Composites with surface-grafted cellulose nanocrystals (CNC)

Hydroxyazetidinium salts were used to surface-modify cellulose nanocrystals (CNC) by grafting the salts onto the sulphate ester groups on the CNC surfaces. The grafting was confirmed by ζ-potential measurements and by the thermal degradation behaviour of the modified CNC. The thermal stability (onset of degradation) of the CNC was improved by the surface modification (almost 100\ua0\ub0C). Composites containing surface-modified or unmodified CNC (0.1, 1.0 and 10\ua0wt%) with an ethylene-based copolymer as matrix were produced by compression moulding. The thermal stability of the composites was not, however, markedly improved by the surface grafting onto the CNC. It is suggested that this is due to a degrafting mechanism, associated with the alkaline character of the system, taking place at high temperatures. Model experiments indicated, however, that this did not occur at the conditions under which the composites were produced. Furthermore, in the case of a reference based on pH-neutralised polymeric system and modified CNC, an upward shift in the onset of thermal degradation of the composite was observed. The addition of the CNC to the polymer matrix had a strong influence of the mechanical performance. For example, the tensile modulus increased approximately three times for some systems when adding 10\ua0wt% CNC. The surface grafting of the hydroxyazetidinium salts appeared mainly to affect, in a positive sense, the yield behaviour and ductility of the composites. The results of the mechanical testing are discussed in terms of interactions between the grafted units and the matrix material and between the grafted groups

Composites with surface-grafted cellulose nanocrystals (CNC)

Hydroxyazetidinium salts were used to surface-modify cellulose nanocrystals (CNC) by grafting the salts onto the sulphate ester groups on the CNC surfaces. The grafting was confirmed by ζ-potential measurements and by the thermal degradation behaviour of the modified CNC. The thermal stability (onset of degradation) of the CNC was improved by the surface modification (almost 100\ua0\ub0C). Composites containing surface-modified or unmodified CNC (0.1, 1.0 and 10\ua0wt%) with an ethylene-based copolymer as matrix were produced by compression moulding. The thermal stability of the composites was not, however, markedly improved by the surface grafting onto the CNC. It is suggested that this is due to a degrafting mechanism, associated with the alkaline character of the system, taking place at high temperatures. Model experiments indicated, however, that this did not occur at the conditions under which the composites were produced. Furthermore, in the case of a reference based on pH-neutralised polymeric system and modified CNC, an upward shift in the onset of thermal degradation of the composite was observed. The addition of the CNC to the polymer matrix had a strong influence of the mechanical performance. For example, the tensile modulus increased approximately three times for some systems when adding 10\ua0wt% CNC. The surface grafting of the hydroxyazetidinium salts appeared mainly to affect, in a positive sense, the yield behaviour and ductility of the composites. The results of the mechanical testing are discussed in terms of interactions between the grafted units and the matrix material and between the grafted groups

The structural correlates of the rabbit light chain b allotypes: Sequence studies of b5 and b6 chains

Rabbit kappa light chains of allotype b5 and b6 were prepared from antibodies of restricted heterogeneity made by animals hyperimmunized with, respectively, strain III and strain II pneumococcal vaccines. The amino-acid sequence of several tryptic peptides were determined. The variable region fragments of the b5 and b6 chains appear to be quite similar to the corresponding fragments of b4 and b9 chains, albeit some residues seem to be allotype associated. In contrast the chains of different allotypes vary right from the start of the constant region in a number of positions, suggesting that b allotypes correlate with amino-acid substitutions in this region. The number of substitutions between the b5 and b6 and the previously determined b4 and b9 constant regions sequences ranges from 20 to 35%. Serological studies suggest that Leporidae b allotypes diverged no more than 2 × 106 years ago. By this time only 1% of the substitutions could be generated by 'conventional evolution'. Duplication and mutation of the individual CK genes could account for the high level of divergence observed. The data reported here support the notion that the structural genes encoding the light chain constant regions of the various b allotypes coexist on the same chromosome and that the allelism is controlled by a regulatory mechanism. © 1979.SCOPUS: ar.jinfo:eu-repo/semantics/publishe