Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Thermoplastic shopping experience:
1. Compare - without doubt the biggest advantage that the Thermoplastic offers shoppers today is the ability to compare thousands of Thermoplastic at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.
2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about
3. Testimonials - don't know anybody that has bought a Thermoplastic? Wrong! If the Thermoplastic is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.
4. Questions - Got a question about Thermoplastic then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....
5. Reputation - Never heard of the company selling Thermoplastic? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Thermoplastic and build up a picture of their reputation for sales, returns, customer service, delivery etc.
6. Returns - still worried that even after all of the above your Thermoplastic wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.
7. Feedback - happy with your Thermoplastic then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.
8. Security - check for the yellow padlock on the Thermoplastic site before you buy, and the s after http:/ /i.e. https:// = a secure site
9. Contact - got a question about Thermoplastic, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.
10. Payment - ready to pay for your Thermoplastic, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.
A
thermoplastic is a plastic that
melts to a liquid when heated and freezes to a
brittle, very
glassy state when cooled sufficiently. Most thermoplastics are high molecular mass
polymers whose
Chain (sequence)s associate through weak Van der Waals force forces (polyethylene); stronger dipole interactions and
hydrogen bonding (nylon); or even stacking of
aromatic rings (polystyrene). Thermoplastic polymers differ from thermosetting plastic polymers (Bakelite;
vulcanization rubber) as they can, unlike thermosetting polymers, be remelted and remoulded. Many thermoplastic materials are addition polymers; e.g., vinyl chain-growth polymers such as polyethylene and
polypropylene.
Temperature dependence
Thermoplastics are elastic and flexible above a
glass transition temperature Tg, specific for each one — the midpoint of a temperature range in contrast to the sharp melting point of a pure
crystalline substance like
water. Below a second, higher melting temperature,
Tm, also the midpoint of a range, most thermoplastics have crystalline regions alternating with amorphous solid regions in which the chains approximate
random coils. The amorphous regions contribute
Hooke's law and the crystalline regions contribute strength and rigidity, as is also the case for non-thermoplastic
fibrous proteins such as
silk. (Elasticity does not mean they are particularly stretchy; e.g., nylon rope and fishing line.) Above
Tm all crystalline structure disappears and the chains become randomly inter dispersed. As the temperature increases above
Tm, viscosity gradually decreases without any distinct
phase (matter) change.
Thermoplastics can go through melting/freezing cycles repeatedly and the fact that they can be reshaped upon reheating gives them their name. This quality makes thermoplastics recyclable. The processes required for recycling vary with the thermoplastic. The plastics used for pop bottles are a common example of thermoplastics that can be and are widely recycled. Horn (anatomy), made of the
protein keratin, softens on heating, is somewhat reshapable, and may be regarded as a natural, quasi-thermoplastic material.
Some thermoplastics normally do not crystallize: they are termed "amorphous" plastics and are useful at temperatures below the
Tg. They are frequently used in applications where clarity is important. Some typical examples of amorphous thermoplastics are PMMA, PS and PC. Generally, amorphous thermoplastics are less chemically resistant and can be subject to stress cracking. Thermoplastics will crystallize to a certain extent and are called "semi-crystalline" for this reason. Typical semi-crystalline thermoplastics are PE, PP, PBT and PET. The speed and extent to which crystallization can occur depends in part on the flexibility of the polymer chain. Semi-crystalline thermoplastics are more resistant to solvents and other chemicals. If the crystallites are larger than the wavelength of light, the thermoplastic is hazy or opaque.Semi-crystalline thermoplastics become less brittle above
Tg. If a plastic with otherwise desirable properties has too high a
Tg, it can often be lowered by adding a low-molecular-weight plasticizer to the melt before forming (Plastics extrusion; molding (process)) and cooling. A similar result can sometimes be achieved by adding non-reactive side chains to the
monomers before
polymerization. Both methods make the polymer chains stand off a bit from one another. Before the introduction of plasticizers, plastic
automobile parts often cracked in cold winter weather. Another method of lowering
Tg (or raising
Tm) is to incorporate the original plastic into a
copolymer, as with
graft copolymers of polystyrene, or into a composite material. Lowering
Tg is not the only way to reduce brittleness.
Drawing (manufacturing) (and similar processes that stretch or orient the molecules) or increasing the length of the polymer chains also decrease brittleness.
Although modestly vulcanized natural and synthetic rubbers are stretchy, they are
elastomeric thermosets, not thermoplastics. Each has its own
Tg, and will crack and shatter when cold enough so that the cross-link polymer chains can no longer move relative to one another. But they have no
Tm and will decompose at high temperatures rather than melt. Recently,
thermoplastic elastomers have become available.
List of thermoplastics
See also
A
thermoplastic is a plastic that
melts to a liquid when heated and freezes to a brittle, very glassy state when cooled sufficiently. Most thermoplastics are high
molecular mass polymers whose Chain (sequence)s associate through weak
Van der Waals force forces (
polyethylene); stronger
dipole interactions and hydrogen bonding (nylon); or even stacking of
aromatic rings (
polystyrene). Thermoplastic polymers differ from
thermosetting plastic polymers (
Bakelite;
vulcanization rubber) as they can, unlike thermosetting polymers, be remelted and remoulded. Many thermoplastic materials are addition polymers; e.g.,
vinyl chain-growth polymers such as polyethylene and
polypropylene.
Temperature dependence
Thermoplastics are elastic and flexible above a glass transition temperature
Tg, specific for each one — the midpoint of a temperature range in contrast to the sharp
melting point of a pure crystalline substance like water. Below a second, higher melting temperature,
Tm, also the midpoint of a range, most thermoplastics have crystalline regions alternating with
amorphous solid regions in which the chains approximate
random coils. The amorphous regions contribute
Hooke's law and the crystalline regions contribute strength and rigidity, as is also the case for non-thermoplastic fibrous proteins such as silk. (Elasticity does not mean they are particularly stretchy; e.g., nylon rope and fishing line.) Above
Tm all crystalline structure disappears and the chains become randomly inter dispersed. As the temperature increases above
Tm, viscosity gradually decreases without any distinct
phase (matter) change.
Thermoplastics can go through melting/freezing cycles repeatedly and the fact that they can be reshaped upon reheating gives them their name. This quality makes thermoplastics recyclable. The processes required for recycling vary with the thermoplastic. The plastics used for pop bottles are a common example of thermoplastics that can be and are widely recycled. Horn (anatomy), made of the
protein keratin, softens on heating, is somewhat reshapable, and may be regarded as a natural, quasi-thermoplastic material.
Some thermoplastics normally do not crystallize: they are termed "amorphous" plastics and are useful at temperatures below the
Tg. They are frequently used in applications where clarity is important. Some typical examples of amorphous thermoplastics are PMMA, PS and PC. Generally, amorphous thermoplastics are less chemically resistant and can be subject to
stress cracking. Thermoplastics will crystallize to a certain extent and are called "semi-crystalline" for this reason. Typical semi-crystalline thermoplastics are PE, PP, PBT and PET. The speed and extent to which crystallization can occur depends in part on the flexibility of the polymer chain. Semi-crystalline thermoplastics are more resistant to solvents and other chemicals. If the crystallites are larger than the wavelength of light, the thermoplastic is hazy or opaque.Semi-crystalline thermoplastics become less brittle above
Tg. If a plastic with otherwise desirable properties has too high a
Tg, it can often be lowered by adding a low-molecular-weight plasticizer to the melt before forming (
Plastics extrusion; molding (process)) and cooling. A similar result can sometimes be achieved by adding non-reactive
side chains to the monomers before polymerization. Both methods make the polymer chains stand off a bit from one another. Before the introduction of plasticizers, plastic automobile parts often cracked in cold
winter weather. Another method of lowering
Tg (or raising
Tm) is to incorporate the original plastic into a
copolymer, as with graft copolymers of polystyrene, or into a
composite material. Lowering
Tg is not the only way to reduce brittleness.
Drawing (manufacturing) (and similar processes that stretch or orient the molecules) or increasing the length of the polymer chains also decrease brittleness.
Although modestly vulcanized natural and synthetic rubbers are stretchy, they are
elastomeric thermosets, not thermoplastics. Each has its own
Tg, and will crack and shatter when cold enough so that the
cross-link polymer chains can no longer move relative to one another. But they have no
Tm and will decompose at high temperatures rather than melt. Recently, thermoplastic elastomers have become available.
List of thermoplastics
See also
Thermoplastics - Wikipedia, the free encyclopedia
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