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Course: Polymer and Polymerization Technology
Date: 24-26th November, 2016
Organizer: King Fahd University of Petroleum and Minerals (KFUPM)
Instructor: Dr. Mamdouh Al-Harthi
The three day course can be divided into the following sessions:
- Natural resources of Polymers, importance of polymers and polymer application
Crude oil is the single largest source of polymers and petrochemicals. Advantages of polymers are high calorific value, plastics can be molded into intricate part shapes, are cost competitive with metals on volumetric basis, require less energy to produce than metals, some plastics are transparent and hence may substitute glass in some application, high corrosion resistance, low electrical and thermal conductivity. With that there are certain disadvantage as well. Polymers are long molecules, formed by a large number of small molecules called monomer. Recently there application in aircraft industry, drug and drug delivery and implants and prosthetic have seen a significant rise.
- Classification of polymers and polymer morphology
Polymers are classified on the basis of Natural or synthetic, monomer composition, applications (plastics, rubber, adhesive), reaction to temperature (thermoset & thermoplastic), polymerization mechanism (condensation & step-growth), crystallinity (Atactic, syndiotactic, iso tactic).
Polymer morphology is a branch of science which deals with the study of forms and structure. Polymeric chains from lamella which in turn from spherulites. Spherulites have bath amorphous and crystalline region.
- Thermal Properties in polymers
Glass transition temperature is an important thermal property for polymers. The temperature at which a glassy (rigid, stiff) polymer starts to become rubbery (which exhibits highly elastic deformation). Crystallization can occur only in a range of temperatures between the glass transition temperature Tg and the melting point Tm, which is always higher than Tg. Thermal transition in polymers is from liquid to rubbery and then finally glassy or crystalline. Rate of crystallization affects the polymer morphology.
The various molecular motions occurring in an amorphous polymer mass may be broken into four categories.
- Transitional motion of entire molecules
- Cooperative wriggling and jumping of entire segments of molecules
- Motions of few atoms along the main chain
- Vibration of atoms about equilibrium positions
The glass temperature is thought to be that temperature at which motions 1 and 2 are pretty much frozen out. Tg is influenced by flexibility of chain, side groups, additives, plasticization, chain length, intermolecular Forces, tacticity, Annealing and quenching, free volume.
Differential scanning calorimetry or DSC is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. It can be used to measure Tg, Tm, and crystallization temperature Tc. The graph is unique for every material.
- Mechanical properties of polymers
Stress, strain and strength are the mechanical properties of polymers. Strength of a material are measured along several axis and hence on the basis of this, there are tensile strength, Compression strength, flexural strength and torsional strength. Stress strain curve is unique for any material and the above mechanical properties can be determined through this curve. Two important parameters come out of these mechanical properties, Hardness and toughness. Hardness is the property of material to resist deformation and toughness is the property of material to absorb deformation forces until it breaks.
Temperature effects the material strength or modulus and material shifts from glassy to ductility. Extensive cross link also affects modulus by increasing stiffness and hardness.
- Free Radical Polymerization (FRP)
- Polymerization: is a process of reacting monomer molecules together in a chemical reaction to form polymer. There are several ways to classify the polymerization
- Based on the kinetic scheme (chain vs. step)
- Based on the number of monomers present in the reactor (homo, co, and ter-polymer)
- Based on the used process (bulk, solution, suspension, gas phase, or emulsion)
Free radical polymerization is a chain growth polymerization. Presence of carbon carbon double bond is very important for free radical polymerization. However, the reactivity may decrease with bulky groups around the double bond. The main cause of this reactivity pattern is the steric size of the substituents.
Advantages of FRP:
- very robust technique
- wide range of vinyl monomers
- wide range of operating conditions
- aqueous media: emulsion polymerization
Examples of FRP are LDPE, PVC, PMMA, EPS and HIPS. Free Radical Polymerization propagates takes place through three major steps, Initiation, Propagation and Termination.
Free_radical_polymerization_reaction_mechanism.gif
- Coordination polymerization
- ZN (Ziegler-Natta) is the most common catalyst for coordination polymerization. Other catalyst are Philip catalyst and metallocene catalyst. Catalyst productivity is the kilogram of polymer produced per kilogram of catalyst. The raw materials in coordination polymerization should be of high purity to prevent catalyst deactivation and various equipment are used for this such as degassing column, fixed bed adsorbent, dryers, molecular sieves.
- Polymerization steps include:
- Catalyst activation i.e. formation of active sites
- monomer insertion into active site
- Chain propagation: Chain growth through successive monomer insertion.
One important step in these type of polymerization is pre-polymerization. The catalyst grain react under mild conditions before entering the main reactor in order for the monomer to slowly form a polymer shell around it. This shell protects catalyst particle from uncontrolled disintegration, and also prevents possible reaction runaways which, in turn, would lead to local overheating and even partial polymer melting. It is used to prevent polymer particle breakage and loss of catalyst performances.
The reactivity of also called heterogeneous catalyst depends on reaction time, temperature, catalyst concentration, raw material purity, co-catalyst, external donor, hydrogen concentration.
Reaction processes:
- High pressure (autoclave and tubular reactors): Only for LDPE
- Low pressure (Gas phase, slurry phase, super critical and solution): All other polyolefins.
Conclusion:
The course was related to my job and hence provided me some insights for the lessons I had known earlier regarding polymers and polymerization. Some topics of the course were completely new for me while others were superficially known to me.
KFUPM Short course Polymer and polymerization technology-Certificate
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