (\(n=6\)) with low crystallinity and small crystallite sizes are included. A good linear correlation (\(r^{2} \ge 0.90\)) between the five most common methods suggests that they agree on large-scale crystallinity differences between samples. For small crystallinity differences, however, correlation was not seen for samples that were from distinct sample sets. The least-squares fitting using an amorphous standard shows the smallest crystallite size dependence and this method combined with perpendicular transmission geometry also yielded values closest to independently obtained cellulose crystallinity values. On the other hand, these values are too low according to the Rietveld refinement. All analysis methods have weaknesses that should be considered when assessing differences in sample crystallinity.     

Comparison of changes in cellulose ultrastructure during different pretreatments of poplar

One commonly cited factor that contributes to the recalcitrance of biomass is cellulose crystallinity. The present study aims to establish the effect of several pretreatment technologies on cellulose crystallinity, crystalline allomorph distribution, and cellulose ultrastructure. The observed changes in the cellulose ultrastructure of poplar were also related to changes in enzymatic hydrolysis, a measure of biomass recalcitrance. Hot-water, organo-solv, lime, lime-oxidant, dilute acid, and dilute acid-oxidant pretreatments were compared in terms of changes in enzymatic sugar release and then changes in cellulose ultrastructure measured by ¹³C cross polarization magic angle spinning nuclear magnetic resonance and wide-angle X-ray diffraction. Pretreatment severity and relative chemical depolymerization/degradation were assessed through compositional analysis and high-performance anion-exchange chromatography with pulsed amperometric detection. Results showed minimal cellulose ultrastructural changes occurred due to lime and lime-oxidant pretreatments, which at short residence time displayed relatively high enzymatic glucose yield. Hot water pretreatment moderately changed cellulose crystallinity and crystalline allomorph distribution, yet produced the lowest enzymatic glucose yield. Dilute acid and dilute acid-oxidant pretreatments resulted in the largest increase in cellulose crystallinity, para-crystalline, and cellulose-I_β allomorph content as well as the largest increase in cellulose microfibril or crystallite size. Perhaps related, compositional analysis and Klason lignin contents for samples that underwent dilute acid and dilute acid-oxidant pretreatments indicated the most significant polysaccharide depolymerization/degradation also ensued. Organo-solv pretreatment generated the highest glucose yield, which was accompanied by the most significant increase in cellulose microfibril or crystallite size and decrease in relatively lignin contents. Hot-water, dilute acid, dilute acid-oxidant, and organo-solv pretreatments all showed evidence of cellulose microfibril coalescence.     

Supramolecular Structure - A Key Parameter for Cellulose Biodegradation

Summary: Three different cellulosic substrata, like microcrystalline cellulose, cotton cellulose and spruce dissolving pulp, were chosen for biodegradation. The kinetics of the enzymatic hydrolysis of these celluloses by Trichoderma reesei, has been investigated. The experiments proved the fact that both the morphological structure and the crystalline one are crucial to the process and the ratio of the reactions. In addition, in order to obtain the most accessible cellulose substratum it was studied the biodegradation of cellulose allomorphs of spruce dissolving pulp. The insoluble cellulose fraction remaining after enzymatic hydrolysis was examined by X-ray diffraction method and it was established the degree of crystallinity and the average crystallite size. The enzymatic degradation is also proved by the decrease in the degree of polymerization of hydrolyzed samples.     

Use of solvent sorption to detect structural changes in rigid PVC compounds

The effects of type of PVC and its thermal history on solvent sorption behaviour were investigated. Samples were immersed in toluene at 25°C, and the equilibrium solvent uptake and sorption half-times were measured for a variety of samples. The shape of the sorption curve was also observed. Equilibrium sorption was found to decrease with increasing amount of crystallinity in the sample. Sorption half-time increased with increased crystallinity, but minimum equilibrium sorption did not correspond with maximum half-time, possibly due to the type of crystallinity present. The shape of the sorption curve (Fickian or Case II sorption) also depended on the ype of PVC used and is thermal history. The solvent sorption technique was shown to be a sensitive method for detecting small structural changes in PVC.