Effects of hydroxyvalerate contents in thermal degradation kinetic of cellulose acetate propionate/poly(3-hydroxyalkanoates) blends

Thermal stability of polymers is an important parameter that determines the application as well as the processing conditions. The green polymers have shown low thermal stability, such as the polyhydroxyalkanoates (PHAs). The PHAs with different comonomers containing hydroxyvalerate (HV) were studied. It was seen that the green polymer showed a fast thermal degradation process. The addition of the HV comonomer modified this profile and the thermal degradation kinetic. The blend prepared between the PHAs and other polymers can modify the thermal degradation process of the green polymers. In the present study, blends of cellulose acetate propionate and PHAs were prepared, and the thermal degradation kinetics of these blends were evaluated. It was observed that the cellulose acetate propionate (CAP) phase in the blends modified the thermal degradation process and kinetic profile of the PHA phase. In the blends, the thermal stability of the PHAs was slightly modified because of CAP reducing the reactivity of the PHAs. On the other hand, the thermal stability of the CAP phase in the blends is not largely modified by the PHA phase. However, the hydroxyvalerate comonomer decreases the reactivity of the CAP phase at the start of thermal degradation of the same. The interaction between the phases promotes the synergetic interaction, which slightly improves the thermal stability of the two polymers blends.     

Modified cellulose acetate flat membranes for desalination

In this article, the radiation grafting of acrylamide on to cellulose acetate flat membranes using UV-irradiation on the initiator is described. The modified membranes thus obtained have been characterized by IR, DSC, and TGA. Their transport properties have been studied. The modified membranes exhibit higher salt rejection with slightly reduced water flux as compared with cellulose acetate membrane. The work is further extended to study the thermal stability of these modified membranes in a dry state. These modified membranes up to 330°C are stable.     

Permeation of water as a tool for characterizing the effect of solvent, film thickness and water solubility in cellulose acetate membranes

Cellulose acetate membranes have been used in many applications; of particular interest are reverse osmosis systems, and as a neutral matrix for incorporation of different polymers (e.g., conducting polymers), inorganic ions (e.g., lanthanides) and organic (e.g., pharmaceutical) compounds. The properties of the new polymers derived from cellulose acetate or blends depend on those of cellulose acetate. This work presents an attempt to find links between thermodynamic and kinetic properties of cellulose acetate membranes in equilibrium with water. Water diffusion coefficients in cellulose acetate membranes are reported, measured with a simple water permeation technique. The comparison of these values with the percentage of water uptake and polymer thickness leads to interesting conclusions related with different polymer properties.     

Cellulose Acetate-g-Polycaprolactone Copolymerization Using Diisocyanate Intermediates and the Effect of Polymer Chain Length on Surface,Thermal, and Antibacterial Properties

The need for biodegradable and biocompatible polymers is growing quickly, particularly in the biomedical and environmental industries. Cellulose acetate, a natural polysaccharide, can be taken from plants and modified with polycaprolactone to improve its characteristics for a number of uses, including biomedical applications and food packaging. Cellulose acetate-g-polycaprolactone was prepared by a three-step reaction: First, polymerization of ε-caprolactone via ring-opening polymerization (ROP) reaction using 2-hydroxyethyl methacrylate (HEMA) and functionalization of polycaprolactone(PCL) by introducing NCO on the hydroxyl end of the HEMA-PCL using hexamethyl lenediisocyanate(HDI) were carried out. Then, the NCO–HEMA-PCL was grafted onto cellulose acetate (using the “grafting to” method). The polycaprolactone grafted cellulose acetate was confirmed by FTIR, the thermal characteristics of the copolymers were investigated by DSC and TGA, and the hydrophobicity was analyzed via water CA measurement. Introducing NCO-PCL to cellulose acetate increased the thermal stability. The contact angle of the unreacted PCL was higher than that of cellulose acetate-g-PCL, and it increased when the chain length increased. The CA-g-PCL50, CA-g-PCL100, and CA-g-PCL200 showed very high inhibition zones for all three bacteria tested (E. coli, S. aureus, and P. aeruginosa).     

Reactions with 1.3 propane sultone for the synthesis of cation-exchange membranes

For several reasons it is interesting for membrane technology to introduce strongly anionic groups in membranes. Therefore the possibilities of 1.3 propane sultone were studied to modify cellulose, cellulose acetate and polyacrylonitrile.The results showed that cellulose and cellulose acetate could be modified by a direct reaction of 1.3 propane sultone with the available hydroxyl groups. The nitrile groups in polyacrylonitrile had to be reacted first with hydrogen sulphide to give reactive thioamide groups, able to react with the sultone. These results give evidence for 1.3 propane sultone being a useful chemical for modification of polymers, its carcinogenic properties will however prevent applications.     

CELLULOSE ACETATE AND EPOXY RESIN BLEND ULTRAFILTRATION MEMBRANES: REPARATION,CHARACTERIZATION, AND APPLICATION

ABSTRACT

Membranes based on cellulose acetate used in ultrafiltration applications lack good, chemical, mechanical and thermal resistance. In order to prepare membranes with improved properties, modification of cellulose acetate with epoxy resin through solution blending was attempted. In the present work, the membrane casting solutions with different polymer blend compositions of cellulose acetate and diglycidyl ether of bisphenol-A (DGEBA) were prepared at 30±2°C. The maximum percent compatibility of the two polymers, cellulose acetate and diglycidyl ether of bisphenol-A, was estimated to be 60/40%. Ultrafiltration blend membranes based on various blend compositions were prepared, characterized in terms of compaction, pure water flux, water content, membrane hydraulic resistance and molecular weight cut-off. The application of these membranes, in rejection of proteins of various molecular weights, are discussed.     

Dioxouranium (VI) complexes with cellulose acetate

Dioxouranium [UO₂(VI)] complexes with three degrees of substitution of cellulose acetate, prepared from viscose pulp (DS = 2.2, 2.45 and 2.86), have been synthesis and characterized. Degree of substitution (DS) is defined as the average number of CH groups substituted on each anhydrocellulose repeat unit. Probable structures of the cellulose acetate complexes were inferred from the elemental analysis data, conductance measurements, IR, electronic and ¹H NMR spectra. The results obtained show that the formula of UO₂(VI) complex with cellulose acetate of DS = 2.2 and 2.45 [(CA)₄.UO₂] is more probable than [(CA)₂.UO₂].2(CH₃COO), while the reverse is true for the case of a UO₂ complex with CA of DS = 2.86. For the former formula, cellulose acetate acts as a uni-negatively charged bidentate ligand and reacts with UO₂²⁺ through the ether-carbon-oxygen of the secondary acetylated hydroxyl group of the anhydroglucose unit and the oxygen atom of the residual secondary unacetylated hydroxyl group, forming a five-membered chelate ring. For the later formula, cellulose acetate of DS = 2.86 acts as a neutral bidentate chelating agent through the two ether oxygen atoms of the vicinal ester groups of secondary acetylated hydroxyl groups in anhydroglucose units also forming a five-membered chelate ring. The uranium atom in these complexes is 8-coordinate. The thermal behaviour of cellulose diacetate (DS = 2.2) and cellulose triacetate (DS = 2.86) and their complexes with uranyl acetate in nitrogen atmosphere has been also studied by differential thermal analysis from room temperature to 600 °C. The obtained DTA curves were analyzed using the Prout-Tompkins law. The method of least squares was applied to estimate the appropriate order of the reaction (n), and consequently the thermodynamic parameters. The results revealed that chelation of cellulose acetate with uranyl acetate led to increased thermal stability.     

甲苯二异氰酸酯改性醋酸纤维素膜材料

本文研究了用甲苯二异氰酸酯对醋酸纤维素进行改性,以增强高聚物的物理性能和耐菌性能。探讨了反应时间、原料配比、反应温度、催化剂用量及产物分离用的溶剂等因素对合成高聚物材料的影响。对交联后的醋酸纤维素苯基氨基甲酸酯铸成的反渗透膜的水通量、脱盐率、耐水解性和耐微生物的稳定性能的测试表明,经改性的醋酸纤维素膜具有较好的上述性能,是一种良好的膜材料。     

The Effect of Flower-Like Magnesium Hydroxide Nanostructure on the Thermal Stability of Cellulose Acetate and Acrylonitrile–Butadiene–Styrene

Flower-like magnesium hydroxide (Mg(OH)₂) nanostructures were synthesized via a simple hydrothermal reaction at relatively low temperature. The Mg(OH)₂ nanostructures were then added to acrylonitrile–butadiene–styrene (ABS) and cellulose acetate (CA) polymers. The effect of Mg(OH)₂ nanostructures on the thermal stability of the polymeric matrixes has been investigated. The thermal decomposition of the nanocomposites shifts towards higher temperature in the presence of the Mg(OH)₂. The enhancement of thermal stability of nanocomposites is due to endothermically decomposition of magnesium hydroxide that releases of water and dilutes combustible gases. Nanostructures and nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), UL-94 test and limiting oxygen index (LOI) analysis.     

Effects of natural polymer acetylation on the anaerobic bioconversion to methane and carbon dioxide

The successful production of novel biodegradable plastic copolymers incorporating both synthetic plastic formulations, such as polystyrene, and naturally occurring biodegradable polymer components, such as cellulose, starch, or xylan, requires stable chemical bonding between these polymers. Modification of the natural polymers through acetylation of the available hydroxyl groups permits the formation of appropriate film-forming plastic copolymers. However, modification of natural polymers has been demonstrated to result in decreased attack by microbial catalysts. For this study, the abundant natural polymers cellulose, starch, and xylan were substituted with acetate to various degrees, and the effect of this modification on the anaerobic biodegradation was assessed using the biochemical methane potential (BMP) protocol. Significant reduction in anaerobic biodegradability resulted with all polymers at substitution levels of between 1.2-1.7. For the xylan acetate series, the trends for anaerobic biodegradation were in good agreement with reduced enzymatic hydyolysis using commercially available xylanase preparations.     

1. History of CA and evolution of the markets

An overlook is given of the 100 years of technical, industrial and chemical development of cellulose acetate. CA has been used as raw material in the fields of laquer, plastics, textile, Filter Tow, film, membrane and others. In the field of applications for plastics and textiles CA was quite successful for many years, but was then slowly substituted by other polymers. Total cellulose acetate demand is growing, especially for Filter Tow in cigarettes filters and film for polarisers in LCD-displays.     

Electrochemical studies on surfactant-modified cellulose acetate membrane

The possibility of electrochemical modification of cellulose acetate membrane upon immobilization of the anionic surfactant (SDS) has been explored on the basis of membrane potential studies. Surface tension measurements with and without cellulose acetate membrane were carried out to ascertain the extent of immobilization of the surfactant. Cellulose acetate membrane practically does not exhibit any ion selectivity. However, modified membrane exhibits cation selectivity which varies with concentration of the surfactant till its critical micelle concentration is reached. An attempt has also been made to demonstrate correspondence between the immobilized surfactant and the permselectivity of the membrane.     

改性羧甲基羟丙基纤维素在聚醋酸乙烯乳液中的增稠效应

用旋转粘度计研究了改性羧甲基羟丙基纤维素在聚醋酸乙烯乳液中的增稠效应。通过与非离子型羟乙基纤维素及离子型羧甲基纤维素的比较试验表明,改性羧甲基羟丙基纤维素用作聚醋酸乙烯乳液增稠剂有良好的增稠性、稳定性和配伍性。     

Physical and mechanical testing of essential oil-embedded cellulose ester films

Polymer films made from cellulose esters are useful for embedding plant essential oils, either for food packaging or air freshener applications. Studies and testing were done on the physical and mechanical properties of cellulose ester-based films incorporating essential oils (EO) from lemongrass (Cybopogon citratus), rosemary pepper (Lippia sidoides) and basil (Ocimum gratissimum) at concentrations of 10 and 20% (v/w). Results obtained showed that, in all films, the addition of the essential oil caused a decrease in the water vapor permeability due to the hydrophobic nature of the oil. The use of 20% of EO caused lower transparency of the films, although the change was not observed visually. Mechanical testing was done on cellulose acetate, cellulose acetate propionate and cellulose acetate butyrate. It was found that incorporation of lemongrass, basil and rosemary pepper EO significantly affected the Young's modulus, tensile strength and elongation at break of the cellulose ester films. The results suggested that the essential oils interacted with the polymers like plasticizers. The results were confirmed with thermal and microscopic studies.     

Synthesis, characterization and thermal studies on cellulose acetate membranes with additive

Cellulose acetate (CA) membranes are used in ultrafiltration applications, although they show low chemical, mechanical and thermal resistance. In order to prepare membranes with improved properties, modification of cellulose acetate with polyethelene glycol (PEG 600) has been attempted. In this study, CA has been mixed with PEG 600 as an additive in a polar solvent. The effects of CA composition and additive concentration given by a mixture design of experiments on membrane compaction, pure water flux, water content and membrane hydraulic resistance have been studied and discussed. The efficiency of protein separation by the developed CA membranes have been quantified using model proteins such as pepsin, egg albumin (EA) and bovine serum albumin (BSA). The thermal stability of the developed membranes prepared with PEG 600 additive has also been investigated using thermogravimetric analysis and differential scanning calorimetry.     

Biodegradable systems: Thermodynamics, rheological properties, and biocorrosion

Systems based on starch and chitosan blends with synthetic polymers and cellulose derivatives (poly(ethylene oxide) and methyl cellulose of various molecular masses, PA, and ethylene-vinyl acetate copolymers containing different amounts of vinyl acetate groups) have been studied. The thermodynamic characteristics of the formation of blends have been determined. The rheological properties characterizing formation of blends from melts have been investigated. The biocorrosion ability of the blends after their use has been estimated by various methods. The concentration dependences of the thermodynamic functions of mixing of components (change in the Gibbs energy, enthalpy, and entropy) change sign in a wide composition range, indicating the complexity of mixing of rigid-chain natural polysaccharides with synthetic polymers. The rheological study of blends in which starch or chitosan plays the role of a biodegradation modifier shows that they are non-Newtonian fluids. The absolute values of viscosity and the activation parameters of melts increase with the content of polysaccharide in the system. The values of viscosity correspond to those typical for commercially processable polymers. The blends under study are biodegradable in a wet and water-soil medium with the content of the natural component being in the range 15–30 wt %.     

Preparation,Characterization and Properties of Cellulose Acetate-Grafted-Poly(glycidyl methacrylate) Copolymers

The cellulose acetate-grafted-poly(glycidyl methacrylate) copolymers were synthesized successfully by free radical polymerization. The resulting copolymer was characterized by proton nuclear magnetic resonance (¹H-NMR), solid-state ¹³C-NMR, Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). The crystallization behavior, thermal properties, specific particle surface area, moisture sorption behavior of the modified cellulose acetate were investigated by wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) method and Dynamic Vapor Sorption (DVS) instrument. It was found that the poly(glycidyl methacrylate) (PGMA) grafting was effective in improving the water adsorption of cellulose acetate (CA) changing the specific surface area, and reducing the T_g of copolymers.     

Reinforcement of aligned cellulose fibers by lignin-polyester copolymers

With an ever-increasing attention on the climate change and the growing amount of plastic wastes generated, the search for an alternative to the petroleum-based plastics has never been as imperative. Inspired by the structure of natural wood, we aim to reproduce artificial equivalent using modified lignin and cellulose acetate. As natural wood are made up of an aggregation of fibers, electrospinning was used to produce the fiber component. Besides exploring the influence of various polymers on the properties of the eventual fibers, its properties were also examined in terms of its orientation – random and aligned. The addition of lignin copolymers was shown to remarkably improve the tensile strength and the Young’s modulus of cellulose acetate fibers up to 500% and 7,000% respectively. In contrast to the random fibers, the aligned fibers demonstrated better tensile strength and Young’s modulus which could be attributed to the higher crystallinity. Among the fibers, the longitudinal aligned C.A. + Lig-PHB fibers exhibited the best tensile strength and Young’s modulus which could be explored for load bearing applications.     

Modification of cellulose by graft polymerization for use in drug delivery systems

Cellulose-based biodegradable polymers—as microspheres or hydrogels—are suitable for drug delivery systems. In this work, cellulose microfibers were converted to cellulose esters for subsequent graft copolymerization either by free radical or atom transfer radical polymerization (ATRP). For the former, carboxymethyl cellulose (CMC) was prepared and then modified through grafting of poly(hydroxyethyl acrylate) or polyacrylamide. ATRP was achieved by chloroacetylation of cellulose followed by graft copolymerization of hydroxyethyl acrylate or acrylamide monomers. The degree of substitution for CMC and chloroacetylated cellulose (CAC) was determined by the method described in US Pharmacopeia NF24 and by titration method, respectively. CMC, CAC, and the grafted copolymers were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetric analysis, X-ray diffraction, and atomic force microscopy; the latter technique clearly shows the chain growth of the synthetic polymers on the backbone surface. Furthermore, cephalexin antibiotic was loaded on the copolymers, and the resultant in vitro drug release studied in three different media (buffer solutions with pH equal to 3, 6.1, and 8).     

Thermal analysis of cellulose acetate modified with caprolactone

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.