Development, control, and monitoring of foam produced during rotational moulding

  • Alex Pritchard

Student thesis: Doctoral ThesisDoctor of Engineering


Rotational foam mouldings provide increased buoyancy and mechanical properties, which are beneficial for lightweight marine structures. For optimal performance, appropriate material and process parameters must be used. However, establishing these for large products is challenging. The work aimed to develop processes and procedures to enable the optimisation of foam structures for large-scale lightweight rotationally moulded multi-layer products. The main objectives were: to establish the parameters that control foam, and quantify their effect; and, to determine if ultrasound could be used to monitor polymer behaviour during moulding. Two unique test methods were created to study the evolution of foams, allowing the analysis of the live behaviour of structures made both with and without CBAs. The main conclusions were that CBA developed foams could be successfully controlled using PST, heating rate, polymer rheology, or CBA concentration, in agreement with the literature. It is also identified that the structures could also be significantly controlled in terms of foam density range by developing them in a vacuum environment (0.134-0.291 g/cm3), by polymer particle size (0.227-0.351 g/ cm3), or to a much lesser extent by the cooling rate used (0.313-0.329 g/cm3). The parameters controlling foams produced without CBAs are studied for the first time, finding that they may be effectively controlled by minimising the polymer particle size and maximising the heating rate, achieving a cell density improvement of 115 %. A novel ultrasonic monitoring method is successfully developed and used to monitor polymer thickness changes during the heating, and the formation of air gaps during the cooling of a moulding. Foam mouldings are also observed using the method, finding a 16 % reduction in signal amplitude at CBA decomposition. The processes and procedures created are ready to be exploited in industry, and will enable foams for large-scale lightweight rotationally moulded multi-layer products to be optimised.

Date of AwardJul 2022
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsEuropean Union’s INTERREG VA Programme, Special EU Programmes Body, Northern Ireland Department for the Economy & Department of Jobs, Enterprise & Innovation
SupervisorPeter Martin (Supervisor) & Eoin Cunningham (Supervisor)


  • Rotational
  • moulding
  • polymer
  • foam
  • control
  • development
  • monitoring
  • ultrasound
  • ultrasonic
  • process

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