University of Manchester

Visualisation of the internal bridging ligaments and pore channels in porous poly(methyl methacrylate) materials.

Katy Amos
Project Completed

Scientific Case

Sanitaryware has traditionally been produced by slip casting in which a clay slip is poured into a plaster mould made from gypsum, which is employed due to its low cost, versatility and strength. However, gypsum moulds have a number of disadvantages, including: deterioration on contact with water; deformation; and long set times, with a large number of moulds being required to maintain a commercial process. These drawbacks have led to attempts to find a replacement material for gypsum, but despite their commercial importance, the development of new materials has received little academic attention.
Synthetic polymer moulds are made from porous poly(methyl methacrylate) (PMMA), produced by polymerising methyl methacrylate (MMA) from an MMA-in-water emulsion into which pre-formed PMMA beads are dispersed. The present PhD project has shown that the composition of the emulsion dramatically affects the final properties of the material. Control of the emulsion stage of the reaction allows for tuning of the porous PMMA properties, enabling porosity and strength to be tailored. The overall objective of the PhD research is to probe the fundamental chemistry underlying the preparation of porous PMMA materials in order to facilitate a scientifically-based rationale for their design.
Polymers

Experiment Design

Pore channels; the dimensions of the ligaments linking PMMA beads together; overall porosity.

Pore Size: about 50 microns upwards with overall porosity of 30–35 %. PMMA Bead size: about 90 microns in diameter. We estimate that the ligaments will be about 10–40 microns in diameter and 1–10 microns in thickness.
Scanners and Rigs
Nikon Custom 320kV Bay
2

Sample & Safety

6-10
Low Hazard

Scan Records

Nikon Custom 320kV Bay
45
171
-
2012-12-12
Scan dates: 2012-12-12 to 2012-04-11 for 14 scans.

Project Report

Samples of porous PMMA were X-rayed using the Nikon Custom Bay scanner (45 kV, 171 ?m) to aid in the visualisation of the internal bridging ligaments.

Samples of porous PMMA were X-rayed using the Nikon Custom Bay scanner (45 kV, 171 ?m).  The differences in the formulation from the standard blend are detailed below:



  • Linear alkyl ethoxylate surfactant at high and low levels of MMA

  • Octyl phenol surfactant at high and low level of MMA

  • Octyl phenol surfactant at high and low surfactant concentrations

  • Linear alkyl ethoxylate surfactant at high and low surfactant concentrations

  • Increase in bead molar mass to 2.5MW.

  • Substitution of MMA monomer by styrene in polymerisation


 


Once reconstructed and analysed, the porosity of the materials was determined using segmentation.  In all cases the porosity value obtained from x-ray tomography differed from those previous obtained using water uptake techniques.  As X-ray tomography includes both open and closed pores, further analysis is now being undertaken to segment the samples to segregate the different pore types within the material.


The results enabled the 3D visualisation of the materials indicating higher porosity than previous though and a number of features only partially visible with alternative techniques, including large holes in the samples and variation of porosity through the layers.


However, visualisation of the ligaments and calculation of the volume of ligaments has not yet been achieved due to considerable difficultly in segmenting the materials without crude assumptions.  It is hoped further analysis of the scans may lead to further output from the initial data including modelling the flow rate through the pores as well as the continuation of work on porosity and ligament analysis.