FUNDAMENTALS OF PLASTICS

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FUNDAMENTALS  OF   PLASTICS

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Why Plastics

Complex parts in one operation
Wide range of properties
Coloring
7 j. C, A; x$ j; a* s8 ]Low energy requirements
Good insulators
Low cost & weight
Resistance to chemicals
From monomers to polymers        
Examples : (in between   : monomer )
% h2 n7 \5 `& \Polyethylene:  (catalytic polymerization of ethylene gas  under high pressure)
      —CH2 — CH2-- CH2 — CH2 -- CH2 —
Polypropylene: (catalytic polymerization of propylene gas under pressure)
      —CH2 — CH-- CH2 — CH -- CH2 —
& i& H5 q2 y" p1 W& k2 x% V& t                     CH3                       CH3
Polyvinylchloride :
5 z0 X+ A) S/ d- R8 k4 v     — CH2 — CHCl -- CH2 — CHCl -- CH2 — CHCl —

Molecular weight        

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Polymer structures
Homopolymers (ie PP homo)
( s8 b% g% z3 C0 xCopolymers (ABS, SAN)
: q' d* N( C. }1 vrandom
regular
$ G7 o* v  q+ J9 ]2 t( M7 f0 \sequenced
linear
grafted
3 T) X9 l% v9 L" b& W# Y- g4 p1 mBlends and alloys

Polymer structures        
% l( F( ?+ D' l; UWhy using Blends and alloys?
5 O, g4 q  c+ L! v) n, MTo combine properties of different polymers.
Examples: what brings each polymer in                 blends below?
  l/ w  e7 x0 \- x& {" J* x6 b+ vABS/PC
PC/PBT
PPO/PS
PA/PPO

) p/ |# ?, v) iPolymer structures        
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Crystalline vs Amorphous resin
Are the resin different?
Are the resin processed the same way?
Can the resin be used in the same applications?

Amorphous resin
Non organized structure
/ ^  F' e5 G  H  UBroad softening range: 20°C
9 M# j  T, o* a3 \8 oHigh viscosity usually
Poor chemical properties in general
Can be transparent
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Amorphous resin



2 _8 W' k: b3 B9 N* U$ o: C/ |, DCrystalline resin
, t$ a# X5 t4 E6 T' W, B+ v7 T  O8 i( UOrganized structure

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Melting point: within 5°C
; O  p8 k4 i; f7 o' m- bLow viscosity usually
Good chemical properties in general
+ b! n3 D4 Z. ~$ N2 P) nUsually not transparent

2 G0 k+ w, ?* ]. I5 ~! KCrystal structures (1)
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1 H6 A% M! g) Y. pCrystal structures: the unit cell (2)



! e9 l, y0 H" {+ J3 c7 eMacro structure: the spherulite (1)
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Most of the semi-crystalline resins crystallize into a spherulitic macro structure. The macromolecules loop on themselves to shape a lamella. The lamellas are assembled into a spherical super structure called spherulite. The spherulite is growing from a center point, the nucleation point.



Macro structure: the spherulite (2)

6 i7 s* s1 X- h, ~8 r: i2 F4 NThe crystalline entities can also be discs or rods. Once the crystalline entities growth is blocked up by other crystralline entities, the primary crystallization is over and start the secondary crystallization between crystalline entities or lamellas.

Macro structure

. J  m" T+ |% u+ A: UCrystalline resin


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4 T8 A5 B/ e* t& C& T1 @1 a0 n( bSemi-crystalline resin

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Semi-crystalline vs amorphous resin (DSC)
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! h; o. r5 Y0 R" }5 lTg and Tm: some examples
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Typical process temperatures

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( Y/ Z4 V& s* O: C# m/ ^Physical properties

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/ k: M* @& ]1 `4 R; nThermoplastic families / Applications



5 l+ L+ A4 e+ F/ K5 o6 t$ _! WThermoplastic families / Applications
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8 e5 B# v9 c1 N9 {8 WThermoplastic families / Applications
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Thermoplastic families / Applications
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; H% ?7 S$ G6 [" QThermoplastic families / Applications / where to focus

- N  \4 K: E0 w; r; T) pAdditives

Plasticizers (Phtalates in PVC)
- J0 @$ R( A& U: y0 q* jStabilizers (UV stabilizer, carbon black)
% m1 k4 f5 D$ S& p& n9 o0 K8 p& H$ ^Colorants
3 \  ]; l, A. r* {5 V+ y$ z3 pNucleating agents (Talc in PP)
Fillers (Talc in PP)
: L7 F5 y2 X! C$ X. WReinforcements (GF, CF, Kevlar)
Lubricants (Calcium stearate)
Plasticizer
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$ Y! p( W. N# q+ nNucleating agent effect
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Fillers

. m) F- U% {! ~5 x3 S0 LPurpose
. O% ?' z& {+ _/ nDimensional stability
Rub- resistance
8 M7 ]9 I+ \  P3 |8 K/ jCompressive strength
Cost
Materials
; f  F3 U) z( d, LCalcium Carbonate
, `# w- |( @* u) A% C2 _( cGlass beads
, P% F: \/ k; FTalc, Mica, Glass flakes
Reinforcements
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6 G3 K; x! y" T. y7 zPurpose
Tensile Strength
- n, _1 c* }2 M. ~+ A. VImpact Strength
; P3 e5 V( n+ B5 DHeat Deflexion Temperature (HDT)
Tensile Modules
Materials
Glass Fibers
1 R7 Z% x8 f4 O" F) I. xCarbon Fibers
/ W9 F5 n. f. H4 V1 d6 T5 _0 b) DTalc
$ ?3 g% `6 s% X( c$ v9 P9 eConsequences on processing

Consequences on processing

Flow Behavior
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Viscosity
1 W; \+ N9 N% o6 q- O8 ]- c! q7 vShear
6 K. g) u! r! q  W/ B* U' v4 {Temperature Rise & Residence Time
+ W% N2 h5 G8 u/ U# r' Z: {; j. k( | degradation
0 ^& V0 {& e6 X& H/ y& L3 G8 m, \Viscosity
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/ W1 I5 G: m% CResistance to flow
* y1 I$ C9 q0 cIf a force is applied to a liquid, the rate of flow is a measure of viscosity.
Rapid flow = low viscosity liquid
4 z/ g7 m$ \' [" ?: e3 USlower flow = high viscosity liquid
, A8 |2 P4 I, n& V) PUsually the viscosity is given in Pa.s
Do not confuse with MFR or MFI
$ b! h- d1 `& k5 w' y4 ?: {Viscosity / MFR
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Viscosity / MFR

8 U( n; @2 [, u" a$ ]Example:
Polycarbonate PC:        MFR 12
9 t8 h1 w8 {: b. _$ F/ ~Test conditions:        Temperature 300°C
- e. j" t6 }; E- A; w3 z% F                                Load 10 kg
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0 B9 X& R" P% j/ TPolypropylene PP:         MFR 12
Test conditions:        Temperature 230°C
* o' H: C1 ?5 R3 a+ o                                Load 2.16 kg
Shear rate

What is the shear rate?
If we consider a laminar flow (we have a problem  if the plastic flow is not laminar!). The shear rate can be described as the speed difference between 2 layers.

Shear rate
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The resin speed is minimum (almost 0 in the HR channels, normally 0 in the tool cavity) at the wall contact and maximum in the middle of the flow. The shear rate is maximum where dV/dY is maximum.
What happen if the shear is too high?
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7 |8 W2 i) a% e! V. mNewtonian Fluids
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Non-Newtonian Fluids
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Viscosity vs shear rate
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Viscosity vs shear rate
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$ h3 }) L4 a0 S- t/ M" U+ D1 NViscosity vs molecular Wt.

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