MIKAELA BÖRJESSON ABSTRACT - PDF

Description
ABSTRACT First of all I would like to thank my examinator Mats Andersson at the division of polymer technology at Chalmers University of Technology. I would also thank my supervisor at SIK, Lilia Ahrné,

Please download to get full document.

View again

of 35
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Information
Category:

Book

Publish on:

Views: 6 | Pages: 35

Extension: PDF | Download: 0

Share
Transcript
ABSTRACT First of all I would like to thank my examinator Mats Andersson at the division of polymer technology at Chalmers University of Technology. I would also thank my supervisor at SIK, Lilia Ahrné, for her many good advices and ideas of how to continue my work and made it go forward. Selection of packaging material suitable for infrared heating of food Master of Science Thesis in the Master Degree Programme, Materials and Nanotechnology MIKAELA BÖRJESSON Department of Chemical and Biological Engineering Division of Polymer Technology CHALMERS UNIVERSITY OF TECHNOLOGY Göteborg, Sweden, 2010 Report no. 374 REPORT NO. 374 Selection of packaging material suitable for infrared heating of food MIKAELA E. C. BÖRJESSON Department of Chemical and Biological Engineering CHALMERS UNIVERSITY OF TECHNOLOGY Göteborg, Sweden 2010 Selection of packaging material suitable for infrared heating of food MIKAELA E. C. BÖRJESSON MIKAELA E. C. BÖRJESSON, Technical report no. 374 Department of Chemical and Biological Engineering Chalmers University of Technology SE Göteborg Sweden This work was carried out at: SIK The Swedish Institute for Food and Biotechnology Box 5401 SE Göteborg Sweden Cover: A piece of bread inside a plastic pouch is exposed for IR heating. ABSTRACT Abstract Today there is a large industrial interest in infrared (IR) heating of packaged foods. The requirements on these types of packaging materials are that they need to be transparent and heat resistant. The IR treatment of packaged food can reduce the number of microorganisms and also increase storage time without using preservatives. Infrared light belongs to the electromagnetic spectra and the IR wavelengths can be divided into three groups; short-ir (0.7 µm-2 µm), medium-ir (2 µm-4 µm) and long- IR radiation (4 µm-1 mm). In this study only short-ir radiation has been used and it has also the highest intensity of the three groups. The advantages with IR heating compared to ordinary convection heating are faster heating, higher efficiency, less energy required and a more uniform heating. All the incident energy that hits the object will be reflected, absorbed or transmitted. Since as much energy as possible should be absorbed of the food product, it is important that the packaging material transmit as much energy as possible, i.e. the packaging material should have a high transmittance and a low absorbance and reflectance. The most common packaging materials for foods are metal, glass, paperboard and plastics, but it is only plastics that fulfil the requirements of high transparency and low absorption. In this study twelve different packaging materials were tested and they consist of different varieties of the polymers polyethylene (PE), polyamide (PA), polypropylene (PP), polyethylene terephthalate (PET) and barriers of ethylene vinyl alcohol (EVOH). To find a method that could be used to evaluate the twelve different materials, it was necessary to first evaluate the heating conditions of the IR oven and then do tests with a black body. The black body was made of two copper plates that were painted black and had a thermocouple in between, which measure the temperature in the centre of the black body. A black body absorb all incident energy and do not reflect or transmit anything. Because of this, the black body could be used as a reference since the tested materials will be either on top of the black body or shaped as a pouch around the black body. The tested materials were evaluated with respect to their transmittance, reflectance and changes in tensile strength. The three best suited materials as a packaging material for IR heating were chosen for further tests with bread, to see how the materials behave in contact with food. To study the changes of the IR treated bread with a plastic film on top, the water activity and the weight of the bread was measured before and after IR treatment. A plastic film on top of the bread did not influence the heating time significantly and the water activity and weight of the bread changes less with a plastic film on top of the bred during heating compared to an IR treated bread without a film on top. I SAMMANFATTNING Sammanfattning Idag finns det ett stort intresse av att kunna värma paketerad mat genom infraröd (IR) strålning och kravet på ett paketeringsmaterial för detta användningsområde är att det måste vara transparent och värmetåligt. Genom att IR behandla paketerat livsmedel kan mängden mikrobiella bakterier på livsmedlet minskas samt att hållbarhetstiden kan förlängas utan användning av konserveringsmedel. IR strålning tillhör det elektromagnetiska spektrumet och våglängderna på IR strålning kan delas in i tre olika kategorier; kortvågig IR (0.7 µm-2 µm), medelvågig IR (2 µm-4 µm) och långvågig IR (4 µm-1 mm). I denna studie har endast kortvågig IR strålning använts och det är även den typ som är den mest intensiva av de tre olika IR vågorna. Fördelarna med att värma livsmedel med IR strålning istället för i en traditionell ugn är att uppvärmningen går snabbare, mer effektiv process, mindre energiåtgång och det blir en mer jämnare värmning. Av den totala energin som når ytan på ett objekt kommer energin att reflekteras, absorberas eller transmitteras. Då så mycket som möjligt av energin ska nå livsmedlet är det viktigt att förpackningsmaterialet släpper igenom så mycket energi som möjligt, dvs. förpackningsmaterialet behöver ha en hög transmittans samt låg absorption och reflektants. De vanligast förekommande förpackningsmaterial för livsmedel består av metall, glas, kartong eller plast men det är bara plast som uppfyller kravet på hög transmittans och låg absorption. I studien användes tolv olika förpackningsmaterial för livsmedel som bestod av olika varianter av polymererna polyeten (PE), polyamid (PA), polypropylen (PP) och polyetentereftalat (PET) samt även barriärer av etylen vinyl alkohol (EVOH). För att ta fram en metod som kunde användas för utvärdering av de tolv olika materialen var det nödvändigt att först granska IR ugnens värmningsförhållanden och sedan göra tester med en så kallad svart kropp. Den svarta kroppen bestod av två stycken svartmålade kopparplattor med ett termoelement emellan som mäter temperaturen i mitten av den svarta kroppen. En svart kropp absorberar all infallande energi och reflekterar eller transmitterar ingen energi, därför kunde den svarta kroppen användas som referens då de testade materialen lades antingen på den svarta kroppen eller som en påse runt den svarta kroppen. De testade materialen utvärderades i transmittans, reflektants och skillnad i dragstyrka och de tre bästa materialen, lämpliga som förpackningsmaterial för IR värmning, valdes ut för fortsatta tester med bröd för att se hur materialen betedde sig vid kontakt med livsmedel. För att studera förändringarna i det bröd som IR behandlats med en plastfilm över sig, mättes vattenaktiviteten och vikten på brödet före och efter IR värmning. En plastfilm över brödet under IR värmning påverkade inte värmningstiden speciellt mycket och vattenaktiviteten hos brödet förändrades mindre när en plastfilm låg över brödet, jämfört med ett IR behandlat bröd utan plastfilm. II ACKNOWLEDGEMENTS Acknowledgements First of all I would like to thank my examiner Mats Andersson at the Division of Applied Chemistry/Polymer Technology at Chalmers University of Technology. I would also like thank my supervisor at SIK, Lilia Ahrné, for her many good advices and ideas of how to continue my work and made it go forward. The department of process technology at SIK for their good advices and nice coffee breaks and especial thanks to Lars-Göran Vinsmo and Emma Holtz for their guiding of the equipment it turned out that I would spend a lot of time with. Lars Anninger at Kontikigroup AB, Karl Nideborn at Flextrus AB and Lennart Skoglund at Gäsene Mejeri for the plastic films that have been used in the study. Finally I would like to thank all my friends and family that have supported me during those weeks I have been working with my master thesis. Thank you all. III CONTENT Content Abstract... I Sammanfattning... II Acknowledgements... III Content... IV Glossary... VI 1 Introduction and objective of work Objective Literature review Infrared (IR) Infrared heating Optical properties Black body Basic laws of black body radiation Stefan-Boltzmann s law Planck s law Wien s displacement law Heat transfer Conduction Convection Radiation Packaging material Different types of packaging materials Paperboard Glass Metal cans Plastics Materials used in plastic packaging for food products Polyethylene (PE) Polypropylene (PP) Polyethylene terephthalate (PET) Polyamide (PA) Ethylene Vinyl Alcohol (EVOH) Important mechanical properties of packaging materials Tensile test Heat treatment of packed foods Selection of packaging for IR heating Materials and methodological considerations Materials Equipment IR treatment chamber Black body Mechanical properties IV CONTENT Water activity Experimental setup Placement in the oven Distance between IR lamps and material Intensity Effect of the oven walls Measurement of IR transmittance in materials Measurements on a black body with a thin film Measurements on a black body in a packaged environment Method to measure tensile testing Tests with bread A plastic film on top of the bread A piece of bread in a pouch Results and discussion Placement in the oven Distance, intensity and time Distance between IR source and object IR intensity Time in oven Effect of the oven walls Heat flux IR effects on materials Plastic film on top of the black body Materials in a packaged environment Size of the plastic bag Heat flux in a package environment Behaviour of the plastic films during IR treatment Reflectance Changes of film packaging quality during IR heating Thickness Ranking and scoring Tests with bread Conclusions Further work References Suppliers to the plastic films: Appendix A Appendix B Appendix C V GLOSSARY Glossary Absorption: A process where gas, liquid or energy is taken up by another substance. Acetal: An organic chemical compound and a functional group with the formula RCH(OR )(OR ), where R, R and R are different chemical groups. Acetal is used in chemical synthesis to prevent undesirable reactions (Nationalencyklopeden 2010). Amorphous: An amorphous material has no shape e.g. areas in polymers where no regular structural pattern (such as crystallinity) occurs. Black body: A body that absorbs all incident energy and do not reflect or transmit anything. The emissivity of a black body is equal to 1. Bulk polymer: The easiest and most common polymers belong to this group of polymers e.g. PE and PP. Copolymer: A polymer formed from a number of monomers. A copolymer is a polymer with properties from two or more separated polymers. Crystals: A very organized and regular group of atoms that forms crystals within a material. The degree of crystallinity influences hardness, density, transparency etc. Electromagnetic spectrum: The electromagnetic spectrum is the range of all possible frequencies from the electromagnetic radiation. The spectrum extends from long, low frequent radio waves to short and high frequent gamma rays. Emissivity (ε): A body s ability to emit electromagnetic radiation (heat or light). A black body have the highest possible emissivity (ε=1). Engineering polymer: Polymers with properties that compete with properties of metals. Better properties than bulk polymers but not as good as advanced polymers. EVOH: Ethylene vinyl alcohol. A copolymer between ethylene and vinyl alcohol and this combination is commonly used as a barrier. Glass transition temperature (T g ): T g is where a material goes from a glass-like to a rubber-like material or vice verse, i.e. hardness and stiffness changes significantly. Grey body: A body that is not totally black. A grey body does not absorb as much energy as a black body and the emissivity for a grey body is between 0 and 1. Infrared (IR): Infrared light consists of waves between 0.7 µm and 1 mm and is placed next to the visible light in the electromagnetic spectra. Melting temperature (T m ): Melt temperature (T m ) or melting point. T m is the temperature at which a material changes from a solid to a liquid or in the other way. Microwave: Longer waves than IR waves and also lower frequency. Microwaves are between 1 mm to 1 m. VI GLOSSARY Modulus: The slope of the stress-strain curve in the elastic region. PA: Polyamide or nylon is a polymer which consists of amide bonds. PE: Polyethylene belongs to the bulk polymer and is one of the easiest processing polymers. PET: Polyethylene terephthalate, the most common of the thermoplastic polyesters. Polyester: A class of polymers consisting of ester bonds. Polyolefin: Plastics that contains only carbons and hydrogen. PE and PP belongs to this group. PP: Polypropylene belongs to the bulk polymers. PP has higher strength and stiffness than PE. PVdC: Polyvinyldiene chloride. A polymer derived from vinyldiene chloride and is common used as a moisture barrier. Radiation: Heat transport through waves. Reflectance: That part of the incident light or energy that scatters back from the object. Semi crystalline: A material that has both amorphous parts and crystalline parts. Specific heat capacity (C P ): The specific heat indicates how much heat that is needed to change the temperature of a material. Tensile strength: A measure of the force needed to pull a material apart. Thermocouple: A connection between two different metal plates that generate a voltage when the temperature is changing. Thermocouples are used as temperature sensors for measurements. Thermoplastic: A polymer that become softer and melts during heating. Because of this thermoplastics can be re-melted and recycled. Thermoset: A thermoset is a polymer that just can be moulded once by heat and if heated again, it will start to degrade. Transparency: The ability of a material to let light or energy to pass through the material. Ultraviolet (UV): Ultraviolet light consists of waves between 10 nm and 400 nm and is placed next to the visible light. UV-light has a higher frequency than IR-light. The sun consist of e.g. UV which makes polymers degrade faster. Water activity (a w ): a w is the moisture pressure above the food material divided by the moisture pressure above pure water i.e. a w =P/P 0. VII INTRODUCTION 1 Introduction and objective of work Heating of packed foods by infrared (IR) radiation has large industrial interest. IR is a rapid heating method allowing for example surface decontamination of packed foods without affecting food quality. One of the most important properties on a package material for this application is that the packaging material has to allow the transmission of IR radiation to the product without reducing the amount of energy transmitted to the food product. Today there is a lack of information about how the optical properties of different packaging materials affect the IR radiation, and consequently the amount of energy absorbed by the food. By knowing how a material behaves during IR heating it can help to select material for IR treatment of packed foods. The IR treatment of package food can reduce the amount of microbiological growth and also increase storage time without using preservatives. 1.1 Objective The aim with the project is to evaluate the effect of selected packaging materials on IR heating and select the most suitable packaging materials for food products. The work will only focus on already existing packaging materials for food products. Expected results are to evaluate the heating conditions in an IR oven and find a methodology to assess packaging material for IR heating and evaluate the performance of different packaging material regarding IR heating. 1 LITERATURE REVIEW 2 Literature review The literature review is divided into two main parts. The first part (chapter ) consists of information about the IR technology. The second part (chapter ) consists of information about packaging material, their properties and behaviour in contact with heat and food products and also how to evaluate their mechanical properties. 2.1 Infrared (IR) Infrared light is a type of electromagnetic waves with a wavelength between 0.7 µm and 1 mm and is placed next to the visible light in the electromagnetic spectra (see figure 2.1). The IR wavelengths can be divided into three parts (Richardson 2001), (Krishnamurthy, et al. 2008); Short waves or near-infrared (NIR), wavelengths between 0.7 µm and 2 µm. Medium waves or mid-infrared (MIR), wavelengths between 2 µm and 4 µm. Long waves or far-infrared (FIR), wavelengths between 4 µm and 1 mm. Short IR waves have the highest frequency of the three different IR waves and it also appears at higher temperatures (above 1000 C). Medium IR waves have a lower frequency than short IR and therefore also a lower temperature and long IR waves have even lower frequency and working at temperatures below 400 C. Long IR waves are the main heat transfer mechanism in ordinary ovens and most food components absorb radiative energy in that wavelength area (Krishnamurthy, et al. 2008). A new technique in food processing is to use short IR waves in applications like drying, baking, frying and surface decontamination of foods. Figure 2.1. Electromagnetic wave spectrum. Infrared waves are in between the visible spectra and microwaves Infrared heating There are many advantages with IR heating compare to convection heating methods. One of the main reasons to use IR heating is that it can reduce both processing time and manufacturing costs. This mostly because the oven does not heat the surrounding air so the heat is only absorbed by the product. The heating time is reduced and also the energy consumption and consequently the processing costs. Other advantages and some disadvantages with IR heating are listed on the next page (Richardson 2001), (Staack 2008), (Krishnamurthy, et al. 2008). 2 LITERATURE REVIEW Advantages: High thermal efficiency. Fast heating rate. Uniform drying temperature. Uniform heating. High degree of process control. Disadvantages: Low penetration power. Prolonged exposure of biological materials may cause fracturing. IR heating has many application areas in industries, for example in the car industry or in the paper processing, where drying is a common technique (Richardson 2001). Today, IR heating is introduced more and more in the food processing industry and the main reason to heat food products is to extend their shelf life or to enhance the taste of the food (Krishnamurthy, et al. 2008). The absorbed amount of IR radiation at a product is dependent on many factors. Some of them are (Ircon Drying Systems 2001); The distance between the IR source and the exposed object, a shorter distance gives a faster heat transfer. The colour of the object. The darker the object is, the more radiation it will absorb e.g. a black body absorb as much radiation that is possible for a certain situation. At the same time a colourless material will transmit almost all radiation. The angle that the IR radiation hits the object. The fastest heat transfer is when the IR radiation hits the object perpendicular. The thickness of the object. It takes longer time to heat a thick object compared to a thin, but a thick material will keep the heat for a longer time. A too thin object will transmit some of the radiation. A large surface area which is exposed to IR radiation will have a higher heat transfer than a smaller surface area Optical properties When IR waves hits an object the incident waves will be reflected, absorbed or transmitted (see figure 2.2). The reflection of IR radiation depends on the surface structure and properties of the surface material. A metal reflect more radiation
Related Search
Similar documents
View more...
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks