Compatibility of plastics and phase change materials: comparative study via gravimetric analysis and tensile tests of plastics exposed to inorganic, organic and bio-based phase change materials

Concept of the climate-neutral buildings require two key measures: increased energy efficiency of the buildings and direct integration of renewable energy sources in buildings. Thermal energy storage capacity of building structures plays important role in both measures and should be significantly increased by the integration of latent heat thermal energy storage technology represented by phase change materials (PCMs). The aim of this study is to evaluate the interactions between the selected commercially available PCMs (including one bio-based PCM) and four commonly used plastics designed as materials for encapsulation. Four different types of PCMs were selected: Rubitherm SP24E (inorganic), Rubitherm RT24 (organic), Parafol 17-97 (organic), and coconut oil (bio-based organic). Four plastic types were tested: polycarbonate (PC), polypropylene (PP-H), polyethylene (PE 500), and polyethylene terephthalate (PET). The plastic samples were immersed in PCMs and exposed to thermal cycling for 112 days, followed by an evaluation of mass change and change in tensile properties. The first phase of the experiment tests the compatibility of the selected plastics with different groups of PCMs. As for results, no visual surface changes were observed on any plastic samples exposed to PCMs. Analysis of weight changes revealed that inorganic PCM (Rubitherm SP24E) and organic bio-based coconut oil exhibited good compatibility with all plastics (maximum weight changes less than 0.90%). Contrary, the organic PCMs (Parafol 17-97, Rubitherm RT24) showed significant penetration of the PP-H and PE 500 (weight changes up to 5.80%, 128.2 mg). Coconut oil, the representative of the organic group, demonstrated behaviour similar to inorganic PCMs rather than selected organic PCMs. The finding presents coconut oil as a sustainable, encapsulation-friendly alternative to inorganic PCMs. The second phase of the study consisted of tensile testing of PP-H and PE 500 samples exposed to organic Parafol 17-97. The samples showed significant reductions in Young's modulus values (28-35% decrease) with minimal changes in strength characteristics (2-4 MPa reduction), indicating a Plasticizing effect. This research represents one of the first quantifications of long-term compatibility between the sustainable bio-based coconut oil and multiple plastic encapsulation materials. • no visual changes were observed on the surface of the samples exposed to PCMs • maximum weight changes were observed for the plastics immersed in the organic PCMs • maximum mass changes were 5.80 % for PE 500 and 5.37 % for PP-H immersed in RT 24 • samples in coconut oil has weight changes similar to samples in inorganic PCM