Fiber dispersion during compounding/injection molding of PP/kenaf composites: Flammability and mechanical properties

Published Date
Materials & Design
5 December 2015, Vol.86:500–507, doi:10.1016/j.matdes.2015.07.126

• Author 

• A.D.L. Subasinghe ^,
• R. Das
• D. Bhattacharyya

• Centre for Advanced Composite Materials, Department of Mechanical Engineering, The University of Auckland, New Zealand

Received 8 April 2015. Revised 21 July 2015. Accepted 23 July 2015. Available online 29 July 2015.

Highlights

• •
  Kenaf fibers undergo significant attrition rates during twin screw compounding.
• •
  Considerable fiber damage occurs during extrusion compared to injection molding.
• •
  Fiber dispersion improves the mechanical performance of PP/kenaf composites.
• •
  PP/kenaf composites enhance the fire control behavior by reducing the dripping.
• •
  Significant heat release rate reduction can be observed with PP/kenaf composites.

Abstract

The primary aim of this paper is to analyze the fiber length retention capacity of extrusion and injection molding processes for short and long kenaf fiber reinforced polypropylene composites. The composites were manufactured by adding maleic anhydride grafted polypropylene (MAPP) and an antioxidant (Irganox) using twin-screw extrusion and injection molding processes. A higher level of fiber attrition rate was observed during the twin-screw compounding compared to that in the injection molding. During high-temperature shear mixing, both processes caused a reduction in fiber length below the calculated critical fiber length along with considerable fiber damage. The mechanical and thermal properties of the resultant composites were subsequently characterized. Cone calorimeter tests demonstrated that the peak heat release rate for the kenaf fiber composites (30 wt.%) was reduced by 37% compared to pure polypropylene (PP). In the UL-94V tests, the presence of lignin in kenaf reduced the dripping time considerably, which further led to the formation of char residue after burning. Although the fiber length obtained was below the critical fiber length under high shear processing (twin-screw compounding and injection molding), effective fiber dispersion, orientation and opening led to significantly improved mechanical performance of the PP/kenaf composites, irrespective of the initial fiber length.

Graphical abstract

Keywords

• Kenaf fiber
• Degradation
• Twin-screw extrusion
• Injection molding
• Fiber dispersion

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• ⁎ 
  Corresponding author at: University of Auckland – Newmarket Campus Private Bag, 92019, Auckland Mail Centre Auckland, 1142, New Zealand.

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