Injection Molded PP Foams Using Food Ingredients for Food Packaging Applications

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.

Carbonation Curing and Kinetics of Wood-Sodium Silicate Composites

“…The thermal degradation properties determined from the DTG plots for all samples are given in Table S5. For the reference compounds, T onset of 156 °C and residual ash of 62% were observed for NaHCO 3 and are consistent with literature . Na 2 CO 3 remained highly stable until 900 °C .…”

“…For the reference compounds, T onset of 156 °C and residual ash of 62% were observed for NaHCO 3 and are consistent with literature. 54 Na 2 CO 3 remained highly stable until 900 °C. 55 SiO 2 was stable and showed minor water loss below 200 °C.…”

Effect of coupling agent on polylactic acid/polypropylene and polylactic acid/polyamide 6 foam composites

“…Furthermore, the phase changes and degradation steps were evaluated from the DSC and TGA thermograms and the results allowed to detect that the Hyd 812 agent was PE-based and was composed of citric acid and sodium bicarbonate, while the Hyd 822 agent was also PE-based and was composed of citric acid. [24][25][26][27][28] Maleic anhydride (MA) used in the PLA-g-MA synthesis was supplied from Sigma-Aldrich, dicumyl peroxide was purchased from Acros Organics, toluene and hexane were supplied from Riedel-de Haen.…”

“…In addition, the inorganic additives in the agent were determined by phase analyzes performed from XRD analysis. Furthermore, the phase changes and degradation steps were evaluated from the DSC and TGA thermograms and the results allowed to detect that the Hyd 812 agent was PE‐based and was composed of citric acid and sodium bicarbonate, while the Hyd 822 agent was also PE‐based and was composed of citric acid 24–28 …”

Applications and Challenges of Supercritical Foaming Technology

“…However, EPS has environmental problems because it is non-degradable and difficult to recycle. Polyolefin foam, represented by polypropylene (PP) foam, is also widely used in food packaging and, although it poses some environmental hazards, is considered a promising polymer foam due to its low cost and recyclability [ 31 ]. In addition, another concern in this area is the consumer demand for foods with a longer shelf life.…”