Cellulose-based Polymers Research Articles

Programmed-life plastics from polyolefins: a new look at sustainability.

The term "sustainable" is often assumed to be synonymous with "renewable". However, polymers made from renewable natural resources are not necessarily eco-efficient. Cellulose-based polymers utilize more nonrenewable fossil fuels and are more polluting during manufacture than petro-based polymers. Sustainable polymers also have to be industrially acceptable, and although ultimate biodegradability in the natural environment is important, polymer-based products are required to biodegrade in a controlled way. Service life may be a year or more before the commencement of environmental degradation occurs. Many natural polymers such as rubber, lignin, and humus, like the synthetic polyolefins, biodegrade by an oxidative mechanism (oxo-biodegradation), and consequently much of nature's biological waste cannot satisfy the rapid mineralization criteria currently advocated by standards committees for synthetic polymers. Although biometric tests are more convenient to use than full composting tests, they are meaningless when applied to hydrocarbon polymers, whether natural or synthetic, since oxo-biodegradation is a slower process than hydro-biodegradation at ambient temperatures. Biodegradation standards currently proposed are unrealistic and will need to be modified on the basis of recent scientific evidence.

Encapsulation of antihypertensive drugs in cellulose-based matrix microspheres: characterization and release kinetics of microspheres and tableted microspheres

This study is an attempt to prepare microspheres loaded with two anti-hypertensive drugs viz., nifedipine (NFD) and verapamil hydrochloride (VRP) using cellulose-based polymers viz., ethyl cellulose (EC) and cellulose acetate (CA). Emulsification and solvent evaporation methods were optimized using ethyl acetate as a dispersing solvent. The particles are spherical in shape and have smooth surfaces, as evidenced by the scanning electron microscopy. The microspheres were characterized for their particle size and distribution, tapped density and encapsulation efficiency. Smaller sized particles with a narrow size distribution were produced with EC when compared to CA matrices. Molecular level drug distribution in the microspheres was confirmed by differential scanning calorimetry. The microspheres were directly compressed into tablets using different excipients. The drug release from CA was faster than EC microspheres and, also, the VRP release was faster than NFD. The excipients used in tableting showed an effect on the release as well as the physical properties of the tablets.

Interactions between hydroxypropylcelluloses and vapour/liquid water

Understanding of the uptake of water vapour or liquid water by cellulose-based polymers is important because of the influence of these processes on many of the biologically or technologically relevant properties of these polymers. In this work we studied these processes in the cases of twelve hydroxypropylcelluloses with low or medium-high degrees of substitution (L-HPCs and HPCs, respectively), characterization of which showed significant differences in structural and physical parameters (substitution pattern, crystallinity, particle size, specific surface area, and intraparticular porosity). Water vapour sorption–desorption isotherms determined to characterize the uptake of water vapour were fitted well by the Young–Nelson model, the optimized parameters of which indicated that at all relative humidities the capacity to bind water vapour as a surface monolayer is greater for HPCs than L-HPCs, but the capacity to absorb water vapour internally is greater for L-HPCs than HPCs. Guggenheim–Anderson–deBoer (GAB) models fitted the sorption–desorption isotherms less well. Differential scanning calorimetry (DSC) experiments showed all sorbed water vapour to be held as non-freezing water. Isoperibol microcalorimetry experiments carried out to investigate interactions with liquid water showed enthalpies of hydration/dissolution of between −62.86 and −71.35 J g −1 for L-HPCs and between −82.95 and −99.80 J g −1 for HPCs, and DSC showed average numbers of non-freezing water molecules per polymer repeat unit of 2.65–4.19 for L-HPCs and 18.10–22.42 for HPCs. DSC characterization of the kinetics of the water uptake by 10 mg compacts obtained by direct compression of hydroxypropylcelluloses showed faster uptake by L-HPC compacts than by HPC compacts, among which there were significant differences in capacity for diffusive uptake. The explanations of the above differences in terms of the different substituent contents, particle sizes and porosities of the HPCs is supported by multiple linear regression analyses.

Activation of human neutrophils after contact with cellulose-based haemodialysis membranes: intracellular calcium signalling in single cells.

In vitro contact of human leukocytes with cellulose-based dialysis membranes under complement-independent conditions results in activation of various leukocyte functions. To analyse signals involved in the mechanism of cell activation, we measured changes in cytosolic free calcium ([Ca2+]i) in individual human blood neutrophils (PMN) upon contact with flat sheet haemodialysis membranes. By confocal laser-scanning microscopy (CLSM), changes in [Ca2+]i were monitored in Fluo-3-labelled cells up to 10 min after contact with a regenerated cellulose (RC) membrane. Multiple [Ca2+]i transients were observed for cells in contact with RC; biostochastic analysis showed that up to 67% of the PMN responded with a high increase in [Ca2+]i, the rest were low- or non-responding cells. After contact with the new synthetic polycarbonate-polyether (PC-PE) membrane only non-responding cells were seen, indicating reduced cellular contact activation. The increase in [Ca2+]i of cells on RC could be inhibited by 5mM L-fucose. This monosaccharide was recently found to be present in cellulose-based polymers in picomolar concentrations. The data supports the hypothesis that dialysis-membrane-associated L-fucose residues participate in complement-independent leukocyte activation during haemodialysis therapy.

Liquid crystal elastomers based upon cellulose derivatives

Crosslinked networks displaying both thermotropic and lyotropic liquid crystalline phases have been prepared from hydroxypropyl cellulose. The phase transitions from the liquid crystal to isotropic state are reversible for materials with moderate levels of crosslinking. These materials show characteristic optical textures similar to uncrosslinked cellulose-based liquid crystal polymers although well defined patterns typical of cholesteric structures were not observed. The samples were insoluble in water, but high levels of swelling with acetone and benzene were observed and in the steady state condition a lyotropic phase was present even though the level of swelling was in excess of 500%. A reversible liquid crystalline to isotropic phase was observed with the swollen materials as the fraction of swellant was adjusted. The elastomers show marked global orientation effects when mechanically deformed but surprisingly the response was less dramatic than in some side-chain liquid crystal elastomers.

Synthesis and Solution Properties of Water-Soluble Sulfonated Cellulose-Based Polymers and Their Polyacrylamide Copolymers

Abstract Water-soluble sulfopropylcellulose (SPC) was synthesized by the reaction of 1,3-propane sultone with sodium cellulose in dioxane. The degree of substitution (0.3-1.0) was calculated by elemental analysis. The corresponding water-soluble polyacrylamide graft copolymer was prepared by Ce4+ ion-initiated graft copolymerization of acrylmide onto sulfopropylcellulose dissolved in dilute nitric acid solution at room temperature under argon. The graft copolymerization was carried out in 0.2 M NaNO3 solution in order to suppress the ionic interaction between the sulfonate ion and eerie ion. The average number of grafts per SPC was found to be 1.1 or less, depending on the reaction conditions.

Synthesis and Solution Properties of Water-Soluble Sulfonated Cellulose-Based Polymers and Their Polyacrylamide Copolymers

Synthesis and Solution Properties of Water-Soluble Sulfonated Cellulose-Based Polymers and Their Polyacrylamide Copolymers

Aliphatic polyesters and cellulose-based polymers for controlled release applications.

The general technologies for fabricating drug delivery systems are briefly discussed in the present review. Furthermore, two types of commonly used polymers, biodegradable aliphatic polyesters for parenteral administration and cellulose-based polymers for oral uses, are presented by means of selected examples of their properties and applications to control drug release.

Chemical characteristics of cellulosic liquid crystals

Cellulosic derivatives form an interesting range of polymer liquid crystals. They belong to a class of mesophases in which the polymer chain is stiff or semiflexible and is chemically homogeneous. The cellulose backbone, a single-stranded homopolymer of β-linked 1,4-anhydroglucose units, contains three hydroxy groups per anhydroglucose unit which provide convenient sites for substitution reactions, leading to a wide variety of cellulose ethers and esters. Many of these derivatives form cholesteric liquid-crystalline phases in suitable solvents, and some derivatives with relatively large (but non-mesogenic) side chains form both lytropic and thermotropic liquid crystals.Published observations on the phase separation of cellulose-based polymers indicate that the mesophases form at critical volume fractions of polymer ranging from 0.3 to 0.5 for high molar mass samples at room temperature. The critical volume fractions for a given polymer and solvent decrease with increasing molar mass to approach these asymptotic values. The critical volume fraction increases with temperature. The nature of the solvent is also important; highly polar or acidic solvents generally favour mesophase separation at lower critical concentrations than simple organic solvents. Furthermore, whereas heavily substituted derivatives with long flexible side-chains form mesophases easily in a wide range of solvents, the more familiar derivatives with smaller substituents seem to form mesophases with specific solvents, but not with others.We have measured the critical concentrations of fractions of (acetoxypropyl)cellulose in dialkyl phthalate solvents over a large temperature range and compared the results with predictions of theories for the phase separation of freely jointed and worm-like chains. The results indicate that chain geometry and stiffness are the major factors controlling liquid-crystalline phase formation and that anisotropic inter-chain interactions play a minor role. Thus the chemical structure of polymer and solvent govern the phase separation indirectly in these systems, primarily through effects on the chain conformation.

Relation between the inhibition of the laminar diffusion flame of polymers, soot formation, and radiation

This article investigates the action of effective combustion inhibitors of premixed C/sub 2/F/sub 4/Br/sub 2/ and CC1/sub 4/ mixtures on the flame propagation rate over a polymer surface in an oxidizer counterflow. The cellulose-based polymers (paper, methyl cellulose, cellophane) examined included specimens in the form of films in a frame, polymethyl methacrylate (PMMA), polystyrene in the form of plates 4 mm thick and 20 mm wide on an asbestos substrate, and STD (a copolymer of formaldehyde with trioxane) in the form of cylindrical 10-mm-diameter specimens. The flame propagation rate is related to the total heat flux, which includes the conductive or convective flux and radiation on the polymer surface. It is concluded that when considering the inhibition of diffusion flames it is necessary to take account of the possible effect associated with the change in flame luminance, and not only the chemical effects of the inert dilution of the flame by the inhibitors.

Thermal Stability of Starch- and Carboxymethyl Cellulose-Based Polymers Used in Drilling Fluids

Abstract Starch- and cellulose-based polymers have been used to control water loss for many years. Thermal degradation of the polymers is the most important problem with their use. Representative starch and cellulose fluid loss reducers were tested for their thermal stability in mud systems. The thermal decomposition was found to be dependent on both exposure time and temperature. The rate of decomposition can be predicted using first-order reaction rate kinetics and the decomposition activation energy estimated for both polymer types. This technique allows the calculation of a polymer's usable lifetime at a given temperature. A table of half-lives (time for fluid loss to double) vs. exposure temperature is presented for both starch- and cellulose-based polymers. This paper discusses the results of the calculations and the method used to obtain the data. The method is generally applicable to any material used in drilling fluids that is subject to thermal degradation.