Cracking & Polymerisation

Cracking in this case means breaking chemical bonds in molecules so they split apart. They are cracked into smaller molecules.

Cracking and Refining

Crude oil is made of long hydrocarbon chains which can be distilled or refined  into various products such as diesel and petrol.

Longer hydrocarbon chains (such as diesel) are  harder to ignite and slower to burn. Short hydrocarbon chains (for example petrol), ignite very easily and burn more quickly.

You might want more petrol. You can’t distill anymore from your crude oil but you can break up refined hydrocarbon chains to get shorter chains. You you  can crack  diesel into petrol.

Cracking

So heavy hydrocarbon molecules are broken up into lighter molecules. This is done by means of heat, pressure, and sometimes catalysts.

  • Thermal cracking was invented in 1930 by William Meriam Burton.
  • Catalytic cracking process was invented by Eugene Houdry in 1937.

The end result is in smaller hydrocarbon molecules.

But you don’t just use cracking to transform one product into another. You can rebuild the hydrocarbon molecules into something else. You can use them as building blocks for an entirely new product. For example plastic.

Polymerisation & Plastic

These smaller hydrocarbon molecules can be mixed and matched then  stuck back together or chemically processed to make a whole load of new hydrocarbon monomers –  for example  products like styrene, vinyl chloride, acrylonitrile  used in plastics.

These new monomers can be joined together to create more complex substances called polymers. This process is called polymerisation. Plastics are an example of a manmade, synthetic polymer

Different polymers result in different types of plastic.

More

Find out more about plastic and how it is made here.

Don’t know your polymers form you Pollyannas? Here’s a list of definitions.

Plastic and the E.U.

Gosh in 2013 the E.U.  realised that

“Dozens of millions of tonnes of plastic debris end up floating in world oceans broken into microplastic, the so-called plastic soup. Microplastics are found in the most remote parts of our oceans. Entanglement of turtles by floating plastic bags, sea mammals and birds that die from eating plastic debris and ghost fishing through derelict fishing gear produce shocking pictures. Moreover, plastic is not inert and chemical additives, some of them endocrine disruptors, can migrate into body tissue and enter the food chain.

The massive pollution of world oceans with plastic debris is therefore emerging as a global challenge that requires a global response. The European Union should be a showcase for how to build a coherent strategy to optimize plastic waste policy.

A second challenge is linked to resources conservation. Nearly 50% of plastic waste in the EU is still landfilled. Therefore, much energy and processed raw material is lost instead of being recycled into new products.

Until now there is no comprehensive policy response to such challenges.” Eye roll!

“Specific aspects are addressed in various pieces of legislation, like the Waste Framework Directive with its 2015 separate plastic waste collection target or its 50% household waste collection target by 2020. The Packaging and Packaging waste Directive also has a specific plastic waste target.

Since there is an obvious and urgent need to take a focused and strategic approach towards plastic waste management as well as plastic product management, we are launching the consultation on the “Green Paper on a European Strategy on Plastic Waste in the Environment”. This should be the start of a broad public reflection on possible responses to all public policy challenges posed by plastic waste and which are presently not specifically or not effectively addressed in European waste legislation.”

Rather late to the party guys but at least you showed up…. lets see what you got. You can read their report here.

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Plastic packed food & storage times

This post does not deal with using plastic to protect food in transit rather than the plastic used to pre-package food for sale in stores.

Plastic is used to pack food for a number of reasons. The most simple are

  • to contain it – to stop it falling about
  • protect it from bruising
  • wrapping products in plastic reduces moisture loss which helps to keep certain veg fresh for much longer and so prolongs shelf life. This type of packaging is used for root vegetables and cucumbers. 

However plastic packaging can be far more sophisticated then that.

Modified Atmosphere Packaging

Wikipedia defines this as  the “Re-balancing of gases inside the packaging can be achieved using active techniques such as gas flushing and compensated vacuum or passively by designing “breathable” films known as equilibrium modified atmosphere packaging (EMAP).”

Heres a bit more on these processes

Gas flushing and compensated vacuum techniques

This massively extends the shelf life of fresh food products. Here products are enclosed in a plastic container (the packaging), then the air inside the pack is changed (the modified atmosphere). Basically they actively suck out the oxygen and shove in a gas (you may need to look up those technical terms).
The modification process varies depending on the product. Different amounts of oxygen will be needed and the gas composition will change depending on the food being packed. Red meat needs high oxygen to maintain the red color, bread requires low oxygen to avoid mould and vegetables often need a three-gas mixture. Yum!
A wide variety of products are gas flushed including

  • Fresh meat /
    Processed meat /
    Cheese /
    Milk powder
    Fresh pasta / Fruit & Vegetables / Ready Meals
    Case ready meat / Fresh poultry / Fish & Seafood

Is it Safe? You might want to consider this

The Committee therefore concluded that there is no health concern associated with the use of 0.3%-0.5% CO in a gas mixture with CO2 and N2 as a modified atmosphere packaging gas for fresh meat provided the temperature during storage and transport does not exceed 4°C. However the Committee wishes to point out that, should products be stored under inappropriate conditions, the presence of CO may mask visual evidence of spoilage.

Specially Designed Films

Specially designed plastic films and bags can be used to modify the atmosphere round the product are used. One example is;
PrimePro® is a packaging technology designed to extend the shelf life of fresh fruits and vegetables. It extends shelf life by removing ethylene gas, a powerful plant hormone that triggers the process of ripening and decay.
PrimePro® is a polyethylene plastic film contains a proprietary additive that is specially designed to remove ethylene from the air around fresh produce.”

Breathable plastics

Unlike most food products, fresh fruits and vegetables continue to respire after they have been harvested. They need some oxygen and will continue to  produce carbon dioxide and water vapor. Packaging here has to allow for this. It has to be breathable. There are plastic films that can accommodate that process.

Vacuum packing

This process removes all the oxygen before sealing the plastic container. Here the non breathable impermeable plastic is shrink fitted to the product thereby allowing no contact with the oxygen in the air around it.

Reduction In Food Waste

Plastic packed food means that food can be stored for longer which should reduce food waste. This is often used to justify plastic packaging.

Plastic wrapped food certainly benefits the retailer as it lasts considerably longer on the supermarket shelves giving them a longer sales time. The producers and importers of pre packaged food also benefit from this increased timescale to sell their food.

And yet somehow it hasn’t cut food waste. In fact as a food waste preventive measure it seems remarkably ineffective. For example

“UK retailers and wholesalers are still wasting around 200,000 tonnes of food each year, and when their supply chains are factored in this figure rises to over 4,000,000 tonnes annually.”

or

“Supermarket giant Tesco has revealed it generated almost 30,000 tonnes of food waste in the first six months of 2013. Using its own data and industry-wide figures, it also estimated that across the UK food industry as a whole, 68% of salad to be sold in bags was wasted – 35% of it thrown out by customers.

Plastic Waste

Of course it rather depends on what you do with food waste and how you define it. If you compost it you return those nutrients to the soil and they are then used to sustain more plants. If you feed it to animals it can be used to make bacon. In fact calling it waste is really rather misleading. It is a resource and is often used as such.

Food waste is biodegradable, plastic waste is not. Food waste can be dealt with locally and if dealt with properly is a resource rather than a waste product. At worst if littered round the environment it will rot away. Plastic waste has to be specially disposed of at proper facilities. If not it will end up as permanent litter.

And thanks to food packaging there is an awful lot of it.

11% of household waste is plastic, 40% of which is plastic bottles, during 2002 plastic bottles worth around £27 million were disposed of at a cost of £45 million

In the UK  Waste on line, another government agency, are keen to tell us that we generate 3 million tonnes of plastic waste annually 56% of which is used packaging, three-quarters of which is from households. They estimated that only 7% of total plastic waste is currently being recycled. How Big Is Your Pile

Just A Different Kind Of Waste

Creating a huge pile of plastic waste to prevent food waste does not resolve the waste problem.. It merely shifts it to a different sector.

Packaging & Pre-Portioning

One response to the salad fiasco was to suggest making smaller bags of salad. This is of course another issue with prepackaged food. You can only buy what is there not what you want. Over purchasing obviously leads to increased food waste but is sometimes almost unavoidable. If you only want one pepper buying a three pack is unnecessary and despite good intentions often leads to food waste

Waste & The Consumer

Waste in the home is the responsibility of the purchaser. For sure a wrapped sealed product will last longer but one assumes fresh food was bought to be eaten within a fairly short time scale so the benefits of packaging, in that sense at least, are not so great.

A WRAP report into the subject claims that consumers do not understand how to use packaging specially designed to reduce waste any way. However more education on the subject could help. They also have some interesting observations on consumer attitudes to packaging. See their report Consumer attitudes to food waste and packaging

And we are still throwing away huge amounts and food plus huge amounts of plastic packaging.

Food Safety

Packed food is safer food. Yes, but food can still be stored and kept safely without plastic packaging. Plus There is a considerable body of evidence that chemicals leach from the plastic packaging into the food. Some claim the chemicals in plastic can have adverse effects on health.

There is a consensus of opinion, (though sadly not so much in the way of hard facts), that fruit and vegetables start to loose nutrients once harvested. Plastic packaging certainly slows down the aging process wether it slows down nutrient loss is less clear. But all advice seems to be eat your fruit and veg as fresh as possible. Plastic packaging means you don’t know how old that cucumber is. Wether that is relevant or not I cannot say but s the Committee points out when discussing gas flushing for meat, that unless the meat is stored properly, the presence of CO may mask visual evidence of spoilage.

Conclusions

The issues of food waste, the convenience of pre-packaged, longer-lasting food have to be weighed against environmental costs of plastic; the savings made by being able to store food for longer against the clean up costs for plastic. Bearing in mind that much of the latter is not paid for by the producers  but by the end consumer. The supermarket/producer does not pay for the disposal of the plastic wrapper, street cleaning or for the environmental damage it causes when it flies into the canal.

  • It uses a lot of resources to plastic wrap food.
  • While it might reduce food waste (debateable), it means a huge increase in plastic waste.
  • Food waste is biodegradable. Plastic waste is not.
  • Plastic rubbish goes on to pollute the environment in many ways.
  • It costs a lot of money to treat plastic waste and a lot of plastic waste is food packaging.
  • Pre-portioning can actually increase food waste
  • There are many hundreds of different plastic used to package food. Many of them are difficult to recycle.
  • There is a considerable body of evidence that chemicals leach from the plastic packaging into the food. Some claim the chemicals in plastic can have adverse effects on health.
  • You don’t know how old that fruit is. Gas flushing might disguise food rot.

I feel that plastic packing benefits the producers and retailers more than the consumer and the environment. Personally I prefer buying seasonally grown, unpacked food  from local suppliers, only buying what you need and eating it as quickly as possible.

Why package produce http://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-8/

http://en.wikipedia.org/wiki/Modified_atmosphere

http://www.modifiedatmospherepackaging.com

https://www.heart.org/HEARTORG/GettingHealthy/NutritionCenter/HealthyCooking/Keep-Fruits-Vegetables-Fresher-Longer_UCM_445190_Article.jsp

 

 

Burning plastic in the home

Some feel my worrying about plastic in the home is taking it too far?  Disposables? Yes, they can see I might have a point. But nylon carpet, foam-filled pillows and  polyester drapes…. what could possibly go wrong?

Well good taste aside…. you know how we were talking about hydrocarbons containing a lot of energy? Well all that energy means they burn hot. And that plastic is made from hydrocarbons. You got it. Plastic is a fuel too. So much so  that it actually has a higher BTU than coal. Great for waste to energy incinerators not so good for house fires.

For generations, firefighters’ had, “on average, 17 minutes to get anyone inside out of the building before they succumbed to smoke inhalation.” Because of modern fast burning synthetic furnishings that time is down to 4 minutes. Natural fibres and fillings do not burn as fast.

You can find lots more scary stats here plus a spooky burning chair that shows just how quickly you can be overcome.

Please people make sure your smoke alarm is working and maybe pay a bit more for cotton curtains and a wool rug.

Found this very interesting table on fumes released by burning. Hers an example…

Upholstery • Nylon Polybrominated diphenyl ethers Hydrogen chloride Hydrochloric acid Hydrogen cyanide Dioxins Possible carcinogen; poison by ingestion. Highly corrosive irritant to eyes, skin and mucous membranes; mildly toxic by inhalation. Corrosive; mildly toxic by inhalation; when heated to decomposition emits toxic fumes of chlorides. Asphyxiant; deadly human and experimental poison by all routes. Carcinogen; a deadly experimental poison by ingestion, skin contact and intraperitoneal routes. Immobile in contaminated soil and may be retained for years. No Yes Yes Yes Yes

https://denr.sd.gov/des/wm/sw/documents/OpenBurningChemicalList.pdf

And this

Burning a small sample of a synthetic fibre yarn is a handy way of identifying the material. Hold the specimen in a clean flame. While the specimen is in the flame, observe its reaction and the nature of the smoke. Remove the specimen from the flame and observe its reaction and smoke. Then extinguish the flame by blowing. After the specimen has cooled, observe the residue.

https://www.tensiontech.com/tools-guides/burning-characteristics

And this on toxic fibres and fabrics

https://fashionbi.com/newspaper/the-health-risks-of-toxic-fibers-and-fabrics

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Plastic Costs A Lot

According to some “the environmental cost, including carbon pollution released during production [of plastic], is staggering. At $40 billion a year, …. it’s more than the annual profits of the plastics industry.”

Acoording to the UNEP Report 2014

It finds that the overall natural capital cost of plastic use in the consumer goods sector each year is US$75 billion – financial impacts resulting from issues such as pollution of the marine environment or air pollution caused by incinerating plastic.

The report says that over 30 per cent of the natural capital costs of plastic are due to greenhouse gas emissions from raw material extraction and processing. However, it notes that marine pollution is the largest downstream cost, and that the figure of US$13 billion is likely a significant underestimate.

Concern is growing over the threat that widespread plastic waste poses to marine life, with conservative estimates of the overall financial damage of plastics to marine ecosystems standing at US$13 billion each year, according to two reports released on the opening day of the first United Nations Environment Assembly.

The Ellen MacArthur Foundation claims, in their report on plastic,  that

“Assessing global plastic packaging flows comprehensively for the first time, the report finds that most plastic packaging is used only once; 95% of the value of plastic packaging material, worth $80-120 billion annually, is lost to the economy. Additionally, plastic packaging generates negative externalities, valued conservatively by UNEP at $40 billion.[1] Given projected growth in consumption, in a business-as-usual scenario, by 2050 oceans are expected to contain more plastics than fish (by weight), and the entire plastics industry will consume 20% of total oil production, and 15% of the annual carbon budget.[2]

New economic study shows marine debris costs California residents millions of dollars

Thanks to Fabiano of www.globalgarbage.org for keeping us well informed ….

AUGUST 12, 2014 — Marine debris has many impacts on the ocean, wildlife, and coastal communities. A NOAA Marine Debris Program economic study released today shows that it can also have considerable economic costs to residents who use their local beaches.

The study found that Orange County, California residents lose millions of dollars each year avoiding littered, local beaches in favor of choosing cleaner beaches that are farther away and may cost more to reach. Reducing marine debris even by 25 percent at beaches in and near Orange County could save residents roughly $32 million during three months in the summer.

In order to better understand the economic cost of marine debris on coastal communities, the NOAA Marine Debris Program and Industrial Economics, Inc. (IEc) designed a study that examines how marine debris influences people’s decisions to go to the beach and what it may cost them. We selected Orange County as a study location because beach recreation is an important part of the local culture and residents have a wide variety of beaches from which to choose, some of which are likely to have high levels of marine debris.

http://marinedebris.noaa.gov/sites/default/files/MarineDebrisEconomicStudy.pdf
http://marinedebris.noaa.gov/sites/default/files/MarineDebrisEconomicStudy.pdf

The World Bank

estimates the yearly global cost of dealing with waste is more than $200 billion and predicts annual waste will exceed 11 million tons per day by 2100 if current trends continue. From the true cost of our waste

Local authorities, industry and coastal communities spend approximately £14 million a year to clean up beach litter in England and Wales alone (Environment Agency, 2004).
Annually the UK and maritime leisure industry is worth up to £11 billion.

Harbour authorities also have to pay to keep navigation channels free of litter – a survey of 42 harbour authorities reported that £26,100 is spent per year in some ports to clear fouled propellers and remove debris from the water

Some estimates put the cost of marine litter to the fishing industry at over £23 million a year (Environment Agency, 2002).

How much energy?

“Our previous work had suggested that bottled water production was an energy-intensive process, but we were surprised to see that the energy equivalent of nearly 17 million barrels of oil are required to produce the PET bottles alone,” Cooley told PhysOrg.com.

Read more at: http://phys.org/news156506896.html#jCp

Act Now

Let’s stop using plastic to make everlasting litter. And rather then wait for governments to act or the clean up bill get even bigger I invite you to join me in a plastic boycott. You can find loads of plastic free alternatives listed here on my blog.

 

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Fork in turtles nose…

…seems like those dumb turtles just cant stop damaging themselves on our everlasting litter. This one has a plastic fork stuck in its nose. It was only last month I reported on a turtle with a straw in its snout.  And here are some more stupid animals killing themselves with plastic.

Now watch the video….

 

 

So easy to take your own cutlery – or at least use biodegradable.

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Epoxy Resin

To understand plastic you need a lot of time and a good working knowledge of chemistry at the very least. Currently I am trying to find out what epoxy resin actually is. Sigh! Here’s what I got….

It is a thermoset plastic which means it can only be heated and shaped once.

Most epoxy resins are petroleum derived but some plant derived sources are now becoming commercially available such as plant derived glycerol.

Properties Good electrical insulator, hard, brittle unless reinforced, resists chemicals well

Principal uses Casting and encapsulation, adhesives, bonding of other materials. And lining tin cans.

Epoxy resin can be mixed with additives, plasticizers or fillers to create different products with a range of properties Use of blending, additives and fillers is often referred to as formulating.”

Bisphenol A (BPA)

And of course the one everyone is concerned about ….. BPA is an integral part of most epoxy resins.

“The most common and important class of epoxy resins is formed from reacting epichlorhydrin with bisphenol A to form diglycidyl ethers of bisphenol A.”

Many consider BPA to be a health hazard.

Nearly all tin cans are lined with epoxy resin. and have been since the 50s. The liner can be white or yellow or transparent in which case it is undetectable. BPA can leach from the liner into the contents of the can. For more on this read Why Does My Can Have A Liner & Is It Bad For Me.

Other Resins

  • Bisphenol F epoxy resin
  • Novolac epoxy resin
  • Aliphatic epoxy resin
  • Glycidylamine epoxy resin
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Recycled Plastic Lumber

Plastic lumber is often the end product of the plastics (mechanical) recycling chain.

Which may go as follows

  • Virgin PET bottle to fleece or carpet
  • Carpet fibers to plastic lumber.
  • Plastic lumber to waste disposal plant – though manufacturers claim that plastic lumber can be recycled again.

This process is sometimes called DOWNCYCLING.

It is a versatile product especially good for wet or high risk situations and it is very easy to make 

Key points to note about recycled plastic lumber (as taken from the industry website)

  • Reduction of energy consumption by 66%plastic lumber featured
  • Production of only a third of the sulphur dioxide
  • Production of only half of the nitrous oxide
  • Reduction of water usage by nearly 90%
  • Reduction of carbon dioxide generation by two-and-a-half times
  • 1.8 tonnes of oil are saved for every tonne of recycled polythene produced
  • Lasts 5 times longer than timber
  • Rot and algae proof
  • Crack, chip and splinter proof
  • Insect and animal resistant
  • Non slip
  • UV resistant
  • Vandal Resistant
  • Less Flammable than timber
  • Easy to clean
  • Can be worked like timber
  • Holds screws and fittings well
  • Reduced Whole Life Costs
  • Diverting Material from Landfill
  • Reduces the carbon footprint of any project
  • Labour saving – minimal maintenance

Find out more at British Recycled Plastics

More on recycling here

Other ways to recycle and reuse plastic trash here

Recycling and  waste plastic – a discussion

And find more recycled plastic products here

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Polypropylene

Polypropylene (PP) plastic code 5

It is the second most important plastic after polyethylene.

It is a thermoplastic polymer that is rugged and unusually resistant to many chemical solvents, bases and acids.

It is used to make soup pots, margarine tubs, most bottle tops, waterproof clothing, carrier bags, ropes, non woven fibre products like the fluffy cottonwool type stuff used in tampons and nappies.

Does not biodegrade.

UK Collection Rates for recycling.Not generally collected for household recycling, although it has good potential.However, mixed plastic recycling is expected to be under way within five years. (please note this information is always changing. Updates will be posted here first so you may wish to double check.)

It is expected to net US$145 billion by 2019 and the sales of this material are forecast to grow at a rate of 5.8% per year until 2021.

In 2013, the global market for polypropylene was about 55 million metric tons. Wikkipedia.

Polypropylene is made from propylene. This in turn is made from propane.

Propane is derived from hydrocarbons

Hydrocarbon chains are refined by cracking and polymerising.

Very basically cracking breaks the existing chains and polymerisation is remixing them into something new.

Using high-temperature furnaces, propane is cracked into propylene,

Using a catalyst, a reactor and some heat propylene joins together to create a polymer called polypropylene.

Propane can be derived from Naptha ( which is distilled from crude oil)

90% of propylene is made from oil though that figure is rapidly changing as more is made from shale gas as a result of fracking.

“North America plans to build 6 new plants to to make “on purpose” propylene from propane “In the past the price of propylene and propane were so close in the U.S. that it wasn’t cost effective to dehydrogenate propane, but now with low cost propane from shale gas, it is. “

Polypropylene was discovered in  1951 by two chemists working for Phillips Petroleum Company.

In 2008, researchers in Canada asserted that quaternary ammonium biocides and oleamide were leaking out of certain polypropylene labware, affecting experimental results.

 

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Whats your food wrapped in…..

Long ago I bought myself some lentils from a major retailer of whole foods. They came in a clear, crinkly, sharp kind of plastic bag with colorful, crisp images.  The bag had no plastic code so I  set about researching the packaging. I phoned and asked the producer/ retailer but they couldn’t help me. So I had the packaging analyzed. I can now tell them that it was in fact a film consisting of a series of bonded layers including a 70 micron thick polypropylene and ethylene layer, laminated and printed. Or to put it more simply several layers of plastic each with different properties stuck together.

This method of making plastic films leads to a very versatile product that looks good and has a wide range of uses.

On the down side these films are difficult to recycle. Because they consist of different plastics bonded together it is difficult to know what they are and how to treat them and separating the films is tricky and so very expensive. Films therefore often don’t get recycled but burnt or landfilled.

Just to remind you

Another barrier to [plastic] recycling is the widespread use of dyesfillers, and other additives in plastics. The polymer is generally too viscous to economically remove fillers, and would be damaged by many of the processes that could cheaply remove the added dyes. Additives are less widely used in beverage containers and plastic bags, allowing them to be recycled more often. . Yet another barrier to removing large quantities of plastic from the waste stream and landfills is the fact that many common but small plastic items lack the universal triangle recycling symbol and accompanying number. From  Wikipedia on plastic recycling

So if you need to buy something in plastic, try avoid the film and go for easily recycled polythene. You can find some suppliers here….

Plastics used to package food include the following. Copied from practical action 

Films

Film Type

Coating

Barriers to Moisture

Air/Odours

Strength

Clarity

Normal Thickness Micrometers

Cellulose

*

***

*

***

21 – 40

Cellulose

PVDC

***

***

*

***

19 – 42

Cellulose

Aluminium

***

***

*

21 – 42

Cellulose

Nitro- cellulose

***

***

*

21 – 24

Polythene (low density)

**

*

**

*

25 – 200

Polythene (high density)

***

**

***

*

350 – 1000

Polypropylene

***

*

***

***

20 – 40

Polypropylene

PVDC

***

***

***

***

18 – 34

Polypropylene

Aluminium

***

***

***

20 – 30

Polyester

**

**

***

**

12 -23

Polyester

***

***

***

**

Polyester

***

***

***

20 -30

Table 1: Properties of selected packaging materials
* = low ** = medium *** = high. Thicker films of each type have better barrier properties than thinner films. PVDC = polyvinylidene chloride.

Laminated films

Lamination of two or more films improves the appearance, barrier properties or mechanical strength of a package.

Coextruded films

This is the simultaneous extrusion of two or more layers of different polymers. Coextruded films have three main advantages over other types of film:

  • They have very high barrier properties, similar to laminates but produced at a lower cost.
  • They are thinner than laminates and are therefore easier to use on filling equipment.
  • The layers do not separate.
    Examples of the use of laminated and coextruded films are as follows:

Type of laminate

Typical food application

Polyvinylidene chloride coated polypropylene (2 layers)

Crisps, snackfoods, confectionery, ice cream, biscuits, chocolate

Polyvinylidene chloride coated polypropylene- polyethylene

Bakery products, cheese, confectionery, dried fruit, frozen vegetables

Cellulose-polyethylene-cellulose

Pies, crusty bread, bacon, coffee, cooked meats, cheese

Cellulose-acetate-paper-foil- polyethylene

Dried soups

Metallised polyester-polyethylene

Coffee, dried milk

Polyethylene-aluminium-paper

Dried soup, dried vegetables, chocolate

Type of coextrusion

Application

High impact polystyrene- polyethylene terephthalate

Margarine, butter tubs

Polystyrene-polystyrene- polyvinylidene chloride-polystyrene

Juices, milk bottles

Polystyrene-polystyrene- polyvinylidene chloride-polyethylene

Butter, cheese, margarine, coffee, mayonnaise, sauce tubs and bottles

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Thermoplastics and Thermoset Plastics

Plastics are divided into thermoplastics and thermoset plastics.

Thermoplastics can be heated and shaped many times.

Thermoplastics pellets soften when heated and become more fluid as additional heat is applied. The curing process is completely reversible as no chemical bonding takes place. This characteristic allows thermoplastics to be remolded and recycled without negatively affecting the material’s physical properties.

Thermoset plastics can only be heated and shaped once.

Thermoset materials are usually liquid or malleable prior to curing and designed to be molded into their end form, or used as adhesives. Others are solids like that of the molding compound used in semiconductors and integrated circuits (IC

Thermoset plastics contain polymers that cross-link together during the curing process to form an irreversible chemical bond. The cross-linking process eliminates the risk of the product remelting when heat is applied, making thermosets ideal for high-heat applications such as electronics and appliances.

These polymers are highly cross-linked, which means the molecules have extremely strong chemical bonds. Once you’ve initially heated them up to set them into the shape you want – hence the name “thermoset” – they’re irreversibly bound. That means they’re much stronger than thermoplastics, but also that heating them up again won’t break down the bonds in a way that enables you to usefully reshape them, as with thermoplastics. It’ll just char them and crack them instead.

Thermoset plastics that can be remoulded and recycled several times over when heated to about 100ºC are possible, claim researchers in The Netherlands. 

The self-healing polymers make use of the Diels-Alder and Retro-Diels-Alder reactions between thermosetting polyketones and bis-maleimide, allowing the strong covalent bonds of the thermoset materials to be broken and reformed.

Examples of some thermoplastics.

Name Properties Principal uses
Polyamide (Nylon) Creamy colour, tough, fairly hard, resists wear, self-lubricating, good resistance to chemicals and machines Bearings, gear wheels, casings for power tools, hinges for small cupboards, curtain rail fittings and clothing
Polymethyl methacrylate (Acrylic) Stiff, hard but scratches easily, durable, brittle in small sections, good electrical insulator, machines and polishes well Signs, covers of storage boxes, aircraft canopies and windows, covers for car lights, wash basins and baths
Polypropylene Light, hard but scratches easily, tough, good resistance to chemicals, resists work fatigue Medical equipment, laboratory equipment, containers with built-in hinges, ‘plastic’ seats, string, rope, kitchen equipment
Polystyrene Light, hard, stiff, transparent, brittle, with good water resistance Toys, especially model kits, packaging, ‘plastic’ boxes and containers
Low density polythene (LDPE) Tough, good resistance to chemicals, flexible, fairly soft, good electrical insulator Packaging, especially bottles, toys, packaging film and bags
High density polythene (HDPE) Hard, stiff, able to be sterilised Plastic bottles, tubing, household equipment

Properties and uses of the thermoset plastics.

Name Properties Principal uses
Epoxy resin Good electrical insulator, hard, brittle unless reinforced, resists chemicals well Casting and encapsulation, adhesives, bonding of other materials
Melamine formaldehyde Stiff, hard, strong, resists some chemicals and stains Laminates for work surfaces, electrical insulation, tableware
Polyester resin Stiff, hard, brittle unless laminated, good electrical insulator, resists chemicals well Casting and encapsulation, bonding of other materials
Urea formaldehyde Stiff, hard, strong, brittle, good electrical insulator Electrical fittings, handles and control knobs, adhesives

http://www.bbc.co.uk/schools/gcsebitesize/design/resistantmaterials/materialsmaterialsrev3.shtml

Find out more about the above plastics and many others here .

Don’t know your PETS from your hamster. Think Polymer is a girl’s name? Check out this collection of definitions essential for understanding plastic!


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biodegradable plastic from methane

this is very clever …. from the website

Mango Materials produces biodegradable plastics from waste biogas (methane) that are economically competitive with conventional oil-based plastics.

Methane of course is the second-most common greenhouse gas  and is a major contributor to global warming.

and in term of biodegradability….”The rate of degradation depends on the environment and thickness of the material. The Mango Materials product can break down in aerobic and anaerobic conditions and is expected to pass all relevant ASTM and other bio-related certification tests.”

A plastic that cuts methane and biodegrades. Well worth watching….