Civil Engineering Reference
In-Depth Information
Wood and agro-based resources
Mechanical
Chemical
Enzymatic
Combined
Pulping
Chemical
Size reduction
Cellulose
Nano-cellulose
Mechanical
Synthesis
Tunicates/Amoeba
Bacteria
Fungi
Animals ans microorganisms
Figure 9.2
Cellulose and Nanocellulose sources and isolation methods.
lignocellulosic biomass, such as crushing, grinding, steam explosion and irradiation,
have been proven to be ef ective in creating accessibility to chemicals and enzymes.
9.1.2.1
Cellulose Isolation, Purii cation and Preparation Methods
9.1.2.1.1 Isolation Methods or Pulping Processes
h e extraction of cellulose microi brils from the wood matrix can be done in three dif-
ferent ways: mechanically, chemically or enzymatically. h is process is referred to as
pulping, which derives from the paper making industry. Mechanical methods are
energy consuming, usually demanding high levels of pressure or kinetic energy. h e
product obtained by mechanical pulping has the same composition as the original feed-
ing. Chemical pulping involves several agents aimed at dissolving the lignin-hemicel-
lulose matrix that surrounds the cellulose i bers. Biological or enzymatic pulping relies
on the ability of certain microorganisms and their secreted enzymes (i.e., xylanase) to
directly depolymerize hemicellulose and attack the lignin/cellulose interface. Each of
the presented methods has its own advantages and disadvantages. For that reason, it is
not uncommon to i nd reports of studies combining mechanical and chemical pulping
processes in order to achieve higher yields of cellulose with lower energy consumption
and a reduced use of chemical agents.
9.1.2.1.2 Mechanical Pulping Methods
Dif erent intensive mechanical processes have been used to extract cellulose i brils
from diverse cellulose sources. h e main mechanical methods include grinders/rei ners
[24-27], cryocrushing [28-32], and high-intensity ultrasonic treatments [33]. Ground
wood pulp is produced by pressing round wood logs against a rotating cylinder made
of sandstone, scraping the i bers of . Dry grinding increases biomass reactivity without
any el uent production. However, energy consumption is held to be the limiting fac-
tor for applying biomass i ne grinding in industry [34]. Another type of mechanical
pulping is referred to as rei ner pulping and is obtained by feeding wood chips into the
center of rotating, rei ning discs in the presence of water spray [35]. h is mechanical
treatment produces irreversible changes in the i bers, increasing their bonding poten-
tial by modii cation of their morphology and size. Finally, another mechanical pulping
