Abstract
A new approach to the creation of polypropylene (PP) based foaming materials was developed using food grade foaming agents that were coated on the PP pellets. More specifically, sodium bicarbonate and organic acids were used to coat PP pellets using either polyethyleneoxide (PEO) or lipid esters as coating stabilizers. In order to overcome the problem of the thermal decomposition of sodium bicarbonate at temperatures lower than the PP melting temperature, which makes the direct foaming during melt mixing impossible, the proposed methodology was proved quite efficient. Thus, new PP masterbatches were prepared, where the foaming agents were incorporated as coating at PP pellets at contents up to 10%, and initially used in Lab scale injection machines in order to find the best combination of materials that resulted in the production of foamed articles. Subsequently selected material combinations were tested in an industrial scale injection molding machine, where an optimization of the injection parameters was attempted. The outcome of this was the production of PP articles with significantly increased void fraction, up to 14%, decreased thermal conductivity, up to 20%, and various pore sizes as was observed via microscopic examination using SEM and CLSM.
Highlights
Due to the fact that the ATR-FTIR analysis focuses on the surface of the sample, the presence of deposited NaHCO3 on the raw materials is confirmed, as it can be seen but the amount of unreacted NaHCO3 in the final products cannot be detected through this technique
The results showed that, in several cases, the
This work illustrates the efficient coating of polypropylene pellets with food grade coating agents like sodium bicarbonate and organic acids to create foamed polypropylene articles
Summary
Foaming in thermoplastic polymers has attracted attention, since it provides the produced materials with a combination of desirable properties like thermal insulation and high specific strength, with low density [1]. Different foaming approaches like mechanical physical and chemical have been used [2,3,4]. The polymeric foams are known as porous polymeric material, as they consist of a polymeric matrix, which contains an important number of small pores. Polymer foams can develop a different geometry, such as open cells or closed cells, depending on the raw materials and the method used for their creation. Polymeric foams—because of their advantages—can fit in different fields, such as packaging, thermal insulation systems, sporting equipment and automotive parts [5,6]
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