No abstract

Highly porous cellulose was formed by gelation of cellulose carbamate solutions in caustic soda. Two methods for gel preparation were optimized for the formation of beads and bulky materials – the chemical precipitation from dilute sulfuric acid and the thermal gelation by annealing at elevated temperatures. Various methods were used for characterizing of the pores of low density materials: scanning electron microscopy, small angle X‐ray scattering, mercury intrusion and nitrogen sorption. These methods were optimized and used for characterizing the complete pore system from micro to macro pores. The effects of different preparation (cellulose carbamate concentration in caustic soda) and processing (precipitation, drying and pyrolysis) on the pore structure were studied by the set of complementary methods. Aerocell samples with a minimum density of 0.06 g/cm3 were prepared from cellulose carbamate. They are characterized by a broad pore size distribution ranging from 0.5 nm to 1 mm, specific internal surfaces of up to 660 m2/g and total pore volumes of up to 18 cm3/g.

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

Summary: Bio‐based nanocomposites were manufactured by melt intercalation of nanoclays and cellulose acetate (CA) with and without plasticizer. Glycerol triacetate (triacetin) as plasticizer up to 30 mass%, and different types of organo‐modified and unmodified montmorillonites (MMTs) as filler were used. X‐ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM), were used to study clay dispersion, intercalation/exfoliation, and structure of the composites. XRD and TEM revealed very good dispersion and exfoliation of modified clay throughout the CA matrix. While for unmodified clay agglomeration and poor dispersion but an intercalated structure was observed. The mechanical properties of injection moulded test bars were determined by a tensile experiment giving tensile strength, Young's modulus and elongation at break. Adding plasticizer facilitated the processing and up to 20 mass%, increased the tensile strength, Young's modulus and elongation at break as well. Higher amount of plasticizer diminished the tensile properties except elongation showing a slight increase. In all plasticized composites, organo‐modified clay improved the tensile strength and at the same time, young's modulus and elongation almost remained constant. On the other hand, plasticized CA compounded with unmodified clay revealed lower properties. In a particular case, compounding of unplasticized CA with unmodified clay resulted in superior mechanical properties with a novel structure. So that, in optimum percentage –5 mass%‐ of unmodified clay, tensile strength and young's modulus increased significantly by 335% and 100%, to 178 MPa and 8.4 GPa, respectively. This is a dramatic improvement in strength and stiffness of CA. Adding organo‐modified clay resulted in a little improvement in tensile properties. SEM pictures of the optimum composite showed a core/shell structure with high orientation in the shell part. It is supposed that this behaviour is caused by the interaction between CA hydroxyl groups and free cations existing in the galleries of unmodified clay.