A selection criteria for tackifier addition to paraffin wax based hybrid rocket fuels

Abstract

Physical properties of paraffin wax/tackifier blends are investigated in order to provide a material based selection criteria. Within a case-study framework, 4 different tackifier resin types namely an aromatic C9, an aliphatic C5, a gum rosin ester resin, and a styrenated terpene resin, are investigated. Tackifiers are classified with respect to their C/H ratio (aromaticity), polarity, molecular weights, densities and melting characteristics. Each tackifier candidate is then melt compounded with paraffin wax at four different weight fractions (5,10,15 and 20 wt.%). In liquid (melt) phase, kinematic viscosity of samples are measured. Blend fusion is monitored by differential scanning calorimetry and relative crystallinity measurements. Melt compounds are then cast into identical moulds while controlling sample and melt blend temperatures in order to obtain mechanical test specimens For mechanical characterization, three point bending tests are chosen for their relatively small and easy to cast specimen dimensions., Flexural strain and flexural stress characteristics are reported and failure is evaluated with fracture surface analysis. A material based ranking is then performed in order to find and identify the best candidate suitable for hybrid rocket fuel grain application where adjustable melt viscosity,improved strain bearing capability and characteristic velocity (c*) are typically required. Results suggested that tackifier addition to PW (Paraffin Wax) has very small effect on melt viscosity and characteristic velocities of fuel grains whereas significant improvements in mechanical performance are recorded up to 400% strain bearing capability that may improve their in-service performance and avoid in-operation fuel breakage with no viscosity and density cost.