The glass transition and crystallization of ball milled cellulose

Abstract

Samples of ball milled cellulose were prepared by ball milling pulps from eucalyptus and softwood (spruce/pine). Water sorption isotherms were obtained by both dynamic vapor sorption and equilibration over saturated salt solutions, in the water content range of 5-42% db (db = dry basis; water as a % age of total solids). Dynamic mechanical analysis using a pocket technique showed a water content dependent thermal transition occurring at the same temperature for the two pulp samples, which was interpreted as a glass transition. Fitting the data to a Couchman-Karasz relationship predicted a value for T g of the dry cellulose of approximately 478 K, which was similar to values previously reported for other dry polysaccharides. No clear glass transition could be observed calorimetrically, although an endotherm at approximately 333 K was measured, which in polymers is normally attributed to enthalpic relaxation, however the lack of dependence of this endotherm on water content suggests that the melting of some weak associations, such as residual hydrogen bonds, could be a more credible explanation. An exotherm was also observed on heating, which was dependent on water content and which was attributed to partial crystallization of the cellulose. This was confirmed by Wide angle X-ray diffraction and cross polarization magic angle spinning 13C NMR (CPMAS NMR). The recrystallisation was predominantly to form I of cellulose. This was thought to be caused by a small amount of residual form I (probably less than 5%) acting as a template for the crystallizing material. Differential scanning calorimetry reheat curves showed the appearance of freezable water for water contents higher than 20%, as a result of a transfer of water to the amorphous phase following crystallization. The increase in cellulose rigidity following crystallization was also confirmed by CPMAS NMR relaxation. Low resolution proton NMR T 2 relaxation suggested the presence of proton water/cellulose exchange, which was active at water contents of 20% and above

A novel approach for extracting cellulose nanofibers from lignocellulosic biomass by ball milling combined with chemical treatment

“…ball milling treatments. This result is in contrast to those reported in some of the literatures 31,32,48 where the authors report that the celluloses converted into amorphous celluloses or cellulose II by ball milling technique. Ciolacu et al reported that the ball milled cellulose regenerated in ethanol does show any peak corresponding to planes 101, 101, and 002.…”

Extraction of Lignin from a Coproduct of the Cellulosic Ethanol Industry and Its Thermal Characterization

“…8. Paes et al 2010). The soluble sample only shows a broad peak, which is characteristic of amorphous lignin.…”

“…Ash content was measured following the NREL method (Sluiter et al 2005), and it was 2.13%. The hydrolysis lignin was dried in an oven at 105 °C for 12 h. The material was ground in a planetary ball mill (Retsch PM100) at 200 rpm for 24 h. This rate is low enough to preserve the crystallinity of cellulose (Paes et al 2010), which might be present in the sample as an impurity. The milled lignin was sieved to obtain two samples with different particle size.…”

Effect Of High Pressure Homogenization (HPH) On The Rheological Properties Of Pineapple Leaf Cellulose/[BMIM]Cl Solution

“…Nanocellulose was prepared through ball-milling process [5] and hydrolysis method in previous studies [6]. However, mechanical method has the shortcoming of high energy consumption and low production efficiency [7].…”