Civil Engineering Reference
In-Depth Information
modii cation and selection of proper processing techniques were found to improve the
composite properties.
Microi brillated celluloses were i rst isolated by Turbak and coworkers in the 80s.
Over the last three decades there have been many reports on dif erent methods of
extraction and their ef ect on i ber property. Selective degradation of i bers results
in the formation of micro/nanoi bers and their properties depending on their ori-
gin, processing techniques adopted, etc. Dif erent methods such as physical, chemi-
cal, mechanical and a combination of these methods have been used to extract micro/
nanoi bers from various sources of natural i bers. h e main chemical methods reported
are acid hydrolysis, alkali hydrolysis, use of organic solvents and ionic liquid treatment.
Chemical treatments with alkaline solutions at dif erent concentrations were reported
for the isolation of microi brils from sugar beet [36], potato tuber cell [37], soya bean
[33] lemon and maize [38]. Liu and Hu [39] extracted cellulose from bamboo i bers by
using sodium hydroxide. h e ef ect of dif erent chemicals and theirconcentrations and
treatment times on the properties of i bers have been reported by many researchers.
Eromosele
et al.
[40] treated four dif erent types of natural i bers such as roselle, okra,
baobab and kenaf with four dif erent percentages of sodium hydroxide. h e ef ect of
alkaline treatment on structural and morphological features of CMF obtained from
banana rachis was investigated by Zuluaga
et al.
[41]. He reported that potassium
hydroxide showed better treatment performance compared to other alkaline treatment.
Cellulose microi bers obtained by strong acid hydrolysis of bagasse and rice straw were
reported by Ambuji and Dhake [42], proving that lignocellulose waste materials could
also be converted into valuable microcrystalline cellulose. Another group of research-
ers extracted cellulose microi bers from bagasse in three distinct steps: conventional
pulping, mechanical separation and acid hydrolysis [43]. h e SEM and AFM stud-
ies indicated that the particle size of CMF varied between 200 nm to a few microns
depending on the type of treatment methods adopted.
h e generally adopted mechanical methods of extraction are super-grinder treat-
ment [44-47] , microl uidizer [48], high-pressure homogenizer treatment [36, 47, 49,
50], cryocrushing [51-53] and simple crushing [54]. Microi brillated celluloses (MFC)
from wheat straw and soy hulls have been extracted by Alemdar and Sain using cryo-
crushing [53] . h e obtained microi brillated celluloses have a diameter in the range
of 30-40 μm. Iwamoto
et al.
[55] obtained i brillated celluloses from
Pinus radiata
by
passing two or three times through the grinder. Spence
et al.
[56] made a compara-
tive study on the energy consumed and physical properties of MFC obtained by dif-
ferent mechanical treatments such as homogenizer, microl uidzer and grinder from
unbleached and bleached hardwood krat pulps. h e report shows that the homog-
enizer process is the best mechanical treatment to extract MFC with less energy con-
sumption and high surface area.
Physical methods such as ultrasonication [57, 58], microwave [59, 60] and gamma
radiation have also been reported. Steam explosion is reported to be an excellent alter-
native to the conventional methods such as CMP (chemical mechanical pulps) and
chemical thermomechanical processes. h e principle of steam explosion technique
are that the steam under pressure with increased temperature penetrates through the
space between the i bers, thus the middle lamella and the i ber adherent substance
become sot and water soluble [61, 62]. Marchessault [63] described the steam explosion
