Barrier Properties Of Films 03 12


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Barrier Properties Of Films 03 12

  1. 1. BARRIER PROPERTIES of FILMS current technology & applications Henky Wibawa AMCOR FLEXIBLES INDONESIA Technical Director March 2012
  2. 2. Introduction
  3. 3. IntroductionThe primary functions of packaging are containment, protection,information and convenience.Probably the most basic function of a packaging is to contain its fillinggood. Milk, loose peas or potato chips would have a hard time findingits way to the consumer without retail packaging.Protection is often considered as the most important functionality ofthe package. Shielding the food from the attack of animals (mice,insects etc.), micro-organisms, impede its contamination with dust,dirt or chemicals, resist the impact of shocks, vibrations orcompressive forces and guarding the filling good from the adverseeffects of too much or too little moisture, light or oxygen is the ‘raisond’être ‘ of the package.
  4. 4. Introduction Packaging at the POS/POP
  5. 5. Packaging Materials
  6. 6. Aluminium FoilsAluminium foil is essentially impermeable to gasses and water vapourabove a thickness of approx. 20 microns. For thinner gauges one candetect a small but non-zero permeability due to pinholes (e.g. a 7mmfoil has a water vapour transmissions rate (WVTR) of approx. 0.2 g/m² *day at 38°C and 90 % rel, humidity and a O2 transmission rateof 0.1-0.2 ml /m2*day*bar).Aluminium foil exhibits desirable deadfold characteristics ; i.e. whenwrapped around an object, it will assume its profile with no springback(e.g. butter wrapper). Typical applications are in coffee packaging (PET/Al/LDPE), medicaland consumer health care packaging (hard annealed Al foil for blisters,sachets), dry soups (BOPP/Al/LDPE) or lidding material for readymeals (PET/Al/PP) and dairy products (heat seal lacquered foil).
  7. 7. Biaxially Oriented PolypropyleneWith 0.9 g/m³, BOPP has the lowest density of the common packaging materials.Its melting point lies with 169 °C high enough to allow for sterilisationapplications.BOPP prominent qualities are: excellent moisture barrier, toughness, clarity andlow cost. Low tear resistance make it suitable for easy-open applications. Someof the disadvantages (low gas and aroma barrier, poor sealabilty, printability andmaschinability) are surmounted by co-extrusion or coatings:Co-extrusion with PP-PE co-polymer sealabilityAcrylate coating increased gloss, printability andmachinabilityPVDC coating increased gas and aroma barrier,sealabilityPVOH oxygen barrier, printabilityMetallisation oxygen, aroma, moisture and lightbarrierBOPP can also be produces in an opaque variety either by filling with whiteparticles or by cavitation. This latter method leads to pearlised, light weightmaterial with low light transmission and high gloss. The combination of the abovementioned variables leads to a broad spectrum of possible applications in foodpackaging. Main applications are chocolate bars, biscuits, snacks, ice cream,sweets etc.
  8. 8. Biaxially Oriented PolyesterPolyethyleneterephthalate has density of 1.40 g/m3 and a meltingpoint of 260°C. PET films are almost exclusively used in the bi-oriented, heat stabilised form.PET posses outstanding tear resistance, high transparency and gloss aswell as remarkable resistance to scratching and abrasion. In additionits excellent printability combined with an advantageous machinabilityand dimensional stability makes it one of the converters preferredmaterials. PET can be used a temperature range of –50 °C to +150°C.It exhibits good barrier properties with respect to water vapour, gasesand fats. Typical examples where PET is used are PET/AL/LDPE (coffeepouches, medical sachets), PET met./LDPE (snacks, coffee, biscuits) orPET/Al/PP as peelable, sterilisable lidding material for ready meals.PET is furthermore the prevailing substrate for special barrier layers.The most common one is certainly the metallisation. Others includeclay platelets, SiOx and PVDC. They will be discussed further on.
  9. 9. Biaxially Oriented PolyamideThe denomination polyamide refers to whole family of polymer. Nylon(PA-6) is produced by a ring opening reaction of e-caprolactam, amolecule that already contains the amid group in its initial structure.The most widespread polyamides in flexible packaging are PA 6 andPA 6-6 with a density of 1.13 and a melting point of 220 °C, allowingfor 140°C sterilisation procedures. Nylon films are characterised byhigh impact resistance and high tensile strength. They exhibit goodstiffness and are resistant to fats, oils, dilute bases and acids. Theirbarrier with respect to gases is very good in dry conditions, butdeteriorates rapidly with increasing humidity. Water vapourtransmission rate is quite high and increases with rising moisturecontent of the material. BOPA are produced showing up to threefoldimproved tear resistance, increased impact strength, improved opticalproperties and higher barrier values.The main applications of polyamides are to be found in the field ofMAP/ vacuum packaging of cured meat and cheese products(OPA/PE).
  10. 10. EVOHEthylene-vinyl alcohol resins are hydrolysed co-polymers of ethyleneand vinylacetate. The resulting structure combines the excellent gasbarrier properties of vinyl alcohol and the chemical resistance andprocessability of polyethylene. EVOH exhibits under dry conditions anexceptional gas barrier. Under the influence of humidity, these barrierproperties deteriorate however dramatically. This is due to the factthat EVOH contains large amounts of hydrophilic hydroxy groups,which readily interact with water.EVOH films are usually embedded in polyolefin layers with a good waterbarrier.EVOH resins are highly crystalline, thermally stable, have highmechanical strength, elasticity and surface hardness, very high gloss,low haze, good abrasion resistance, very high resistance to oils andorganic solvents, and provide an excellent barrier to odours. EVOHmulti-layer materials are often employed in modified atmospherepackaging of ready meals, cured meat, bakery products or fresh pasta.(PE/EVOH/PE or PA/EVOH/PE for lidding PS/EVOH/PE for tray material).
  11. 11. PVdCVinylidene chloride is usually co-polymerised with vinyl chloride(typically 20%) to yield a soft, tough and relatively impermeable film.It is an especially heavy polymer (density 1.68 – 1.75 g/m3). PurePVdC results in a stiff, brittle film hardly suitable for packagingpurposes. Co-polymers of PVdC show a unique combination of lowwater vapour transmission rate and oxygen permeability (SARAN® 25 m: WVTR 2.4 g/m2*day (38°C/90%RH), O2 -TR: 16ml/m2*day*bar (23°C/50%RH)).PVdC lattices are very often applied as aqueous dispersion to paperand plastics films to provide barrier to gases and moisture and odours.It provides furthermore a reasonable sealability to any substrate.Typical applications are medical blister (PVC 250 m / 40 g/m2 PVDC)or biscuit wrapping (PAP 60 g/m2 / PVDC 20 g/m2).
  12. 12. BAREXBAREX is a tradename for rubber-modified co-polymers of acrylonitrile andmethyl acrylate. They were originally developed for beverage bottle usagebecause of their excellent barrier properties, clarity, high impact strength andinsolubility in many organic solvents. In flexible packaging its outstandingresistance to oils, fats and aggressive products are appreciated. It replacespolyethylene as a sealant in cases where the product is too aggressive to be indirect contact with polyolefins. In laminates with paper/aluminium foil/BAREX itis frequently used in form of sachets for packaging soups, spices, aromas,perfumes or lemon juice.
  13. 13. Coated materials: metallisingMetallised film is developed by vapourising molten metal, anddepositing it onto a cold polymer web. Aluminium is most commonlyused because of its cost-effectiveness. The process takes place in avacuum chamber; the amount of metal applied is carefully controlled byinstrumentation, and the vacuum temperature of the metal and speedof the web feed must also be closely monitored. The thickness of thedeposited layer is approximately 30 nm. Metallisation improves themoisture- and gas-barrier properties of the film and prevents light fromreaching the product. It also confers the material a glossy metalappearance. It is therefore also used for decorative purposes e.g. in theconfectionery market segment. The two most common substrates arePET and OPP. HDPE and OPA are less frequently metallised. Applicationsare very wide spread in packaging of water- and oxygen sensitive fillinggoods
  14. 14. Raw materials - Barrier films Vacuum coated films Metallization process THE KEY PARAMETERS OF THE METALLIZING PROCESS ARE: •stable vacuum for even and consistent coating;•temperature control to avoid deformation and damage to the material; •accurate winding control especially on the low tension range.
  15. 15. Coated materials: SiOx, AlOx As an alternative to Al-metallisation transparent barrier layers canbe employed. The so-called glassy barrier layers consist ofamorphous metal oxides of approx. 30 nm thickness. In practise onlytwo play a significant role, namely silicon oxide (SiOx) and aluminiumoxide (Al2O3) layers. Three different methods of deposition exist:Thermal evaporation of SiO, electron beam induced evaporation ofSiO/SiO2 and Plasma enhanced chemical vapour deposition.Main applications are packaging of oxygen/ moisture sensitive foodsin areas where it is desirable to see the product (transparent barrier).Substrates are mainly PET but also to some extend OPP. Both aremicrowaveable. When the fragile and rather brittle glassy layer isprotected by an additional layer, the structure becomes retortable.Another target market is the replacement of triple structures such asPET/Al/PE by duplex structures such as PET-SiOx/PE.Yet another method to create a thin transparent layer is to apply anorganic lacquer with dispersed clay platelets, creating a tortuous pathfor gases, organic solvents, aromas and UV light. This trick leads to ahigh barrier material with a WVTR of about 25g/m²*day and anoxygen permeability of < 1cm3/m²*day (23°C/85%RH).
  16. 16. Low density polyethylene and derivativesPE is the largest volume single polymer used in food packaging. Theway in which the gaseous monomer ethylene is polymerised determinesto large extend the density and the properties of the final product.The crystallinity of low density polyethylene LDPE usually variesbetween 50 – 70 % and its density between 0.915 – 0.935 g/cm3. Thesoftening point of LDPE is just below 100°C thus precluding itsutilisation in sterilisation applications. LDPE is tough, with good tensilestrength, impact and tear resistance and posses an exceptional barrierto water. The permeability for oxygen and other gases is however veryhigh. It has very good chemical resistance to acids, alkalis but issensitive to hydrocarbons, oils and greases. Oils and many otherorganic compounds including many aromas are absorbed by LDPEleading to swelling of the polymer. The most outstanding property ofLDPE is its ability to be fusion welded to itself to yield good, tough,liquid tight seals.LLDPEs can be produced in wide range of densities ranging from 0.90 to0.935 g/cm3. A mayor feature of LLDPE is that its molecular weightdistribution is narrower than that of LDPE leading to a an improvedchemical resistance, tear resistance and impact strength, higher surfacegloss, and higher melting point.
  17. 17. IonomersWith density 0.94g/cm3 are co-polymers of ethylene and a smallamount of an unsaturated short chain carboxylic acid (e.g. methacrylicacid). The resulting polymer is than neutralised to varying degrees withmetal derivatives (e.g. zinc acetate) leading to an ionisation of thecarboxylic acid groups. As a consequence ionic cross-linking occursbetween different branches of the polymer leading to enhancedstiffness and toughness. In comparison with LDPE ionomers have animproved oil and grease resistance, which particularly appreciated whensealing packages with oily or greasy contents, as it allows for correctsealing even through fat contaminated sealing areas. Ionomers alsoexhibit increased clarity and abrasion resistance with respect to LDPEs.The moisture barrier is however reduced due to a lower degree ofcrystallinity. The most prevalent trade name for ionomers is Surlyn® byDuPont. The two captions currently used are sodium and zinc. Theformer has a better hot tack and better fat resistance while the latterresults in a better adherence to aluminium and metallised surfaces. Atypical application is in combination with polyamide for MAP/vacuumpackaging of meat and poultry and cheese products.
  18. 18. More polymers
  19. 19. Packaging Industries Can Take Advantage of Innovative Technology.New Microwave Packaging ConceptsActive Packaging ConceptsReactive coatings (micro contact inks,polymer electronics etc.)Digital print technologies/ Ink jetBarrier packagingVariable labels & labelingPackage security featuresNanotechnology
  20. 20. Transport Properties
  21. 21. WVTRThe water vapour transmission (WVTR) rate of a packaging materialdepends on two mayor factors: the permeation rate through thematerial and the difference in water vapour pressure in- and outsidethe package (the chemical potential gradient, Dm). To give an example, the water vapour pressure at 23°C, 85% rel. humidity is 23,5 mbar isonly about a third of that at 38°C and 90% rel. humidity (72,6 mbar).The permeation rate is again a function of two mayor factors: thesolubility of water in the polymer and its diffusion coefficient (P = D xS. The solubility of water depends on the interaction between the polarwater molecule and the polymer molecular structure. The more polargroups the polymer contains, the higher the enthalpy of solution andthe higher the solubility. The diffusion depends on the degree ofcrystallinity and on the moisture content of the polymer. The higher thecrystallinity, the lower the diffusion speed is. The moisture content hastwo opposing effects on the diffusion process. On the other hand doesinteraction with the polymer bind the water reducing its mobility.The temperature dependence is thus expressed in the form. WVTR alsodepends on the thickness of the relevant material. It is often assumedto be a linear relationship.
  22. 22. Gas permeabilityFor ambient gases other than water vapour the same is true as for theabove mentioned WVTR except that the solubility is to a much lesserdegree dependent on the nature of the polymer. It turns out that thepermeability ratio of a pair of gases will be relatively constant over aseries of polymers. The ratios of the permeabilities of CO2 to N2 varyonly by a factor of approx. 2 whereas the individual film permeabilitiesexhibit a factor of up to 500. It can also be seen that independent ofthe film material oxygen permeates about six times as fast as nitrogenand CO2 about four times as fast as oxygen and about 24 times as fastas nitrogen. There is no pattern for the ratios of water vapour to any ofthe three gases. It might seem strange that CO2, the largest of thethree gas molecules, has the highest permeability coefficient.Some of the factors influencing the permeability of polymers are :the chemical nature of the polymer (polymer – permeant interaction)microstructure of the polymer – crystallinity, thickness of the film,temperature, relative humidity (swelling, plasticising), and othervolatile compounds (such as solvents) which lead to swellingadditional layers such as metallisation, SiOx, Ormoceres®, CHx,diamond-like layers, clay platelets, PVdC or others.
  23. 23. Raw materials - Plastics Barrier filmsMaterial Characteristic O.D. µm O2 TR WV TR 2 cc/m *24h g/m2*24hPET Standard PET / 12 110 50 23°C 0% RH 38°C 90% RHPET PVDC coated / 12 8 8 23°C 85% RH 38°C 90% RHPET SiOx coated / 12 3.5 39 23°C 85% RH 38°C 90% RHPET Al2O3 coated / 12 2 2 23°C 0% RH 38°C 90% RHPET metallised 2.0 12 1.5 1.5 23°C 75% RH 38°C 90% RHPET white and metallised 2.2 12 1.5 1.5 23°C 75% RH 38°C 90% RHPET with inorganic coating / 12 1 25 23°C 60% RH 38°C 90% RHPET metallised very high barrier 2.6 12 0.08 0.04 25°C 85% RH 38°C 90% RHPEN Polyethylen naphtalate / 19 <1 3.8 38°C 90% RHPAN Polyacrilonitrile / 0.8 5 23°C 75% RH 38°C 90% RH
  24. 24. Raw materials - Plastics Barrier filmsM aterial Characteristic O.D. µm O 2 TR W V TR cc/m 2 *24h g/m2*24hBOPP Standard bioriented PP / 20 2000 7.5 23°C 0% RH 38 °C 90% RHBOPP Acrylic coated / 26 750 5 23°C 0% RH 38°C 90% RHBOPP PVdC coated / 26 25 4.2 23°C 0% RH 38°C 90% RHBOPP metallized 2.3 20 100 0.7 23°C 0% RH 38°C 90% RHBOPP cavitated and metallized 2.4 40 130 2 23°C 0% RH 38°C 90% RHBOPP metallised high barrier 2.2 16 30 1.5 23°C 0% RH 38°C 90% RHBOPP PVOH coated / 25 3 5 23°C 0% RH 38°C 90% RHBOPP metallized very high barrier ? 18 0.5 0.3 23°C 0% RH 38°C 90% RHBOPP cavitated - metallized very high barrier 3.6 35 0.2 0.4 23°C 0% RH 38 °C 90% RHOPA Standard oriented polyamide / 15 30 180 23°C 0% RH 38 °C 90% RHPA PA - EVOH - PA / 10 evoh 0.5 180 23°C 0% RH 38°C 90% RHPP PP - EVOH - PP / 15 evoh 0.3 100 23°C 0% RH 38°C 90% RHPE PE - EVOH - PE / 15 evoh / 130 38°C 90% RH
  25. 25. SealSealing has a decisive influence on the whole package permeability, thefactor that in the end determines the total amount of oxygen or gasthat enters or leaves the package. Whatever you again with a highbarrier layer you might loose by improper sealing. Replacing a laminatePET/Al/PE-LD with a structure OPP (high barrier) / OPP coex. withoutadjusting the packaging machine might lead to a flawed seal. Thesecond problem with the seal is the drainage effect; if the barrier layeris not close enough to the filling good. In this case oxygen and /orwater might diffuse via the cutting edge of the seal along the morepermeable layer towards the filling good without having to pass thebarrier. An example of such a packaging material was the structure(from outside to inside) : OPP 20mm / Al 12 mm / Paper 40 g /m²/waxwhich was used for packaging Ritter Sport Chocolate for a long time.
  26. 26. Converting of packaging materials
  27. 27. Converting Procedure Photos Scanning for Colour Separation CylinderCustomer Design & EngravingConcept Artwork Flexo Text Composing Sleeves (Text + Images) C o n v e r t i n g Metallising Waxing /Coating (Co) Extrusion Lamination Printing -adhesives - inks / - primers -lacquers - aluminium - resins - primers film/ foil/ paper - paraffins - film/ foil/ paper - solvents Slitting Die Cutting Bag-Making
  28. 28. ExtrusionExtruders consist of barrel, screw, drive mechanisms and control. Thesolid polymer is fed into the extruder as powder, flakes or pellets andthen melted and mixed by being passed through an Archimedeanscrew. The shear friction of the pellets between each other and to themachine causes heating of the polymer, which finally leads to melting.The extruder is heated additionally in various zones to be able tocontrol the temperature distribution, but this heating itself does noteffect the melting of the solid polymer. The polymer melt temperaturedepends mainly on the rotation speed of the screw, the demandedoutput and the pressure of the polymer melt at the outlet filter.Extrusion can also be used for coating with polymer blends, theextruder then requires different feeder stations. Because foodpackaging can require a wide range of properties, two or morepolymers are often coextruded through a single die to form a multi-layer film structure. Coextrusion is recommended for producing multi-layer films because of its lower cost; it can be used instead oflamination, avoiding the problem of double handling that occurs whena film lamination is being produced. Coextrusion is sometimespreferred because laminations require a separate manufacturingprocess for each film used in the final laminate.
  29. 29. LaminationA lamination is created when two or more individual films are bondedtogether with special adhesives and run through rolling, heatedcylinders to produce a composite film structure.One talks about wet bond laminating when the adhesive is wet in themoment of joining of the two webs, whereas dry bonding lamination iseffected when the adhesive is dried before bonding. In the case of wetbond laminating one of the webs has to be permeable to the solvent(e.g. water based casein glue used to laminate paper and aluminiumfoil). Solvent-based adhesives are very often two componentpolyurethane – isocyanate systems with ethylacetate as the principalsolvent. Curing occurs after lamination during the following few days.Solvent-free adhesive systems are usually based on short chainprecursor polymers e.g. oligourethanes which serve as their ownsolvent and a curing agent.Lamination is preferred when a specific film composition cannot beeffectively run on coextrusion systems due to equipment limitations,and also when the high temperatures required in coextrusion would beharmful to films. Lamination is also recommended when it is desirableto produce a composite film with properties superior to those affordedby a single film layer of the same gauge.
  30. 30. Lamination Arrangementsn roller arrangements for different types of lamination 1. Wax lamination 2. Wet lamination 3. Solvent-free lamination 4. Dry lamination 5. Dry lamination uncoated web coated web laminate
  31. 31. CoatingThe coating process involves the application of various materials to thefilm-web substrate to special features, improve properties, or changethe handling characteristics (sticking, slipping, etc.) of a film. Twomain families of coating exist: protective coatings (overlacquer) andcoatings with a sealing function. The former have to be hard, scratchresistant and thermally stable (e.g. NC-, epoxy- or PET-basedsystems), the latter have to be flexible, tight, chemically resistant andsealable (eg.g EVA-, PVA-, PVC- or PVDC-based systems). In practise ahole panoply of different resins, additives and solvents exists fromwhich the converter can choose to find the right combination for eachindividual application. Coating equipment consists of a coating head,often an engraved rotogravure cylinder, a drying unit, and the film-handling system.
  32. 32. PrintingPrinting is one important step in producing a package material. Thechoice of the printing technique and inks will to a large extendinfluence on the visual and sensory (off-flavours, rest solvents) qualityof the final material. Two different methods are commonly employed inflexible packaging :Rotogravure printing technique commonly used in packaging. Printingcan be performed on foil, film and paper/carton. Rotogravure machinesusually range between 6 to 12 colours. Printing speed is 100-300m/min. In rotogravure an engraved cylinder is rotating partiallywithin the printing ink, where its indentions are filled with therespective ink. Excess ink is removed by a doctor blade. The ink fromthe indentions is then transferred onto the substrate, which is pressedto the rotogravure cylinder by a second press cylinder. The quality ofthe print is very high, but set-up of the printing machine takesapproximately 10min per colour.Flexo printing is the second standard printing method in packaging.Printing plates are mounted to a cylinder, which then transfers the inkfrom a cylinder dipping into the ink reservoir to the substrate withnearly no pressure applied. Set-up times are somewhat shorter thanfor rotogravure. Also available with UV curing inks as UV Flexo.
  33. 33. Snacks example ... what are on the market?
  34. 34. Packaging machines and gas flushing
  35. 35. Application and controlPackaging line and material performances
  36. 36. Pillow packsThe HFFS is employed for the making of pillow packs.A tube is formed from hot or cold sealable wrappingfilm by means of an unwinder and correspondingturning system. The product slugs, in an exactlydefined interval, are then inserted into this tubemeans of an in-feed chain (Fig. 3a). The tube is thensealed along its length. In order to firmly seal thepackage ends, it is passed through a cross-sealingstation (Fig. 3b). Thanks to our unique cross sealingtechnology, a tight seam is created between theportioned slugs. Cutting occurs simultaneously. Theresult: A pillow pack characterised by the typical“end fins".
  37. 37. Flat bottom pouchesVertical bag formation: The bags are manufacturedby forming a pack around a vertical moulded tube.The passage over the form-giving shoulder is thecritical step in the making of the pouch as it imposesconsiderable mechanical strain on the packagingmaterial. The so-formed tubular pack is then sealedlengthways. At the end of the moulded tube, thepack is sealed along the bottom and the individualsare separated. This yields an open-top bag is thenconveyed to the cup filler of the packaging system.There are also variations where filling occurs directlyfrom the moulded tube.
  38. 38. Coffee vacuum packagingManufacturing a bag on the mandrel wheel is aunique procedure. Firstly, for each paper or filmsection fed from the reel stack is precisely positionedand placed around one of the metal mandrels themandrel wheel. The intermittently mandrel wheelnow conveys the so formed package cases to furtherstations at which the bottom and side seams arecreated sealed to yield neatly formed bags left openat the top. These are then transferred to the cupfiller of the packaging system. After they have beenfilled, the bags closed and sealed at the top.Depending on the product and the customerrequirements, various seals are possible. Evacuationvacuum wheel with up to 30 chambers gas flushingalso number among the possible designs.
  39. 39. Product sensitivity-food deteroriation mechanism Factors that influence shelf-life are basically to beclassified into three areas: Food properties, packageproperties and climatic storage condition. The formerhave been treated previously, the latter clearly affect the kinetics of the shelf-life determining process of food degradation in multiple ways. Foods are complex blends of often hundreds of different compounds. Their chemical and physicalproperties determine they sensitivity with respect to inevitable degradation. Here it gives an overview of the principal factors influencing the degradation of foods.
  40. 40. PhysicalBruising and mechanical deterioration of products is of principalconcern to food producers and packaging engineers. Examples arephysical abuse of fruits or vegetables during packaging or distributionor crushing of biscuits or chips.Temperature induced texture changes are usually the result ofphase changes. Examples are sugar and fat bloom as a case of re-crystallisation and phase segregation respectively. Freezer burnconstitutes an example of water sublimation and temperaturefluctuations around the dew point may lead to unwanted condensationof water in the package.Flavour scalping The absorption of flavour and aromacompounds by the packing materials inner liner is on of the mostimportant problems of compatibility in flexible packaging]. The mostprominent example is certainly the case of fruit juice in contact withpolyolefin sealing layers.
  41. 41. PhysicalMoisture gain or loss can alter considerably the texture of foods.Intermediate moisture foods such as pet food or cakes may hardendue to an excessive loss of humidity. Pasta turns brittle when itchanges from the rubbery to the glassy state and inversely snackssuch as potato chips or curls turn soggy when they move in theinverse direction. Caking is yet another example where the increase ofmoisture and temperature induce a glass – rubbery transition leadingto the agglomeration in powdery products.The sorption behaviour of foods is quantified with the aid of so-calledwater absorption isotherms. They put into relation the amount ofabsorbed water (moisture in g/g dry solid) with the relative ambienthumidity. This is true for a specific temperature, hence the termisotherm and after an equilibrium state has been reached. A typicalwater absorption isotherm of a biscuit is shown in aw stands for wateractivity which relates to the relative humidity RH like RH = 100*aw.
  42. 42. ChemicalDuring processing and storage of food stuffs a great variety ofchemical reactions can alter the food chemical composition and lead todegradation in terms of nutritive value or organoleptic properties. Themayor modes are mentioned below:Enzymatic During processing of foods, tissue damage occurswhich causes the release of various chemical constituents into thecellular fluid. These chemicals can then react with each other or withcompounds from the environment. For example lipoxidase enzymesreleased from certain cell constituents (mitochondria) can attack fatsand cause rancidity. Similarly, the polyphenol oxidase can react withsome parts of the cell and oxygen to form the well known brown colourof bruised or cut fruit (e.g. apples or bananas).Lipid oxidation Many foods contain unsaturated fats, which areimportant for human nutrition. Unfortunately, these fats are subject todirect attack by oxygen through an auto-catalytic free radicalmechanism. This results in rancid off-flavours which render the foodundesirable to consume. Very little fat has to oxidise for the consumerto detect rancidity and reject the food. Light and trace metals canunder certain circumstances catalyse the reaction rate by orders ofmagnitude.
  43. 43. ChemicalNonenzymatic Browning (NEB) NEB stands for another mayor family ofchemical reactions leading to a loss of nutritional and organolepticvalue of the affected food. NEB is the result of reactions betweenreducing sugars such as glucose, fructose or lactose and amino groupcontaining compounds such as proteins. Browning can also occur byheating sugars to high temperatures (or very long reaction times) orthrough the oxidation of vitamin C. Undesirable aspects of NEB are theproduction of bitter flavours, darkening of light-coloured dry productssuch as infant formulae or juices and the staling of coffee. Factorswhich influence the rate of NEB are temperature, water activity andacidity (pH).Moisture Moisture changes may induce food deterioration by physicalmeans (see above) or chemical means. All the above mentioned modesof deterioration enzymatic, lipid oxidation, NEB and also microbialgrowth are strongly affected by water. The rates at which thesereactions take place depend markedly on the water activity of the food.One also has to take into consideration that water activity rather thantotal moisture content is the relevant parameter determining undesiredchemical changes in foods.
  44. 44. MicrobialMicro-organisms constitute an important mechanism by which manyfoods, especially fresh ones , lose their quality. This is becausemicrobes are ubiquitous in the environment and grow very fast.Knowledge of the rate of growth of microbes as a function of theenvironmental conditions is very essential in the prediction of shelf-lifeof foods such as fresh meat, poultry and fish as well as dairy productssuch as milk, cheese and yoghurt. Also affected are brad, cured meat,fruit juices and fruits and vegetables.The basic methods for the control of micro-organisms are thefollowing:- Lower temperature to slow growthRaise temperature to kill themRemove or bind water to slow or prevent growthLower pHControl O2 or CO2 level to control populationManipulate food composition to remove nutrients needed by themicrobesAdd preservatives (e.g. sodium benzoate)
  45. 45. MAP, CAP and Active Packaging
  46. 46. Active packagingActive packaging does more than simply provide a barrier to outsideinfluences. It can control, and even react to, events taking place insidethe package.Fresh foods just after harvest or slaughter are still active biologicalsystems. The atmosphere inside a package constantly changes asgases and moisture is produced during metabolic processes. The typeof packaging used will also influence the atmosphere around the foodbecause some plastics have poor barrier properties to gases andmoisture. The metabolism of fresh food continues to use up oxygen inthe headspace of a package and increases the carbon dioxideconcentration. At the same time water is produced and the humidity inthe headspace of the package builds up. This encourages the growth ofspoilage micro-organisms and damages the fruit and vegetable tissue.Many food plants produce ethylene as part of their normal metaboliccycle. This simple organic compound triggers ripening and ageing. Thisexplains why fruit such as bananas and avocados ripen quickly whenkept in the presence of ripe or damaged fruits in a container andbroccoli turns yellow even when kept in the refrigerator.
  47. 47. Ethylene scavengingA chemical reagent, incorporated into the packaging film, traps theethylene produced by ripening fruit or vegetables. The reaction isirreversible and only small quantities of the scavenger are required toremove ethylene at the concentrations at which it is produced.Systems developed are already commercially available. These usuallyinvolve the inclusion in the package of a small sachet, which containsan appropriate scavenger. The sachet material itself is highlypermeable to ethylene and diffusion through the sachet is not a seriouslimitation. The reacting chemical for ethylene is usually potassiumpermanganate, which oxidises and inactivates it. However many otherpossibilities are conceivable: activated charcoal impregnated with anoxidising agent such as KBRO3; electron deficient aromatic compounds(e.g. dicarboxyoctyl ester substituted benzene); or simply ethyleneabsorbing compounds such as activated charcoal, molecular sieves orclay materials.
  48. 48. Carbon dioxide releaseHigh carbon dioxide levels are desirable in some food packagesbecause they inhibit surface growth of micro-organisms. Fresh meat,poultry, fish, cheeses and strawberries are foods, which can benefitfrom packaging in a high carbon dioxide atmosphere.However with the introduction of modified atmosphere packaging thereis a need to generate varying concentrations of carbon dioxide to suitspecific food requirements. Since carbon dioxide is more permeablethrough plastic films than is oxygen, carbon dioxide will need to beactively produced in some applications to maintain the desiredatmosphere in the package.So far the problems associated with diffusion of gases, especiallycarbon dioxide, through the package, have not been resolved and thisremains an important research topic.
  49. 49. Other developmentsOther systems of active packaging which are eitheralready available or could soon be seen in the marketplace include:- sachets containing iron powder and calciumhydroxide which scavenge both oxygen and carbondioxide. These sachets are used to extend the shelflife of ground coffee.- film containing microbial inhibitors other thanthose noted above. Other inhibitors beinginvestigated include metal ions and salts of propionicacid.- specially fabricated films to absorb flavours andodours or, conversely, to release them into thepackage.
  50. 50. Innovations and Trends Looking ahead Innovation is an essential Factor ? Product Material Machine Packaging Trends: - Differentiation - Existing function - New Technologies ....types of packaging - User Obser- to create new ap- - Fast speed and serving size vation plication - Greater flexibility trends. - Socioeconomic - Reduce cost-in- - Mass customi- use sation - Health and SafetyMarket Trends and Drivers: Competitive Trends:- Kids and Teenagers - Competing on Convenience- Ready-to-use Products on Hand - Importance of being smaller- Cooking Trends - Meals and Side Dishes- Parameters for Convenience - Dairy Products- Expanding Distribution - Beverages- Package Sizes - Snacks and Confectioneries- Vending Machine Trends - Health & Personal Care- Natural Food Store Trends - etc.- Warehouse Club Trends- Convenience Store Trends