Optimisation of Ball Milling Parameters for Refinement of Waste Jute Fibres to Nano/Micro Scale in Dry Conditions

Abstract

Abstract Inpresentstudy,optimizationoffouroperatingparametersofhighenergyplanetaryballmill(i.e.millingtime,millingspeed,balltomaterialratioandballsize)ondrygrindingofjutefibrewastewasperformed.Athree-levelBox-Behnkendesigncombiningaresponsesurfacemethodologywasemployedtostudytheresponseintermsofparticle size and % sticking of material to mill. Analysis of variance of milling parameters showed coefficient ofdetermination of 0.927 and 0.903 for particle size and material sticking respectively. The model equations weresubsequently optimized using the canonical analysis with the help of SYSTAT software to minimize the particlesizeandmaterialsticking.Theoptimumconditionswerefound12mmforballsize, 47minformillingtime, 9forballtomaterialratioand870rpmfor milling speed. KeyWords :Jutefibrewaste,Highenergy planetary ball milling, Particle size distribution, Material sticking,Box-Behnkendesign 1. Introduction Thenanofibrilsornanocrystalsofcellulosehavebeenextractedinpreviousresearchworkfromseveralnaturalsourceslikecotton[1],sisal[2],jute[3-5],soybean[6],wheatstrawandsoyhulls[7],hemp[8],etcbymechanical[9-10],chemical[2],enzyme[11]orcombination of techniques [12]. The chemical method employsstrongacidhydrolysistreatmenttoremovetheamorphousregionsof cellulose fibres and separate nanocrystalline cellulose (NCC)whereas mechanical method involves high-pressure shear refiningtreatment to produce nanofibrillar cellulose (NFC) together withcrystalline and amorphous regions [13]. However the use of acidtreatmentovermechanicaltreatmentwasfoundtohavenumberofdrawbacks, such as longer time of separation of nanocrystals,potential degradation of cellulose, corrosivity, and environmentalincompatibility[13-14].Thereforesomeresearchersemployedthealternative route of mechanical treatment through various wayslike grinding [13, 15,16], high pressure homogenizing [16],cryocrushing [6, 8], ultrasonic treatment [12, 14], etc to extractNFC rather than NCC. This paper deals with preparation ofnanocellulose from waste jute fibres in the textile industry bysimple, quick and environment friendly ball milling process. Themain objective of the present study was to utilise the short fibreswhich could not be spun into yarn, for reinforcement inbiodegradable composite applications.Ballmillingprocessisamechanicalprocesswhichreliesontheenergyreleasedatthepointofcollisionbetweenballsaswellasonthe high grinding energy created by friction of balls on the wall[17]. When the mill rotates, balls are picked up by the mill walland rotate around the wall due to centrifugal force leading togrinding of material due to frictional effect. On the other handthere is also reverse rotation of disc with respect to mill whichappliescentrifugalforceinoppositedirectionleadingtotransitionof balls on opposite walls of mill giving impact effect.Basedonourpreviousresearch[13,15,18],duringdrygrindingofjutefibres,significantincreaseintemperatureduetoimpactofballs resulted in sticking of material on the milling media.Consequentlythedepositedmassofmaterialsloweddowntherateof refinement of particles and provided wider size distribution. Inorder to avoid increase in temperature and to increase millingefficiency, ball milling parameters for dry pulverisation of jutefibres must be optimised. The objective of present study is tooptimize the four milling parameters i.e. milling time (MT),millingspeed(MS),balltomaterialratio(BMR)andballsize(BS)with use of Box-Behnken design and response surfacemethodology.