ΕΙΣΑΓΩΣΗ ΣΤΗ ΡΕΟΛΟΓΙΑ ΚΑΙ ΚΑΤΕΡΓΑΣΙΑ … ·...
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820 (2500) 2017-2018
: . Email: [email protected]
INTRODUCTION TO POLYMERRHEOLOGY AND PROCESSING
UNIVERSITY OF THESSALY SCHOOL OF ENGINEERINGDEPARTMENT OF MECHANICAL ENGINEERING
820 (2500)UNDERGRADUATE COURSE 2017-2018
Instructor: Dr. Nickolas D. PolychronopoulosEmail: [email protected]
: 7/10 ,
6/10 . =(70.5)+(60.5)= 6.5/10
Fundamentals of Polymer Science
POLYMER comes from Greek and means many parts. Polymers i.e. plastics andrubber are substances whose molecules form long chains.
repeating unit (part)
Polymers are characterized through the physical and chemical natureof the repeating units in the chains.
The world PLASTICS usually implies materials Having low strength and stiffness Having temperature limitations Deforming continuously under applied force
By 1980s, volumetric consumption of plastics hasexceeded steel annually
Why ?? Easily shaped or molded into complex shapes with minimum
fabrication and finishing Low densities i.e. low-weight products or parts Thermal and electrical insulators Other special properties e.g. flexible, transparent, chemical
MAJOR COMMERCIAL PLASTICS
High Density Polyethylene (HDPE)containers, bottles, wire and cableinsulation and household appliances.
Low Density Polyethylene (LDPE)bottles, film, garment bags, wirecoating and toys.
Linear Low Density Polyethylene (LLDPE)thin high-strength film.
Polyvinyl Chloride (PVC)RIGID PVC: pipe and housing applications.PLASTICIZED PVC: flexible film sheet, upholstery
Polypropylene (PP)automotive parts, appliances, fibers, luggage, etc..
Polystyrene (PS)sporting goods, radio and TV housings,automotive parts etc..
Nylon (polyamides)food and health packages,endovascular devices (balloon catheters)
Polyethylene Terephthalate (PET)film, bottles, fibers etc.
Polycarbonate (PC)compact disks (CD), optical fibers
Polymethyl Methacrylate (PMMA)
New types of fiber-reinforcedcomposites exhibit highperformance and long servicelife.
Extensively used inaircraft/aerospace applicationsnot only for military aircraft butalso in commercial aviation
They replace metal parts,providing more strengthand lower weight, in theworld's largest passengerjet AIRBUS A380(600+passengers),
Lyon PPS 32, 2016, AIRBUS
Blades must be:- very large- very light- and very strong
glass fiber?, carbon fiber? graphene?environmental, cost considerations?
Another example: Wind turbines
PLASTIC PIPES CYPRUS-TURKEY https://www.youtube.com/watch?v=ixacYA-fjOY
80 KM Long, 1600 mm diameter, POLYETHYLENE pipe for FRESH WATER FROM TURKEY TO CYPRUS
A few, but expensive, parts for aircraft/aerospace applications.
Now, greater emphasis is being put on automotive, electrical,housing and packaging applications.
We must produce many parts at high production speeds andlow costs, but with high performance and long service lifecharacteristics.
MONOMER e.g. ETHYLENE (gas) ~ 0.80 EURO/kg (2017)
POLYMER e.g. POLY-ETHYLENE (solid) ~ 1.4 EURO/kg (2017)
melt it and shape it
PROCESS e.g. EXTRUDE to produce film, pipe, etc. (processingcost ~ 2 1.4 = 2.8 EURO/kg)
Roughly, the raw materials cost accounts for about 50% of the final product, but, of course, itwill depend on the performance requirements.
POLYMER PRODUCERSIn Greece: ECO Thessaloniki (PVC), Northern Greece PP plant, more ??? DOW in Lavrio???
SABIC, BASF, BAYER, EXXONMOBIL, SHELL, DOW-DUPONT, BP, TOTAL, etc.perhaps 50 big chemicalcompanies in the world.
PROCESSORSIn Greece: PLASTIKA KRITIS (films for greenhouses), HELLENIC CABLES (large diameter cables) and lots of
other small manufacturers
In the whole world: roughly 100,000 companies (10~10,000 people)
MACHINE MANUFACTURERSIn Greece: NONE
In the world: Reifenhuser, Huskey Injection Molding, Krauss-Maffei, Erema, Milacron, Battenfeld-Cincinnati etc.
Global total business of plastics: 1 TRILLION US DOLLARS per year. Volume of plastics produced per year is about 325 MILLION tons (2017)
PLASTICS GET A LOT OF BAD PRESS BECAUSE OF POLLUTIONIN OCEANS ETC
SOLUTIONS:1. RECYCLING (most difficult problem is collection) PLASTIC isPERHAPS THE ONLY MATERIAL THAT IS 100% RECYCLABLE(recycling requires efforts by individuals and governments).
2. BIODEGRADABLE POLYMERS (yes they exist, they areproduced, but more expensive)
A FEW HISTORICAL REMARKS
Polymers have been around since life began in this planet (leather,wood, wool, cotton and DNA are polymeric substances)
Synthetic polymers were an important part of the industrialrevolution
o In 1839 the U.S. inventor Charles Goodyearinvented the process of vulcanization (heattreatment of a rubber and sulfur compound)which lead to products of considerabledurability.
A FEW HISTORICAL REMARKS
Spoke first time in a conferencein 1917 for the above. But facedconsiderable opposition.
single polymer chain (simulation)
A major step toward the Age ofPlastics was a German scientist,Hermann Staudinger (1953 NobelPrize, Chemistry) who realized thatpolymers were not colloids butrather long chains of repeatingunits (macromolecules)
In the simplest case, a polymer consists of a simple repeating unit:
The most important type of linear polymers are vinyl polymers:
If R H POLYETHYLENE (PE)
R CH3 POLYPROPYLENE (PP)
R Phenyl POLYSTYRENE (PS)
R Cl POLYVINYL CHLORIDE (PVC)
Polymer chains may be:
LINEARBRANCHED(the branches may beeither short or long andmay themselves havebranches)
CROSS-LINKED(to form a 3D Network Structure, e.g.like vulcanized rubber. They are unableto flow and are hard solids)
Thermoplastics: Melted by heating. Solidified by cooling. Can be re-melted (PS, PE, PVC, etc..)
Thermosets: Long-chain molecules in fluid state. Harden usually byapplication of heat and pressure, due to cross-linking. They cannot besoftened again to make them flow (e.g. phenol formaldehyde, epoxies,most polyurethanes, etc..). Typical product Bakelite black phones.
Elastomers: Cross-linked network structures with large deformabilityand complete recoverability due to high degree of chain flexibility (e.g.natural rubber) RUBBERS
Thermoplastics and thermosets are usually called plastics.
They are compounded, i.e. combined with other materials to give acompound in the form of pellets, granules, powder, flakes or liquid.
Combinations involve: AdditivesFillers or ReinforcementsOther polymers
Commercial Classification of Thermoplastics
COMMODITYLDPE, HDPE, PP, PS, PVC Low performance
ENGINEERINGPC, NYLON 66 + 30% glass, PPS
ADVANCEDLiquid Crystal Polymer (LCP), PTFE, PEEK, PES Very high performance
GLASS TRANSITION AND MELTING POINT
Polymers exist in crystalline (ordered)
or amorphous (random) states.
For amorphous polymers there is a certain temperature called theGLASS TRANSITION TEMPERATURE, Tg, below which the materialbehaves like glass, i.e. it is hard and rigid.
Crystalline polymers also exhibit Tg, but this is masked to some extendby the crystalline structure. It corresponds to low mobility in thebackbone of the chain.
We consider Tg as the lowest temperature at which we canconsider the material FLOWABLE LIKE A LIQUID.
The melting point Tm is more meaningful for semi-crystalline polymers.
Polymer TgoC Tm
oC Usual melt processing
Melt density kg/m3
HDPE -100 135 160-240 780
LDPE -100 110 160-240 760
PP -15 165 180-240 720
PVC (rigid) 80 240 170-200 1270
PS 100 - 180-240 1000
Rubber -70 35 90-110
PET 70 265 275-290 1210
Nylon-66 40 265 275-290 980
Nylon-6 40 220 230-260 980
NOTE: solid density is roughly 15% -20% HIGHER THAN MELT DENSITY
MOLECULAR WEIGHT AND MOLECULAR WEIGHT DISTRIBUTION
Molecular Weight (MW) of WATER HO: 21+16=18
Ethylene monomer -(CH)- molecular weight (MW): 122+41=28
POLYETHYLENE (many monomer units)
(CH) WAX (MW: 5028=1400)
(CH) FILM RESIN (MW: 500028=140000)
Commercial polymers generally contain a distribution ofmolecular weights. This distribution is specified in terms ofaverage molecular weights:
Number Average: Mn
Weight Average: Mw
Z Average: Mz
Z+1 Average: Mz+1
A typical Molecular Weight Distribution (MWD) curve
If the number of molecules with molecular weight Mi is given by ni, thetotal weight of the sample is niMi and the total number of molecules is ni
This is the number-average molecular weight. If the weight fraction ofmaterial having a molecular weight Mi is wi, we have
Definition of Mn:
Definition of weight-average molecular weight:
the z-average molecular weight:
and the z+1-average molecular weight:
Example: Consider a polymer for which 99% of the weight is material with M=20,000 and1% with M=109. Determine Mn, Mw, Mz and Mz+1.
The ratio Mw/Mn is often called POLYDISPERSITY. For mostcommercial polymers, Mw ~ 10,000 400,000. The polydispersityvaries according to the polymerization method, etc.
Commercial PS: Mw/Mn ~ 2.5-4Commercial PP: Mw/Mn ~ 5-10Commercial PE: Mw/Mn ~ 5-30
Sometimes, the dilute solution viscosity of the polymer is usedto characterize molecular weights
=solution viscosity K, a=empirical constants available in bookso=solvent viscosity Mv=viscosity-average molecular weightC=concentration
Like in metals (e.g. steel) we can measure tensile properties i.e. stress() vs strain (), =, where E the Youngs modulus (or tensilemodulus) (N/m2=Pa)
Slope in a stress-strain diagram E
Typical values of tensile modulus are usually in GPa (=106 Pa)
LDPE 0.2 GPa
HDPE 1.0 GPa
NYLON-66 2.0 GPa
PVC 2.5 GPa
PS 3.4 GPa
STEEL 210 GPa
The strength of steel comes from primary chemical bonds The weakness of plastics comes from the weak cohesive forces (Van der
Waals) between the entangled and coiled long chains
So, to produce SUPER STRONG plastics we must align the chains thecarbon-carbon bonds will give us a lot of strength!!!e.g. Single PE filaments have been produced with E=260 GPa (steel=210 GPa)
Can be achieved by special processing techniques e.g. extrusion and drawingof fibers at low temperatures.
Tensile modulus E depends on temperature
It is all a question aboutchain mobility (none forglass, a lot for melt)
Crystallinity inhibits chainmobility and gives hardnessto polymer.
One important characteristic ofSOLID polymers is the timedependence of their properties. e.g.Rigid PVC may have a high modulusat high extension rates while it haslower modulus at low extensionrates
While simple tensile test is adequate for design purposes with steel, plasticsmust be subjected to additional testing especially for their long-timeproperties. Under constant stress, polymers tend to creep i.e. strainincreases with time
TENSILE MODULUS VS TENSILE STRENGTH
The TENSILE MODULUS is determined fromthe tangent at the origin in the stress-straindiagram
TENSILE STRENGTH is the ratio of the forceapplied to the material at rupture to itsoriginal cross-section area (B=F/A). Thisproperty is typically called ultimate tensilestrength, i.e. the strength at break.
For commodity plastics: E=O(1 GPa)=(20 MPa)
Diagrams of TENSILE STRENGTHversus TENSILE MODULUS areavailable (mainly used forclassification purposes).
For design with plastics we needthe tensile modulus and strength,flexural modulus, compressivestrength, impact strength andtime dependent properties likecreep.
SINGLE SCREW EXTRUSION
TWIN SCREW EXTRUSION
blown film extrusion
Selective Laser Sintering (SLS)
Fused Deposition Modeling (FDM)
In all of the previous processes the polymer is a MELT(in high temperature) which means that it FLOWS likea LIQUID inside the many channels of the processingequipment (e.g. inside the extruder and the extrusiondie).
Understanding the FLUID MECHANICS is essential!!