Electrospinning short polymer micro-fibres with average aspect ratios in the range of 10-200

Ultra fine short fibres have a variety of applications. Short aligned fibres or a mixture of short and long fibres can reinforce brittle materials, alter the appearance, texture and durability of synthetic fibres, and adjust the strength, toughness and stiffness of a composite material. Among electrospun products, short fibres are usually produced by secondary processing of continuous as-spun fibres. However, this is not entirely straightforward or cost-effective due to the efficiency of the secondary process and the relatively low tensile strength of the electrospun ultrafine fibres. Besides, sub-micrometre size fibres with an average aspect ratio (AR) < 200 have not been directly produced without further processing by changing collector geometry in electrospinning. Using a model polymer, polymethylsilsesquioxane (PMSQ), short micro-fibres with 10 < AR < 200 were electrospun directly in this work, i.e. without the need for a secondary process. The AR and particularly fibre length were shown to be strongly influenced by the solvent system used for electrospinning and the molecular weight ((M) over bar (w)) of the polymer. When using PMSQ1 ((M) over bar (w) = 7500) in methanol instead of acetone, short fibres with AR < 200 were produced instead of continuous fibres. Moreover, when <(M)over bar>(w) of the polymer was decreased from 7500 (PMSQ1) to 4300 (PMSQ2), with all other conditions kept constant, significant reduction in the AR of the as-spun fibres was observed. Short fibres with average AR of 15 were produced from PMSQ2 solution in 3:2 v/v dimethylsulphoxide:2-nitropropane. The average AR of short fibres spun from PMSQ2 solution in 2:3 v/v methanol:propanol was 31. Also PMSQ1 in both of the above-mentioned binary solvent systems produced long continuous fibres with AR > 3000 under the same spinning conditions.