Polymer Technology

The [Rise of the] Macro-Molecular Concept

• Hermann Staudinger

- 1917 proposed “macro-molecules”

gaint longchain molecules whose small-molecule constituents were linked together by chemical bnds no different to those in ordinary organic compounds

1953 Nobel Prize

• Wallace Hume Carothers

- DuPont 1920′s

-  synthesized high-molecular weight polymers

from bi-functional reactants, using normal organic condensation reactions

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Plastics – the beginnings

• 1839 Natural Rubber  – Charles Goodyear
• 1843 Vulcanite          – Thomas Hancock
• 1843 Gutta-Percha     - William Montgomerie
• 1856 Shellac              – Alfred Critchlow, Samuel Peck
• 1856 Bois Durci          - Francois Charles Lepage

History of Industrial Polymers

• 1939 PS             
  Eduard Simon[a German apothecary]
• 1926 PVC          
  Dr. Waldo Semon[BFGoodrich, hired to develop a cost-effective synthetic rubber]
• 1935 LDPE 
  Eric Fawcett and Reginald Gibson[ICI]
• 1941 PET          
  Rex Whinfield and James Dickson[Calico Printer's Association]
• 1951 HDPE 
  Robert Banks and and Paul Hogan[Phillips Petroleum]
• 1951 PP            
  Robert Banks and and Paul Hogan[Phillips Petroleum]

The Plastic Era – Thermosetting Plastics and Thermoplastics

• 1909  Phenol-Formaldehyde (Bekelite) – Leo Hendrik Baekeland
• 1926  Vinyl (PVC) – Walter Semon
• 1927  Cellulose Acetate
• 1935  Low-density polyethylene (LDPE) – Reginald Gibson and Eric Fawcett
• 1936  Acrylic or Polymethyl Methacrylate
• 1938  Polystyrene made practical
• 1938  Polytetrafluoroethylene (PTFE) Teflon – Roy Plunkett
• 1939  Nylon – Wallace Carothers
• 1941  Polyethylene Terephthalate (PET) – Whinfield and Dickson
• 1942  Low Density Polyethylene
• 1942  Unsaturated Polyester
• 1951  High-density Polyethylene (HDPE) – Paul Hogan and Robert Banks
• 1951  Polypropylene (PP) – Paul Hogan and Robert Banks
• 1958  Polycarbonate – Daniel Fox – GE  plastics
• 1964  Polyimide – DuPont – Noryl
• 1970  thermoplastic Polyester
• 1978  Linear Low Density Polyethylene
• 1985  Liquid Crystal Polymers

There are some models of fluid:

• Newton
• Bingham body
• Dilatant fluids
• Pseudoplastics fluids

The correlation between Shear viscosity-shear rate axis and the fluids will be shown in figure 3.

Figure 3:Shear Viscosity – Shear rate

The correlation between Shear stress-shear rate axis and the fluids will be shown in figure 4.

Figure 4: Shear Stress – Shear Rate

Descriptions for each fluid model:

»Newtonian fluid

• Have constant viscosity and not depend on shear rate
• For Fluid with low molecular weight (water, benzene)

» Bingham body

• Newton fluid after yield stress
• Highly filled polymer

»Dilatant fluids:

• Fluids, that the viscosity will be higher with increasing shear rate
• PVC plasticized

» Pseudoplastics:

• Fluids, that the viscosity will be lower with increasing shear rate
• Polymer molten

Those effects (Newton’s, Psedoplastics, dilatant) are depending on the shear rate but not depend on the time (time independent). Several fluids show the viscosity’s changing that depend on the time when it is loaded with constant shear stress.

» Thixotropy fluid: It’s the properties, that viscosity IS decreasing with constant shear stress (painting material)
» Rheopexy fluid: It’s the properties, that viscosity IS increasing with constant shear stress (Suspension PVC)

Several properties of-polymer are shown in figure5.

(a) Poly(methyl  methacrylate) at 240°C; (b) Polyethersulphone at 350°C; (c) LDPE (MFI 20 g/lO min) at 170 °C; (c) Polyamide 66 at. 285 °C.
Figure 5: Flow of curves of some typical Thermoplastics melts

The typical shear rate per second [1/s] of polymer melts In the processing as follows:

• Injection molding                10³ - 10⁵
• Compression molding           10⁰ - 10¹
• Calendering                       10¹-10³
• Extrusion                           10⁰ - 10³

By increasing temperature of polymer melts, the shear stress will be lower, so that the energy need to process will be lower for turning the screw. These properties will be shown in figure 6.

Figure 6: Shear Stress – Shear rate by different temperature

The shape of flow is described as follows:

Figure2:Model of Elongation flow

Deformation :

Tensile Stress:

Viscosity is ability of material to flow (easy or difficult):
> High viscosity > it is difficult to flow
> Low viscosity > Its easy to flow

For examples:

Table 1: Viscosity of some fluids.

Model of flow will be shown as figure1:

Figure1: Model of flow

Viscosity
When a force is applied to a volume of material then a displacement (deformation) occurs. If two plates (area A), separated by fluid distance (separation height H) apart, are moved ( at velocity V by a force, F) relative to each other, Newton’s law states that the shear stress (The force divided by area parallel to the force,F/A) is proportional to the shear strain rate (V/H). The proportionally constant is known as the (dynamic) viscosity ().
The effect (shear strain) is quantified by the displacement per unit height (D/H) and the rate of this effect (strain rate) is the velocity per unit height (V/H), where the height is the distance to relatively unaffected position. The viscosity () is the tendency of the fluid to resist flow and is defined by:

Increasing the concentration of a dissolved or dispersed substance generally gives rise to increasing viscosity (i.e. thickening), as does increasing the molecular weight of a solute.
With Newtonian fluids (typically water and solutions containing only low molecular weight material) the viscosity is independent of shear strain rate and a plot of shear strain rate (e.g. the rate of stirring) against shear stress (e.g. force, per unit area stirred, required for stirring) is linear and passes through the origin.

The definition of rheology’ from Bingham (1928) is the science about the flow and deformation of materials. The content of the rheology subject include the investigation of flow properties, it means polymer melting. This subject is very importance basic to understand about the polymer processing.

The flow ability of polymers is very strong depending on the motion of molecule segment.

The aims of study of rheology are:

• To know the behavior of polymer flow in relationship with the process until end product
• To measure quantitative the response of material
• To predict the behavior of polymer during the process

Basic of rheology is:

• Correlation between deformation, stress and time.
• modeling of flow

There are two types of geometry flow:

1. Simple shear
2. Elongation flow