Cellulose-reinforced composites: From micro-to nanoscale

Abstract

This paper present the most relevant advances in the fields of: i) cellulose fibres surface modification; ii) cellulose fibres-based composite materials; and iii) nanocomposites based on cellulose whiskers or starch plateletlike nanoparticles. The real breakthroughs achieved in the first topic concern the use of solvent-free grafting process (plasma) and the grafting of the matrix at the surface of cellulose fibres through isocyanate-mediated grafting or thanks to "click chemistry". Concerning the second topic, it is worth to mention that for some cellulose/matrix combination and in the presence of adequate aids or specific surface treatment, high performance composite materials could be obtained. Finally, nanocomposites allow using the semi-crystalline nature and hierarchical structure of lignocellulosic fibres and starch granules to more deeply achieve this goal profitably exploited by Mother Nature

Whiskers de fibra de sisal obtidos sob diferentes condições de hidrólise ácida: efeito do tempo e da temperatura de extração

“…Segundo Dong et al [11] uma hidrólise incompleta pode gerar whiskers mais largos e com baixa carga superficial. A hidrólise ácida destrói as regiões amorfas das fibras e promove a enxertia dos grupos sulfatos na superfície da celulose [5,18] . Estes possibilitam a formação de uma suspensão coloidal em meio aquoso neutro (pH entre 6,0 e 7,0) cuja estabilidade da mesma é devido à repulsão eletrostática entre as cargas negativas advindas dos grupos sulfatos incorporados na superfície da celulose [19] .…”

“…Os whiskers têm diferentes razões de aspecto (comprimento/diâmetro (L/D)) dependendo das condições de extração e da origem da celulose [4] . Apresentam-se na forma de finas hastes (acicular) e devido à sua alta área superficial e rigidez, apresentam grande potencial como reforço em matrizes poliméricas [2,5] . A fibra de sisal (Agave sisalana) tem uma produção anual de 4,5 milhões de toneladas e o Brasil é o maior produtor mundial (Li et al; Satyanarayana et al apud Siqueira et al) [6] .…”

Isolation of whiskers from natural sources and their dispersed in a non-aqueous medium

“…Sulfuric acid, sodium hydroxide and hydrogen peroxide were purchased from Lafan Química Fina, and dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were supplied by Nuclear (Brazil). Cellulose was purchased from Merck and lignin obtained by isolation from the raw materials (SCB and CCS) according to regulation TAPPI T222 om-88 [24] . All of the chemical reagents were used without further purification.…”

“…However, this restricts their use in the matrices of hydrophobic polymers due to difficulties related to their dispersion in these systems. Studies have been directed toward obtaining an adequate dispersion of whiskers in hydrophobic matrices, using approaches such as the addition of anionic surfactants or tert-butanol to the dispersing medium [19] , the use of a cationic surfactant [20] , the use of partially hydrolyzed poly(vinyl alcohol) [21] , surface functionalization of the whiskers [22][23][24] , the use of lyophilization and redispersion in a non-aqueous solvent. Of these proposed methods, the redispersion of the whiskers in non-aqueous solvents has proved to be a promising technique which allows homogeneous dispersion in hydrophobic polymers, it being necessary to assess the process conditions in relation to the polymer matrix.…”

Treatments of jute fibers aiming at improvement of fiber-phenolic matrix adhesion

“…Treatment of natural fibers with an alkaline solution (mercerization) is widely used. This treatment can increase the fiber surface roughness, separate the fiber bundles and remove cell wall components [1][2][3][4][5][6] . Usually, the wettability of the mercerized fibers is greater than that of unmodified fibers, thus improving strength of bonding between the fibers and the matrix [7] .…”