Willer de Oliveira

Hydrogels from polysaccharides. I. Cellulose beads for chromatographic support

Cellulosic hydrogels in bead form were prepared by dropwise addition of cellulose solutions in N,N-dimethylacetamide (DMAc) and lithium chloride (LiCl) to azeotropic methanol or isopropanol as nonsolvent. Bead properties were examined in relation to cellulose solution concentration, viscosity, and molecular weight. Bead properties were defined in terms of solids content, flow characteristics, mechanical strength, bead size, and pore dimensions. Results suggest that (a) beads can be prepared with solids content ranging from 2 to 12 wt %, depending on solution concentration; (b) uniform spherical shapes require a viscosity range between 100 and 300 cS: (c) beads can be produced in different sizes, within the diameter range of 100 to 1,500 μm; (d) linear flow velocities of packed bead columns are in the range of 70 to 350 cm/min; and (e) pore sizes of beads vary between 8 to 200 A. Beads with low cellulose concentration show a wide fractionation range of up to 200,000 g/mol for polyethylene oxide.

Multiphase materials with lignin: 13. Block copolymers with cellulose propionate

Abstract Block copolymers consisting of rubbery lignin derivative components (i.e. hydroxypropyl lignin, L) and cellulose propionate (CP) segments ranging in size from degree of polymerization ( DP ) 5 to 60 were synthesized using chemistry described previously. The block copolymers (LCP) varied in relation to architecture and size of component. The copolymers were characterized by solution, thermal and optical techniques, and their effect on the properties of L/CP blends was determined by mechanical tests. The results suggest that copolymer properties are dictated primarily by CP segment size. Whereas copolymers with short CP segments behaved like spherical macromolecules, copolymers with large CP segments had rod-like behaviour. All block copolymers displayed T m values, even if CP arm length was as low as 5. Crystallinity was highest at CP chains of DP 60. Copolymer morphologies varied; they revealed patterns resembling dispersed fibrils, spheres and alternating lamella types depending on composition and segment geometries. The block copolymers had surprisingly little effect on L/CP blend properties. This was attributed to the overall- compatibility of lignin derivatives with CP.

Hydrogels from polysaccharides. II. Beads with cellulose derivatives

The generation of hydrogels from solutions of cellulose ester derivatives of various types using an atomization device, in which the solution travels through air before phase inversion occurs in a nonsolvent, was unable to produce beads in spherical shape. Instead, irregularly shaped particles were formed. The cellulose derivatives included a series of cellulose esters with a high and low degree of substitution (DS) and with acyl substituents ranging in size from C3 to C12 (laurate). Starch was tested as a noncellulosic polysaccharide, and the list of cellulose derivatives included a fluorine containing ester. The formation of spherical hydrogel beads by this method became possible only when cellulose derivatives or starch were blended in solution with unmodified cellulose. The resulting beads had dynamic flow characteristics, for instance, linear velocity vs. pressure drop relationships, that closely followed the rule of mixing. An exception was cellulose laurate, which retained most of the strength of unblended cellulose even at 60% derivative content. The results suggest (a) that cellulose is needed for the formation of droplets with sufficiently high surface tension capable of withstanding the collision with the nonsolvent surface; (b) that cellulose derivatives require the presence of unmodified cellulose to attain sufficient gel strength; and (c) that waxy ester substituents provide the basis for hydrophobic interactions which contribute to gel strength retention.

Optimization of pressure-flow limits, strength, intraparticle transport and dynamic capacity by hydrogel solids content and bead size in cellulose immunosorbents

Abstract The design of existing beaded adsorbent materials for column-mode protein purification has emphasized the impact of diffusional transport phenomena upon adsorbent capacity. A design model is presented here that optimizes molecular accessibility of proteins relative to the mechanical stability at low operating pressures by manipulation of size and solids content for uncross-linked cellulose beads. Cellulose beads of several different sizes ranging from about 250 to 1000 μm diameter and having different solids contents were evaluated. Solids content of greater than about 9% cellulose greatly reduced the permeability of large proteins such as thyroglobulin and β-amylase into the beaded matrix at bead contacting times of about 5 and 50 s. Furthermore, the amount of permeation at 3% solids content by thyroglobulin at bead contacting times of about 5 s was about tenfold larger than predicted by diffusion models using the binary diffusivity in a purely aqueous continuum. The utility of a low solids content, large bead cellulose support was shown with immobilized IgG (Mr 155 kDa) capturing recombinant human Protein C (Mr 62 kDa). A 1000 μm diameter beaded cellulose immunosorbent having 3% solids content gave equivalent capacity to a 140 μm diameter beaded, cross-linked agarose support containing 4% solids. In contrast to the smaller diameter, cross-linked beaded agarose, the low solids content beaded cellulose benefitted from greater physical stability due to more optimal pressure-flow characteristics imparted by large bead size.

Lignin impact on fibre degradation. 2. A model study using cellulosic hydrogels

The impact of lignin on cellulose degradation was studied in vitro using lignocellulosic hydrogels. Hardwood lignin (methoxyl content, 191 mg g -1 ) was blended with cellulose in homogeneous phase solution (dimethylacetamide/LiCl solvent) in two concentrations (100 and 300 mg g -1 ) and formed into lignocellulosic beads by dropwise addition of the lignocellulose solutions to an appropriate nonsolvent. The lignin was used before and after hydroxypropylation of the phenolic hydroxyl group. Cellulose degradation from these beads after 24 and 72 h incubation in buffered ruminal fluid was compared to that of control (cellulose) beads and to that of cellulose beads incubated in the presence of lignin. The rate of cellulose degradation from the hydrogels was low (12-16% degradation after 24 h). At 72 h, 21-50% of the cellulose was degraded. Cellulose degradation was enhanced (P < 0.01) by lignin blended into the beads, but depressed (P < 0.01) by lignin added to the incubation medium. The effect of lignin increased (P<0.001) with lignin concentration. Hydroxypropylation of lignin, which blocks the formation of quinone methide intermediates, enhanced (P < 0.001) the increase in cellulose degradation with lignin blending, and reduced (P < 0.001) the inhibitory effect of lignin included in the incubation medium.

Novel cellulose derivatives. II. synthesis and characteristics of mono-functional cellulose propionate segments

Mono-functional cellulose propionate segments for use in ter- or star-block polymers have been prepared by the depolymerization (step 1) of cellulose propionate in homogeneous phase using a mixture of HBr and propionic anhydride in methylene chloride solution. The anomeric mixture of glycosyl bromide has subsequently (step 2) been hydrolyzed in aqueous acetone. Functionality was determined by H-NMR spectroscopy of triethyl silane derivatives in combination with gel permeation chromatography. The cellulose ester segments were semi-rigid, highly crystalline materials with melting points between 180° and 250°C. The lowest useful segment size, based on crystallinity and Mark-Houwink-Sakurada exponential factor, appeared to be DP 20, with an optimum around DP 40 to 50.