LISTS OF ACCEPTABLE POLYMERS FOR USE IN FOOD PACKAGING APPLICATIONS ppsx

37 714 0
LISTS OF ACCEPTABLE POLYMERS FOR USE IN FOOD PACKAGING APPLICATIONS ppsx

Đang tải... (xem toàn văn)

Tài liệu hạn chế xem trước, để xem đầy đủ mời bạn chọn Tải xuống

Thông tin tài liệu

1 Food Packaging Materials Food Packaging Materials LISTS OF ACCEPTABLE POLYMERS FOR USE IN FOOD PACKAGING APPLICATIONS Tables to 12 list polymers that have been granted no objection status by the Food Packaging Materials & Incidental Additives Section of the Chemical Health Hazard Assessment Division (Food Directorate) for use in food packaging applications The polymers are coded and categorized as shown in the following table POLYMER CATEGORIES Table No Polymer Type Code polyethylenes PE polypropylenes PP polystyrenes PS polyvinyl chlorides PVC ionomers I polyethylene terephthalates PET polyvinyl acetates PVAc polycarbonates PC polyamides PA 10 polyvinyl alcohols PVOH 11 polyvinylidene chlorides PVDC 12 Others O Food Packaging Materials For polycarbonate at a glance, click here Polycarbonate, or specifically polycarbonate of bisphenol A, is a clear plastic used to make shatterproof windows, lightweight eyeglass lenses, and such General Electric makes this stuff and sells it as Lexan Polycarbonate gets its name from the carbonate groups in its backbone chain We call it polycarbonate of bisphenol A because it is made from bisphenol A and phosgene This starts out with the reaction of bisphenol A with sodium hydroxide to get the sodium salt of bisphenol A The sodium salt of bisphenol A is then reacted with phosgene, a right nasty compound which was a favorite chemical weapon in World War I, to produce the polycarbonate What? You want the gritty details of the reaction? Then click here and you will not be disappointed Another polymer used for unbreakable windows is poly(methyl methacrylate) Food Packaging Materials Seeing Another Polycarbonate More Clearly Up until now, we've been talking about only one polycarbonate, polycarbonate of bisphenol A But there's another polycarbonate out there, that some of us look at all the time In fact, some of us, like me, never look at anything without the help of this polycarbonate This is the polycarbonate that is used to make ultra-light eyeglass lenses For people with really bad eyesight, like me, if the lenses were made out of glass, they would be so thick that they'd be too heavy to wear I know I used to have glass lenses My glasses were so heavy that wearing them gave me a headache But this new polycarbonate changed all that Not only is it a lot lighter than glass, but it has a much higher refractive index That means it bends light more than glass, so my glasses don't need to be nearly so thick So what is this wonderful new polycarbonate? It's very different from polycarbonate of bisphenol A We make it by starting with this monomer: You can see that it has two allyl groups on the ends These allyl groups have carboncarbon double bonds in them This means they can polymerize by free radical vinyl polymerization Of course, there are two allyl groups on each monomer The two allyl groups will become parts of different polymer chains In this way, all the chains will become tied together to form a crosslinked material that looks like this: Food Packaging Materials As you can see, the carbonate-containing groups (shown in blue) for the crosslinks between the polymer chains (shown in red) This crosslinking is makes the material very strong, so it won't break nearly as easily as glass will This is really important for kids' glasses! If only this stuff had been invented when I was a kid! There is a fundamental difference in the two types of polycarbonate described here that I should point out Polycarbonate of bisphenol A is a thermoplastic This means it can be molded when it is hot But the polycarbonate used in eyeglasses is a thermoset Thermosets not melt, and they can't be remolded They are used to make things that need to be really strong and heat resistant For polyethylene at a glance, click here! Polyethylene is probably the polymer you see most in daily life Polyethylene is the most popular plastic in the world This is the polymer that makes grocery bags, shampoo bottles, children's toys, and even bullet proof vests For such a versatile material, it has a very simple structure, the simplest of all commercial polymers A molecule of polyethylene is nothing more than a long chain of carbon atoms, with two hydrogen atoms attached to each carbon atom That's what the picture at the top of the page shows, but it might be easier to draw it like the picture below, only with the chain of carbon atoms being many thousands of atoms long: Sometimes it's a little more complicated Sometimes some of the carbons, instead of having hydrogens attached to them, will have long chains of polyethylene attached to them This is called branched, or low-density polyethylene, or LDPE When there is no branching, it is called linear polyethylene, or HDPE Linear polyethylene is much stronger Food Packaging Materials than branched polyethylene, but branched polyethylene is cheaper and easier to make Linear polyethylene is normally produced with molecular weights in the range of 200,000 to 500,000, but it can be made even higher Polyethylene with molecular weights of three to six million is referred to as ultra-high molecular weight polyethylene, or UHMWPE UHMWPE can be used to make fibers which are so strong they replaced Kevlar for use in bullet proof vests Large sheets of it can be used instead of ice for skating rinks Food Packaging Materials Polyethylene is vinyl polymer, made from the monomer ethylene Here's a model of the ethylene monomer It looks like some sort of art nouveau teddy bear if you ask me Branched polyethylene is often made by free radical vinyl polymerization Linear polyethylene is made by a more complicated procedure called Ziegler-Natta polymerization UHMWPE is made using metallocene catalysis polymerization But Ziegler-Natta polymerization can be used to make LDPE, too By copolymerizing ethylene monomer with a alkyl-branched comonomer such as one gets a copolymer which has short hydrocarbon branches Copolymers like this are called linear low-density polyethylene, or LLDPE BP produces LLDPE using a comonomer with the catchy name 4methyl-1-pentene, and sells it under the trade name Innovexă LLDPE is often used to make things like plastic films Food Packaging Materials For polypropylene at a glance, click here! Polypropylene is one of those rather versatile polymers out there It serves double duty, both as a plastic and as a fiber As a plastic it is used to make things like dishwasher-safe food containers It can this because it doesn't melt below 160 oC, or 320 oF Polyethylene, a more common plastic, will anneal at around 100 oC, which means that polyethylene dishes will warp in the dishwasher As a fiber, polypropylene is used to make indoor-outdoor carpeting, the kind that you always find around swimming pools and miniature golf courses It works well for outdoor carpet because it is easy to make colored polypropylene, and because polypropylene doesn't absorb water, like nylon does Structurally, it is a vinyl polymer, and is similar to polyethylene, only that on every other carbon atom in the backbone chain has a methyl group attached to it Polypropylene can be made from the monomer propylene by Ziegler-Natta polymerization and by metallocene catalysis polymerization This is what the monomer propylene really looks like: Wanna know more? Food Packaging Materials Research is being conducted on using metallocene catalysis polymerization to synthesize polypropylene Metallocene catalysis polymerization can some pretty amazing things for polypropylene Polypropylene can be made with different tacticities Most polypropylene we use is isotactic This means that all the methyl groups are on the same side of the chain, like this: But sometimes we use atactic polypropylene Atactic means that the methyl groups are placed randomly on both sides of the chain like this: However, using special metallocene catalysts it is believed that we can make polymers which contain blocks of isotactic polypropylene and blocks of atactic polypropylene in the same polymer chain, as is shown in the picture: This polymer is rubbery, and makes a good elastomer This is because the isotactic blocks will form crystals by themselves But because the isotactic blocks are joined to the atactic blocks, each little hard clump of crystalline isotactic polypropylene will be tied together by soft rubbery tethers of atactic polypropylene, as you can see in the picture on the right To be honest, atactic polypropylene would be rubbery without help from the isotactic blocks, but it wouldn't be very strong The hard isotactic blocks hold the rubbery isotactic material together, to give the material more strength Most kinds of rubber have to be crosslinked to give them strength, but not polypropylene elastomers Elastomeric polypropylene, as this copolymer is called, is a kind of thermoplastic elastomer However, until the research is completed, this type of polypropylene will not be commercially available The polypropylene which you can buy off the shelf at the store today has about 50 - 60% crystallinity, but this is too much for it to behave as an elastomer Food Packaging Materials For poly(ethylene terepthalate) at a glance, click here! Polyesters are the polymers, in the form of fibers, that were used back in the seventies to make all that wonderful disco clothing, the kind you see being modeled on the right But since then, the nations of the world have striven to develop more tasteful uses for polyesters, like those nifty shatterproof plastic bottles that hold your favorite refreshing beverages, like the blue bottle in the picture below So you see, polyesters can be both plastics and fibers Another place you find polyester is in balloons Not the cheap ones that you use for water balloons, those are made of natural rubber I'm talking about the fancy ones you get when you're in the hospital These are made of a polyester film made by DuPont called Mylar The balloons are made of a sandwich, composed of Mylar and aluminum foil Materials like this, made of two kinds of material, are called composites A special family of polyesters are polycarbonates Polyesters have hydrocarbon backbones which contain ester linkages, hence the name The structure in the picture is called poly(ethylene terephthalate), or PET for short, because it is made up of ethylene groups and terephthalate groups (duh!) I realize that terephthalate is not the kind of word most English-speaking mouths are used to saying, but with practice you should be able to say it with only a slight feeling of awkwardness when it rolls off your tongue Food Packaging Materials 10 The ester groups in the polyester chain are polar, with the carbonyl oxygen atom having a somewhat negative charge and the carbonyl carbon atom having a somewhat positive charge The positive and negative charges of different ester groups are attracted to each other This allows the ester groups of nearby chains to line up with each other in crystal form, which is why they can form strong fibers The inventor who first discovered how to make bottles from PET was Nathaniel Wyeth He's the brother of Andrew Wyeth the famous painter But others had tried before Go read this story of someone who may have been the first person to try to make a shatterproof bottle Now I'm sure everyone out there is just dying to have two questions answered The first one is: Why can't you return plastic soft drink bottles to get a cool nickel per bottle like you could with the old glass bottles? And the second one which I'm positive everyone is wondering about is: How come peanut butter comes in neato shatterproof jars but jelly doesn't? These two riveting questions, as it turns out, have the same answer The answer is that PET has too low a glass transition temperature, that is the temperature at which the PET becomes soft Now reusing a soft drink bottle requires that the bottle be sterilized before it is used again This means washing it at really high temperatures, temperatures too high for PET Filling a jar with jelly is also carried out at high temperatures Down at your local jelly factory, the stuff is shot into the jars hot, at temperatures which would cause PET to become soft So PET is no good for jelly jars PEN Saves the Day! There is a new kind of polyester that is just the thing needed for jelly jars and returnable bottles It is poly(ethylene naphthalate), or PEN PEN has a higher glass transition temperature than PET That's the temperature at which a polymer gets soft The glass transition temperature of PEN is high enough so that it can withstand the heat of both sterilizing bottle washing and hot strawberry jelly PEN is so good at standing the heat that you don't even have to make the bottle entirely out of it Just mixing some PEN in with the old PET gives a bottle that can take the heat a lot better than plain old PET Food Packaging Materials But Kevlar® is different When it tries to twist into the cis- conformation, the hydrogens on the big aromatic groups get in the way! The cis conformation puts the hydrogens just a little closer to each other than they want to be So Kevlar ® stays nearly fully in the transconformation So Kevlar® can fully extend to form beautiful fibers 23 Food Packaging Materials Now it may help to look at a close-up picture of this Look at the picture below and you can see that when Kevlar® tries to form the cis- conformation, there's not enough room for the phenyl hydrogens So only the trans- conformation is usually found 24 Food Packaging Materials 25 But there's another polymer that stretches out even better called ultra-high molecular weight polyethylene It even replaced Kevlar® for making bullet-proof vests! For polyacrylonitrile at a glance, click here! Polyacrylonitrile is used for very few products an average consumer would be familiar with, except to make another polymer, carbon fiber Homopolymers of polyacrylonitrile have been uses as fibers in hot gas filtration systems, outdoor awnings, sails for yachts, and even fiber reinforced concrete But mostly copolymers containing polyacrylonitrile are used as fibers to make knitted clothing, like socks and sweaters, as well as outdoor products like tents and such If the label of some piece of clothing says "acrylic", then it's made out of some Food Packaging Materials 26 copolymer of polyacrylonitrile Usually they're copolymers of acrylonitrile and methyl acrylate, or acrylonitrile and methyl methacrylate: Also, sometimes we make copolymers of acrylonitrile and vinyl chloride These copolymers are flame-retardant, and the fibers made from them are called modacrylic fibers But the slew of copolymers of acrylonitrile doesn't stop there Poly(styrene-coacrylonitrile) (SAN) and poly(acrylonitrile-co-butadiene-co styrene) (ABS), are used as plastics SAN is a simple random copolymer of styrene and acrylonitrile But ABS is more complicated It's made by polymerizing styrene and acrylonitrile in the presence of polybutadiene Polybutadiene has carbon-carbon double bonds in it, which can polymerize, too So we end up with a polybutadiene chain with SAN chains grafted onto it, like you see below Food Packaging Materials ABS is very strong and lightweight It is strong enough to be used to make automobile body parts, but it is so light that Wassana can lift this front bumper fascia over her head with only hand! Using plastics like ABS makes automobiles lighter, so they use less fuel, and therefore they pollute less ABS is a stronger plastic than polystyrene because of the nitrile groups of its acrylonitrile units The nitrile groups are very polar, so they are attracted to each other This allows opposite charges on the nitrile groups to stabilize each other like you see in the picture on the left This strong attraction holds ABS chains together tightly, making the material stronger Also the rubbery polybutadiene makes ABS tougher than polystyrene Polyacrylonitrile is a vinyl polymer, and a derivative of the acrylate family of polymers It is made from the monomer acrylonitrile by free radical vinyl polymerization 27 28 Food Packaging Materials For cellulose at a glance, click here! Cellulose is one of many polymers found in nature Wood, paper, and cotton all contain cellulose Cellulose is an excellent fiber Wood, cotton, and hemp rope are all made of fibrous cellulose Cellulose is made of repeat units of the monomer glucose This is the same glucose which your body metabolizes in order to live, but you can't digest it in the form of cellulose Because cellulose is built out of a sugar monomer, it is called a polysaccharide Now take a look at glucose in 3-D! Cellulose has an important place in the story of polymers because it was used to make some of the first synthetic polymers, like cellulose nitrate, cellulose acetate, and rayon Click here to find out more Clean hair Another cellulose derivative is hydroxyethylcellulose It differs from plain ol' regular cellulose in that some or all of the hydroxyl groups (shown in red) of the glucose repeat unit have been replaced with hydroxyethyl ether groups (shown in blue) Food Packaging Materials These hydroxyethyl groups get in the way when the polymer tries to crystallize Because it can't crystallize, hydroxyethylcellulose is soluble in water In addition to being a great laxative, it's used to thicken shampoos as well It also make the soap in the shampoo less foamy, and it helps the shampoo clean better by forming colloids around dirt particles Normally, particles of dirt are insoluble in water But a chain of hydroxyethylcellulose (shown in blue) can wrap itself around a dirt particle (shown in red) This mass can be thought of as a snack cake, with the polymer chain as the cake and the dirt as the creamy filling This snack cake is soluble in water, so by wrapping around the dirt like this, the hydroxyethylcellulose tricks the water into accepting the dirt In this way, the dirt gets washed away instead of being deposited back onto your hair 29 30 Food Packaging Materials Starch is important because we eat it! Starch is found in potatoes, and in grains such as corn and wheat Starch is made up of glucose repeat units Click on the glucose to see it in 3-D In your body, special proteins called enzymes (which are also polymers, by the way) break starch down into glucose, so your body can burn it for energy If you're eating a healthy diet, you get most of your energy from starch in this way Because it is made of sugar molecules it is called a polysaccharide It is very similar to cellulose To see just how the two are different, click here Starch has a few other uses other than food It's used in pressing clothes to keep them from wrinkling It's also used to make a foam packing Starch is biodegradable, so starch foam packing is an environmentally-friendly alternative to styrofoam packing But be careful! Entropy, the black labrador retriever on the right, likes to eat starch packing, so don't turn your back on her if you've got a box of it around! 31 Food Packaging Materials Polyurethanes are the most well known polymers used to make foams If you're sitting on a padded chair right now, the cushion is more than likely made of a polyurethane foam Polyurethanes are more than foam Much more than foam! Polyurethanes are the single most versatile family of polymers there is Polyurethanes can be elastomers, and they can be paints They can be fibers, and they can be adhesives They just pop up everywhere A wonderfully bizarre polyurethane is spandex Of course, polyurethanes are called polyurethanes because in their backbones they have a urethane linkage The picture shows the a simple polyurethane, but a polyurethane can be any polymer containing the urethane linkage in its backbone chain More sophisticated polyurethanes are possible, for example: Food Packaging Materials Polyurethanes are made by reacting diisocyanates with di-alcohols To find out how, click here Sometimes, the dialcohol is replaced with a diamine, and the polymer we get is a polyurea, because it contains a urea linkage, rather than a urethane linkage But these are usually called polyurethanes, because they probably wouldn't sell well with a name like polyurea Polyurethanes can hydrogen bond very well, and thus can be very crystalline For this reason they are often used to make block copolymers with soft rubbery polymers These block copolymers have properties of thermoplastic elastomers 32 33 Food Packaging Materials Spandex One unusual polyurethane thermoplastic elastomer is spandex, which DuPont sells under the trade name Lycra It has both urea and urethane linkages in its backbone What gives spandex its special properties is the fact that it has hard and soft blocks in its repeat structure The short polymeric chain of a polyglycol, usually about forty or so repeats units long, is soft and rubbery The rest of the repeat unit, you know, the stretch with the urethane linkages, the urea linkages, and the aromatic groups, is extremely rigid This section is stiff enough that the rigid sections from different chains clump together and align to form fibers Of course, they are unusual fibers, as the fibrous domains formed by the stiff blocks are linked together by the rubbery soft sections The result is a fiber that acts like an elastomer! This allows us to make fabric that stretches for exercise clothing and the like Codes Descriptions Polyethylene Terephthalate (PET, PETE) PET is clear, tough, and has good gas and moisture barrier properties Commonly used in soft drink bottles and many injection Properties Packaging Applications Recycled Products Clarity, strength, toughness, barrier to gas and moisture, resistance to heat Plastic soft drink, water, sports drink, beer, mouthwash, catsup and salad dressing bottles Peanut butter, pickle, jelly and jam jars Ovenable film and ovenable prepared food trays Fiber, tote bags, clothing, film and sheet, food and beverage containers, carpet, strapping, fleece wear, luggage and bottles 34 Food Packaging Materials molded consumer product containers Other applications include strapping and both food and non-food containers Cleaned, recycled PET flakes and pellets are in great demand for spinning fiber for carpet yarns, producing fiberfill and geo-textiles Nickname: Polyester High Density Polyethylene (HDPE) HDPE is used to make bottles for milk, juice, water and laundry products Unpigmented bottles are translucent, have good barrier properties and stiffness, and are well suited to packaging products with a short shelf life such as milk Because HDPE has good chemical resistance, it is used for packaging many household and industrial chemicals such as Stiffness, strength, toughness, resistance to chemicals and moisture, permeability to gas, ease of processing, and ease of forming Milk, water, juice, cosmetic, shampoo, dish and laundry detergent bottles; yogurt and margarine tubs; cereal box liners; grocery, trash and retail bags Liquid laundry detergent, shampoo, conditioner and motor oil bottles; pipe, buckets, crates, flower pots, garden edging, film and sheet, recycling bins, benches, dog houses, plastic lumber, floor tiles, picnic tables, fencing 35 Food Packaging Materials detergents and bleach Pigmented HDPE bottles have better stress crack resistance than unpigmented HDPE bottles Vinyl (Polyvinyl Chloride or PVC): In addition to its stable physical properties, PVC has excellent chemical resistance, good weatherability, flow characteristics and stable electrical properties The diverse slate of vinyl products can be broadly divided into rigid and flexible materials Bottles and packaging sheet are major rigid markets, but it is also widely used in the construction market for such applications as pipes and fittings, siding, carpet backing and windows Flexible vinyl is used in wire and cable insulation, film and sheet, Versatility, clarity, ease of blending, strength, toughness, resistance to grease, oil and chemicals Clear food and nonfood packaging, medical tubing, wire and cable insulation, film and sheet, construction products such as pipes, fittings, siding, floor tiles, carpet backing and window frames Packaging, loose-leaf binders, decking, paneling, gutters, mud flaps, film and sheet, floor tiles and mats, resilient flooring, cassette trays, electrical boxes, cables, traffic cones, garden hose, mobile home skirting 36 Food Packaging Materials floor coverings synthetic leather products, coatings, blood bags, medical tubing and many other applications Low Density Polyethylene (LDPE).Used predominately in film applications due to its toughness, flexibility and relative transparency, making it popular for use in applications where heat sealing is necessary LDPE is also used to manufacture some flexible lids and bottles and it is used in wire and cable applications Polypropylene (PP) Polypropylene has good chemical resistance, is strong, and has a high melting point making it good for hot-fill liquids PP is found in flexible and rigid packaging to fibers and large molded parts for automotive and consumer products Polystyrene (PS) Polystyrene is a versatile plastic that can be rigid or foamed General purpose polystyrene is clear, hard and brittle It has a relatively low melting point Typical applications include protective Ease of processing, strength, toughness, flexibility, ease of sealing, barrier to moisture Dry cleaning, bread and frozen food bags, squeezable bottles, e.g honey, mustard Shipping envelopes, garbage can liners, floor tile, furniture, film and sheet, compost bins, paneling, trash cans, landscape timber, lumber Strength, toughness, resistance to heat, chemicals, grease and oil, versatile, barrier to moisture Catsup bottles, yogurt containers and margarine tubs, medicine bottles Automobile battery cases, signal lights, battery cables, brooms, brushes, ice scrapers, oil funnels, bicycle racks, rakes, bins, pallets, sheeting, trays Versatility, Compact disc insulation, clarity, jackets, food service easily formed applications, grocery store meat trays, egg cartons, aspirin bottles, cups, plates, cutlery Thermometers, light switch plates, thermal insulation, egg cartons, vents, desk trays, rulers, license plate frames, foam packing, foam plates, cups, utensils 37 Food Packaging Materials packaging, containers, lids, cups, bottles and trays Other Use of this code indicates that the package in question is made with a resin other than the six listed above, or is made of more than one resin listed above, and used in a multilayer combination DISCLAIMER Dependent on resin or combination of resins Three and five Bottles, plastic lumber gallon reusable applications water bottles, some citrus juice and catsup bottles APC MAKES NO WARRANTY, EXPRESS OR IMPLIED, RESPECTING THE ACCURACY OR COMPLETENESS OF THE INFORMATION PROVIDED HEREIN INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE OR PURPOSE APC SHALL NOT BE RESPONSIBLE FOR ANY DIRECT, INDIRECT, INCIDENTAL OR CONSEQUENTIAL DAMAGES, DAMAGES FROM LOSS OF USE OR PROFITS, OR COST OF PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES, IN CONTRACT, TORT OR OTHERWISE ARISING OUT OF GOODS OR IN CONNECTION WITH THE INFORMATION CONTAINED HEREIN RECYCLING OF PLASTICS MAY NOT BE AVAILABLE EVERYWHERE CHECK TO SEE IF PLASTICS RECYCLING IS AVAILABLE IN YOUR COMMUNITY * Cần thêm thông tin vào trang web sau: www.gc.ca/main_e.html www.hc-sc.gc.ca/food-aliment/cs-ipc/chha-edpcs/e_food_packaging.html www.psrc.usm.edu/macrog/plastic.htm www.psrc.usm.edu/macrog/xlink.htm#thermoset ... "vinyl" siding used on houses is made of poly(vinyl chloride) Inside the house, PVC is used to make linoleum for the floor In the seventies, PVC was often used to make vinyl car tops PVC is useful... it''s a polystyrene chain with chains of polybutadiene growing out of it Food Packaging Materials These rubbery chains hanging off of the backbone chain some good things for polystyrene Polybutadiene... UHMWPE can be used to make fibers which are so strong they replaced Kevlar for use in bullet proof vests Large sheets of it can be used instead of ice for skating rinks Food Packaging Materials

Ngày đăng: 01/08/2014, 07:20

Từ khóa liên quan

Mục lục

  • LISTS OF ACCEPTABLE POLYMERS FOR USE IN FOOD PACKAGING APPLICATIONS

    • Seeing Another Polycarbonate More Clearly

    • Wanna know more?

    • Why can't you return plastic soft drink bottles to get a cool nickel per bottle like you could with the old glass bottles?

    • How come peanut butter comes in neato shatterproof jars but jelly doesn't?

    • PEN Saves the Day!

    • The Polystyrene of the Future

    • Why? Why?

    • Clean hair

    • Spandex

Tài liệu cùng người dùng

  • Đang cập nhật ...

Tài liệu liên quan