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.     

PREPARATION AND PHYSICAL PROPERTIES OF BLEND FILMS FROM SODIUM ALGINATE AND POLYACRYLAMIDE SOLUTIONS

Blend films of sodium alginate and polyacrylamide (PAAm) were prepared by mixing the aqueous solution of both samples at a different ratio. All blend films obtained are optically clear to the naked eye. The structure and physical properties of the films were studied by FT-infrared (FT-IR), wide angle X-ray diffraction (WAXD), differential thermal analysis (DTA), thermogravimetic analysis (TGA), scanning electron microscopy (SEM), and tensile strength test. The results showed that the occurrence of interactions between -COO^?, -OH groups of sodium alginate and -CONH₂ groups of PAAm in the blends through hydrogen formation. The blend films exhibited the higher thermal stability and improved mechanical properties in dry states. These properties had the maximum value around 20 wt% PAAm content in the blend film. The morphological transition of the blend films from sodium alginate-like to PAAm-like was observed by scanning electron microscopy.     

Properties of Starch Blends with Biodegradable Polymers

Abstract

Starch, one of the most inexpensive and most readily available of all natural polymers, can be processed into thermoplastic materials only in the presence of plasticizers and under the action of heat and shear. Poor water resistance and low strength are limiting factors for the use of materials manufactured only from starch, and hence the modification of starch is often achieved by blending aliphatic polyesters. In this review, the literatures concerning the properties of various blends of starch and aliphatic polyesters have been summarized. The biodegradable rates of blends can be controlled to a certain extent depending on the constitutions of blends, and the mechanical properties of blends are close to those of traditional plastics such as polyethylene and polystyrene. The reduction of their sensitivity to humidity makes these materials suitable for the production of biodegradable films, injection-molded items, and foams.     

Formation of Co-continuous Structures in Melt-Mixed Immiscible Polymer Blends

Abstract

Co-continuous structures can be regarded as the coexistence of at least two continuous structures within the same volume. Blends with co-continuous structures may combine the properties of both components in a favorable way, for example, mechanical moduli. This review article deals with the identification, characterization, and properties of co-continuous structures as well as with the development of co-continuous structures during the melt blending process. Co-continuous structures usually can be formed within a composition region about the phase inversion composition, which mainly depends on the viscosity ratio. On the other hand, co-continuous structures can be found independent of composition as intermediate stages during the initial state of morphology development and during phase inversion process in blends in which the component finally forming the dispersed phase forms the matrix in early mixing states. In addition, even at low volume fractions of one component, stable co-continuous morphologies can be created using suitable processing conditions, forming long elongated interconnected structures that do not break up because of the flow. The interfacial tension plays an important role for the stability; a lower interfacial tension leads to broader composition ranges of co-continuous structures. Another factor enhancing the formation and stability of co-continuous structure is melt yield stress of one or both components of blends. In addition, this article reviews the stability of co-continuous structures during further processing and the influence of compatibilization on the structure formation and stability. Subsequently, two models describing the co-continuous composition range are discussed.     

Highly phosphonated polypentafluorostyrene: Characterization and blends with polybenzimidazole

In this study we present results of the conductivity and resistance to thermooxidative and condensation reactions of a highly phosphonated poly(pentafluorostyrene) (PWN2010) and of its blends with poly(benzimidazole)s (PBI). This polymer, which combines both: (i) a high degree of phosphonation (above 90%) and (ii) a relatively high acidity (pK_a (–PO₃H₂ ↔ –PO₃H⁻) ∼ 0.5) due to the fluorine neighbors, is designed for low humidity operating fuel cell. This was confirmed by the conductivity measurements for PWN2010 reaching σ = 5 × 10⁻⁴ S cm⁻¹ at 150 °C in dry N₂ and σ = 1 × 10⁻³ S cm⁻¹ at 150 °C (λ = 0.75). Furthermore, this polymer showed only 48% of anhydride formation when annealing it at T = 250 °C for 5 h and only 2% weight loss during a 96 h Fenton test. These properties combined with the ability of the PWN2010 to form homogeneous blends with polybenzimidazoles resulting in stable and flexible polymer films, makes PWN2010 a very promising candidate as a polymer electrolyte for intermediate- and high-temperature fuel cell applications.     

Synthesis of styrene-maleic anhydride copolymer esters and their surface enriched properties when blending with polyethylene

Three kinds of comb-like amphiphilic copolymers based on styrene-maleic anhydride copolymer (SMA) backbone and long fatty alcohol grafts were synthesized by esterification of SMA with octanol, tetradecanol and octadecanol, respectively. SMA and the esters were used as surface modifiers to blend with high density polyethylene (HDPE). The surface composition of the binary blends has been determined by Attenuated Total Reflection Fourier Transform infra-red (ATR-FT-IR) spectroscopy. It was found that grafting of alcohols onto SMA can promote the enrichment of the modifiers on the surface of the blending film, and that the enrichment effect enhances when using shorter fatty alcohols. The data of contact angle measurements and surface tension of the blend film show that the addition of SMA esters to HDPE can improve the hydrophilicity of the HDPE surface.     

Pervaporation separation of water + 1,4-dioxane and water + tetrahydrofuran mixtures using sodium alginate and its blend membranes with hydroxyethylcellulose—A comparative study

Sodium alginate and hydroxyethylcellulose blend membranes were prepared by solution casting, crosslinked with glutaraldehyde and urea–formaldehyde–sulfuric acid mixture. Crosslinking was confirmed by Fourier transform infrared spectroscopy, while the blend compatibility was studied by differential scanning calorimetry and scanning electron microscopy. Membranes were tested for pervaporation separation of feed mixtures ranging from 10 to 50 mass% water in water + 1,4-dioxane and water + tetrahydrofuran mixtures at 30 °C. For 10 mass% of the feed mixture, pervaporation experiments were also carried out at higher temperatures (40 and 50 °C). By increasing the temperature, a slight increase in flux with a considerable decrease in selectivity was observed for all the membranes and for both the mixtures. The blend membranes exhibited different pervaporation performance for both the binary mixtures investigated. For water + 1,4-dioxane mixture, the pervaporation performance did not improve much after blending, whereas for water + tetrahydrofuran mixture, the pervaporation performance has improved considerably over that of plain sodium alginate membrane.     

PEG modified poly(amide-b-ethylene oxide) membranes for CO2 separation

In the present work, membranes from commercially available Pebax^® MH 1657 and its blends with low molecular weight poly(ethylene glycol) PEG were prepared by using a simple binary solvent (ethanol/water). Dense film membranes show excellent compatibility with PEG system up to 50 wt.% of content. Gas transport properties have been determined for four gases (H₂, N₂, CH₄, CO₂) and the obtained permeabilities were correlated with polymer properties and morphology of the membranes. The permeability of CO₂ in Pebax^®/PEG membrane (50 wt.% of PEG) was increased two fold regarding to the pristine Pebax^®. Although CO₂/N₂ and CO₂/CH₄ selectivity remained constant, an enhancement of CO₂/H₂ selectivity (∼11) was observed. These results were attributed to the presence of EO units which increases CO₂ permeability, and to a probable increase of fractional free-volume. Furthermore, for free-volume discussion and permeability of gases, additive and Maxwell models were used.     

Preparation of PVDF/PEO-PPO-PEO blend microporous membranes for lithium ion batteries via thermally induced phase separation process

Microporous poly(vinylidene fluoride)/polyethylene oxide-co-polypropylene oxide-co-polyethylene oxide (PVDF/PEO-PPO-PEO, or PVDF/F127) blend membranes were prepared via thermally induced phase separation (TIPS) process using sulfolane as the diluent. Then they were soaked in a liquid electrolyte to form polymer electrolytes. The effects of F127 weight fraction on the morphology, crystallinity and porosity of the blend membranes were studied. It was found that both electrolyte uptake of blend membranes and ionic conductivity of corresponding polymer electrolytes increased with the increase of F127 weight fraction. The maximum ionic conductivity was found to reach 2.94 ± 0.02 × 10⁻³ S/cm at 20 °C. Electrochemical stability window was stable up to 4.7 V (vs. Li⁺/Li). The testing results indicated that the PVDF/F127 blend membranes prepared via TIPS process can be used as the polymer microporous matrices of polymer electrolytes for lithium ion batteries.     

Transport properties of PVA/PEI/PEG composite membranes: sorption and permeation characterizations

Poly(vinylalcohol)/poly(ethyleneglycol)/poly(ethyleneimine) blend membranes were prepared by solution casting followed by solvent evaporation. The chemical structure of the prepared membranes was analyzed by FTIR and DSC. The sorption behavior as well as the permeabilities of the membranes for pure CO₂ and N₂ were investigated. The results show that the PVA/PEI/PEG membranes possess a higher permeability of CO₂ and a lower permeability of N₂. The membrane displays a CO₂ permeability of 27 Barrer, and a N₂ permeability of 3 Barrer at 25°C and 1 bar. CO₂ sorption behavior of the composite membrane, which can be classified as a dual-mode sorption model, and N₂ sorption behavior of the copolymeric membrane is in agreement with the Fickian diffusion model.