Polyethylene Terephthalate (PET) has become the preferred material of choice for many packaging applications. A preference over glass due to its low weight, similar transparency to glass and cost consideration, including the availability of recycled PET feedstock via kerbside collection has provided newer opportunities for hot-fill applications. Ostensibly, this material is used for beverage markets requiring cold and hot filling (85 oC) of liquid foods. However due to the poor thermal stability of PET - due to its low glass transition temperature - an increase in elevated temperatures limits the number of market segments the material can be utilised. Current practices incorporate the heat-set process, aimed at improving the crystallisation kinetics within the amorphous and crystalline region. This body of work incorporates a single stage Injection Stretch Blow Moulding machine (ISBM). Modifications to conventional carbonated soft drink (CSD) beverage containers to include heat-set capabilities are incorporated. The current research study investigates the potential benefits of RPET blends for improving thermal stability at elevated temperatures. This study investigates changes in mechanical properties which include Youngs modulus, top load strength, burst strength, Thermal analysis specifically investigating changes in Glass transition temperature, enthalpy changes due to heat-set conditions Percentage crystallinity changes as a function of heat-set conditions Rheological characteristics to all materials used were investigates. Furthermore, changes in the physical properties to each PET beverage container were investigated which include; process shrinkage (S1), hot-fill shrinkage (S2) Density changes via optimised DoE parameters. A combination of cold (80 oC) and hot moulds (150 oC) as measured via Forward Looking Infrared (FLIR) at the exterior to the blow mould and their affect on percentage crystallinity was studied. Preform surface temperature (PST) and strain induced crystallinity, assisting in molecular relaxation is analysed. Upon completion to an exhaustive experimental ISBM trial, a DoE software package - in this case Echip - was used to analyse and predict optimised hot-fill shrinkage values of 2.5 percent with a maximum constrained RPET blend value totalling 40 percent. ISBM optimised conditions demonstrated advantages when combining an increased preform surface temperature, RPET blends and optimised ISBM process conditions as indicated via the DoE at low heat-set temperatures.
| Identifer | oai:union.ndltd.org:ADTP/210447 |
| Date | January 2008 |
| Creators | Patuto, Joseph, jpatuto@bigpond.net.au |
| Publisher | RMIT University. Mechanical and Manufacturing Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.rmit.edu.au/help/disclaimer, Copyright Joseph Patuto |
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