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1.
Slawomir Borysiak 《Journal of Thermal Analysis and Calorimetry》2012,109(2):595-603
Mercerization process is very significant because the alkali treatment facilitates reactivity of lignocellulosic fillers, thus allowing better response to chemical modification. In the present study, the effect of mercerization of pine wood on the nucleation ability of polypropylene was investigated by means of differential scanning calorimetry. We discovered that for the composites with wood containing cellulose II, the decrease in the crystal conversion of the polymer matrix and increase in the half-time of crystallization values are significant. It can be concluded that the amount of cellulose II formed upon alkalization of lignocellulosic fillers determines their nucleation ability. To evaluate the transcrystalline effects caused by various woods, which were untreated or treated with sodium hydroxide, the polarized optical microscopy was also performed. The nucleation of polypropylene on the surface of wood was investigated by induction time measurement. It was found that surfaces of the unmodified wood generate epitaxial nucleation, whereas the mercerized wood generates nonepitaxial nucleation. The differences in the type of nucleation suggest that the effectiveness of formation of transcrystalline structures depends on the contribution of cellulose I and cellulose II. Moreover, the presence of epitaxy is not necessary for the appearance of transcrystalline structures. The results showed that the transcrystalline structures appeared in each system, even with wood containing significant contribution of cellulose II. The only difference noted was the change in the nucleation abilities of the wood surface. Results of this study imply the necessity of quantitative determination of the contributions of cellulose I and cellulose II, whose presence determine the type of nucleation and nucleation ability of the filler surface. 相似文献
2.
S. Borysiak 《Journal of Thermal Analysis and Calorimetry》2007,88(2):455-462
Composites
made from an isotactic polypropylene matrix and wood (pine or beech) have
been prepared and tested. To improve adhesion between components, the wood
modification was performed by esterification with maleic, propionic, crotonic,
succinic and phthalic anhydrides. The surface of wood fillers was also modified
by chemical treatment with NaOH as well as by extraction process. Non-isothermal
crystallisation of polypropylene in wood composites is studied by DSC, and
the basic parameters of crystallisation are determined. We discovered that
the composites containing chemical treated wood fillers showed the tendency
reduction the nucleation efficiency of polypropylene. The ability of wood
filler to induce nucleation in polypropylene matrix is dependent on the kind
of chemical modification of surface wood 相似文献
3.
Slawomir Borysiak 《Journal of Thermal Analysis and Calorimetry》2013,113(1):281-289
Results of the hitherto research work on alkalisation of lignocellulosic materials have been much divergent. In view of the above, the subject of this study is mercerization of cellulose from pine wood. This choice of the subject permitted observation of transformation of cellulose I to cellulose II with no participation of other components of lignocellulosic materials. According to X-ray results, during mercerization the isolated cellulose was easily (completely) transformed into cellulose II variety, while the pine wood was converted more slowly to cellulose II polymorphs. Therefore, it could be concluded that the presence of lignin and hemicelluloses in wood prevented the transformation from cellulose I to II. The main objective of this research was to establish the effect of cellulose varieties on the nucleation ability of different fillers by using differential scanning calorimetry (DSC) and polarizing microscopy. The nucleating effect of the fillers occurs only in the presence of cellulose I variety. In contrast, the presence of cellulose II variety seems to practically eliminate the nucleating effect of the fillers. Moreover, nucleation of the mercerized wood (mixture of cellulose I and II) can be also observed, but this effect is not strong. It should be emphasised that as yet no correlation has been reported between the quantitative composition of cellulose polymorphic forms (appearing not only in wood, but in cellulose isolated from wood as well) and the nucleation ability of lignocellulosic fillers. 相似文献
4.
聚合物结晶成核剂作用的表征方法的比较和研究 总被引:16,自引:4,他引:16
用聚合物的等速降温过程的结晶温度,等温结晶过程的半结晶时间(t1/2)或结晶速度常数(K),结晶过程的晶核密度或球晶尺寸大小和聚合物结晶成核界面自由能(σσe或σe)大小等方法描述了碳酸钙、对苯二甲酸、苯甲酸钠对聚丙烯成核结晶过程的影响.通过对不同方法的比较,结果表明不同方法是从不同角度来反映助剂对聚合物成核结晶过程的影响,聚合物结晶温度的高低和等温结晶过程的半结晶时间或结晶速度常数是描述聚合物整体结晶速度的参数;而聚合物结晶过程中晶核密度或结晶完了时聚合物球晶尺寸,和聚合物结晶成核界面自由能大小与聚合物的成核难易程度直接相关,是判断聚合物结晶成核速度的方法.但不同方法之间存在一定的相关性,所以用不同方法测定的结果之间有较好的可比性,可根据具体条件选用一种方法.多种方法的配合使用可以较全面的了解成核剂的作用. 相似文献
5.
Flammability of wood-polypropylene composites 总被引:1,自引:0,他引:1
Addition of wood particles to polymers can cause a change of properties of the composites which depends on features of lignocellulosic materials and those of polymers. It is also observed in the flammability characteristics of the composites.In this work, the flammability of polypropylene composites with pine wood particles obtained by extrusion and press moulding was analyzed. The amount of wood particles was 50%. Polymers with various melt flow index (MFI) were used (Malen F-401, PP HY-202 and Malen S-702).The samples were tested using Cone Calorimeter at heat flux of 35 kW/m2. Heat release rate (HRR) curves of composites show that thermal decomposition depends on the kind of polypropylene used. In the presence of PP HY-202 and Malen S-702, the flammability characteristic is similar to that of lignocellulosic materials, in contrast to composites with matrices prepared from Malen F-401. The observed phenomenon is interpreted in terms of the wettability of particles of pine wood by polymers of varying melt viscosity. 相似文献
6.
The influences of kaolin content, processing temperature, and shear stress on crystallization of all samples were investigated
by differential scanning calorimetry (DSC). The crystallization activation energy calculated using Kissinger’s method displayed
a decreasing trend with increasing kaolin content, processing temperature, and shear stress. A study of nucleation activity,
which could indicate the influence of filler on polymer matrix, revealed that kaolin filler had a slight nucleation effect
on polypropylene (PP) matrix. A thorough observation on nucleation effect also revealed that the incorporation of kaolin in
tandem with increasing temperature and shear stress have contributed to successive heterogeneous nucleation in the system. 相似文献
7.
Surface characterization of untreated and hydro‐thermally pre‐treated Turkey oak woods after UV‐C irradiation
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Luigi Todaro Maurizio D'Auria Fausto Langerame Anna Maria Salvi Antonio Scopa 《Surface and interface analysis : SIA》2015,47(2):206-215
The aim of this study was to determine the effect of UV‐C irradiation on the Turkey oak wood surface (Quercus cerris L.). In order to compare the effect of irradiation, both untreated wood samples and those treated with steam and heat were analyzed. The steam treatments were carried out in an autoclave at 130 °C; samples were then heated in an oven for 2 h at 180 °C. The physical and chemical changes brought about in the untreated and treated wood samples by the UV‐C light were monitored by colorimetry (color changes), X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) (chemical composition) and scanning electron microscopy (SEM) (microstructure and morphology). A detailed analysis of the results indicates that the UV‐C treatment caused irreversible changes in both the chemical composition and morphology of the wood samples via photooxidation and photodegradation processes. Depending on the type of pre‐treatment used, these processes affected the wood samples differently. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
8.
Simple and convenient methods for determining surface chemical composition of lignocellulosic materials are described. The
methods are based on vapor phase fluorine surface derivatization with either trifluoro acetic anhydride (TFAA), tri-fluoro
ethanol (TFE) or pentafluorophenyl hydrazine (PFPH) and subsequent Electron Spectroscopy for Chemical Analysis (ESCA). Model
cellulosic surfaces with well defined functionalities were used to optimize the derivatization reaction conditions. Detection
and accessibility of surface hydroxyl functional groups were investigated in cotton and regenerated cellulose as models. Carboxymethyl
cellulose (CMC) was used as a model surface for detection and quantification of carboxylic acid groups. Theoretical conversion
curves for derivatization reactions were calculated and used to evaluate the extent of the reactions on the model surfaces.
It was found that the conversion was higher for the regenerated cellulose and CMC than for cotton. The protocols developed
using the model surfaces were applied to a case study on wood fibers with different degrees of complexity, namely dissolving
and chemithermomechanical (CTMP) pulp. Untreated and oxygen-plasma modified pulps were compared with respect to the surface
composition of functional groups. According to the derivatization reactions, functionalities containing oxygen were significantly
increased on the plasma-treated samples. The effect of the treatment was found to be dependent on the type of pulp. Fluorine
derivatization is shown to be an unambiguous method for clear assessment of the chemical functionalities of cellulosic surfaces. 相似文献
9.
Dominik Paukszta Justyna Zielińska-Ma?kowiak 《Journal of Thermal Analysis and Calorimetry》2012,109(2):611-618
Nucleation ability of native and modified rapeseed straw during the polypropylene crystallization from the melt was investigated by the DSC method. Composites were made from isotactic polypropylene and lignocellulosic material using extrusion and injection moulding techniques. They were obtained using polypropylenes differing with respect to melt flow rates and different varieties of rapeseed straw. Chemical modification was carried out in two stages: through mercerisation and treatment with acetic acid anhydride. In the course of investigations, it was found that both native and modified rapeseed straw acted as an active nucleant of polypropylene crystallisation characterised by low values of MFR indices. It was found that for polypropylenes with high MFR values, the values of crystallization temperatures and crystallization half-time in composites were identical when compared with non-filled polymers. The investigations demonstrated that there were insignificant differences among composites containing straw from different varieties of rapeseed. The analysis of crystallization temperatures confirmed that rapeseed straw modification failed to change this parameter of the crystallization process. A similar tendency was observed in the case of changes of the half-time crystallization process. Moreover, the analysis of the crystallization temperature and crystallization half-time showed that the presence in composites of lignified rapeseed straw particles played an important role in the crystallization conditions. 相似文献
10.
R. Bouza C. Marco G. Ellis Z. Martín M. A. Gómez L. Barral 《Journal of Thermal Analysis and Calorimetry》2008,94(1):119-127
Isothermal crystallization and melting of isotactic polypropylene in binary polypropylene-wood flour composites has been studied
by DSC, and the influence of an ethylene-methacrylic acid copolymer interfacial agent analyzed. Wood flour induces a slight
nucleating effect, reducing the basal interfacial free energy of nucleation and increasing the overall crystallization rate.
The interfacial agent generates a compatibilization phenomenon and an increase in the basal interfacial free energies with
respect to the binary composites. In both binary and ternary systems the melting behaviour is a function of undercooling and
is unaltered by the presence of either wood flour or the interfacial agent. 相似文献
11.
Hannes Orelma Atsushi Tanaka Hille Rautkoski Ilkka Nurminen Jarmo Kouko Antti Koponen 《Cellulose (London, England)》2017,24(9):3869-3882
Utilization of mechanically manufactured lignocellulosic fines (LCNFs) was investigated in making filaments and films. The LCNFs particles were prepared by using a mechanical grinding method with a w-profile grinding stone that produces mostly fines with dimensions in the micrometer scale. The chemical and elemental composition of the w-stone ground LCNFs particles was investigated. It was found that the mechanically manufactured material exhibited the chemical structure of native wood. The LCNFs particles had an anionic surface charge making them colloidally semi-stable in water. The short length of the fines particles prevents their effective mechanical entanglement, which sets some limitations on preparation of filaments and films. Filament manufacturing required the use of a composite approach with carboxymethyl cellulose (CMC) as a binder polymer. The filament was manufactured by using dry-jet wet spinning with aluminium sulfate crosslinking. The chemical composition, crosslinking mechanism, and mechanical properties of the composite filaments were investigated. The composite approach with CMC was also used to prepare composite films with good mechanical performance. The investigated LCNFs material could be utilized in all-lignocomposite applications with cellulose derivatives, where biodegradability and biobased characteristics are desired properties. 相似文献
12.
13.
M. L. Cerrada V. Rodríguez‐Amor E. Pérez 《Journal of Polymer Science.Polymer Physics》2007,45(9):1068-1076
Several composites of a metallocene syndiotactic polypropylene with an organophilic silicate have been prepared and analyzed to investigate the effects of the nanoparticles on the crystallization of syndiotactic polypropylene. Moreover, the influence of an electron‐irradiation dose of 166 kGy on the different materials has been studied. Although the melting temperatures are practically unchanged, irradiation leads to a considerably slower crystallization rate of the syndiotactic polypropylene homopolymer in such a way that an important cold crystallization has been observed in the second melting along with a much higher value of the isothermal crystallization half‐time. On the contrary, the nanocomposites are much less sensitive to irradiation because only a small shift of the crystallization temperature has been observed, and the isothermal crystallization half‐time remains practically unaffected. However, irradiation leads to important changes in the low‐angle region of X‐ray diffractograms. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1068–1076, 2007 相似文献
14.
纳米CaCO_3/相容剂/PP中的界面相互作用研究 总被引:1,自引:0,他引:1
采用不同相容剂(PP-g-MAH、POE-g-MAH和EVA-g-MAH)制备了不同界面相互作用的纳米CaCO3(CC)/相容剂/PP体系,研究了相容剂/PP和相容剂/CC界面相互作用对PP/CC的结晶形态、结晶行为、熔融特性和力学性能的影响.观察到PP/CC界面相互作用提高PP结晶温度和PP/CC的模量和冲击强度,但降低了屈服强度.相容剂/CC界面相互作用进一步提高了PP/CC的结晶温度.PP/相容剂界面相互作用取决于PP与相容剂相容性.PP/PP-g-MAH相容性高有利于提高PP/CC的异相成核作用和PP/CC屈服强度和模量,但降低冲击强度.PP/POE-g-MAH部分相容对相容剂/CC界面的异相成核作用、PP/CC屈服强度和模量影响不大,可明显提高冲击强度.但PP/EVA-g-MAH不相容导致PP/CC冲击强度明显降低. 相似文献
15.
利用Avrami方程和Lauritzen-Hoffman结晶动力学理论研究了一种镧配合物LaC对等规聚丙烯(iPP) 等温结晶行为的影响. 差示扫描量热法(DSC)和X射线衍射技术(XRD)研究表明, LaC的加入并未改变iPP的结晶形态, 但LaC的存在能提高体系的结晶度并显著加速iPP的结晶过程. 在130 ℃进行等温结晶时, 含0.5%LaC(质量分数)的iPP与纯iPP相比, Avrami指数n值无显著差异, 但前者总的结晶速率常数k值比后者提高约4倍,而半结晶时间t1/2值减少到后者的62%, Avrami方程分析结果表明LaC的存在主要起到增加晶核的作用. 利用Lauritzen-Hoffman结晶动力学理论, 通过对iPP在121 ℃、124 ℃、127 ℃和130 ℃下等温结晶的数据进行分析可知, 加入0.5%的LaC后, 体系的成核常数kg从纯PP的3.3×105 K2增加到PP/LaC的3.8×105 K2, 而结晶生长时大分子在垂直于分子链方向折叠的界面自由能σe从纯PP的0.223 J·m-2降低到PP/LaC的0.154 J·m-2, 表明LaC在iPP结晶过程中不仅起到增加晶核的作用, 同时使大分子链更易排入晶格, 即起到促进结晶成长的作用. 相似文献
16.
Crystallization of compression-molded isotactic polypropylene and polyethylene is invariably spherulitic; generally, nucleation occurs randomly throughout the sample. In a special case where nucleation predominates at the surface, spherulitic growth centers become crowded and are forced to propagate unidirectionally into the bulk (transcrystallinity). Conditions for the formation of transcrystallinity have been investigated by optical and scanning electron microscopy. The occurrence of transcrystallinity is attributed to heterogeneous nucleation induced at the mold surface. To be effective, the mold surface must have a nucleating efficiency equal to or greater than that of adventitious nuclei present in the polymer. As the crystallization temperature approaches the melting point, the activity of mold surfaces is found to increase leading invariably to transcrystalline formation. The degree of activity of various mold surfaces correlates with the known activity of specific dispersed nucleating agents having similar chemical structures. Contrary to claims in the literature, the surface energy of the mold surface and temperature gradients across the melt surface do not play a primary role in transcrystalline formation of polypropylene. 相似文献
17.
A.B. Lugo B.W.H. Artel A. Yoshiga L.F.C.P. Lima D.F. Parra J.R. Bueno S. Liberman M. Farrah W.R. Terariol H. Otaguro 《Radiation Physics and Chemistry》2007,76(11-12):1691-1695
High melt strength polypropylene (HMS-PP) has been recently developed and introduced in the market by the major international producers of polypropylene. Therefore, BRASKEM, the leading Brazilian PP producer, together with EMBRARAD, the leading Brazilian gamma irradiator, and the IPEN (Institute of Nuclear Energy and Research) worked to develop a national technology for the production of HMS-PP. One of the effective approaches to improve melt strength and extensibility is to add chain branches onto polypropylene backbone using gamma radiation. Branching and grafting result from the radical combinations during irradiation process. Crosslinking and main chain scission in the polymer structure are also obtained during this process. In this work, gamma irradiation technique was used to induce chemical changes in commercial polypropylene with two different monomers, Tri-allyl-isocyanurate (TAIC) and Tri-methylolpropane-trimethacrylate (TMPTMA), with concentration ranging from 1.5 to 5.0 mmol/100 g of polypropylene. These samples were irradiated with a 60Co source at dose of 20 kGy. It used two different methods of HMS-PP processing. The crosslinking of modified polymers was studied by measuring gel content melt flow rate and rheological properties like melt strength and drawability. It was observed that the reaction method and the monomer type have influenced the properties. However, the concentration variation of monomer has no effect. 相似文献
18.
A series of ternary blends of polypropylene/ethylene-propylene random copolymer/ethylene-propylene segmented copolymer(HPP/EPR/Eb P) whose microstructures are similar to those of impact polypropylene copolymer(IPC) were prepared in order to systematically investigate the effects of composition on microstructure and crystallization behavior of IPC. The observation of primary phase morphology reveals that the dispersed phase with core-shell structure could be rebuilt in certain composition and excessive EPR leads to a bicontinuous phase structure in ternary blends. After undergoing same quiescent crystallization including isothermal and non-isothermal crystallization, these blend samples exhibit special composition-dependent melting behavior, i.e., the melting point increases markedly with the increase of EPR content until it turns down at a critical content(about 30 wt%). The crystallization behavior is mainly ascribed to the different nucleation abilities. It is suggested that although the compatibility between EPR and HPP components becomes worse with the increase of EPR content due to the increased interfacial area and the decreased concentration of Eb P, higher EPR content in the blend facilitates to heterogeneous nucleation except for the appearance of obvious bicontinuous phase structure. 相似文献
19.
H. Ito Y. Tsutsumi K. Minagawa J. Takimoto K. Koyama 《Colloid and polymer science》1995,273(8):811-815
High pressure crystallization of polypropylene was studied by means of PVT measurements and computer simulations. The isothermal crystallization behaviour were described by using a model which takes into account the effect of pressure on the temperature dependence of nucleation rate and linear growth rate. The agreement between the simulation and the experiments was seen in the tendency that the crystallization was accelerated by the high pressure. The non-isothermal crystallization behavior was also simulated by applying a generalized Avrami equation. The simulation curves well reproduced the experimental values below relative crystallinity 0.5 and below 100 MPa. 相似文献
20.
A nucleation rate function is proposed for use in analyzing the overall crystallization kinetics of polymers. This function allows for the possibility that the nucleation rate varies substantially during the crystallization. This feature is particularly useful in analyzing nonisothermal crystallization, but it can be used to analyze isothermal crystallization as well. The nucleation rate function was used in the derivation of a modified transformation kinetics equation of the Avrami type. The modified Avrami equation was found to be suitable for kinetics analysis for the data obtained from nonisothermal crystallization at rapid cooling rates. Kinetics parameters used to describe nonisothermal crystallization under rapid cooling rates are presented and discussed. These include crystallization induction time, plateau (crystallization) temperature, crystallization half-time, crystallization rate constant, Avrami index, and newly defined quantities called nucleation index, geometric index, and nucleation rate constant. The procedure used to obtain the nucleation rate constant and nucleation index for the nucleation rate function is described and illustrated by application to the analysis of the crystallization kinetics of polypropylene. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1077–1093, 1997 相似文献