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|Type:||Artigo de periódico|
|Title:||Molecular Assembly In Kraft Pulping Of Eucalyptus [organização Molecular Na Polpação Kraft De Eucalipto]|
|Abstract:||Kraft pulp is a nanostructured material which is produced under chemical degradation conditions where less ordered components are removed and new (supra)molecularly organized systems are created. The effects of kraft pulping on the chemistry of eucalyptus pulp were investigated here by using X-ray Diffraction (XRD), Cross Polarization Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance (CP/MAS 13CNMR) and Near Infrared Spectrometry (NIR) combined with Principal Component Analysis (PCA). Cellulose, hemicellitloses, uronic acids, lignin and extractive amounts in pulp were determined using either chromatographic or different specific methods. The elastic modulus and tensile strength of pulp hand sheets and fiber morphological parameters such as length, width, cell wall thickness and lumen diameter were also measured. Pulping experiments were conducted varying the active alkali range while temperature, sulfidity, heating rate and liquor-to-wood ratio were kept constant. Two molecular assemblies were suggested and identified as function of active alkali used in pulping. Each molecular assembly had characteristic degree of crystallinity and affected the elastic modulus and tensile strength of the hand sheets. A transition point between the two assemblies was also identified and ascribed to hydrogen bond intermolecular interactions due to removal of lignin, hemicelluloses and bounded water. A mechanism of assembly of cellulose nanofibrils, driven by freeenergy of interaction, was proposed to affect the fibre morphology, decrease fibre wall flexibility and lower inter-fibre bonds. Our results also suggested that the variations in alkali charge usually present in industrial digesters can cause the formation of different molecular assemblies in a very sensitive limit. As a consequence, impacts on mechanical andphysicochemical properties of fibres are expected.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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