Plastic bags also called "poly bags" are shaped like two identically-sized rectangular plastic sheets (usually less than 250 micron thickness) fused together on three of the sides, with one side left for the opening.
How it is made?
Most Plastic bags are made from polyethylene - more commonly known as polythene, which is made from crude oil and natural gas, non-renewable resources.
The most common way to produce polythene bags is by blown film extrusion, also called the "tubular film process."
In Blown film production process - polythene melt is extruded through an annular slit die, usually vertically, to form a thin walled tube. Air is introduced via a hole in the centre of the die to blow up the tube like a balloon. into the tube causing it to expand and form a bubble. Mounted on top of the die, a high-speed air ring blows onto the hot film to cool it. The tube of film then continues upwards, continually cooling, until it passes through nip rolls where the tube is flattened to create what is known as a ' lay-flat' tube of film. This lay-flat or collapsed tube is then taken back down the extrusion ' tower' via more rollers. The lay-flat film is then either kept as such or the edges of the lay-flat are slit off to produce two flat film sheets and wound up onto reels. If kept as lay-flat, the tube of film is made into bags by sealing across the width of film and cutting or perforating to make each bag. This is done either in line with the blown film process or at a later stage.
Common resins used to make plastic bags are:
- Low density polythene (LDPE): Ethylene polymer with densities ranging from about 0.916 to 0.925 grams per cubic centimetre
- High density polythene (HDPE): Ethylene polymer with densities ranging from 0.941 to 0.965 grams per cubic centimetre
- Liner low density polythene (LLDPE): Ethylene polymer with densities ranging from 0.900 to 0.939 grams per cubic centimetre
- Medium density polyethylene (MDPE): Ethylene polymer with densities ranging from 0.926 to 0.940 grams per cubic centimetre
- Polypropylene (PP): A thermoplastic resin made by the polymerization of high-purity propylene gas in the presence of catalyst at relatively low pressures and temperatures. It is used to make film, fibres, rope and moulded articles
- Ethylene Vinyl Acetate (EVA): EVA compounded with LDPE is widely used to prevent plastic film/bags from cracking down to -30 degrees centigrade
- Polyvinyl chloride (PVC): Thermoplastic resin produced by the polymerization of the gas vinyl chloride [CH2CHCl]. Used in soft, flexible films for food packing. Also used in rigid products such as pipes or window profile.
Special options available in plastic bags or polythene film
- Clear or Coloured Polythene bag/film - Standard plastic bag either clear or coloured (tint, opaque)
- Plain or Printed Polythene bag/film - Standard plastic bag either plain or printed (1, 2 or multicoloured)
- Flat Polybags - Standard plastic bag often called by flat polybags
- Gusseted Poly bags - Plastic bags with fitted bottom and expandable sides (gusset) form to the shape of your product.
- Zipper/Zip lock bags - Bags with simple slide zipper which back and forth to open and close the bag.
- Seal seal/Reclosable bags - Grip seal bags have a simple plastic ridge that clicks shut and pulls open for continual re-use.
- Shrink film or bags - Bag/film which shrinks fit with the contents.
- Stretch film or bags - Stretch film also called a stretch wrap. Stretch film can stretch up to 100%.
- Drawstring bags - A bag that is closed at the top with a drawstring.
- Merchandise bags - A bag usually coloured and printed with logo, design or slogan which can be used for presentation.
- Single wound sheeting - Lay flat polythene tubing slit on both sides, creating 2 sheets on top of each other and wound separately called SWS(single wound sheeting)
- Centrefold sheeting - Lay flat tubing slit on one side before winding so that a long sheet is formed, that opens out to twice the film width
- Lay flat tubing - Polythene bubble collapsed and wound up forming a tube. Can be Gusseted at sides (so the bubble opens out to a larger width). Ideal for packaging long 'difficult to wrap' items. Insert into tubing and cut to required length then heat seal both ends to create made-to-measure bags.
- Double wound sheeting - Lay flat polythene tubing slit on both sides, creating 2 sheets on top of each other but wound together known as DWS (double wound sheeting)
- J-fold - A strip of material is removed from the polythene film before winding.
- Centre slit tubing - A polythene film slited from the centre and wounded on two different cores.
- Bags on roll - Bags attached by perforation and rolled up on a core
- Polythene or Polybags individually cut
- Carrier bags with Cut handle, Loop handle, Clip Close or Vest style
Major UK Suppliers:
Standards for plastic bags/film to use for food contact and medical application
Food Contact - To use Polythene film or bags inside European Union, in contact with food should comply with the relevant legislation on food contact including Great Britain.
- Great Britain: Statutory Instrument, 1998 No. 1376 and BPF-BIBRA (1995), Polymer Specification 4, Polyethylene
- EU: Commission Directive 90/128/EEC, 92/39/EEC, 93/9/EEC, 95/3/EEC and 96/11/EC, Section A.
- Example of a company comply with food contact: Polybags Limited
Medical use - Similarly, to use Polythene film or bags inside European Union, to produce containers for preparations for medico-pharmaceutical purposes should comply with the following regulation:
- European Pharmacopoeia - Monograph 3.1.3 "Polyolefin's" for medico-pharmaceutical purposes.
- The final responsibility for the decision of whether a material is fit for a particular application lies with the pharmaceutical firm.
- Example of a company comply with medical use: Polybags Limited
Normally, plastic bags/film in Great Britain should be within the tolerances according to British Standard - see BS7344, 1990
- Width: Plus or minus 3mm (0.125") or 2% whichever is greater
- Length: Plus or minus 6mm (0.25") or 2% whichever is greater
- Gauge: Plus or minus 10%
Great Moments in Plastic Bag History
- 1957 The first baggies and sandwich bags on a roll are introduced.
- 1958 Poly dry cleaning bags compete with traditional brown paper.
- 1966 Plastic bag use in bread packaging takes over 25 to 30 percent of the market.
- 1966 Plastic produce bags on a roll are introduced in grocery stores.
- 1969 The New York City Sanitation Department's "New York City Experiment" demonstrates that plastic refuse bag kerbside pickup is cleaner, safer and quieter than metal trash can pick-up, beginning a shift to plastic can liners among consumers.
- 1974/75 Retailing giants such as Sears, J.C. Penney, Montgomery Ward, Jordan Marsh, Allied, Federated and Hills make the switch to plastic merchandise bags.
- 1973 The first commercial system for manufacturing plastic grocery bags becomes operational
- 1977 The plastic grocery bag is introduced to the supermarket industry as an alternative to paper sacks.
- 1982 Kroger and Safeway start to replace traditional craft sacks with polyethylene "t-shirt" bags.
- 1990 The first blue bag recycling program begins with kerbside collection.
- 1990 Consumer plastic bag recycling begins through a supermarket collection-site network.
- 1992 Nearly half of U.S. supermarkets have recycling available for plastic bags.
- 1996 Four of five grocery bags used are plastic.
- Garbage bags & liners: black refuse sacks, wheelie bin sacks, trash bags, bin liners, clear waste sacks, asbestos bags, clinical waste bags, recycling bag, dustbin bags etc.
- Agricultural films: greenhouse film, crop forcing film, silage film, silage stretch film, mulching films
- Grocery bags - carrier bags, counter bags, freezer bags, sandwich bags, food bag, net bag, candy bags
- Thin films for Paper & Tissue products
- Industry packaging: shrink film, stretch film, bag film or container liners
- Consumer Packaging: mailing bags, courier bags, specimen bags, gift bags, card bags, display bags, garment covers, flower bags
- Electronic packaging: antistatic bags, static dissipative bags, conductive bags
- Film/bags for packaging food or medical
Check more uses of plastic bags than you think!
63 Uses For Walmart Bags
Don't you just love the plastic shopping bags? Actually it's not just Wally World that has plastic carry-out bags. In any case, these plastic bags are incredibly useful for all sorts of things other than carrying your purchases out to your vehicle. Plastic bags find themselves reincarnated in a million different ways. I've long thought about starting a list of these uses, some seriously useful and some uses downright funny. So here's a list of uses, not necessarily in any sort of order of usefulness.
- Make a purse out of them by sewing a bunch of them together
- Use them as small trash can liners.
- Use them as containers for soiled diapers
- Use them as containers for used cat litter
- Use them as a container for dog poop retrieved out of the yard by turning the bag inside-out, putting your hand in it like a make-shift glove and grabbing the poop. Once you've grabbed the poop, use your other hand to turn the bag right side out and the poop will magically be inside the bag. Be sure to use a bag that doesn't have any holes in it!!!!!
- Use them as mattress stuffing
- Use them as pillow stuffing
- Use them as packing material in lieu of the dreaded white foam peanut
- Tear a piece of the bag off and use it a seal before screwing a cap back onto a bottle or jar that might decide to leak
- Use them as a food-stain-proof cook book cover
- Use large plastic bags to keep lawn furniture covered
- Use them as small-but-handy lawn clean-up bags
- Use them to store wet beach towels in
- Use them to avoid putting money in a parking meter -- put the bag over the meter and tie the bag's handles together, then take a black magic marker and write "broken" on both sides in large block letters. Preferably use bags that are a solid colour, such as red or yellow
- Use them as luggage when travelling. Use the Wally World smiley-faced bags as matched luggage for that extra designer touch...
- Use them as you would a rubber glove when you don't have rubber gloves handy
- Use them to carry large amounts of mail in
- Use them to help make a credit card or other magnetic stripped card swipe when the card by itself won't swipe by putting it inside the bag. Not sure why this one works but it does. I see people do it in truck stops constantly. Once we've gone to mandatory hand chip implants I wonder if the tip in number 15. will help make reluctant implant chips scan by using them as a make-shift rubber glove?
- Use them as a kite to keep a kid (or yourself) amused
- Use them to catch stray paint droplets when you are painting
- Use them as flags
- Use a solid white one tied onto a pole as a truce flag
- Use a solid white one tied to your car antenna or rolled up in a road-facing window when you are parked on the side of the road in case your car breaks down
- Use them as rubber boots to keep your feet dry
- Use them as back packs for kids by putting their arms through the handles
- Use them as socks
- Use them as a doggie bag when you are in a restaurant and want to take a piece of chicken home with you in a purse or pocket
- Use them to store dirty clothes in when you are travelling
- Use them as a shoe-horn when trying on shoes at a garage sale
- Use them to protect the plaster cast so you can take a shower after you break your foot
- Use them as diapers
- Use them as bandages
- Use them as freezer bags
- Use them to wrap up leftovers to keep them from drying out in the refrigerator
- Use them as bread bags for home-made bread made in an electric bread maker
- Use large ones to cover clothes in a closet or while travelling to keep the clothes clean
- Use large ones to slip over ceiling fan blades when cleaning the blades to catch the dust and keep it from falling on the floor
- Use them as a toy parachute
- Use them as handy sick bags when someone is sick to their stomach...
- Use one to wrap your lunch sandwiches in to keep it from getting soggy in a cooler with other items that might sweat
- Use a small one as a rain bonnet
- Use a big one as a raincoat
- Put them on your wiper blades and mirrors in the winter to keep them free from snow and ice
- Use them as a cheap collectable -- nearly everyone seems to collect plastic bags either in their home or car or both
- Use one to hold your clothespins when you are hanging your clothes out to dry
- Use them as a trash can
- Store your shoes in plastic bags when you have them inside your suitcase to keep from making the rest of your clothing stink like your smelly feet
- Use one as a makeshift condom
- Use one to carry popcorn in
- Store wet paint brushes in them after you've washed out the paintbrush
- Use them to store rags in
- Use them as inexpensive home insulation
- Use them when re-upholstering boat seats between the foam padding and the vinyl upholstery to make the seats semi-water proof
- Use them to put used oil filters in to keep them from contaminating the rest of the trash
- Use them as flexible molds for the spray foam that hardens to fill in holes in walls, etc.
- Use them as kindling to start fires with, even in the rain, since once they start burning the heat is intense -- just avoid inhaling the toxic fumes they give off !!!!!!
- Use them as a porta-potty liner
- Use them for emergency toilet paper
- Use them for emergency tissue paper
- Use them to carry your Wally World purchases home...
- Use them as emergency socks
- Use them as emergency underwear
- Use them as an emergency barf bag
- Weave them into an inexpensive rug!!!!
Plastic Bags - From the book Extraordinary Uses for Ordinary Things
These everyday items are useful all-around -- and cost next to nothing!
Around the House
Line a cracked flower vase
Grandmother's beautiful flower vase is a sight to behold when it's filled with posies. The problem is the vase leaks from a large crack that runs its length. Line the vase with a plastic bag before you fill it with water and add a bouquet, giving fresh life to a treasured heirloom.
Bulk up curtain valances
You've picked out snazzy new curtain balloon valances for your bedroom. The problem is the manufacturer has only sent you enough stuffing to make the valances look a bit better than limp. Recycle some plastic bags by stuffing them in the valances for a resilient pouf.
Stuff crafts or pillows
There are a number of ways to stuff a craft project: with beans, rice, fabric filler, plastic beads, pantyhose, and so on. But have you ever tried stuffing a craft item or throw pillow with plastic bags? There are plenty on hand, so you don't have to worry about running out, and you're recycling.
Make party decorations
Here is an easy way to create streamers for a party using plastic bags. Cut each bag into strips starting from the open end and stopping short of the bottom. Then attach the bag bottom to the ceiling with tape.
Drain bath toys
Don't let Rubber Ducky and all of the rest of your child's bath toys get moldy and create a potential hazard in the tub. Instead, after the bath is done, gather them up in a plastic bag that has been punctured a few times. Hang the bag by its handles on one of the faucets to let the water drain out. Toys are collected in one place, ready for the next time.
Keep kids' mattresses dry
There's no need to buy an expensive mattress guard if bed-wetting is a problem. Instead, line the mattress with plastic garbage bags. Big bags are also useful to protect toilet-training toddlers' car seats or car upholstery for kids coming home from the swimming pool.
Make a laundry pocket pickin's bag
You may think that the laundry's all done, until you open the dryer to find a tissue paper left in someone's pocket has shredded and now is plastered all over the dryer drum. Hang a plastic bag near where you sort laundry. Before you start the wash, go through the pockets and dump any contents in the bag for later sorting.
Treat chapped hands
If your hands are cracked and scaly, try this solution. Rub a thick layer of petroleum jelly on your hands. Place them in a plastic bag. The jelly and your body's warmth will help make your hands supple in about 15 minutes.
For Storing Stuff
Store extra baby wipes
Shopping at the warehouse grocer, you picked up a jumbo box of baby wipes at a great price. You've got enough wipes to last for several months, as long as they don't dry out before you can use them. To protect your good investment, keep the opened carton of wipes in a plastic bag sealed with a twist tie.
Collect clothes for thrift shop
If you're constantly setting aside clothes to give to charity, but then find them back in your closet or drawers, try this solution: Hang a large garbage bag in your closet. That way, the next time you find something you want to give, you just toss it in the bag. Once it's full, you can take it to the local donation center. Don't forget to hang a new bag in the closet.
Cover clothes for storage
You'd like to protect that seersucker suit for next season. Grab a large, unused garbage bag. Slit a hole in the top and push the hanger through for an instant dustcover.
Store your skirts
If you find you have an overstuffed closet but plenty of room to spare in your dresser, conduct a clothes transfer. Roll up your skirts and place them each in a plastic bag. That will help them stay wrinkle-free until you're ready to wear one.
Keep purses in shape
Ever notice that if you've changed purses and leave an empty one in your closet, it deflates and loses its shape? Fill your purse with plastic bags to retain its original shape.
Tip: Storing Plastic Bags
All those shopping bags are spilling out of the utility drawer in your kitchen? Here are some better ways to store them:
- Stuff them inside an empty tissue box for easy retrieval
- Poke a bunch down a cardboard tube, such as a paper towel or mailing tube or even a section of a carpet tube
- Fill a clean, empty gallon (4-litre) plastic jug. Cut a 4-inch (10-centimetre) hole in the bottom. Stuff with bags and hang by its handle on a hook. Pull the bags out of the spout
- Make a bag "sock." Fold a kitchen towel lengthwise with the wrong side facing out. Stitch the long edges together. Sew 1/2-inch (1.25-centimetre) casings around the top and bottom openings and thread elastic through them, securing the ends. Turn the sock right side out, sew a loop of ribbon or string on the back to hang it up, stuff bags into the top opening, and pull them out from the bottom one
Keeping Things Clean
Protect hand when cleaning toilet
When cleaning your toilets with a long-handled brush or a shorter tool, first wrap your hand in a used plastic bag. You'll be able to do the appropriate scrubbing without your hand getting dirty in the process.
Prevent steel wool from rusting
A few days ago you got a new steel wool pad to clean a dirty pot. Now that steel pad is sitting useless in its own pool of rust. Next time, when you're not using the pad, toss it into a plastic bag where it won't rust and you'll be able to use it again.
Make bibs for kids
The grandkids just popped in, and they're hungry. But you don't have any bibs to protect their clothes while they eat. Make some by tying a plastic bag loosely around the kids' necks so their clothes stay free of stains. You can make quick aprons this way too.
Create a high-chair drop cloth
Baby stores are quite happy to sell you an expensive drop cloth to place under your child's high chair. Why spend the money on a sheet of plastic when you have all those large garbage bags that can do the job? Split the seams of a bag and place it under the high chair to catch all the drips and dribbles. When it gets filthy, take it outside and shake, or just toss it.
Line the litter box
Nobody likes to change the cat's litter box. Make the job quick and easy by lining the box with an open plastic bag before pouring in the litter. Use two bags if you think one is flimsy. When it's time to change the litter, just remove the bags, tie, and throw into the trash.
Needle-free Christmas tree removal
O Christmas tree, how lovely are thy branches! Until those needles start dropping. When it's time to take down your tree, place a large garbage bag over the top and pull down. If it doesn't fit in one bag, use another from the bottom and pull up. You can quickly remove the tree without needles trailing behind you.
Keep polish off your hand
You want to polish up your scruffy white sandals. The problem is, you're going to get more polish on your hands than your shoes. Before you polish, wrap your hand in a plastic bag before inserting it into the sandal. Then when polish runs off the sandal straps, your hand is protected. Leave the bag in the sandal until the polish is dry.
In the Kitchen
Cover a cookbook
You're trying a new recipe from a borrowed cookbook that you don't want to get splattered during your creation. Cover the book with a clear plastic bag. You'll be able to read the directions, while the book stays clean.
Bag the phone
Picture this: You're in the middle of making your famous snickerdoodle cookies. You're up to your elbows in dough. The phone rings. Now what? Wrap your hands in a plastic bag and answer the phone. You won't miss a call or have to clean the phone when you're done.
Your extended family of 25 has just finished their Sunday dinner. Time to clean the dishes. Here's an easy way to get rid of the table scraps: Line a bowl with a plastic bag and scrape scraps into it. Once it's full, just gather up the handles and toss. Place the bowl in a prominent place in your kitchen so everyone can scrape their own dishes when bringing them to the sink.
Crush graham crackers
Don't spend hard-earned grocery dollars on a box of pre-crushed graham crackers or a ready-to-fill graham cracker crust. It's much cheaper and a real snap to crush graham crackers yourself. Just crumble several graham crackers into a plastic bag. Lay the bag on the kitchen counter and go over it several times with a rolling pin. In no time, you'll have as many graham cracker crumbs as you need, plus the remainder of a box of crackers to snack on as well.
Replace a mixing bowl
If you're cooking for a crowd and are short on mixing bowls, try using a plastic bag instead. Place all the dry ingredients to be mixed in the bag, gather it up and gently shake. If the ingredients are wet, use your hands to mix.
Spin dry salad greens
The kids will enjoy helping you with this one. Wash lettuce and shake out as much water as you can in the sink. Then place the greens in a plastic grocery bag that has been lined with a paper towel. Grab the handles and spin the bag in large circles in the air. After several whirls, you'll have dry lettuce.
Some of the fruit from that bushel of peaches you just bought at the local farm stand are hard as rocks. Place the fruit with a few already ripe pieces or some ripe bananas in a plastic bag. The ripe fruit will help soften the others through the release of their natural gas. But don't leave them for more than a day or two or you'll have purple, mouldy peaches.
In the Yard
Protect plants from frost
When frost threatens your small plants, grab a bunch of plastic bags to protect them. Here's how: Cut a hole in the bottom of each bag. Slip one over each plant and anchor it inside using small rocks. Then pull the bags over the plants, roll them closed, and secure them with clothespins or paper clips. You can open the bags up again if the weather turns warm.
Start poinsettia buds for Xmas
You want that Christmas poinsettia to look gorgeous by the time the holidays arrive. You can speed up Mother Nature by placing the poinsettia in a large, dark garbage bag for several weeks to wake up the plant's buds.
Protect fruit on the tree
Are there some apples in your orchard you want to protect or some plums that need a little more time on the tree? Slip the fruit into clear plastic bags while still on the trees. You'll keep out critters while the fruit continues to ripen.
Protect your shoes from mud
It rained hard last night, and you need to get out in the garden to do your regular weeding. But you're worried about getting mud all over your shoes. Cover them in plastic bags. The mud gets on the bag, not on the shoes, and your feet stay dry so you can stay out longer in the garden.
Clean a grill easily
That neighbourhood barbecue was a blast, but your grill is a sorry mess now. Take the racks off and place them in a garbage bag. Spray oven cleaner on the grill and close up the bag. The next day, open the bag, making sure to keep your face away from the fumes. All that burned-on gunk should wipe right off.
Cover garage-sale signs
If you've gone to the trouble of advertising your upcoming garage sale with yard signs but worry that rain may hurt your publicity campaign before even the early birds show up, protect the signs by covering them with pieces cut from clear plastic bags. Passersby can still see the lettering, which will be protected from smearing by the rain.
Store outdoor equipment manuals
Your weed-whacker spindle just gave out and you have to replace it. But how? Stash all your outdoor equipment's warranties and owner's manuals in a plastic bag and hang it in your garage. You'll know exactly where to look for help.
Protect your car mirrors
A big snowstorm is due tonight, and you've got a doctor's appointment in the morning. Get a step ahead by covering your car's side mirrors with plastic bags before the storm starts. When you're cleaning off the car the next morning, just remove the bag. No ice to scrape off.
Make a jump rope
"I'm bored!" cries your child as you're trying to finish your yard work. Here's a simple solution: Make a jump rope by twisting up several plastic bags and tying them together end to end. Talk about cheap fun.
On the Go
Pack your shoes
Your next cruise requires shoes for all types of occasions, but you worry that packing them in the suitcase will get everything else dirty. Wrap each pair in its own plastic bag. It will keep the dirt off the clothes, and you can rest assured you've packed complete pairs.
Protect your hands when pumping gas
You've stopped at the gas station for a fill-up while on your way to meet friends for lunch. The last thing you want is to greet them with hands that smell of gasoline. Grab one of those plastic bags you keep in your car and cover your hands with it while you pump.
Stash your wet umbrella
When you're out in the rain and running to your next appointment, who wants to deal with a soggy umbrella dripping all over your clothes and car? One of those plastic bags that newspapers are delivered in is the perfect size to cover your umbrella the next time it rains. Just fold the umbrella up and slip it into the bag.
Make an instant poncho
Leave a large garbage bag in your car. The next time it rains unexpectedly, cut some arm slits and one for your head. Slip on your impromptu poncho and keep dry.
Scoot in the snow
Your neighbourhood just got 6 inches (15 centimetres) of snow and the kids are hoping to take advantage of it right now. Grab some garbage bags, tie one around one each of their waists, and let them fanny-slide down the hills.
For the Do-It-Yourselfer
Cover ceiling fans
You're painting the sun porch ceiling, and you don't want to remove the ceiling fans for the process. Cover the blades with plastic bags to protect them from paint splatters. Use masking tape to keep the bags shut.
You're halfway through painting the living room, and it's time to break for lunch. No need to clean the paintbrush. Just stick it in a plastic bag and it will remain wet and ready to use when you return. Going to finish next weekend, you say? Stick the bag-covered brush in the freezer. Defrost next Saturday and you are ready to go.
Contain paint overspray
If you've got a few small items to spray-paint, use a plastic bag to control the overspray. Just place one item at a time in the bag, spray-paint, and remove to a spread-out newspaper to dry. When you're done, toss the bag for a easy cleanup.
Check more uses of Plastic bags on following website
Turning plastic bags into steel!
Your plastic shopping bag could one day be turned into steel to make your next car, according to Professor Veena Sahajwalla at the University of NSW.
Instead of being discarded as waste, polyethylene plastic - the type used in shopping bags, soft packaging and some drink containers - potentially can be recycled as both a raw material and a source of energy for making iron and steel, says Professor Sahajwalla.
Professor Sahajwalla is based at the UNSW School of Materials Science and Engineering and she leads the School's Sustainable Materials Processing Program.
"Plastic is just another form of carbon," she says. "When it comes to making iron and steel there's essentially no difference between polyethylene and natural resources such as coal."
Her experiments hold promise of an environmental win-win, significantly cutting the steel industry's use of coal and its production of greenhouse gases, as well as stopping thousands of tonnes of plastic waste from being discarded every year in landfill dumps.
Polyethylene typically is about 15 per cent hydrogen - a potential energy source to fuel blast-furnace processes - and about 85 per cent carbon, roughly the same carbon content as the high-quality coal used for steelmaking.
Under controlled conditions, Professor Sahajwalla experimented with various mixtures of pulverised plastic and coal by injecting them into a furnace.
"By adding plastic into a molten 'melt' at more than 1,500 degrees C we have shown that carbon from plastic can dissolve into iron," she says. "This is exciting because what would otherwise become waste is recycled to become a raw material for this vital industry and it reduces our use of coal in the process. If we want to move along the path to sustainability, this is one way to go."
In 2002, the latest year for which figures are available, Australians used almost 1.2 million tonnes of plastic but recycled only about 13 per cent. Of the resulting one million tonnes of waste, polyethylene accounted for about half.
"If we substituted recycled polyethylene for only five per cent of the coal we use in blast furnaces, that would save about 40,000 tonnes of coal a year. That much coal would make about 80,000 tonnes of iron."
A question mark remains over whether burning polyethylene might release unwanted air pollutants: "We need to do more research on that question, because experience with burning plastics in waste incinerators suggests it may be an issue.
"But incinerators typically operate at about 1,000 degrees C, whereas a blast furnace operates at around 1,500 to 1,600 degrees and is likely to burn the plastic more completely, with fewer troublesome pollutants.
"Polyethylene actually has fewer impurities than coal, such as sulphur and oxides, so there's less of a residue problem after burning it."
Sahajwalla's findings have emerged from her work on other materials used in iron and steel making.
She credits her collabourator in Japan, Professor Masanori Iwasi, of Kyoto University, with having the original idea of using plastic waste as a raw material in blast-furnace ironmaking, but she is extending the technique for the first time into electric-furnace steelmaking, which uses scrap steel to recycle into new materials. Dr Sahajwalla's research is being done in co-operation with BHP Billiton and BlueScope Steel and with support from the Co-operative Research Centre for Coal in Sustainable Development.
Plastic Spaceships - 8.25.2005
A "designer material" derived from plastic could help protect astronauts on their way to Mars
August 25, 2005: After reading this article, you might never look at trash bags the same way again.
We all use plastic trash bags; they're so common that we hardly give them a second thought. So who would have guessed that a lowly trash bag might hold the key to sending humans to Mars?
Most household trash bags are made of a polymer called polyethylene. Variants of that molecule turn out to be excellent at shielding the most dangerous forms of space radiation. Scientists have long known this. The trouble has been trying to build a spaceship out of the flimsy stuff.
But now NASA scientists have invented a groundbreaking, polyethylene-based material called RXF1 that's even stronger and lighter than aluminium. "This new material is a first in the sense that it combines superior structural properties with superior shielding properties," says Nasser Barghouty, Project Scientist for NASA's Space Radiation Shielding Project at the Marshall Space Flight Center.
To Mars in a plastic spaceship? As daft as it may sound, it could be the safest way to go.
Less is more
Protecting astronauts from deep-space radiation is a major unsolved problem. Consider a manned mission to Mars: The round-trip could last as long as 30 months, and would require leaving the protective bubble of Earth's magnetic field. Some scientists believe that materials such as aluminium, which provide adequate shielding in Earth orbit or for short trips to the Moon, would be inadequate for the trip to Mars.
Barghouty is one of the skeptics: "Going to Mars now with an aluminium spaceship is undoable," he believes.
Plastic is an appealing alternative: Compared to aluminium, polyethylene is 50% better at shielding solar flares and 15% better for cosmic rays.
The advantage of plastic-like materials is that they produce far less "secondary radiation" than heavier materials like aluminium or lead. Secondary radiation comes from the shielding material itself. When particles of space radiation smash into atoms within the shield, they trigger tiny nuclear reactions. Those reactions produce a shower of nuclear byproducts -- neutrons and other particles -- that enter the spacecraft. It's a bit like trying to protect yourself from a flying bowling ball by erecting a wall of pins. You avoid the ball but get pelted by pins. "Secondaries" can be worse for astronauts' health than the original space radiation!
Ironically, heavier elements like lead, which people often assume to be the best radiation shielding, produce much more secondary radiation than lighter elements like carbon and hydrogen. That's why polyethylene makes good shielding: it is composed entirely of lightweight carbon and hydrogen atoms, which minimizes secondaries.
Ethylene, the building block of polyethylene, is rich in hydrogen and carbon. [More]
These lighter elements can't completely stop space radiation. But they can fragment the incoming radiation particles, greatly reducing the harmful effects. Imagine hiding behind a chain-link fence to protect yourself in a snowball fight: You'll still get some snow on you as tiny bits of snowball burst through the fence, but you won't feel the sting of a direct hit from a hard-packed whopper. Polyethylene is like that chain link fence.
"That's what we can do. Fragmenting -- without producing a lot of secondary radiation -- is actually where the battle is won or lost," Barghouty says.
Made to order
Despite their shielding power, ordinary trash bags obviously won't do for building a spaceship. So Barghouty and his colleagues have been trying to beef-up polyethylene for aerospace work.
That's how Shielding Project researcher Raj Kaul, working together with Barghouty, came to invent RXF1. RXF1 is remarkably strong and light: it has 3 times the tensile strength of aluminium, yet is 2.6 times lighter -- impressive even by aerospace standards.
"Since it is a ballistic shield, it also deflects micrometeorites," says Kaul, who had previously worked with similar materials in developing helicopter armour. "Since it's a fabric, it can be draped around moulds and shaped into specific spacecraft components." And because it's derived from polyethylene, it's an excellent radiation shield as well.
Raj Kaul, co-inventor of RXF1, holding a brick of the material. [More]
The specifics of how RXF1 is made are secret because a patent on the material is pending.
Strength is only one of the traits that the walls of a spaceship must have, Barghouty notes. Flammability and temperature tolerance are also important: It doesn't matter how strong a spaceship's walls are if they melt in direct sunlight or catch fire easily. Pure polyethylene is very flammable. More work is needed to customize RXF1 even further to make it flame and temperature resistant as well, Barghouty says.
The Bottom Line
The big question, of course, is the bottom line: Can RXF1 carry humans safely to Mars? At this point, no one knows for sure.
Some "galactic cosmic rays are so energetic that no reasonable amount of shielding can stop them," cautions Frank Cucinotta, NASA's Chief Radiation Health Officer. "All materials have this problem, including polyethylene."
Cucinotta and colleagues have done computer simulations to compare the cancer risk of going to Mars in an aluminium ship vs. a polyethylene ship. Surprisingly, "there was no significant difference," he says. This conclusion depends on a biological model which estimates how human tissue is affected by space radiation--and therein lies the rub. After decades of spaceflight, scientists still don't fully understand how the human body reacts to cosmic rays. If their model is correct, however, there could be little practical benefit to the extra shielding polyethylene provides. This is a matter of ongoing research.
Because of the many uncertainties, dose limits for astronauts on a Mars mission have not been set, notes Barghouty. But assuming that those dose limits are similar to limits set for Shuttle and Space Station flights, he believes RXF1 could hypothetically provide adequate shielding for a 30 month mission to Mars.
Today, to the dump. Tomorrow, to the stars? Polyethylene might take you farther than you ever imagined.
Jokes on Plastic bag
A Man's Dilemmas: Two guys were working at a sawmill one day when one of the guys got too close to the blade and cut off his arm. His buddy put the severed arm in a plastic bag and rushed it down to the hospital to get re-attached. The next day he goes to see his chum, and finds him playing tennis.
"Incredible!," says his friend. "Medical science is amazing."
Another month goes by and the same two guys are again at the sawmill working when the same guy gets too close to the spinning blade and this time his leg gets cut off. Again his buddy takes the leg, puts it in a plastic bag and takes it to the hospital to get re-attached. The next day, he goes down to see his chum and finds him outside playing football. "Incredible!," says his friend. "Medical science is amazing!"
Well another month goes by and again the same two friends are at the mill cutting wood when suddenly the same guy bends down too close to the blade and off comes his head. Well his friend takes the head, puts it in a plastic bag, and heads to the hospital to get it re-attached. The next day he goes to see his friend but can't find him.
He sees the doctor walking down the hall and says, "Doc, where is my friend? I brought him in yesterday."
The doctor thinks for a minute and says, "Oh yeah, some idiot put his head in a plastic bag and he suffocated."
Reference: The dailystar