Smart Packaging PDF

Smart Packaging Active packaging uses active principles that are generated by or originate from the package and exert a specific effect on the packed food product like antimicrobial agents, oxygen absorbers, ethylene scavengers, etc. The purpose of its use is to preserve and maintain the f...

Smart Packaging Active packaging uses active principles that are generated by or originate from the package and exert a specific effect on the packed food product like antimicrobial agents, oxygen absorbers, ethylene scavengers, etc. The purpose of its use is to preserve and maintain the food quality throughout the supply chain and the storage period at the consumer. Intelligent packaging uses different principles to monitor the status of the packed product and to communicate it. DEFINITIONS OF ACTIVE PACKAGING Packaging may be termed active when it performs some role other than providing an inert barrier to the external environment. Active packaging can be defined as a system in which the product, package, and the environment interact in a positive way to extend the shelf life or to achieve some characteristics. It has also been defined as a type of packaging that changes the condition of the packaging to extend shelf life or to improve safety or sensory properties while maintaining the quality of the packaged food. According to regulations 1935/2004/EC and 450/2009/EC, active materials and articles are intended to extend the shelf life or to maintain or improve the condition of packaged food. They are designed to deliberately incorporate components that would release or absorb substances into or from the packaged food or environment surrounding the food. GOAL OF ACTIVE PACKAGING The goal of active packaging is to enhance the preservation of food in the package and prolonging shelf life involves application of various strategies like temperature control, oxygen removal, moisture control, addition of chemicals such as salt, sugar, carbon dioxide or natural acids or a combination of these with effective packaging. ACTIVE PACKAGING  Some examples…PASSIVE vs ACTIVE O2 SCAVENGER IN A SACHET O2 ABSORBER IN A PLASTIC FILM ACTIVE ACTIVE COMPONENT COMPONENT Other substances that do not play a role in active PASSIVE FILM function, belong to the passive part of the PASSIVE FILM packaging If the internal O2 is absorbed too but the effect is UNINTENTIONAL or LIMITED, it is NOT considered an ACTIVE PACKAGING If there is an INTENTIONAL EFFECT on FOOD or ENVIRONMENT around it, it is considered an ACTIVE PACKAGING O2 SCAVENGER IN A SACHET O2 ABSORBER IN A PLASTIC FILM ACTIVE ACTIVE COMPONENT COMPONENT Other substances that do not play a role in active PASSIVE FILM function, belong to the passive part of the PASSIVE FILM packaging If the role of oxygen absorber is to scavenge any oxygen and PREVENT it from permeating from the environment outside the package through the package wall into the food or the environment surrounding the food, it is NOT considered an ACTIVE PACKAGING under Reg. EC 450/2009, but a barrier enhancer The free-oxygen absorbing agent, AGELESS™, absorbs oxygen in a sealed container and creates a deoxidized environment where the concentration of oxygen is 0.1% or lower. Oxygen Barrier Films Carbon Dioxide Absorbers and Emitters CO2 scavengers, another active packaging technology, used not as much as O2 scavengers, are commercialized to avoid gas pressure buildup inside rigid packaging or volume expansion in flexible packaging by absorbing CO2 produced by fermented or roasted foods CO2 scavengers can be composed either of a physical absorbent (zeolite or an active carbon powder) or of a chemical absorbent (calcium hydroxide, Na2CO3, Mg(OH)2, etc.) CO2+CaOH→HCO3Ca CO2 scavengers are mainly used in freshly roasted coffees, which produce a significant amount of CO2 if hermetically sealed in packs directly after roasting leading to the bursting of the package The use of CO2 scavengers replaces the ‘aging’ process after coffee roasting and thereby prevents the loss of desirable coffee volatiles OR one-way gas valve Antimicrobial Food Packaging ❑To enhance quality and safety ❑To reduce the growth rate of microorganisms Examples; Silver ions Ethyl Alcohol Chlorine Dioxide Nisin Organic Acids (Acetic, Benzoic, Lactic, Tartaric and Propionic) Allyl isothiocyanate Spice based essential oils Metal oxides  Wasaouro® is a material that ingeniously employs the Wasaouro antibacterial and antifungal powers found in nature to extend the freshness of foods. Used for over 1000 years in the preparation of a variety of foods such as sushi and sashimi, wasabi (or Japanese horseradish) is known the world over as a Japanese condiment with a rich flavour and invigorating bite. In addition to its affinity with the Japanese palate, wasabi has another special trait: it possesses an antibacterial action that curbs the growth of bacteria and prevents the formation of mould on foods. Specifically, the volatile oil contained in wasabi a substance known as allyl mustard oil has a scientifically proven potent antibacterial action which can be used to extend the shelf-life of foodstuffs and similar materials. The antibacterial agent Wasaouro® is the product of a research and development project that employed the latest technology and expertise to harness the antimicrobial activity of allyl mustard oil for the purpose of foodstuff preservation. Wasaouro® is currently used extensively in the areas of product quality maintenance and sanitary management for food products. ANTIOXIDANT RELEASE ❑ Antioxidants are widely used in food to improve the oxidation stability of the food to prolong the shelf life. ❑ Antioxidants are incorporated in packaging films as a source of antioxidants in some foods since the increased consumer demand for reduced antioxidants and additives in foods. ❑ Antioxidant incorporation can also stabilize the polymer in order to protect the films from degradation ❑ The effect of Butylated Hydroxy toluene (BHT) incorporated HDPE packs for oat flake was studied. But the effect of BHT on human health is been questioned due to accumulative effect of BHT in human adipose tissue. ❑ Incorporating natural antioxidants like Vitamin C, and E on packaging films can reduce oxidative reactions like development of rancid odour and colour changes in fatty fishes. ❑ Vitamin E is also safe and effective for low to medium water activity cereal and snack food products and proved to be stable under processing conditions with excellent solubility in polyolefins. Flavor or odour absorbers and releasers ❑ The volatile compounds that accumulate inside the package as a result of food degradation such as aldehydes, amines and sulfides can be selectively scavenged. ❑ Flavor scavengers prevent the cross contamination of pungent odour while transportation of mixed loads. ❑ Volatile amines formed due to the protein breakdown in fish muscle can be removed by incorporating acidic compounds like citric acid in polymers ❑ The ANICO bags (Japan) made from film containing ferrous salt and an organic acid such as citric acid or ascorbic acid is capable of oxidizing the amines ❑ Use of high barrier packaging materials can also prevent the absorption of other nonfood odors like taints Moisture Absorbers ❑ Moisture absorbent pads, sheets and blankets are used for controlling liquid from foods like fish, meat, poultry, fruits and vegetables. ❑ Desiccants are mainly used in products like cheese, chips, nuts, candies, spices etc. ❑ Desiccants like silica gel, molecular sieves, calcium oxide are used for dry foods while micro porous bags or pads of inorganic salts and protected layer of solid polymeric humectants are used to buffering the humidity inside the cartons. FDE 418 Food Packaging : Technologies FOOD TECHNOLOGIES Special Packaging Technologies Modified Atmosphere Packaging Vacuum Packaging Active and Intelligent Packaging Aseptic Packaging Product-Specific Packaging Materials and Technologies Meat, Fish, and Poultry Products Dairy and Dairy Products Fruits and Vegetables Cereal and Cereal-Based Products Beverages Snack Foods and Confectionary  How to extend the shelf life of food? By lowering the rate of biochemical, enzymatic and microbial degradation reactions during storage Controlled Atmosphere (CA) ❑Generally refers to decreased oxygen and increased carbon dioxide concentrations by precise control of the gas composition Modified Atmosphere (MA) ❑ is used when the control of the storage atmosphere is not closely controlled, such as in plastic film packaging ❖DIFFERENCE CA: Gas atmosphere is continuously controlled throughout the storage period MA: Gas composition is modified initially and it changes dynamically depending on the respiration rate of produce and permeability of film or storage condition surrounding the produce. Modified Atmosphere Packaging This technology makes use of an internal gas composition in the headspace of the package that differs from the composition of the surrounding atmosphere to preserve the food quality for both fresh (fruits and vegetables, meat, etc.) and processed foods (cakes, pastries, etc.) for a longer time. Whereas fresh foods often create a different internal atmosphere due to their own respiration, processed foods need the admission of specific gas mixtures into the headspace of the package. Why MAP? ❑Food does not stay fresh forever. Enzymatic reactions, lipid oxidation, and microbial growth are important causes of food spoilage during storage. ❑Food additives can be used to extend the shelf life of foods by preventing the undesirable changes aforementioned. ❑Refrigeration – the lower the temperature, the slower most microbes will grow – or treatments such as pickling, curing with salt are other preservation techniques that are commonly used to increase shelf life. ❑To keep food fresh for as long as possible without additives is a challenge, and one key method for achieving this goal is to seal the food product in a package including mixture of gases in optimized proportions that significantly slow down the biochemical changes inhibiting processes of oxidation and the growth of microbes. ❑Modified atmosphere packages achieve this by decreasing the oxygen concentration and filling the packages with gases such as N2, CO2. What is Modified Atmosphere Packaging? Modified Atmosphere Packaging (MAP) is the conversion of the gaseous environment generated by respiration or by the addition and elimination of gases from small sized food packages to manipulate the levels of O2, CO2, N2, C2H4. This method is used to slow down the process of decay by inhibiting process of oxidation and growth of microbes. MAP extends shelf life without using additives.  MAP Gases According to EU and US regulations all manufacturers producing products with a reduced oxygen content or protective atmosphere have to set up critical control points regarding both the gas content and the seal integrity. ALSO ; E-numbers have to be included on the packaging label, according to EU regulations. The correct E-numbers for gasses are: Carbon dioxide E 290 Argon E 938 Helium E 939 Nitrogen E 941 Nitrous oxide E 942 Oxygen E 948 Hydrogen E 949 Modified Atmosphere Packaging of Foods Modified atmosphere packaging (MAP) is an indirect food preservation technique that was initially designed to preserve the quality of fresh produce. As the name implies, the gas composition in a package is modified such that microbial growth and chemical deterioration reactions are to be kept at minimum levels. It is noteworthy to mention that in modified atmosphere packages the atmosphere is not controlled but just modified. There are different storage and packaging techniques that are based on the change in composition of the storage atmosphere. Controlled atmosphere storage (CAS) aims to control the optimum gas composition in a storage room within the specified tolerances. In CAS, a gas generator is usually used to create and control the modified atmosphere in a cold warehouse where the product is kept However, in modified atmosphere storage initial gas composition is modified in an airtight storage room and the atmosphere changes with time due to respiratory activity and the growth of microorganisms CAS is capital intensive and difficult to operate; thus, it is more appropriate for foods that are amenable to long-term changes such as apple, kiwifruits, and pears and meat. Modified Atmosphere Packaging of Foods In MAP, the product is kept in a carefully designed permeable polymer package, and the modified atmosphere is created and maintained through the respiration of the product and the gas permeation of the package. MAP is a more affordable technology since a gas generator is not needed; however, it is also a more difficult technology to implement since the permeability of the packages to the gases should be considered for the best design. Gases Used in MAP O2, CO2, and N2 are the three gases that are mainly used in MAP systems. The proportion of the gases depends on the food commodity that is packed. Noble or inert gases such as argon can also be used to create a modified atmosphere. Research use of carbon monoxide (CO) on meat and sulfur dioxide (SO2) in the form of SO2-generating pads for table grapes has also been reported. CO has been licensed for use in the United States to prevent browning in packed lettuce. Commercial application has been limited because of its toxicity and the formation of potentially explosive mixtures with air. Gases Used in MAP: O2 Oxygen (O2) is a colorless, odorless gas that is highly reactive. It has a low solubility in water (0.040 g kg -1 at 100 kPa, 20 °C) Oxygen is responsible of several biochemical reactions in foods including lipid and pigment oxidation, browning reactions. Most of the common spoilage bacteria and fungi require O2 for growth. Therefore, to increase the shelf life of foods, the package atmosphere should contain a low concentration of residual O2. On the other hand, in some foods a low concentration of O2 can result in quality and safety problems (for example, unfavorable color changes in red meat pigments, senescence in fruits and vegetables, and growth of food poisoning bacteria), and this must be taken into account when selecting the gaseous composition for a packaged food. Gases Used in MAP: CO2 & N2 ❑Carbon dioxide could be considered as the most important gas in MAP of foods due to its antimicrobial properties. ❑CO2 is a colorless gas with a slight pungent odor at very high concentrations. ❑It readily dissolves in water where a small amount is hydrated to carbonic acid (H2CO3). ❑CO2 is also soluble in lipids and some other organic compounds. Solubility increases with decreasing temperature and the antimicrobial activity is markedly greater at lower temperatures. High solubility in water and fat can lead to discoloration, off-flavors, excess purge by muscle foods, and package collapse. ❑Nitrogen is a physiologically inert gas with low solubility in water. It is used in MAP as a filler to exclude oxygen and to prevent collapse caused by dissolution of CO2 in the food. Methods of Creating MAP Conditions Passive Modified Atmosphere ❑Packaging materials used in MAP are mostly plastic polymers. Polymers show different permeabilities for different gases. Modified atmospheres can develop within a hermetically sealed package as a consequence of a commodity’s respiration or due to other biochemical reactions. ❑If oxygen consumption or carbon dioxide formation characteristics are properly matched to film permeability values, then a beneficial modified atmosphere can be passively created within a package. ❑The concentration of gases at which the headspace atmosphere reaches equilibrium depends on the weight and respiration rate of the commodity and on the surface area and gas transmission rate of the packaging material. Methods of Creating MAP Conditions Active Modified Atmosphere ❑By pulling a slight vacuum and replacing the package atmosphere with a desired mixture of CO2, O2, and N2, a beneficial equilibrium atmosphere may be established more quickly than a passively generated equilibrium atmosphere. ❑In another active MAP system no vacuum is used but a gas mixture is injected into the package and the air swept or flushed immediately prior to sealing resulting in residual O2 levels of 2–5% ❑Active MAP systems could also be created using O2, CO2 scavengers/emitters, and SO2-generating pads ❑Such scavengers/emitters are capable of establishing a rapid equilibrium atmosphere within hermetically sealed produce packages. APPLICATION OF MAP Meat and meat products are one of the most demanded food categories throughout the world. The consumer-related quality indicators for fresh red meat are color, juiciness, and microbial safety. Once the animal is slaughtered, the red meat color pigment (myoglobin) tends to oxidize to either to an unwanted grey-brownish color (metmyoglobin) upon exposure to low levels of oxygen or to the red oxymyoglobin at high oxygen levels. The color change towards grey in meat is an undesirable quality, which is determined by consumers during the meat purchase. APPLICATION OF MAP Other changes after slaughter include the exudation of fluid (drip) from meat muscles that besides resulting in shrinkage of myofibrils, allows a pool of spoilage and pathogenic microorganisms to grow on a nutrient-rich substrate. To preserve the meat quality, packaging plays a vital role in maintaining the shelf life and safety of meat and meat products. Several packaging methods are used by the meat industry for marketing the fresh meat. Vacuum packaging has been widely used to pack meat either for retail or bulk storage. Vacuum Packaging This is based on the principle of excluding oxygen to prevent the oxidation in oxygen sensitive foods, for example, nuts, beer, chocolates, fats and oils, fried products, etc. Comparison with Vacuum Packaging In Vacuum packaging, all air is removed. It aims to increase shelf life. MAP is a packaging method and it aims to improve quality and increase shelf life. The special gas mixture in MAP, does not only preserve food from m/o but also keep its freshness and color APPLICATION OF MAP Vacuum packaging may be performed either as shrink packaging, nonshrink packaging, or as thermoformed trays. This method is effective for the prevention of oxidative greying, oxidative rancidity and aerobic microbial spoilage. Some of the limitations to vacuum packaging include proliferation of anaerobic pathogenic bacteria, release of muscle water due to pressure on muscle filaments, and residual oxygen resulting in surface color changes due to oxidation of surface meat pigments. Vacuum packaging is suitable for refrigerated bulk storage with an estimated shelf life of 10–12 weeks at 0 °C. Oxygen permeable trays for meat are in use for a limited shelf life of 2–3 days. The advantage of these packaging systems is the rapid oxidation of the myoglobin to oxymyoglobin, giving the bright red meat color, generally preferred by consumers. When the beef is vacuum-packaged, a bright-red oxymyoglobin (OMb) is oxidized to a brown metmyoglobin (MMb) in a low partial pressure of oxygen. MMb is subsequently converted to a purplish red deoxymyoglobin (DMb) in an anaerobic condition. However, if the residual oxygen exists in a package, the oxidation of DMb could occur fast, accumulating MMb on the surface of beef which could negatively affect the consumer’s choice. APPLICATION OF MAP In the recent years, modified atmosphere packaging (MAP) has emerged as an innovative approach to pack fresh red meats. Modified atmosphere packaging has several advantages over vacuum packaging as it prevents the drip loss, restricts the growth of microorganisms, and retains the meat color. Several gas combinations are in practice and use depending on the type of the meat, for example, high-oxygen MAP, low-oxygen MAP, and ultra low-oxygen MAP. APPLICATION OF MAP Aerobic bacteria cause spoilage Aerobic → needs Oxygen Low oxygen atmosphere is desirable HOWEVER meat have to retain its red color. Myoglobin binds oxygen so gives RED color For red color How do we inhibit bacteria? aerobic bacteria can be significantly inhibited by carbon dioxide gas. APPLICATION OF MAP Attractive appearance and slow spoilage rate can be achieved ! For beef ; Normal shelf life : 2-4 days MAP shelf life : 8 days For poultry ; Normal shelf life : 4- 7days MAP shelf life : 16-21 days APPLICATION OF MAP Poultry meat is also prone to spoilage due to its favorable pH, which supports the growth of several microorganisms during storage and distribution. Although color degradation is not a major concern for poultry, spoilage, and pathogenic microorganisms have been the limiting factor. Vacuum packaging of poultry meat is limited to strict refrigerated storage conditions (anaerobic growth). However, commercially MAP may be suitable at 25–50% CO2 and 50–75% N2 levels. The microbial safety of MAP packed poultry has often raised safety concerns. However, MAP with strict temperature management has been successful in preventing spoilage and foodborne outbreaks. The application of MAP resulted in a shelf life extension of approximately 4–5 days when the chicken cuts were stored at 4 °C. APPLICATION OF MAP Bad fish gives unpleasant odour Carbon dioxide and Nitrogen gases are used with different ratios 20 : 80 Carbon dioxide : Nitrogen 50 : 50 Carbon dioxide :Nitrogen A proportion of carbon dioxide is effective in inhibiting the growth of common aerobic bacteria, so some sea foods contains only carbon dioxide MAP. Since fish contain high fat, oxygen may cause oxidation so, it is not used. APPLICATION OF MAP : PROCESSED MEAT The Red and pink pigments in processed meat can be affected by oxygen in the air and light, which cause them turn a brownish grey color. APPLICATION OF MAP : BREAD Commonly used for tortilla wraps, baguetta, bagels, pita breads Moulds are aerobic and needs Oxygen for their growth Exclude Oxygen and fill Carbon dioxide Carbon dioxide adding increases shelf life from 5 days to 20 days at room temperature storage. By the help of MAP, baked products are easily stored , transported and distributed. APPLICATION OF MAP : CHEESE Fats of some cheese are oxidized by oxygen in air, this makes cheese rancid. 100 % CO2 can be used for hard cheeses, 20-40 % CO2 for soft cheeses Rest is Nitrogen gases. MAP allows to cheese “breathe” and develop more flavor and good appearance. Shelf life extend from 2 -3 weeks in air to up to ten weeks in MAP  APPLICATION OF MAP : FRESH FRUITS AND VEGETABLES Fresh fruit and vegetables keep respiration after they have been harvested. Major aim is to reduce respiration rate without harming the quality of the product. Rate of respiration can be reduced by keeping temperature low having low oxygen level inside package increase level of carbondioxide APPLICATION OF MAP If there is too little oxygen in the packaging atmosphere, anaerobic respiration takes place. This produces unwanted tastes and odors in the product and will cause the food to deteriorate. Furthermore, excessively high carbon dioxide can damage some varieties of product. Packaging material is crucial, how permeable or breathable the material is important. If the products are sealed in an airtight package, oxygen will soon become depleted and undesirable anaerobic conditions could develop. On the other hand if the material is too porous, the modified atmosphere will escape and no benefit will be derived. APPLICATION OF MAP In order to achieve an equilibrium state, equilibrium modified atmosphere (EMA) is produced. Here, oxygen and carbon dioxide can pass between the inside and outside of the package in such a way that as oxygen is consumed within the pack it is replaced by oxygen from outside, and similarly a constant level of carbon dioxide is maintained. By this way ethylene gases production is prevented by MAP. PERFORATIONS APPLICATION OF MAP : READY MEALS Different food materials are contained in a single package (such as pizzas and sandwiches ) and each of these deteriorates in a different way. On their own they would have a different MAP regime. Together a compromise gas mixture must be found. Low oxygen levels have been shown to delay the development of stale off-taste. Applications of MAP Some recent commercial applications of MAP are: a. Flaxseed oil packaged with argon flushing b. Freshly roasted coffee packaged with argon flushing c. Chopped lettuce and salad leaves d. Prawns packaged in an atmosphere typically containing only carbon dioxide and nitrogen e. Hermetic seals maintaining modified atmosphere in a meat package by providing O2 to the package f. Processed meat in tray sealing with modified atmosphere g. Shredded or grated cheese packaged in modified atmosphere with reclosable zipper pillow pack h. Mushrooms packaged in tray sealing in modified atmosphere in rigid trays i. Chicken cut-up packaged in flow pack wrapper in modified atmosphere using a cross-linked polyolefin based soft shrink film  Quality Control of MAP How can you achieve a good quality control procedure? It is crucial to ensure that the gas mixture is correct and the package is not leaking. Seal Integrity and Leak Detection of MAP Products can be achieved by 2 ways 1. WATER BATH 2. TRACE GAS LEAK DETECTION  Quality Control of MAP For most products it is also important to set limits for the maximum and minimum residual oxygen level in the packages. Two ways for control ; *Random testing *On-line monitoring. The instruments used are gas analyzers which measure oxygen (O2) or oxygen/carbon dioxide (O2/CO2), depending on which blend is used in the packages. Quality Control of MAP *Random testing *On-line monitoring CONCLUSION MAP provides longer shelf life without using any additives Potential shelf life increases by 50 to 400 % Quality control and packaging material type have important effects for efficiency of MAP Very large application area Clear view of product is provided It makes easier distribution and storage due to better utilization of labor, space and equipment so cost decreases Packaging Material Properties Mechanical Properties Optical Properties of Glass and Plastic Packaging Barrier Properties of Plastic Packaging Factors Affecting Permeability Tensile Strength The tensile strength of a material quantifies how much stress the material will endure before failing. In general tensile strength increases with polymer chain length.  Tensile Strength Mechanical behavior of amorphous and semi-crystalline polymers is strongly affected by Tg Polymers whose Tg is above the service temperature are strong, stiff and sometimes brittle e.g. Polystyrene (cheap, clear plastic drink cups) Polymers whose Tg is below the service temperature are weaker, less rigid, and more ductile Polyethylene (milk jugs) Optical Properties of Glass and Plastic Packaging Glass, because it has no crystalline structure, is optically isotropic when it is homogeneous and free from any stresses. The optical properties of glass relate to the degree of penetration of light and the subsequent effect of that transmission, transmission being a function of wavelength. Light transmission may be controlled by the addition of coloring additives such as metallic oxides, sulfides, or selenides. Most of the transition metal oxides (e.g., cobalt, nickel, chromium, iron, etc.) give rise to absorption bands, not only in the visible but also in the UV and IR regions of the spectrum. The three main colors of glass used to produce food containers are flint or clear, amber or brown, and green.  Typical light transmission of the glasses Amber glass provides this degree of light protection quite economically. A light-resistant container is defined as one that passes no more than 10% of incident radiation at any wavelength between 290 nm and 450 nm through the average sidewall thickness. Optical Properties of Glass and Plastic Packaging Optical properties of plastics are related to both the degree of crystallinity and the actual polymer structure. Optical properties of importance with thermoplastic polymers include clarity, haze, color, transmittance, reflectance, gloss, and refractive index. Barrier Properties of Plastic Packaging Unlike metal and glass packages, plastic packages are permeable and the concept of permeability is normally associated with the quantitative evaluation of the barrier properties of a plastic. A plastic that is a good barrier has a low permeability. The protection of foods from gas and vapor exchange with the environment depends on the integrity of packages (including their seals and closures), and on the permeability of the packaging materials themselves. The barrier properties of plastics indicate their resistance to sorption and diffusion of substances such as gases and flavor and aroma compounds. Barrier Properties of Plastic Packaging Under steady-state conditions, a gas or vapor diffuses through a polymer at a constant rate if a constant pressure difference is maintained across the polymer. The diffusive flux, J, of a permeant (vapor) in a polymer can be defined as the amount passing through a plane (surface) of unit area normal to the direction of flow during unit time as follows: 𝐽 = 𝑄/𝐴𝑡 where Q is the total amount of permeant that has passed through area A during time t. Barrier Properties of Plastic Packaging The relationship between the rate of permeation and the concentration gradient is one of direct proportionality and is embodied in Fick’s first law: 𝛿𝑐 𝐽 = −𝐷 𝛿𝑥 Equation can be used to calculate the steady-state rate of diffusion assuming that D is constant and the concentration is a function only of the geometric position inside the polymer. Barrier Properties of Plastic Packaging Consider a polymer X mm thick, of area A, exposed to a permeant at pressure p1 on one side and at a lower pressure p2 on the other as shown in Figure. The concentration of permeant in the first layer of the polymer is c1 and in the last layer c2. When steady-state diffusion has been reached, J=constant and ODE can be integrated across the total thickness of the polymer X, and between the two concentrations, assuming D to be constant and independent of c: 𝐽𝑋 = −𝐷(c2 − c1) 𝐷 c2 − c1 𝐴𝑡 𝑄= 𝑋 Barrier Properties of Plastic Packaging By substituting for J, the quantity of permeant Q diffusing through a polymer of area A in time t can be calculated: 𝐷 c2 − c1 𝐴𝑡 𝑄= 𝑋 Rather than the actual concentration, it is more convenient when the permeant is a gas to measure the vapor pressure p, which is at equilibrium with the polymer, rather than measure the actual concentration. Henry’s law applies at low concentrations and c can be expressed as: 𝑐 = 𝑆𝑝 where S is the solubility coefficient of the permeant in the polymer (it reflects the amount of permeant in the polymer). Barrier Properties of Plastic Packaging 𝐷 c2 − c1 𝐴𝑡 𝑄= 𝑐 = 𝑆𝑝 𝑋 𝐷𝑆 𝑝1 − p2 𝐴𝑡 𝑄= 𝑋 The product DS is referred to as the permeability coefficient or constant and is represented by the symbol P: 𝑃 = 𝐷𝑆 Barrier Properties of Plastic Packaging Thus, the permeability coefficient is the product of a kinetic term (D), which reflects the dynamics of the penetrant-polymer system, and of a thermodynamic term (S), which depends on the penetrant-polymer interactions. P represents the ease with which a gas permeates through a polymer when subjected to a pressure gradient. 𝑄𝑋 𝑃= 𝐴𝑡 𝑝1 − p2 or 𝑄 𝑃 = 𝐴(Δ𝑝) 𝑡 𝑋 Barrier Properties of Plastic Packaging 𝑄 𝑃 = 𝐴(Δ𝑝) 𝑡 𝑋 ❑The term P/X is called the permeance; it is not a property of the material but a performance evaluation indicator. ❑Although steady-state is usually attained in a few hours for small molecules such as O2, larger molecules in barrier polymers (especially glassy polymers) can take a long time to reach steady-state, with this time possibly exceeding the anticipated shelf life. ❑Although D and S are independent of concentration for many gases such as O2, N2, and, to a certain extent, CO2, this is not the case where considerable interaction between polymer and permeant takes place (e.g., water and hydrophilic films such as EVOH and PAs, or many solvent vapors diffusing through polymer films). Barrier Properties of Plastic Packaging ❑Although the chemical structure of a polymer can be considered to be the predominant factor that controls the magnitude of P, it also varies with the morphology of the polymer and depends on many physical factors such as density, crystallinity, and orientation. ❑The unit of P is: 𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑝𝑒𝑟𝑚𝑒𝑎𝑛𝑡 𝑢𝑛𝑑𝑒𝑟 𝑠𝑡𝑎𝑡𝑒𝑑 𝑐𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛𝑠 (𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠) 𝑃= 𝑎𝑟𝑒𝑎 𝑡𝑖𝑚𝑒 (𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑑𝑟𝑜𝑝 𝑎𝑐𝑟𝑜𝑠𝑠 𝑝𝑜𝑙𝑦𝑚𝑒𝑟) Barrier Properties of Plastic Packaging ❑The treatment of steady-state diffusion assumed that both D and S are independent of concentration but in practice deviations do occur. ❑It does not hold for heterogeneous materials such as coated or laminated films, or when there is interaction between polymer and permeant. The property is then defined as the transmission rate (TR) of the material, where: 𝑄 𝑇𝑅 = 𝐴𝑡 where Q is the amount of permeant passing through the polymer, A is the area, and t is the time. ❑Permeabilities of polymers to water and organic compounds are often presented in this way, and in the case of water and O 2 , the terms WVTR and oxygen transmission rate (OTR) are in common usage. Barrier Properties of Plastic Packaging It is critical that the thickness of the film or laminate, the temperature and the partial pressure difference of the gas or water vapor are specified for a particular TR. Typically, units of (g m-2 day-1) are used for WVTR and (ml m-2 day -1) for OTR. Often the WVTRs are given for so called tropical conditions of 38 °C/90% RH but sometimes for so-called temperate conditions of 25 °C/75% RH; OTRs are often given for 23 °C/0% RH. TR is related to P as follows: 𝑄𝑋 𝑋 𝑃= = 𝑇𝑅 𝐴𝑡Δ𝑝 Δ𝑝 25 µm (2.5 x 10-3 cm) thickness Permeability Units 𝑄𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑃𝑒𝑟𝑚𝑒𝑎𝑛𝑡 𝑈𝑛𝑑𝑒𝑟 𝑆𝑡𝑎𝑡𝑒𝑑 𝐶𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛𝑠 (𝑇ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠) 𝑃 = 𝑃𝑒𝑟𝑚𝑒𝑎𝑏𝑖𝑙𝑖𝑡𝑦 = 𝑎𝑟𝑒𝑎 𝑡𝑖𝑚𝑒 (𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑑𝑟𝑜𝑝 𝑎𝑐𝑟𝑜𝑜𝑠 𝑡ℎ𝑒 𝑝𝑜𝑙𝑦𝑚𝑒𝑟) ∆𝑄 𝑥 𝑥 𝑃= = 𝑇𝑅 ∗ > 𝑇𝑅 = 𝑇𝑟𝑎𝑛𝑠𝑓𝑒𝑟 𝑅𝑎𝑡𝑒 ∶ 𝑂𝑇𝑅 𝑓𝑜𝑟 𝑜𝑥𝑦𝑔𝑒𝑛 ∆𝑡. 𝐴 𝑝1 − 𝑝2 𝑝1 − 𝑝2 WVTR : Water Vapor Transfer Rate 10−10 (𝑚𝑙 𝑆𝑇𝑃൯ 𝑐𝑚 Barrer = 𝑐𝑚2 𝑠 (𝑐𝑚 𝐻𝑔) EXAMPLE: Calculate the permeability coefficient P of an OPP film to O2 at 23 oC given that the Oxygen Transmission Rate (OTR) through a 2.5*10-2 mm thick film with air on one side and inert gas on the other side is 1550 mL m-2 day-1 EXAMPLE Calculate the permeability coefficient P of an OPP film to O2 at 23 oC given that the Oxygen Transmission Rate (OTR) through a 2.5*10-2 mm thick film with air on one side and inert gas on the other side is 1550 mL m-2 day-1 Air contains approximately 21 % O2 = 0.21 atm=16 cm Hg 𝑂𝑇𝑅 1550 𝑚𝐿 𝑚−2 𝑑𝑎𝑦 −1 𝑃= 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 = ∗ 2.5 ∗ 10−2 𝑚𝑚 ∆𝑝 16 (𝑐𝑚 𝐻𝑔) P= 2.8*10-10 𝑚𝐿 𝑐𝑚 𝑐𝑚−2 𝑠 −1 𝑐𝑚 𝐻𝑔−1 = 2.8 barrer EXAMPLE WVTR of 290 mm thick OPLA at 37.8 oC and 100% RH as 36.7 g m-2 d-1. What is the permeability coefficient in barrer ? Saturated Vapor Pressure of Water @ 37.8 oC is 4.9167 cm Hg 𝑊𝑉𝑇𝑅 𝑃= 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 ∆𝑝 P= 1.88 10−11 kg 𝑚 𝑚−2 𝑠 −1 𝑃𝑎 −1 = 3.12x106 barrer WVTR WVTR could also be expressed based on the relative humidity difference. In that case WVTR will have units of ; kg.m-2.s-1 OR g.m-2.d-1 𝑊𝑉𝑇𝑅 𝑃= 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠s ∆𝑹𝑯 PERMEABILITY OF MULTILAYER PACKAGING MATERIALS These calculations will be valid for dry gas but not for moisture-sensitive materials. For moisture-sensitive material permeability will depend on the average partial pressure at the center thus equation should be modified.  Paper (80%): to provide strength and stiffness Polyethylene (15%): to make packages liquid tight and to provide a barrier to microorganisms Aluminium foil (5%): to keep out air, light, and off flavors - all the things that can cause food to deteriorate Case PET Cola Bottle: What is the loss of carbondioxide and water from a closed bottle of cola in 1 year? Given information: Volume: 1 liter Wall thickness: 0.5 mm Surface area: 0.1 m2 CO2 Transmission Rate: 320 ml/(m2 day bar) for 25 µm PET Amount of CO2 : 4 liter gas/liter cola Water Transmission Rate: 20 g/(m2 day) at RH of 100% Pressure in bottle: 4 bar Cola is store in a RH of 50% CO2: Transmission Rate for 0.5 mm: 320/20 = 16 ml/(m2 day bar) For bottle with area 0.1 m2 and pressure 4 bar: Loss is: 16 x 0.1 x 4 = 6.4 ml/day; in 1 year = 6.4 x 365= 2.3 liter = >50% Water: Transmission Rate for 0.5 mm: 20/20 = 1 g/(m2 day) For bottle with area 0.1 m2 and assumed RH = 50%: Loss is: 1 x 0.1 x 0.5 = 0.05 g/day; in 1 year = 0.05 x 365= 18 g =