Hans-Peter Fink

Evaluation of new organosolv dissolving pulps.Part I: Preparation, analytical characterization and viscose processability

New acidic organosolv pulping processes, such as Acetosolv, Formacell and Milox, promise to have superior potential in terms of purification selectivity and specific investment costs. Consequently, a thorough investigation of these new acidic pulping processes in comparison to state-of-the-art acidic magnesium sulfite technology was conducted. The impact of pulping and bleaching parameters on the physical and chemical characteristics was studied to compare process efficiency and selectivity for each type of pulp made from Eucalypt wood. In addition to a detailed analysis of the chemical composition and physical properties on a molecular and supramolecular level, the TCF-bleached dissolving pulps were tested for their applicability in viscose fiber production. The influence of pulp properties as determined by standard and advanced analytical methods on process performance and selected fiber properties is emphasized.

Cellulose ethers with a block-like distribution of the substituents by structure-selective derivatization of cellulose

Abstract Native cellulose, especially ground cotton linters, was step-by-step carboxymethylated in alcohol-water medium at low concentrations of NaOH. Using the 13 C cross-polarization/magic angle spinning n.m.r. method, it has been found that, under these conditions, initially the non-crystalline regions were selectively etherified; only at higher degrees of substitution were the crystalline regions gradually integrated in the reaction. Therefore, already at relatively low degrees of substitution, the hydrolysates of such cellulose ethers contained higher quantities of di- and trisubstituted glucose units than those of cellulose samples etherified by the conventional method to a comparable degree of substitution. The experimental results confirm the concept of reacting structural fractions proposed for the alkalization of cellulose and indicate the formation of cellulose ethers with a block-like distribution of the substituents along the molecular chains.

X‐ray texture investigations of bacterial cellulose

Never dried highly swollen bacterial cellulose fleeces produced by the bacteria Acetobacter xylinum were deformed uniaxially and kept under strain during the drying process. The orientation of the crystalline nano-fibrils was determined by X-ray pole figure measurements of the (1–10) lattice plane in reflection mode and the (004) interference in transmission mode. Appropriate cuts through the pole figures were used for the determination of planar and axial degrees of orientation. Generally, a uniplanar texture with the (1–10) planes parallel to the fleece surface and an axial component in the draw direction were found. With increasing draw ratio both the axial orientation and the uniplanar orientation in draw direction were improved, whereas transversely the uniplanar texture component broadened slightly. Mechanical strength and modulus were almost doubled and tripled, respectively, for favoured cases. As compared to the wet aqueous samples, a higher coherent deformation of the bacterial cellulose membrane could be achieved by drawing the samples soaked in NaOH solutions with concentrations in the range of 8 to 10 wt.-%. By the presence of the lye significant improvements of the axial chain orientation of up to 100% could be obtained resulting in a maximum strength of 580 MPa. The improved orientability is likely to be explained by a NaOH-induced reduction in the number of inter-fibrillar bridging points formed by H-bonds

The structure of amorphous cellulose as revealed by wide-angle X-ray scattering

Abstract The structure of amorphized cellulose samples prepared by ball milling of cellulose I and II and by saponification of cellulose triacetate is investigated by means of radial distribution functions (RDFs). Experimental wide-angle X-ray scattering results are compared with model calculations assuming atomic positions arising from different crystal structure investigations. At small atomic distances ( r r > 0.5 nm larger differences exist between experimental and model RDFs, indicating increased distances as compared with the crystalline state.

Development and evaluation of methods for determining the pattern of functionalization in sodium carboxymethylcelluloses

SUMMARY: Sodium carboxymethylcellulose (NaCMC) with varying degrees of substitution (DS) was investigated with different analytical methods in order to characterize the functional group distribution. The following methods were tested and adapted: high-resolution 13 C NMR spectroscopy in the solid state ( 13 C CP/ MAS NMR) and 13 C NMR spectroscopy on solutions of NaCMC samples with a reduced molar mass. Partial degradation was accomplished by ultrasonic means and with the enzyme endoglucanase. Combining the two techniques resulted in the greatest reduction in molar mass and hence in the best spectral resolution. Analysis of the NaCMC fragments following ultrasonic and/or endoglucanase degradation also reveals another interesting experimental finding. It appears that ultrasonic degradation is favored at unsubstituted areas near the center of the chain. These methods were compared with the following already familiar techniques of analysis: titrimetric techniques; 13 C and 1 H NMR spectroscopy as well as HPLC on completely hydrolysed solutions (hydrolysis with perchloric acid, trifluoroacetic acid and sulfuric acid). All of the methods characterize the samples as a series with increasing DS, the values of which range from 0.9 to 2.4. Methods that permit analysis of the partial degree of substitution produced the distribution x 2 A x6 A x3. Therefore, they are in principle suited for determining the functionalization pattern of the NaCMC samples relative to one another. The most suitable method can therefore be selected according to the objectives and the apparatus available. However, the measured values do exhibit considerable spread, variances of approx. 20%, thus, place restrictions on using the values of DS or xi in absolute comparisons beyond these methods.

Structure-property relationships in extruded starch, 1 : Supermolecular structure of pea amylose and extruded pea amylose

Separated amyloses with different molecular weight distributions were obtained enzymatically from wrinkled pea starch and processed in a multi-zone twin-screw extruder. The crystalline polymorphs, crystanllinity and crystallite dimensions of amylose (unbranched molecular starch component) and films extruded from it were investigated by wide-angle X-ray scattering. The starting amylose materials exhibit a crystalline V A structure with rather large crystallites (9-25nm) and a degree of crystallinity ranging between 30 and 40%, depending on the history of the amylose sample. The extruded films, on the other hand, recrystallized in the B-type with a slightly higher degree of crystallinity and significantly smaller crystallite dimensions (3-7 nm). In one case, V H -type crystals were observed. The mechanical properties of the extruded materials were determined in tensile tests. The amylose with the highest molar mass produces films with the highest mechanical performance. As compared with cellulose or synthetic polymer films, the mechanical properties of the amylose films appear to be fundamentally limited by the lack of preferred molecular orientation.

The composition of alkali cellulose: a new concept

Abstract A concept of reacting structural fractions is presented to discuss NaOH- and H2O-sorption of cellulose up to a lye concentration of 18% NaOH. The reacting structural fraction has been estimated by wide-angle X-ray scattering combined with a consistent application of a two-phase model (crystalline-non-crystalline) to the cellulose supermolecular structure. As a result, crystalline Na-cellulose I is characterized by an invariable composition definitely below 1 mol NaOH per mole of anhydroglucose units (AGU), whereas non-crystalline regions show a variable composition giving a saturation value of 2 mol NaOH per mole AGU. The swelling maximum of cellulose is determined mainly by the course of water-sorption in the non-crystalline regions.

Supermolecular structure and orientation of blown cellulosic films

N-Methylmorpholine-N-oxide (NMMO) technology provides new possibilities for shaping fibers and films from cellulose. We discuss a blow-extrusion technique can be applied to a cellulose-amine oxide ...

Synthesis of thermoplastic starch mixed esters catalyzed by the in situ generation of imidazolium salts

The concept of using a starch mixed ester to avoid brittleness in starch esters is promising. This paper will present new economical synthesis methods as well as the resulting mechanical properties of different starch mixed esters after thermoplastic processing. The use of imidazole derivatives as precursors to imidazolium salts, also known as ionic liquids, is shown to catalyze the esterification of starch. This simple synthesis pathway allows varying the mechanical properties in starch mixed esters using the substitution pattern. Not only the mechanical properties are unique in comparison of established starch-based materials, but also the water uptake in the resulting material is lower. It can be assumed that the properties of standard plastics are closely matched by these starch mixed esters. 13C NMR spectroscopy, dynamic vapor sorption measurement and tensile tests are applied to examine the noted issues.

Chain conformation of polyacrylonitrile: a comparison of model scattering and radial distribution functions with experimental wide-angle X-ray scattering results

Abstract Scattering and radial distribution functions were obtained for commercial polyacrylonitrile homopolymer in the solid state using wide-angle X-ray scattering. For three kinds of single chains with increasing conformational flexibility, namely (α) the planar zigzag chain, (β) a PCILO (perturbed configuration interaction with localized orbitals) chain based on quantum-chemical conformational energy calculations with the PCILO method and (γ) the restricted-rotation chain, model functions in real and reciprocal space have been calculated and compared with the experimental curves. While (α) can be ruled out, the experimental findings are intermediate between (β) and (γ) with a tendency to (γ). This suggests that energetically favourable single-chain conformations are somewhat distorted by interchain interactions.