DECOUPLING FIBRE DIAMETER FROM FIBRE ORIENTATION: COLLECTOR ROTATION SPEED AS AN INDEPENDENT CONTROL VARIABLE IN ELECTROSPINNING, VALIDATED AGAINST KRENCHEL'S ORIENTATION MODEL

Abstract

Collector rotation speed is widely used to align electrospun fibres, but whether it also alters fibre diameter is usually judged from mean values without testing the difference statistically, so that the two effects remain conflated. This work separates them. Webs were produced on a laboratory system at collector speeds of 200, 1100 and 2000 min⁻¹, corresponding to peripheral velocities of 1.05, 5.76 and 10.47 m s⁻¹ on a 100 mm drum, with all other parameters held constant. Fibre diameters were measured on 100 fibres per specimen and inclination angles on 250–494 fibres per specimen. The mean diameters are 180.11, 175.72 and 182.23 nm; their 95% confidence intervals overlap completely and all pairwise comparisons are non-significant (p = 0.33–0.78), establishing that collector speed does not affect fibre diameter. Over the same range the mean inclination angle falls from 46.3° to 23.7° with high significance, the angular distribution changes from uniform to approximately exponential, and the fraction of fibres deviating by less than 20° from the machine direction rises from 22% to 65%. The breaking load increases from 51.6 to 138.4 cN, a factor of 2.68. Krenchel's orientation efficiency factor, evaluated by integrating the fourth moment of the direction cosine over the measured angular distributions rather than assuming a limiting case, rises from 0.375 to 0.686 and predicts a strength ratio of only 1.83; the ratio of observed to predicted strengthening is 1.46 at 1100 min⁻¹ and 1.47 at 2000 min⁻¹. The constancy of this excess factor identifies a second, multiplicative strengthening mechanism, attributed to mechanical post-drawing of the fibre by the fast-moving collector, which accounts for the remaining third of the effect. The relative elongation at break falls from 27.00% to 16.31%. Collector speed is therefore established as an independent control variable that governs fibre placement without affecting fibre geometry, and the strength gain is attributed specifically to orientation efficiency rather than to any change in the fibres themselves.