73D-40 |
Wall thickness distribution in thermoformed food containers |
S. MIN and Q. H. Zhang. Dept. of Food Science & Technology, The Ohio State Univ., 2015 Fyffe Ct., Columbus, OH 43210 The non-uniformity of wall thickness distribution and delamination of sheets are major limitations in thermoforming of laminated food containers. These defects affect the shelf life of foods with decreased mechanical and barrier properties. There is need for the optimization study of thermoforming. To determine the wall thickness distribution of 4 oz and 6 oz containers by differentiating major thermoforming parameters, forming temperature, forming air pressure, and heating time. A multiplayer roll-stock base material, laminated with high impact polystyrene (HIPS), low-density polyethylene (LDPE), and polyvinylidene chloride (PVDC), was thermoformed into containers by a plug-assist thermoforming unit in a Benco aseptic packaging machine. A forming temperature of 117, 130, 145, 154, 165, 173 and 186°C, a forming air pressure of 1.5, 2.0, 2.5, 3.0 and 3.5bar, and a heating time of 66, 74, 84, 97 and 114 sec were used in this study. With the same index of the material, 4oz. and 6oz. containers were thermoformed. Surface temperature of the sheet was measured by using an infrared thermometer. The wall thickness of containers and the thickness of each layer of the sheet were measured by using a digital micrometer with a thresh force of 0.4 N and an image analysis, respectively. The optimum operating conditions for the thermoforming process were the forming temperature of 148-156°C, the forming air pressure of 2.5-3bars, and 88-97sec for both 4 oz. containers and 6 oz containers. The 4 oz containers had higher thickness than 6 oz cups at the thinnest region of each container (p < 0.05). The thickness of PVDC layer, providing barrier properties, was critically increased when the size of cup was reduced from 6 oz to 4 oz with the same index. The optimization study resulted in thermoforming parameters that significantly improved the thickness distribution, barrier layer and delamination.
Session 73D, Food Packaging
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