Abstract
This study aimed to assess the effect of mechanical pretreatment on bleached eucalyptus kraft pulp fibers and investigate the influence of reaction time and temperature on the properties and yield of nanocrystalline cellulose (NCC) and microcrystalline cellulose (MCC). Two types of pulps were hydrolyzed, pulp 1 (control, whole fibers) and pulp 2 (mechanically pretreated, disintegrated fibers). NCC and MCC particles were obtained by sulfuric acid hydrolysis (60% w/w) of eucalyptus pulps under different conditions of time (30–120 min) and temperature (45–55 °C). Physical treatment of kraft pulp facilitated acid hydrolysis, resulting in higher NCC yields compared with no pretreatment. The morphologic properties and crystallinity index (CI) of NCC and MCC were little affected by pulp pretreatment. NCC particles obtained from pulps 1 and 2 were needle-shaped, with mean diameters of 6 and 4 nm, mean lengths of 154 and 130 nm, and CI of 74.6 and 76.8%, respectively. MCC particles obtained from pulps 1 and 2 were rod-shaped, with mean diameters of 2.4 and 1.4 µm, mean lengths of 37 and 22 µm, and CI of 73.1 and 74.5%, respectively. Pulps 1 and 2 and their respective NCC and MCC derivatives had a cellulose I crystalline structure.
Highlights
Nanocrystalline cellulose (NCC) particles, known as nanowhiskers, and microcrystalline cellulose (MCC) particles can be obtained by means of acidic hydrolysis of fibers
This study aimed to evaluate the effect of mechanical pretreatment on bleached eucalypt kraft pulp fibers and investigate the influence of reaction time and temperature on NCC and MCC yield
At 55 ◦ C, mass losses were even higher, with a mean of 37% in 60 min of reaction, 50% in 90 min, and 70% in 120 min. These findings indicate that hemicelluloses, amorphous cellulose regions, and most regions of crystalline cellulose were solubilized under severe time–temperature conditions
Summary
Nanocrystalline cellulose (NCC) particles, known as nanowhiskers, and microcrystalline cellulose (MCC) particles can be obtained by means of acidic hydrolysis of fibers. NCC exhibits low density, high degree of crystallinity, high stiffness [1,4], high modulus of elasticity [5], low thermal expansion coefficient [6], and high surface area for polymer and resin bonding [7,8,9,10]. Such properties make NCC promising for a wide range of applications with important commercial potential [11,12,13,14]. The properties of MCC are superior to those of native cellulose [15,16], explaining its wide use in chemical and pharmaceutical industries [17,18,19]
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