The effect of low frequency ultrasound on the production and properties of nanocrystalline cellulose suspensions and films

Abstract

Suspension of nanocrystalline cellulose (NCC) produced from bleached cotton by controlled sulphuric acid hydrolysis was treated with low frequency ultrasound at 20 kHz and 60% amplitude for 0, 1, 2, 5 and 10 min and the effects of sonication on the properties of both the cellulose nanocrystals and their aqueous suspensions were investigated. Furthermore, a series of nanocellulose films were manufactured from the suspensions that were sonicated for different periods of time and tested. Laser diffraction analysis and transmission electron microscopy proved that sonication not only disintegrated the large NCC aggregates (Dv50 14.7 μm) to individual nanowhiskers with an average length and width of 171 ± 57 and 17 ± 4 nm, respectively, but also degraded the nanocrystals and yielded shorter and thinner particles (118 ± 45 and 13 ± 3 nm, respectively) at 10-min sonication. The ultrasound-assisted disintegration to nano-sized cellulose whiskers decreased the optical haze of suspensions from 98.4% to 52.8% with increasing time from 0 to 10 min, respectively. Sonication of the suspensions significantly contributed to the preparation of films with low haze (high transparency) and excellent tensile properties. With the increasing duration of sonication, the haze decreased and the tensile strength rose gradually. Irrespectively of sonication, however, all films had an outstanding oxygen transmission rate in a range of 5.5-6.9 cm(3)/m(2)day, and a poor thermal stability.

Cellulose nanocrystal/amino-aldehyde biocomposite films

“…The fabrics were ground using a ball mill (Mixer Mill MM400, Retsch GmBH, Germany), then 10.0 g of the fine powders were hydrolyzed with 64 wt % sulphuric acid (acid to fibre ratio: 8.75 ml/g) at 45 °C for 25 min (Hamad & Hu, 2010). Subsequent to the post-treatments (washing, centrifugation and dialysis), the total volume of the stock suspensions was subjected to ultrasonication for 10 min using an ultrasonic horn type reactor (Vibra-Cell VCX500, Sonics & Materials, Inc. CT, USA) at 60 % amplitude with a driving frequency of 20 kHz (Csiszar, Kalic, Kobol, & Ferreira, 2016). The dry solid content of the suspension was determined by drying (at 80 C) and weighing 2 ml of the suspension.…”

Cellulose Nanocrystals: Production, Functionalization and Advanced Applications

“…However, enzymatic hydrolysis is often not desirable due to the extended time that is required for the process to properly occur. In addition, the use of mechanical energy (such as pressurised homogenisation) is often applied during or after the hydrolysis to help further break down the extracted crystalline regions into the individual whiskers [43].…”

“…The application of sonication post hydrolysis has been explored [43,52] and was found to be helpful to further refine the produced CNC by breaking down the large crystalline regions into individual nanowhiskers and creating smaller crystals with improved aspect ratios. This additional sonication was done at relatively low frequencies of about 20 kHz with the longest application being 10 minutes [43].…”

Kutatómunka a BME Fizikai Kémia és Anyagtudományi Tanszékén

“…41 A keményítõ mellett még cellulóz alapú polimerekkel elsõsorban cellulóz nanokristályok funkcionális tulajdonságaival foglalkozunk és a nanocellulóz szuszpenziók egyedi jellegzetességeit tanulmányozzuk. 42 A hosszú évtizedek óta folytatott témák tapasztalatait természetesen újabb területeken is alkalmazzuk, hiszen a polimerek egyre inkább tért hódítanak az orvosi és biológiai alkalmazások területén is. A hagyományos transzplantációs eljárások hátrányaira például a jövõben a mesterséges szövettenyésztés nyújthat megoldást.…”