doctoralThesis
Desenvolvimento de bionanocompósitos: nano e microcristais de celulose com poli (álcool vinílico) e poli (ácido lático)
Fecha
2014-07-30Registro en:
ROCHA, Brismark Góes da. Desenvolvimento de bionanocompósitos: nano e microcristais de celulose com poli (álcool vinílico) e poli (ácido lático). 2014. 138f. Tese (Doutorado em Engenharia Mecânica) - Centro de Tecnologia, Universidade Federal do Rio Grande do Norte, Natal, 2014.
Autor
Rocha, Brismark Góes da
Resumen
This work has the main objective to obtain nano and microcrystals of cellulose, extracted from
the pineapple leaf fibres (PALF), as reinforcement for the manufacture of biocomposite films
with polymeric matrices of Poly(vinyl alcohol) (PVA) and Poly(lactic acid) (PLA). The
polymer matrices and the nano and microcrystals of cellulose were characterised by means of
TGA, FTIR and DSC. The analysis was performed on the pineapple leaves to identify the macro
and micronutrients. The fibers of the leaves of the pineapple were extracted in a desfibradeira
mechanical. The PALF extracted were washed to remove washable impurities and subsequently
treated with sodium hydroxide (NaOH) and sodium hypochlorite (NaClO) in the removal of
impurities, such as fat, grease, pectates, pectin and lignin. The processed PALF fibers were
hydrolysed in sulfuric acid (H2SO4) at a concentration of 13.5 %, to obtain nano and
microcrystals of cellulose. In the manufacture of biocomposite films, concentrations of
cellulose, 0 %, 1 %, 3 %, 6 %, 9% and 12% were used as reinforcement to the matrices of PVA
and PLA. The PVA was dissolved in distilled water at 80 ± 5 oC and the PLA was dissolved in
dichloromethane at room temperature. The manufacture of biocompósitos in the form of films
was carried out by "casting". Tests were carried out to study the water absorption by the films
and mechanical test of resistance to traction according to ASTM D638-10 with a velocity of 50
mm/min.. Chi-square statistical test was used to check for the existence of significant
differences in the level of 0.05: the lengths of the PALF, lengths of the nano and microcrystals
of cellulose and the procedures used for the filtration using filter syringe of 0.2 μm or filtration
and centrifugation. The hydrophilicity of biocompósitos was analysed by measuring the contact
angle and the thickness of biocompósitos were compared as well as the results of tests of
traction. Statistical T test - Student was also applied with the significance level (0.05). In
biodegradation, Sturm test of standard D5209 was used. Nano and microcrystals of cellulose
with lengths ranging from 7.33 nm to 186.17 nm were found. The PVA films showed average
thicknesses of 0.153 μm and PLA 0.210 μm. There is a strong linear correlation directly
proportional between the traction of the films of PVA and the concentration of cellulose in the
films (composite) (0,7336), while the thickness of the film was correlated in 0.1404. Nano and
microcrystals of cellulose and thickness together, correlated to 0.8740. While the correlation
between the cellulose content and tensile strength was weak and inversely proportional (-
0,0057) and thickness in -0.2602, totaling -0,2659 in PLA films. This can be attributed to the
nano and microcrystals of cellulose not fully adsorbed to the PLA matrix. In the comparison of the results of the traction of the two polymer matrices, the nano and microcrystals have helped
in reducing the traction of the films (composite) of PLA. There was still the degradation of the
film of PVA, within a period of 20 days, which was not seen in the PLA film, on the other hand,
the observations made in the literature, the average time to start the degradation is above 60
days. What can be said that the films are biodegradable composites, with hydrophilicity and the
nano and microcrystals of cellulose, contribute positively in the improvement of the results of
polymer matrices used.