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1.
Using cellulose acetate plastics as an example, it was shown that the search for the optimal concentrations of plasticizers should take into account the compatibility of components, as well as the thermophysical and mechanical properties of plasticized polymers. It was suggested that the temperature range of durability of a plastic, i.e., the difference between its glass-transition and brittle temperatures, be used as a plasticization efficiency criterion. Plasticizers that are well compatible with a polymer at processing temperatures but show a limited compatibility at its service temperatures make it possible to manufacture goods with an extended durable temperature range. 相似文献
2.
Bianka Vidéki Szilvia Klébert Béla Pukánszky 《Journal of Polymer Science.Polymer Physics》2007,45(8):873-883
Cellulose acetate was modified with caprolactone in an internal mixer at temperatures between 120 and 220 °C, and reaction times between 5 and 45 min in the presence of tinoctoate catalyst. The effect of plasticization on the properties of the polymer was studied by dynamic mechanical analysis and tensile testing. The dynamic mechanical spectrum of cellulose acetate exhibits three main relaxation transitions. These can be assigned to segments (α), to smaller structural units of the main chain, probably individual glucose rings (β), and to hydroxyl or hydroxylmethyl groups (γ). Plasticization by caprolactone leads to the decrease of the glass transition temperature of CA, but also to the breakdown of relatively large segments to smaller structural units. Free hydroxyl groups interact with the plasticizer forming larger units with higher transition temperature. Grafting decreases the intensity of the γ‐transition peak. External plasticization creates a larger number of small structural units, but the external plasticizer is less efficient in the decrease of stiffness than grafted polycaprolactone chains. Internal plasticization is more advantageous because it leads to higher flexibility at larger strength than external plasticization, and the migration of the plasticizer is prevented at the same time. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 873–883, 2007 相似文献
3.
Robert Quintana Olivier Persenaire Yahia Lemmouchi John Sampson Stuart Martin Leïla Bonnaud Philippe Dubois 《Polymer Degradation and Stability》2013
Cellulose acetate (CA) with a degree of substitution (DS) of 2.5 has been plasticized using eco-friendly plasticizers such as triacetin, tripropionin, triethyl citrate, tributyl citrate, tributyl 2-acetyl citrate and poly(ethylene glycol) of low molecular weight. Thermo-mechanical properties and hydrophilicity of the modified CA have been measured and correlated with the content and nature of the plasticizer used and compared with unplasticized CA. The increase in toughening and the change in the hydrophilicity by the plasticization were evaluated in terms of aging and weathering stability under accelerated conditions. Samples were exposed to UV-degradation with water spray periods. The treated samples were removed periodically and characterized by several analytical techniques. The results are discussed with particular emphasis toward the effects of plasticization on enhancement of the degradation rate of CA. The plasticization of CA triggered an increase of the weight loss between 50 and 90%, where low molecular weight plasticizers were shown to be more effective. A right balance between hydrophilicity and plasticization efficiency (reduction of Tg) is needed to increase the degradation rate of CA. 相似文献
4.
Th. R. Floyd 《Chromatographia》1988,25(9):791-796
Summary The capability of elution-elution multi-dimensional liquid chromatography was investigated. A column scaling approach was evaluated for the quantification of low-molecular-weight additives in cellulose acetate. A small-bore (1-mm i.d.) gel-permeation column was used to separate the higher-molecular-weight polymer from the lower-molecular-weight components. Once separated these additives were transferred to a C18 reversed-phase column via a switching valve. The reversed-phase system successfully separated and quantified individual additives.Analysis time for an ultraviolet inhibitor, Tinuvin®P, in cellulose acetate, including re-equilibration, was approximately 30 minutes. Both accuracy and precision were good. Precision over a three day period was about 1.5%. 相似文献
5.
The present study aims to create a controlled-release system through the preparation and characterization of starch cellulose acetate co-acrylate (SCAA) polymer for application as a carrier for cancer drugs. SCA was prepared from maize starch and different ratios of cellulose acetate. The obtained product SCA was reacted with acrylic acid monomer to give cellulose acetate co-acrylate. The best ratio of starch to cellulose acetate was found to be 90:10, giving a stable product with acrylic acid. The cancer drug 8-(2-methoxyphenyl)-3,4-dioxo-6-thioxo-3,4,6,7-tetrahydro-2h-pyrimido[6,1-c]-[1,2,4]triazine-9-carbonitrile was dissolved in dimethylformamide then added gradually at the end of the previous reaction under stirring for 15 min. The prepared polymers with and without the drug were characterized by Fourier-transform infrared spectroscopy. Cuboids discs of the prepared polymer/drug were subjected to drug release in aqueous media at different pH values. The release was measured spectrophotometrically. It was found that the release rate depends on the pH of the aqueous medium as well as on the concentration of the drug loaded onto the polymer carrier. Above pH 12, the polymer containing the drug degraded completely within 1 h after being subjected to alkaline media. Sustained release of drug extended to about 20 days. The amount released depended on the pH of the media in the following order: basic media > acidic media > neutral. According to Higuch’s equation, the diffusion coefficient was found to be 4.2 × 10?8 and 5.5 × 10?8 cm s?1 for the two evaluated concentrations (1.5 and 2 %) of active organic compound (drug). 相似文献
6.
Leandro S. Blachechen João Paulo de Mesquita Everton Luiz de Paula Fabiano V. Pereira Denise F. S. Petri 《Cellulose (London, England)》2013,20(3):1329-1342
Cellulose nanocrystals (CNC) prepared from eucalyptus cellulose CNCs were modified by the reaction with methyl adipoyl chloride, CNCm, or with a mixture of acetic and sulfuric acid, CNCa. The CNC were either dispersed at 0.1 wt% in the pure solvents ethyl acetate (EA), tetrahydrofuran (THF) and dimethylformamide (DMF) or in cellulose acetate butyrate (CAB) solutions prepared in these solvents at 0.9 wt%. The colloidal behavior of these dispersions was systematically investigated using a phase separation analyzer LUMiReader®. The mechanical properties and morphological features of the films resulting from the mixtures of CAB and CNC were determined by dynamic mechanical analysis, optical microscopy and atomic force microscopy, respectively. Regardless the functional group attached to the surface of CNC, the best colloidal stability was observed for dispersions prepared in CAB/DMF solution. Higher degree of substitution of modified CNCs favored the colloidal stability in EA and THF. Composite films prepared from CAB/DMF solutions were more homogeneous and presented better mechanical performance than those prepared in CAB/EA or CAB/THF. The mechanical performance of composites and neat CAB prepared from DMF was CAB/CNCs > CAB/CNCm > CAB/CNCa > CAB, indicating that the modification weakens the percolation process, which is mediated by H bonding. 相似文献
7.
《Journal of membrane science》1986,29(2):143-153
Hydraulic permeability (Lp), osmotic permeability (Lπ) and tritium permeability (ωTHO) have been measured for cellulose acetate membranes of varying water contents (Øw). The porosity factor (gp) has been calculated using the above parameters. Thermodynamic properties such as ΔG≠, ΔH≠, and ΔDwS≠ are estimated for the activated complex of the solute in the membrane phase using conductance measurements. 相似文献
8.
Brito de Barros R Ilharco LM 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2001,57(9):1809-1817
Films of pseudoisocyanine iodide in a cellulose acetate matrix were prepared by spin coating and characterized by UV/Vis absorption and fluorescence spectroscopies. The comparison with self-supported films of the same dye enabled analysing the role of the matrix in the aggregation of pseudoisocyanine iodide ([PIC]I). It was proved that cellulose acetate is a suitable support for [PIC]I J-aggregates, which form during spinning, as shown by a very sharp J-band in the absorption spectra. This indicates a perfect coherence between stacked monomers in the supported J-aggregates. It was possible to individualize the emission spectrum of [PIC]I J-aggregates in cellulose acetate, by decomposition of the steady-state fluorescence spectra of the films. The dependence on the excitation wavelength of the relative emission intensities of monomers and J-aggregates, for lambda(em) = 587 nm, lead to confirm that the latter species have an absorption maximum at approximately 500 nm in cellulose acetate. Finally, polarised absorption spectra of films obtained by the vertical spin coating technique showed that cellulose acetate allows a partial orientation of J-aggregates. 相似文献
9.
Structure and properties for binary blends composed of biomass-based cellulose acetate propionate (CAP) and poly(epichlorohydrin)
(PECH) have been studied. It is found from the dynamic mechanical measurements that mutual dissolution takes place to some
degree with remaining CAP-rich and PECH-rich regions in the blends. As a result of the interdiffusion, leading to fine morphology,
the blends exhibit high level of optical transparency although the individual pure components have different refractive index.
Furthermore, the mechanical toughness of CAP, which is one of the most serious problems for CAP, is considerably improved
by blending PECH. This will have a great impact on industries because the blend technique widens the application of CAP. 相似文献
10.
Won Keun Son Ji Ho Youk Taek Seung Lee Won Ho Park 《Journal of Polymer Science.Polymer Physics》2004,42(1):5-11
Electrospinning of cellulose acetate (CA) in a new solvent system and the deacetylation of the resulting ultrafine CA fibers were investigated. Ultrafine CA fibers (∼2.3 μm) were successfully prepared via electrospinning of CA in a mixed solvent of acetone/water at water contents of 10–15 wt %, and more ultrafine CA fibers (0.46 μm) were produced under basic pH conditions. Ultrafine cellulose fibers were regenerated from the homogeneous deacetylation of ultrafine CA fibers in KOH/ethanol. It was very rapid and completed within 20 min. The crystal structure, thermal properties, and morphology of ultrafine CA fibers were changed according to the degree of deacetylation, finally to those of pure cellulose, but the nonwoven fibrous mat structure was maintained. The activation energy for the deacetylation of ultrafine CA fibers was 10.3 kcal/mol. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 5–11, 2004 相似文献
11.
Gy. Számel Szilvia Klébert I. Sajó B. Pukánszky 《Journal of Thermal Analysis and Calorimetry》2008,91(3):715-722
Cellulose acetate (CA) was modified with caprolactone (CL) under various reaction conditions in an internal mixer. The thermal
behavior and relaxation transitions of the samples were determined by dynamic mechanical analysis and differential scanning
calorimetry. Various relaxation transitions were detected in externally and internally modified cellulose acetate by DMTA.
These were assigned to the glass transition of the main chain, to the movement of single glucose units and to hydroxymethyl
groups. The β′ transition must belong to structural units larger than a single glucose ring and their formation must depend
on sample preparation conditions. No transition could be assigned to grafted polycaprolactone (PCL) chains by DMTA. Contrary
to other groups, we could not detect even the transitions of modified CA by DSC. Only the crystallization of oligomeric PCL
homopolymer was observed mostly when it diffused to the surface of the sample. 相似文献
12.
The dependence of water absorption of 2 to 4 μm thick membranes of cellulose acetate on relative humidity was determined by measuring small changes in their asymmetric waveguide properties in the visible spectral region. Simultaneous measurements of changes in film thickness provide a direct method for obtaining the change in film volume as a function of water concentration and a new measure of polymer porosity. Data are presented for a typical film fabricated from cellulose acetate (CA398-30) which illustrate the usefulness of studying water absorption by integrated optics techniques. 相似文献
13.
Anthony Bocahut Jean-Yves Delannoy Caroll Vergelati Karim Mazeau 《Cellulose (London, England)》2014,21(6):3897-3912
Atomistic simulations of cellulose acetates (CAs) differing in their degree of substitution have been performed and analyzed in terms of conformation and interaction schemes. The stabilization of the structure of these cellulose derivatives is understood as a subtle balance between hydrogen bonds and the dipolar acetate-acetate interactions that are associated with important changes in the macromolecular conformation. On the one hand, cellulose and cellulose triacetate (CTA) are characterized by a single stabilization process (H-bonds and dipolar interactions respectively), showing a similar structure in their melt phase together with similar radii of gyration. On the other hand partially acetylated CAs combine both the conformational properties of cellulose and CTA but present an unexpected conformational domain, named C2, which induces a local hydrophobic pocket. These CAs are also further stabilized by hydrogen bonds between the hydroxyl and acetyl groups. Although idealized, the proposed models are realistic since they are in good agreement with literature experimental results. 相似文献
14.
The longitudinal penetration of micromolecular liquid solvents (acetone, dioxane) or swelling agents (methylene chloride, methanol) into unoriented (unstretched) cellulose acetate film has been studied in detail by a variety of techniques, including observation of visible penetrant fronts, birefringence profiles, colored tracer microdensitometry, and microinterferometry. The results, in conjunction with those of Part II, provide a fuller picture of the relevant phenomenology than was previously available, leading to further insight into the mechanism of micromolecular transport in stiff-chain polymers and its dependence on the nature of the penetrant and the structural changes of the swelling polymer. © 1992 John Wiley & Sons, Inc. 相似文献
15.
Changes in waveguide properties of several cellulose acetate membranes and one polyimide membrane were measured as a function of their exposure to varying levels of relative humidity. The volume fraction of water in the films and the occupied pore volumes were determined from refractive index and thickness changes. The dependence of the refractive index on water absorption is related to a competition between two processes: one of filling pores with no film expansion and one of “free expansion” where the film expands to completely accommodate the added water volume. The term “pore” is taken to mean a volume with molecular and not macroscopic dimensions. The hydration properties of these dense cellulose acetate membranes were affected by degree of acetylation, casting temperatures and annealing treatments. Annealing CA398 membranes at 180°C decreased film water concentration by reducing the amount of free expansion. Annealed CA398 membranes that were tested in a reverse osmosis cell were found to have high salt rejection compared to unannealed films. The hydration characteristics of a polyimide membrane are compared to cellulose acetate membranes. 相似文献
16.
P. K. C. Pillai Brijesh K. Gupta Malti Goel 《Journal of Polymer Science.Polymer Physics》1981,19(9):1461-1470
The thermally stimulated current (TSC) technique has been used to study solvent-cast blends of a cellulose derivative with a vinyl polymer. TSC peaks are observed at 56, 80, and 120°C. Their origin is investigated because the TSC spectra of the blends differ from the spectra of the individual components. Data on blends with components in the weight ratios 25:75, 50:50, and 75:25 indicate that the 50:50 blend shows the greatest polarization. The enhancement of depolarization currents observed on blending is explained on the basis of a Maxwell–Wagner–Sillars polarization due to increased heterogeneity in the structure. Effects of forming conditions (time, temperature, field) on polarization have been investigated. Activation energies and relaxation times are calculated; there is good agreement between the values obtained from the initial-rise and the full-curve methods. 相似文献
17.
Controlled grafting of MMA onto cellulose and cellulose acetate 总被引:1,自引:0,他引:1
Homogeneous graft copolymerization of methyl methacrylate onto cellulose and cellulose acetate was carried out in various solvents and solvent systems taking ceric ammonium nitrate, tin (II) 2-ethyl hexanoate [Sn(Oct)2] and benzoyl peroxide as initiators. The effect of solvents, initiators, initiator and monomer concentration, on graft yield, grafting efficiency and total conversion of monomer to polymer were studied. Formation of Ce3+ ion during grafting in presence of CAN enhances the grafting efficiency. Methylene blue was used as a homopolymer inhibitor and controlled the molecular weight of the grafted polymer and its effect on grafting was also studied. In presence of MB, amount of PMMA homopolymer formation reduced and consequently grafting efficiency increased. The number average molecular weights and polydispersity indices of the grafted PMMA were found out by gel permeation chromatography. The products were characterized by FTIR and 1H-NMR analyses and possible reaction mechanisms were deduced. Finally, thermal degradation of the grafted products was also studied by thermo-gravimetric and differential thermo-gravimetric analyses. 相似文献
18.
Microfibrillated cellulose (MFC), which consists of a web‐like array of cellulose fibrils having a diameter in the range of 10–100 nm, was incorporated into a cellulose acetate (CA) matrix to form a totally biobased structural composite. Untreated and a 3‐aminopropyltriethoxysilane (APS) surface treated MFC was combined with a CA matrix by film casting from an acetone suspension. The effectiveness of the surface treatment was determined by infrared spectroscopy and X‐ray photoelectron spectroscopy. The Young's moduli of APS treated MFC composite films increase with increasing MFC content from 1.9 GPa for the CA to 4.1 GPa at 7.5 wt % of MFC, which is more than doubled. The tensile strength of the composite film increases to a maximum of 63.5 MPa at 2.5 wt % compared to the CA which has a value of 38 MPa. The thermal stability of composites with treated MFC is also better than the untreated MFC. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 153–161, 2010 相似文献
19.
Ali Amira S. Mohammed Soliman Moataz M. Kandil Sherif H. Khalil Marwa M. A. 《Cellulose (London, England)》2021,28(10):6417-6426
Cellulose - Mixed matrix membranes (MMMs) for reverse osmosis (RO) have become a significant target in various research. Herein, cellulose acetate membranes (CA) with Linde Type A (LTA) Zeolite... 相似文献
20.
A bistable dynamic coordination polymer [Ni(pca)(bdc)(0.5)(H(2)O)(2)] having a two-dimensional (2D) zigzag sheet structure is synthesized solvothermally. Topological analysis revealed that the frameworks have an hcb type of uninodal net. The compound exhibits guest specific reversible structural transformations accompanying reversible changes in physical properties driven by inherent flexibility and transformability. 相似文献