A Novel Method to Deliver Natural Fibre for Mechanical Reinforcement of Polyurethane Foam

Abstract

Introducing glass fibre to polyurethane foams increases the foam stiffness without raising the isocyanate content. This allows glass fibre reinforced polyurethane foams to be used in structural applications. Glass fibre reinforced polyurethane foams can be manufactured on a large scale using a chopper gun spray system. The glass fibre is commonly supplied as a roving (long strands of fibre wound into a spool) and the chopper gun breaks the roving into equal length pieces, which delivers a stream of glass fibre at a constant mass flow rate. Residual natural fibre is cost-effective, abundant and renewable making it an ideal candidate to replace non-renewable glass fibre in reinforcing polyurethane foam. However, residual natural fibre are often supplied as loose tufts and require multiple steps to be made into roving. In this study, a novel concept was developed that can meter natural fibre at a constant mass flow rate. The concept has the potential for developing natural fibre reinforced polyurethane foams on a large scale, with uniform fibre dispersion and high fibre volume fractions. The concept is verified through mathematical simulations and a prototype.

Preliminary Design and Experimental Investigation of a Novel Pneumatic Conveying Method to Disperse Natural Fibers in Thermoset Polymers

“…In case of natural fiber dispensers, the size of discharge is limited by the amount of fibers needed to make up a certain volume fraction of composites. In this design, the application of a metering system developed previously by Hussain and Kortschot [ 17 ] has been evaluated. Using this metering unit introduces two challenges.…”

“…At the outlet to the hopper, a roll nip consisting of two open hand mixer beaters were turned at low speed to capture the fibres coming through the roll nip at something approaching consistent mass flow. In the prototype, the methods developed by Hussein and Kortschot [ 17 ] to deliver truly constant mass flow rate were not employed.…”

“…In order to incorporate short natural fibers into a composite manufacturing process such as spray lay-up without first creating a roving, a feeding system that can both feed and meter the fibers reliably is needed. Hussain and Kortschot introduced a novel design for metering short form natural fibers with constant mass flow rates [ 17 ]. Their design consisted of a constant pressure roll nip in which the feeding speed was controlled to be inversely proportional to the nip gap.…”

Significance of Ultrasonic Cavitation Field Distribution in Microcellular Foaming of Polymers

“…These conditions favor microcellular nucleation and consequently, a large number of cells get nucleated at this particular radial distance. Further in Figure 5b, it can be seen that the cell density enhances from order of 10 9 cells/ cm 3 to 10 13 cells/cm 3 when the radial distance gets increased from 35 mm to 70 m. Higher cell density offers numerous benefits such as improved specific mechanical properties [16,17], due to which numerous researchers have been attracted towards this captivating research field [18][19][20][21][22][23]. Figure 5c depicts the influence of ultrasonic wave field distribution along the radial direction on the cell size in the eventual foam developed.…”

“…And conversely, at +35 mm and -35 mm distances from center, there occurs node, that is, location with very less cavitation events. The basic mechanism of interaction between ultrasound waves and microcellular foaming has not been fully explored as yet [15,20] and there happens to be a huge development in this particular field of research over the years. But, from this research work, it is very clear that the ultrasound field distribution plays a very significant role in nucleation phenomenon.…”