Investigations of Heat Seal Parameters and Oxygen Detection in Flexible Packages

212 Pages·2012·4.5 MB·English

Investigations of Heat Seal Parameters and Oxygen Detection in Flexible
Packages

by

Suramya Dilrukshi Fernando Mihindukulasuriya

A Thesis
presented to
The University of Guelph

In partial fulfilment of requirements
for the degree of
Doctor of Philosophy
in
Food Science

Guelph, Ontario, Canada
© Suramya Dilrukshi Fernando Mihindukulasuriya, May, 2012
ABSTRACT

INVESTIGATIONS OF HEAT SEAL PARAMETERS AND OXYGEN DETECTION
IN FLEXIBLE PACKAGES

Suramya Dilrukshi Fernando Mihindukulasuriya Advisor:
University of Guelph, 2012 Professor L-T. Lim

Heat sealing is commonly used for making form-fill-seal packages fabricated
from thermoplastic films. One of the challenges frequently faced by the industry is
inadvertent contamination of the film–film interface by the product during filling, an
event that can compromise package seal strength and integrity. In the present study, the
effects of dwell time (0.5–1.5 s), jaw pressure (28–1,860 kPa), jaw configuration, jaw
temperature (150–180°C), and liquid (water and oil) on the interface temperature and seal
strength of a linear low-density polyethylene (LLDPE) film were investigated. In the
presence of liquid contaminants, jaw pressure played an important role in displacing the
liquid from the seal area allowing the formation of intact seals. Within the experimental
conditions investigated, interface temperatures of 130–140°C resulted in optimal seal
strength for both water-contaminated and clean film specimens. Thermophysical
properties of LLDPE and the contact angle between the contaminant liquid and the
polymer films were invoked to explain the seal strength behaviour of the liquid-
contaminated LLDPE seals. Further, finite element analysis (FEA) heat transfer models
were developed to describe the heat transfer phenomena for LLDPE film during heat
sealing, when a liquid contaminant layer is present or absent at the film-film interface.
The model predicted the observed temperatures well with root mean square errors
(RMSE) ranged from 1.6 to 2.5°C. The FEA approach can potentially be applied to
analyze the effect of different contaminant liquids on transient heat transfer during heat
sealing.
In the second part of this thesis research, an UV-activated oxygen indicator was
developed to detect the headspace oxygen within sealed package. The detector involved
encapsulating TiO nanoparticles, glycerol, and methylene blue within poly(ethylene
2
oxide) fibers using electrospinning. The sensitivity characteristics of the indicator to UV-
activation and oxygen detection were investigated. The color recovery rate of the
electrospun indicator related negatively to the UV exposure time and to the TiO fraction
2
in formulation, possibly due to the ratio of higher free electrons to methylene blue
concentration. The indicator can potentially be used as a method to analyze heat seal
integrity in modified atmosphere packaging applications.
Acknowledgements
I express my profound gratitude to my advisor, Dr. Loong-TaK Lim for giving me the
opportunity to expand my horizons, not only in various areas of research, but also in a
study environment different from where I grew up. Besides this, I also appreciate his
encouragement during my hard times with the project, and his patience, advice, guidance,
and support during the entire project. I extend my great appreciation to all my advisory
committee members - Dr. R. Lencki, for spending his valuable time to provide sound
advice, constructive comments on my research, and continuous support; Dr. A.
Marangoni for his valuable advice and support, and for the use of the DSC in his
laboratory; and Dr. M. Misra for her valuable advice and support during my research.
Special thanks go to Dr. Bruce Harte for serving as an external examiner. I would also
like to convey my special thanks to all my examination committee members - Dr. R.
Lencki, Dr. M. Marcone, and Dr. K. Warriner for their valuable time and support. And
I thank all the staff in food science department, and Dr. Sandy Smith for her friendly
support during SEM analyses. I also thank Dr. K. Seetharaman and friends in cereal
laboratory for their support during the use of their spectrometer and Dr. L. Duizer for her
support. I convey my heartfelt thanks to all my lab mates in the packaging and
biomaterial group for sharing difficult times with each other, different cultures, and
friendship. Financial support provided by NSERC and the E.I. DuPont Canada company
is also greatly appreciated. Finally, my deepest gratitude goes to my husband for his
advice on handling stress and technical aspects during my research programme, and
finally to all the members of my family in Sri Lanka and to my all friends, for their life-
long love, care, and support.
iv
Table of Contents
Acknowledgements .......................................................................................................... iv
Table of Contents .............................................................................................................. v
List of Tables .................................................................................................................... xi
List of Figures ................................................................................................................. xiii
List of Abbreviation ....................................................................................................... xix
Nomenclature ................................................................................................................. xxi
CHAPTER 1: LITERATURE REVIEW ........................................................................... 1
1.1 Polyolefins in Food Packaging .................................................................................. 1
1.1.1 Low density polyethylene (LDPE) ..................................................................... 1
1.1.2 Linear low density polyethylene (LLDPE) ........................................................ 2
1.1.3 High density polyethylene (HDPE) .................................................................... 3
1.2 Heat Sealing .............................................................................................................. 4
1.2.1 Molecular dynamic during heat sealing .............................................................. 5
1.2.2 Heat sealing process parameters ....................................................................... 12
1.2.2.1 Effect of jaw temperature........................................................................... 12
1.2.2.2 Effect of dwell time ................................................................................... 13
1.2.2.3 Effect of pressure ....................................................................................... 13
1.2.3 Effect of interface temperature ......................................................................... 14
1.3 Heat Transfer during the Formation of Seal............................................................ 18
1.3.1 Conduction heat transfer during heat sealing ................................................... 19
v
1.4 Evaluation of Seal Integrity in Food Packaging..................................................... 22
1.5 Oxygen Detection in MAP ...................................................................................... 25
1.5.1 Reversible redox dye based indicators ............................................................. 28
1.5.2 Light-activated redox dye based oxygen indicators ......................................... 30
1.5.3 Semiconductor coupled with redox dye based oxygen indicators .................... 31
1.6 Fundamentals of Electrospinning ............................................................................ 32
1.6.1 Factors affecting the electrospinning process ................................................... 34
1.6.1.1 Effect of polymer solution properties ........................................................ 35
1.6.1.2 Effect of processing conditions .................................................................. 37
1.6.1.3 Effect of environmental conditions ............................................................ 38
1.6.2 Electrospun fibers for sensor and indicator applications .................................. 39
1.7 Surface Response Methodology (RSM) .................................................................. 41
CHAPTER 2: RESEARCH OBJECTIVES ................................................................... 43
2.1 Background ............................................................................................................. 43
2.2 Research Hypotheses............................................................................................... 46
2.3 Research Objectives ................................................................................................ 47
CHAPTER 3: EFFECTS OF LIQUID CONTAMINANTS ON HEAT SEAL
STRENGTH OF LINEAR LOW-DENSITY POLYETHYLENE FILM ....................... 48
3.1 Introduction ............................................................................................................. 48
3.2 Materials and Methods ............................................................................................ 51
3.2.1 Polymer films ................................................................................................... 51
vi
3.2.2 Jaw configuration ............................................................................................. 52
3.2.3 Heat sealing ...................................................................................................... 52
3.2.4 Measurement of interface temperature ............................................................. 53
3.2.5 Determination of heat of fusion ........................................................................ 53
3.2.6 Measurement of heat seal strength ................................................................... 55
3.2.6 Evaluation of process variables on seal strength .............................................. 55
3.2.6.1 Upper jaw temperature ............................................................................... 55
3.2.6.2 Dwell time ................................................................................................. 56
3.2.6.3 Sealing pressure ........................................................................................ 56
3.2.7 Measurement of liquid contact angle ................................................................ 56
3.3 Results and Discussion ............................................................................................ 57
3.3.1 Effects of jaw temperature, seal contaminant and jaw type ............................. 57
3.3.2 Effects of dwell time and interface temperature ............................................... 63
3.3.3 Failure modes of seals ...................................................................................... 67
3.3.5 Heat seal strength characteristics with different food emulsions ..................... 74
3.4 Conclusions ............................................................................................................. 75
CHAPTER 4: HEAT SEALING OF LLDPE FILMS: HEAT TRANSFER
MODELLING WITH LIQUID PRESENCE AT FILM-FILM INTERFACE ................. 78
4.1 Introduction ............................................................................................................. 78
4.2 Materials and Method.............................................................................................. 80
4.2.1 Materials ........................................................................................................... 80
4.2.2 Heats of fusion of LLDPE films ....................................................................... 81
vii
4.2.3 Heat sealing ...................................................................................................... 81
4.2.4 Measurement of interfacial temperature ........................................................... 82
4.2.5 Development of heat transfer model ................................................................ 84
4.2.5 Phase change of polymer and apparent specific heat capacity changes ........... 85
4.2.5 TCR in modelling ............................................................................................. 87
4.2.6 Governing equation and boundary conditions .................................................. 88
4.2.7 Development of a heat transfer model with the presence of liquid at the film-
film interface .............................................................................................................. 90
4.2.8 Model fitting and validation ............................................................................. 91
4.3 Results and Discussion ............................................................................................ 92
4.3.1 Changes of apparent specific heat capacity ...................................................... 92
4.3.2 Effect of film-film interface temperatures on TCR .......................................... 93
4.3.3 Effect of jaw temperature on TCR ................................................................... 96
4.3.4 TCR in the presence of water contaminant ...................................................... 97
4.3.5 Validation of heat transfer model ................................................................... 100
4.3.6 Application of the heat transfer model for different food types and materials
................................................................................................................................. 102
4.4 Conclusions ........................................................................................................... 103
CHAPTER 5: PHOTOACTIVATED OXYGEN INDICATOR BASED ON
ELECTROSPUN POLY(ETHYLENE OXIDE) FIBERS AND TIO NANOPARTICLES
2
......................................................................................................................................... 105
5.1 Introduction ........................................................................................................... 105
5.2 Materials and Method........................................................................................... 109
viii
5.2.1 Materials ......................................................................................................... 109
5.2.2 Methods .......................................................................................................... 110
5.2.2.1 Preparation of fiber-forming solution with active components for
electrospinning ..................................................................................................... 110
5.2.2.2 Electrospining of fiber-forming solutions ................................................ 111
5.2.2.3 UVA irradiation and color measurements of the indicator ...................... 112
5.2.2.4 Scanning electron microscopy (SEM) analysis of electrospun fibers ..... 114
5.2.2.5 Fourier transform infrared (FTIR) spectroscopy analysis of electrospun
membrane and cast film ....................................................................................... 115
5.2.2.6 Statistical design for the optimization formula ........................................ 115
5.2.2.7 Effects of oxygen concentrations and relative humidity (RH) on K/S value
.............................................................................................................................. 117
5.3 Results and Discussion .......................................................................................... 117
5.3.1 Effect of ethanol on morphology of fibers and sensitivity of the oxygen
indicator ................................................................................................................... 117
5.3.2 Effect of active components on the sensitivity and reaction mechanism of the
oxygen indicator ...................................................................................................... 120
5.3.2.1 Effects of TiO and MB on K/S ............................................................... 120
2
5.3.2.2 Effect of glycerol on the performance of the indicator ............................ 126
5.3.3.4 Effect of PEO concentration .................................................................... 128
5.3.3 Comparison study between indicator made with electrospinning and casting 130
5.3.4 FTIR study between indicators made by casting and electrospinning ........... 132
5.3.5 Optimization of the chemical formula based on a surface response design ... 137
ix
5.3.6 Oxygen detection characteristics of the indicator made by electrospinning .. 144
5.3.7 Effect of RH on the indicator initial color ...................................................... 149
5.4 Conclusions ........................................................................................................... 151
CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS ................................ 153
6.1 Conclusions ........................................................................................................... 153
6.2 Future Recommendations ...................................................................................... 156
CHAPTER 7: REFERENCES ........................................................................................ 158
CHAPTER 8: APPENDIXES ........................................................................................ 175
8.1 Materials used for the Chapter 3 and Chapter 4 .................................................... 175
8.3 Central Composite Uniform Precision Design Details ......................................... 177
8.3.1 Design description .......................................................................................... 178
8.3.2 Oxygen indicator optimization results ............................................................ 180
8.3.3 Canonical analysis data .................................................................................. 181
8.3.6 Morphology of fibers for tested formulas during optimization ...................... 186
8.4 FTIR spectra obtain for oxygen indicators ........................................ 189

x