Study of Melamine-Formaldehyde/Phase Change Material Microcapsules for the Preparation of Polymer Films by Extrusion

Abstract

n-Eicosane-melamine formaldehyde microcapsules of an average size of 1.1 μm and latent heat of fusion of 146.2 ± 5.3 J/g have been prepared. They have been characterized by scanning electron microscopy, FTIR spectroscopy, calorimetric techniques, and thermogravimetric analyses. Under processing conditions, the microcapsules apparently preserved their properties, also maintaining their n-eicosane loading and heat storage capacity under washing conditions (water with detergent at 60 °C). The microcapsules synthesis has been scaled up for the fabrication of functional films by extrusion. For that, polymer films containing 10 wt.% of microcapsules were prepared at a pilot plant level. In those films, even though a fraction of the n-eicosane loading was lost during the extrusion process, the microcapsules showed good compatibility within the polyamide. The percentage of PCM in the polyamide 6 films was estimated by TGA, verifying also the heat storage capacity predicted by DSC (2.6 ± 0.7 J/g).

Keywords: heat storage; n-Eicosane-melamine formaldehyde microcapsules; phase change material; polyamide 6 films.

Figure 1

(a) Experimental set-up for the preparation of microcapsules; (b) extrusion process of a LDPE film with MF/n-eicosane microcapsules.

Figure 2

SEM images of MF/n-eicosane microcapsules (a) (MC1); (b,c) individual MF/n-eicosane MC with different wall thicknesses (d) MC4; (e) MC8; (f) MC12.

Figure 3

Analysis of the MF/n-eicosane microcapsules (MC1): (a) TGA and its 1st derivative; (b) DSC.

Figure 4

FTIR spectra of n-eicosane, MF polymer, SDBS surfactant and MF/n-eicosane microcapsules MC1.

Figure 5

Influence of scaling: (a) size distribution of MCs in number; (b) distribution of the sphericity factor of the microcapsules in number.

Figure 6

SEM images of MF/n-eicosane microcapsules MC4: (a) after half an hour at 260 °C; (b) after half an hour at 300 °C; (c) after washing with soap and water for 2 h at 60 °C; (d) after washing with soap and water for 72 h at 60 °C.

Figure 7

Heating–cooling cycles of the MF/n-eicosane MCs.

Figure 8

Cross section view of PA6 film made at 256 °C and 50 bar: (a) without MCs; (b–d) with 10 wt.% MF/n-eicosane MCs.

Figure 9

TGA of PA6 film made at 256 °C and 50 bar without MCs and four samples with 10 wt.% MF/n-eicosane MCs. Four different areas of the membrane were considered (MC 1 to MC 4).