The Basics of Polyethylenes

Education & Careers 21 November 2013 | 0 Comments

polyethylenes

Polyethylene, falling under the classification of thermoplastic, is a polymer type that can be melted to liquid form and be physically changed or assume a new form when it solidifies. Polyethylene, as the name suggests is chemically synthetic molecules that have poly or many or long chains of ethylene. Ethylene is a monomer with a characteristic to double bond with other monomers, which are carbon-based, in order to form polymers. Polyethylene is also known popularly as polythene in the United Kingdom or simply abbreviated as PE.

In 1898, polyethylene was first created by in a laboratory by Hans von Pechmann. It was created by accident while heating another compound called diazomethane which he also previously discovered. After 35 years, the synthesis of polyethylene by undergoing extreme heat and pressure in industrial setup was discovered again by accident. After few more years, then a chemist of the same company based in England have come up with a process to manufacture polyethylene under the same conditions. With all these, in the year 1939, polyethylene has become the main source of low-density polyethylene (LDPE) production.

Polyethylene is a substance found in various household items like plastic shampoo bottles, milk containers, toys, plastic bags, food wrappers and many other plastic products. It is also used in manufacturing of artificial knee and hip replacement components, Kevlar vests, and even for glassy flooring of ice skating rinks. The aforementioned are just a few examples of the significance of polyethylene to the plastics industry.

Physical properties

Melting point and glass transition may be noticed but are dependent on certain factors like crystallinity and molecular weight. The temperature for the melting point and glass transition are distinct for every type of polyethylene under consideration. The temperature range of 120 to 130 degrees Centigrade (248 to 266 degrees Fahrenheit) is the typical melting point for commercial grades of medium and high density polyethylene. While for low density polyethylene, the temperature range is only from 105 to 115 degrees Centigrade (221 to 239 degrees Fahrenheit).

Due to the crystallinity property of the polyethylene, low-, medium-, and high-density PE have excellent chemical resistance. Moreover, they do not dissolve at room temperature. They can only be dissolved at high temperatures in aromatic hydrocarbons like toluene or xylene, or with chlorinated solvents like trichloroethane or trichlorobenzene.

Classification of Polyethylenes

There are several classifications of polyethylene. Each is distinguished by the molecular weight and branching properties, which are, in turn, influenced by its crystallization. For example, low-density polyethylene is branched polyethylene. This is because its carbon molecules are connected to long chains of polyethylene and not with hydrogen. If a linear structure consisting of carbon and hydrogen results, this is referred to as high-density polyethylene. Aside from low- and high-density PE, other variants may also be produced like ultra high molecular weight PE, medium-density, and very low-density PE.

Biopolyethylene

BiopolyethyleneDue to the fact that plastics have been a global environmental concern because they are not biodegradable and remains in landfills for long years, scientists are formulating solutions to make plastics biodegradable. They are experimenting on using Sphingomonas, a certain type of anaerobic bacteria which can decrease the length of time to degrade polyethylene in a matter of months. Also, bioplastics are being developed to aid in synthesizing polyethylene from ethanol which is a derivative of sugarcane.

Two companies, Braskem and Toyota Tsusho Corporation formed joint marketing activities to obtain from sugar cane a by-product called green polyethylene. In Triunfo, RS, Brazil , Braskem have built an industrial facility that has a capacity to produce 200,000 short tons (180,000,000 kg) of High Density Polyethylene and Low Density Polyethylene from sugarcane’s derivative, bioethanol.

Polyethylene Terephthalate

Polyethylene TerephthalatePolyethylene terephthalate is commonly abbreviated as PET, PETE, or PET-P is a thermoplastic polymer resin. It is part of the polyester family and finds application in synthetic fibers, food and beverage containers, thermoforming, and engineering resins. This is oftentimes coupled with glass fiber.

World’s PET production is primarily for synthetic fibers which is more than 60%. 30% is for bottle production in a global demand basis. For textile industries, PET is known as “polyester”, but for packaging applications, it is known as “PET”.

PET comes in some trade names. Dacron, Diolen, Terylene, Tergal, Trevira, Clearcut, Eastman PET, and Polyclear bottle resins are just a few trade names. For films, some trade names are Hostaphan, Melinex, and Mylar. For injection molding resins, some examples are Arnite, Ertalyte, Impet, Rynite, and Valox. 18 percent of world polymer production is polyester industry and ranked third following polyethylene (PE) and polypropylene (PP).

Uses of Polyethylene Terephthalate

PET has some characteristics. It can be rigid and semi-rigid, dependent on its size or thickness. Another characteristic of PET is its being lightweight. It finds application as a barrier to moisture, alcohol, and other solvents. It is also colorless and highly transparent.

Another main application of PET is for soft drink bottles. That’s why soft drink bottles are often called PET bottles. For specialized applications requiring reduced permeability to air or oxygen, PET includes additional polyvinyl alcohol inside.

Another common application of PET is in films. Mylar film is known for it. PET can be made reflective and opaque by evaporation of a thin film of metal onto it. This is done in order to reduce its permeability and made reflective. Some examples are flexible food packaging, and thermal insulation.

PET is also used in tape applications for its high mechanical strength. Examples are magnetic tapes and pressure adhesive tapes.

Possible Toxicity of PET

PET may have some ill effects on human. As published in Environmental Health Perspectives in April 2010, a commentary suggested that PET may induce endocrine disruptors as an effect of constant or common use of products containing it. However, there have been some proposals like leaching of phthalates or antimony as mechanisms. There are however some which say that PET does not cause what some publishers fear in the absence of evidence. The possible toxicity of PET are still the subject of researches, and evidence of its harmful effect are still under consideration.

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Is Polyethylene Safe For Storing Food?

Home Science 24 April 2014 | 0 Comments

We have all heard of the toxic properties of polyethylene and yet it is a very common feature in our households. In fact, plastic rules our households with almost everything we use all day being made of plastic.

For example, your toothbrushes and toothpaste containers are possibly made from plastic, the shampoo you use to wash your hair also comes from a plastic container, your fridge where you put your food has plastic handles, the pan you use to fry your eggs and bacon have plastic grips, your water bottles are possibly made from plastic, some of your food containers are plastic, the buttons in your clothes are plastic…..and the cycle continues.

But how safe are we when we use plastic to store the things we consume like water, food and juices?

plastic containerThe reality is that we all love plastic food containers because they are durable, lightweight and cheap. Although many of these products are approved by the relevant authorities, many of us are still not sure about some of these approved plastics.

What we should know is that not all plastics are safe for storing food and other edibles. Food containers are specifically marketed for food and not any other business. All other containers should be avoided as they may contain toxic or poisonous ingredients.

Washing

While some containers can easily be cleaned or washed, there are some that should never be washed for reuse because they are difficult to clean and will therefore harbor bacteria in the unreachable parts. Textures and narrow-necked containers are some of the containers that should not be reused.

Heating

Many people use their plastic containers to heat leftovers in the microwave, this should be avoided because once the container heats up, it will release chemicals into the food. Some containers claim to be microwave-safe but this only means that they cannot melt or squash but they will definitely leach toxins into the food.

Re-using

High density polyethylene (#2 HDPE), commonly used to manufacture milk jugs is safe for reusing because it is believed to not leach any chemicals. Low density polythene (#4 LDPE) is also considered safe and is used to manufacture food bags like sandwich bags and plastic wraps. Polypropylene (#5PP) is also safe and is common in yoghurt tubs.

Other than toxic concerns, plastics are economical and really affordable for producing mass quantities from both the consumer and business market view. They offer excellent alternatives to expensive raw materials that would have made life more difficult for the average household. For example, there was a time when household vacuums were horribly expensive, bulky and almost unmanageable.

Vacuuming was a strenuous chore for those who could afford the vacuums; the others who couldn’t afford them had to seek other ways to make their homes habitable. Individuals who had dust and pet hair allergies suffered the most but today, thanks to polyethylene, vacuums and have become very affordable and you can even get an excellent one for sucking up pet hair here right from the comfort of your living room.

Polyethylene and Household Products

Home Science 20 February 2014 | 0 Comments

household cleaning

Polythene as we have already seen is thermoplastic which in simple terms means that it can melt into liquid form and get remolded as it continues to go back to its normal solid state. Every year, a huge amount of plastics are manufactured for commercial and industrial products, the greater quantity among these products is polyethylene.

In 2011, it is believed that 280 million metric tonnes of polyethylene was manufactured. Products made from PE, the abbreviation for polyethylene, are common and widespread because it is considered the safest and most useful. This is because it remains pliant for a very long time; it is inert and cannot be damaged by most products.

household cleaningIts strength level and softness are easily adjustable and it can easily be dyed into endless colors. This is why it is so often used to manufacture consumer products like grocery bags, toys and shampoo bottles.

In spite of all its goodness, PE has some potential dangers which all depend on the level of toxicity and flammability. For example, polyethylene-glycol also known as PEG is often used as a binding agent during the manufacture of various drugs. It is also present in other products like toothpaste and shampoo.

PEG has been known to negatively affect some people through diarrhea, nausea, flatulence and so on.

PE also comes with environmental impacts. This is because it does not biodegrade easily and is likely to stay in a landfill for endless years. In the US alone, 20-24 percent of all landfill space is occupied by plastics and more so, polyethylene. The good news, however, is that polyethylene can be recycled through melting down and remodeling.

Polyethylene has quickly grown to become an everyday part of our lives, with more than 20 objects in every household being plastic.

For example, the washing detergent and liquid you use every day for cleaning the floor comes in a plastic container and as the many steam mop reviews online will attest and that very same steam mop you use to clean your floors is made of plastic to a certain degree.

In addition to this, there are many other things made of polyethylene in your house and they include the following:

  • That very same hose you use to water your flowers and plants is actually polyethylene.
  • That remote control that you and your family adore so much is mainly polyethylene.
  • The video game controllers in that house are polyethylene.
  • Your washing machine very probably  has plastic buttons
  • The shampoo you use every morning comes in a plastic bottle and so does your cleaning liquid.
  • Your fridge possibly has plastic handles
  • Your cooking pans have plastic grips.
  • The light switches and sockets are plastic.
  • The buttons in your clothes.
  • Your polyester clothes are PET plastic
  • Your tennis shoes have plastic soles
  • Your computer and keyboard are mainly plastic
  • Your telephone
  • Your bread possibly comes in a plastic bag
  • Some of your chairs could be plastic

Human Chorionic Gonadotropin

Body Science 4 February 2014 | 0 Comments

The Basics

the hcg dietHuman Chorionic Gonadotropin, or hcg, is a hormone that is found in pregnant women. The hormone is formed by the same cells that form the placenta and the reason for its being is to nourish the eggs after conception. After conception hgc will become detectable in urine tests after 12 to 14 days and the level of hcg will double every 72 hours until it reaches its peak levels somewhere between 8 to 11 weeks into pregnancy. After this point it will begin to decline for the remainder of the pregnancy.

After reading the above you may be interested to hear that hcg is actually used very heavily in a mainsyream weightloss system named The HCG Diet. While this particular weight loss system has only been popular for the past year or so, hcg has been proven to aid in weight loss way back to the 1950′s. It became popular in maindtream dieting circles after the diet was featured on the popular Dr. Oz TV show.

How Does It Work

There are many souces of information out there where you can find information on the hcg diet but many of them do not do a very good job of explaining exactly how hcg actually works to aid in weight loss. The entire hcg diet protocol can be summed up by the following statement:

“The hcg diet aims to combine the hcg hormone and a very low calorie diet to force your body into burning stored fat cells for energy instead of food and muscle cells. Thus reducing fat whilst maintaining muscle.”

The hcg hormone uses fat stores from the mother to nourish the unborn child during pregnancy which is exactly the same process that takes place on the hcg diet. The main benefit of using hcg is that your body will use stored fat cells to burn as energy without deteriorating its own muscle cells. This is critical to the way the hcg diet works as there is a substantial cut in calorie intake so the addition of the hcg hormone is essential in making sure your body is sufficiently nourished and does not eat away at its own muscle.

Does It Work?

There is absolutly no doubt that almost everyone that is able to stick to the diet will see dramatic results. This is largely due to the lack of calories that are enforced by the hcg diet food list as can be seen at HCG Diet Info. The lack of calories ensures that the percentage of body fat will reduce but in order to maintain long term fat loss it’s important to preserver the muscle tissue during the fat loss period, and thus the addition of the hcg hormone is critical to this particular weight loss program.

Due to the fact that there is such a substantial cut in calories, there is a great deal of debate as to the effectiveness of actually adding the hcg hormone, however trying to survive on around 500 calories per day will certainly see a reduction in muscle tissue as well as fat tissue. For this reason it is highly recommended that people take some measures to help their body maintain the level of muscle tissue while cutting down to such a low calorie intake.

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