Temperature has critical impact on food quality and safety within food supply chain, therefore, food should be kept at the defined storage temperature range. Final consumer should be assured when buying food about actual temperature and thermal history of the selected food product and this is why it should be indi¬cated on the packed or prepacked item. The chromogenic temperature indicator for cold food chain was prepared from suitable active material packed in the properly structured holder. When tem¬perature rises above the defined storage temperature, the active material changes colour and physical state (solid/liquid). Simultaneously, special packaging struc¬ture enables irreversible recording of the time exposed to the elevated temperature. The active material was made of thermochromic composite, consisting of dye, developer and solvent. It changes colour at its melting point, being coloured below and discoloured above it. The temperature is called activation temperature of the composite. Its value was adjusted by appropriate solvent and additives used for preparation of the com¬posite, to reach the desired value. The temperature dependent colour change of the composite was deter¬mined by colorimetric measurements. The conditions for best observation of the change by naked eye were also examined. The structure of the active material’s holder was analyzed for best displaying of the time spend at high temperature (above the activation tem¬perature). Functioning of the indicator was examined with growth of pathogens as a function of migration of the active material at temperature above the required storage temperature of the food. It was found out that the described chromogenic temperature indicator for cold food chain shows the thermal history of food stor¬age by colour-, phase- and migration changes of the active composite material and consequently would be reliable as indicator in cold food chain to indicate tem-perature abuse and would disclose potential growth of psychrophilic microorganisms.
COBISS.SI-ID: 5610522
The colour of some samples is easily seen by naked eye, but is badly or completely wrongly evaluated by measurements. Such examples are thin layers with interference effect and liquid-crystal-based thermochromic printing ink. The directional illumination - directional viewing measurement geometries which are most frequently applied in graphic art fail completely or to a large extent and integrating sphere measurements are required to describe the effect by colorimetry. Various parameters of a selected measuring geometry are also important. The consequences of using integrating sphere with different diameter and sample openings on the derived colour were investigated. The investigated samples include directional-occurring phenomena and those which are directionally independent. This is clearly revealed in colorimetric results. When the samples are observed by naked eye, we often have to change illumination-viewing conditions to get the best vision. Thus, measuring conditions should be of large importance.
COBISS.SI-ID: 5513498
A modified in situ polymerization microencapsulation procedure for the preparation of microcapsules with paraffin wax cores (43 wt.%) and melamine-formaldehyde resin shells having a uniform size distribution and a spherical shape with average diameters of approximately 15 um was developed. The high-density polyethylene/microcapsule blends were prepared via two routes. In the first case, the dry high-density polyethylene powder covered bymicrocapsules was simply hot pressed, whereas, in the second case, the dry high density polyethylene/capsule powder was first blended in the molten stateto obtain better homogeneity before hot pressing. It was observed that both systems behave qualitatively the same with comparable mechanical properties and thermal behavior. The thermal stability of high-density polyethylene/microcapsule blends characterized by thermogravimetry is significantly lower than that of neat high-density polyethylene. The selected characteristic temperatures of degradation decreased by more than 200 °C compared with the related temperatures for neat high-density polyethylene. Ananalysis based on Differential Scanning Calorimetry revealed separated melting and crystallization behavior of wax within the capsules and high density polyethylene in the blends. The enthalpies of melting and crystallization are proportional to the amount of individual components in thematerial. The capsules have a strong plasticizing effect on the high density polyethylene, resulting in a significant decrease in the melting and crystallization temperatures. The plasticizing effect was also confirmed by measurements of the tensile mechanical properties and rheological behavior.
COBISS.SI-ID: 1565532