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PLASTICS MATERIALS & TESTING



  1. PT  301  -  PLASTICS  MATERIALS  &  TESTING

 MACHINE  SHOP TECHNOLOG






Unit-1     Unit-2   Unit-3   Unit-4





 MACHINE  SHOP TECHNOLOG




Index

 
Unit  I  Polymer  Science

(60  Hours) (8  Hours) 

 Introduction  to  Monomers  and  Polymers  –Polymerisation  –types  of  Polymerisation  - condensation  -  addition  -  Copolymerisation,  Characterization  -  Polymer  solution  Measurement  of  molecular  weight  and  size,Structure  and  properties  of  polymers. 

   Unit  II  Thermoplastic  Materials    

   (20  Hours) 
Introduction  –  Types  –  Commodity  &  Engineering  plastics-properties  and  applications  of various  plastics  material  -  Polymer  blends  and  alloys  -  Polymer  composites. 

 Unit  III  Thermoset    Materials        

   (12  hours) 

 Properties  –  Processing  Behaviour  and  Applications  of  Phenol  Formaldehyde  –  Urea Formaldehyde  –  Melamine  Formaldehyde  –  Unsaturated  Polyesters  –  Alkyd  Resins  –  Epoxy Resin  –  Polyurethane  –  Silicones.
   Unit  IV Plastics  Testing  
      (20  Hours) 

 Introduction  &  importance  of  testing  –  Significance  of  Identification  of  plastics  -  necessary manufacturing  properties-Assessment  of  properties  of  finished  products  in  relation  to  service requirements. Standard  &  specifications  -  National  and  International  standards  -  BIS,  ASTM,  ISO  &  NABL. Identification  of  common  plastics  materials  by  simple  tests  e.g.,  visual  inspection,  density, effects  of  heat,  combustion  and  solvents,  analysis  with  common  solvents.   Preconditioning  and  test  atmosphere  -  Testing  of  Mechanical,  Thermal,  Optical,  Electrical properties,  Permeability  properties  and  Rheological  properties. 


Unit:1 polymer science  

▪Monomers:

▪Monomers
A Monomer is an atom or small molecule that may bind chemically to other monomers to form a Polymer (means many parts). A Polymer is defined as a large molecule composed of repeating structural units. Monomer bond together to form polymers during a chemical reaction called Polymerization, where the two molecules link together by sharing electrons. The term monomercame from the Greek word “mono” means “one” and “meros” means “part”. The most common natural monomer is glucose which is linked glycosidic bonds into polymers such as cellulose and starch. It is over 76% of the weight of all plant matters. Most often the term monomer refers to the organic molecules which form synthetic polymers, for instance vinyl chloride which used to produce the polymer 




Exmpels :  Ethylene,Propylene,Vinylchloride,Caprolactame,Tetraflourethylene




 polymers


  1. a substance which has a molecular structure built up chiefly or completely from a large number of similar units bonded together, e.g. many synthetic organic materials used as plastics and resins.


Polymers are made up of many many molecules all strung together to form really long chains (and sometimes more complicated structures, too).
What makes polymers so fun is that how they act depends on what kinds of molecules they're made up of and how they're put together. The properties of anything made out of polymers really reflect what's going on at the ultra-tiny (molecular) level. So, things that are made of polymers look, feel, and act depending on how their atoms and molecules are connected, as well as which ones we use to begin with! Some are rubbery,  like a bouncy ball, some are sticky and  gooey, and some are hard and tough,  like a skateboard
Polymerisation 

 is the process of joining together a large number of small molecules to make a smaller number of very large molecules. The reactants (i.e. the small molecules from which the polymer is constructed) are called Monomers and products of the polymerisationprocess are called Polymers




Characteristics of Condensation Polymers

Condensation polymers form more slowly than addition polymers, often requiring heat, and they are generally lower in molecular weight. The terminal functional groups on a chain remain active, so that groups of shorter chains combine into longer chains in the late stages of polymerization. The presence of polar functional groups on the chains often enhances chain-chain attractions, particularly if these involve hydrogen bonding, and thereby crystallinity and tensile strength. The following examples of condensation polymers are illustrative.
Note that for commercial synthesis the carboxylic acid components may actually be employed in the form of derivatives such as simple esters. Also, the polymerization reactions for Nylon 6 and Spandex do not proceed by elimination of water or other small molecules. Nevertheless, the polymer clearly forms by a step-growth process. Some Condensation Polymers.


Additon
An addition polymer is a polymerwhich is formed by an additionreaction, where many monomers bond together via rearrangement of bonds without the loss of any atom or molecule under specific conditions of heat, pressure, and/or the presence of a catalyst.


Copolymerisation

If a mixture of more than one monomeric species is allowed to polymerise, a copolymer is formed and it contains multiple units of each monomer used in the same polymeric chain.


The composition of the polymer depends not only on the proportion of the monomers but also on their reactivity. Some monomers as such do not polymerize at all but copolymerize. Maleic anhydride does not polymerize but copolymerizes with styrene in a highly symmetrical manner to form styrene maleic anhydride copolymer.
Examples of copolymers are styrene butadiene rubber.


Polymer characterization

 . Polymer characterization is the analytical branch of polymer science. The discipline is concerned with thecharacterization of polymeric materials on a variety of levels. Thecharacterization typically has as a goal to improve the performance of the material.

the Molecular Weight of Polymers


The word “polymer” has been derived from the Greek words 'poly' and 'meros', implying many parts, and refers to a characterizing feature of polymeric materials – their chain like structure. This structure is formed by developing chemical links between a number of monomers or repeating units. For instance, polymerizing styrene, a monomer, under suitable reaction conditions, results in the polymer polystyrene (Figure 1).
Figure 1. A defining feature of polymers is their chain-like structure, made up of repeating monomers.
A polymer’s molecular weight is related to that of the monomer, and the number of monomers present in the polymer molecule. The molecular weight of styrene is 104 Da. Hence, the molecular weight of polystyrene is 104n, where “n” is the styrene molecule number in the polymer chain. Both the distribution shape and the average MW influence the properties of a polymer. Therefore, measuring MW requires measuring the MW of individual chains and the number of chains of any specific weight.
The general distribution of polymer MW is seen in Figure 2. Using statistics, three different moments can be defined for this distribution, each being considered as an average MW. Mn is the number averaged MW, and Mw is the weight averaged MW. The midpoint of the distribution in terms of the number of molecules is Mw. The third moment, Mz, has more weighting with regards to higher MWs. The Mw:Mn ratio is termed as polydispersity, and is used for describing the distribution width.
Figure 2. Average MW can be defined in a number of different ways using different moments of the distribution.
An essential point to consider while examining alternating MW technique measurements is that any absolute MW measurement must involve the absolute measurement of concentration or number of molecules.

Measuring MW - Introducing Static Light Scattering (SLS)

The different methods used for measuring MW are:
  • End group analysis
  • Membrane osmometry
  • Viscometry
  • Light scattering
The standard approach, however, is static light scattering (SLS). The irradiation of a macromolecule by an incident light photon beam causes photons to be absorbed and re-emitted or scattered in all directions. The scattered light intensity and the polymer MW are proportional, the relationship being described by the Rayleigh equation.
Three approaches to SLS have been developed:
  • Right angle light scattering (RALS) - Scattering intensity is determined at 90° to the incident beam. It offers a very good signal to noise ratio, however, does not take into account anisotropic scattering. The assumption is that the scattering intensity at 0° is just as that at 90°. This is a suitable approach for small molecules but not for anisotropic scatterers.
  • Low angle light scattering (LALS) - In LALS, scattering intensity is determined at an angle very close to 0° in order to eliminate the error related to anisotropic scattering. This is fine for all molecules, however, the signal-to-noise ratio becomes challenging for smaller molecules. A combination of RALS/LALS technology is a good prospect.
  • Multi-angle light scattering (MALS) – The approach adopted with MALS is measuring at several angles and extrapolating the same to determine a value for scattering intensity at 0°C. MALS is suitable for all molecule sizes but the method is more complicated than LALS or RAls.
It is possible to use all the three light scattering techniques in batch mode, but they are more frequently applied in flow mode, with the light scattering detector constituting a gel permeation/size exclusion chromatography (GPC/SEC) detector array.

GPC/SEC - Powerful Technique for Measuring MW distribution

As shown in Figure 3, GPC/SEC starts with size fractionation of a sample, after which each sample fraction is detected as it elutes from the separation column. The only disadvantage with GPC/SEC is that separation is based on the polymer molecule size, not on its MW.
Figure 3. Schematic of a GPC/SEC set-up, detectors are positioned at the exit of the column oven to measure the properties of the eluting sample.

In GPC/SEC, the term 'absolute' MW is used for differentiating a method that directly measures MW from one that infers it, especially from calibration techniques relying on the use of a set of relevant standards.


Structure  and  properties  of  polymers. 



Properties of polymers 




Polymers are the most widely used materials in the pharmaceutical and medical devices industry. However, there have been instances of unexpected product failure and yield deterioration driven by changes in the physical and chemical structure of polymer materials that may occur during production, post treatment, transportation, in storage or in use. These structural changes may range from millimeter, micro and up to nano scales, thus eventually affecting the performance of the product. This paper introduces the basic concepts related to polymeric materials’ structure and properties.

How Polymers are ConfiguredIntra- and Inter-Polymer Characteristics:
Glass Transition Temperature (Tg) and its Physical MeaningMelting and Crystallization Temperatures Tm and TcPolymer Molecular Weight and its MeaningsMechanical Properties of Polymers

Polyethylene (PE), having the simple structure, is made from ethylene CH2=CH2 via a polymerization process that opens its double bond and forms a structure as follows.


The average molecular weight for a linear PE ranges between 200,000 g/mole and 500,000 g/mole. A single PE chain can modify its configuration instantly and randomly. The long chain polymer, with a high length to diameter ratio, behaves like a soft rubber wherein highly entangled chains are stretchable under force and can retain their original state upon release. By replacing one H from each repeat unit of PE with Cl, poly-(vinyl chloride) (PVC) can be created.


However, the change in element makes the -C-C- bond rotation in PVC difficult, making it stiff. The structural change from PE to PVC has significantly affected the properties and applications of the two polymers.

Intra-polymer structure characteristics: Polymer chains are mostly ‘soft’, ‘stiff’ or in-between. The intra-polymer structure characteristics of the polymers decide whether a long chain polymer is ‘stiff’ or ‘soft’ or something in between.

Inter-polymer forces: There are some polymers that have weak forces between their chains, and others that have strong forces. van der Waals forces decide this inter-polymer force. These two factors can help in understanding the varied properties of polymers and also the reason why polymers are very different from materials like metals and ceramics.

An important parameter unique to polymers is Tg. The length of a polymer chain segment varies due to intra-and inter-polymer characteristics. Figure 3 illustrates the rapid changes in shape when a rope is moved up and down.


 Figure 3


From this illustration, it has been observed that the stiffness of a polymer chain increases with the length of its segment. Tg can be defined as the transitional temperature at which polymer segments begin to flow from the frozen state (with raise in temperature), or start freezing (with drop in temperature). Figure 4 illustrates this change in the chain segment.


Figure 4


By contrast to majority of the inorganic crystalline materials, polymers are not able form 100% crystals. Polymers always have at least two phases namely, amorphous and crystalline. It is not its Tg, but rather its crystallinity that determines whether the material is a plastic or rubber. The crystals (hard phases) and rubbery (soft phases) make the PE behave as a plastic with toughness, and not as a rubber. Re-crystallization takes place on heating before melting, which increases complexity in polymers.

Figure 5

Both melting and crystallization cover a specific range of temperatures around the peak temperatures Tm and Tc. The uncompleted crystallization process is responsible for the re-crystalllization on heating. Hence, when the polymer is heated, re-crystallization will take place at temperatures before the melting temperature of the existing crystals. Hence, Differential Scanning Calorimetry is not reliable for polymer crystallinity measurement.
There are two ways widely utlized to present molecular weight as a polymer parameter. One is number average of molecular weight Mn, and the other is weight average Mw. Figure 6 illustrates a realistic molecular weight distribution.



Figure 6

Two extreme cases namely a very brittle polymer and a very ductile polymer are illustrated to demonstrate the real performance of polymers in Figure 7.



Structure of polymers :


A polymer is composed of many simple molecules that are repeatingstructural units called monomers. A single polymer molecule may consist of hundreds to a million monomers and may have a linear, branched, or network structure

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