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Development and characterization of a gelatin-based coating with unique sealing properties



The experimental results on the development of thin (∼ 1.5 μm) gelatin-based coatings and the investigation on their sealing attribute when applied onto oriented polypropylene (OPP) are reported. The sealing performance, expressed as the strain energy required to separate the sealed joints, was studied as a function of three different influencing factors. pH of the hydrogel solution was varied between 5 and 11. The highest seal strength values were obtained for pH values beyond the isoelectric point (IEP) of the gelatin molecule. The effect of the plasticizer (glycerol) was studied by changing its concentration from 2.5 wt % to 7.5 wt % to the total weight of the hydrogel solution. Glycerol concentration = 7.5 wt % was found to be the best for achieving adequate strain energy values. The influence of a hydrophobic component on the capability of the coating to act as a sealant has also been assessed. The hydrophobic component had a positive effect only up to a certain level (1 wt %, weight percent), whereas beyond this value, it affected the seal strength attribute. According to the best setting conditions, seal strength values for the OPP biocoated films of ∼ 61 N × mm were attained, with a corresponding maximum force required to break the joints of 2.4 N. These results are discussed by taking into consideration the modality of seals opening. Interestingly, the heat-seal (temperature: 90°C; dwell time: 1 s; pressure: 4 bar) failed in both peeling and tearing mode failure, as confirmed by microscopy, spectrophotometric, and particle size analyzes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010