Presentation on theme: "Chemical Engineering Department Polymer Technology (64572) Eng. Shadi Sawalha."— Presentation transcript:
Chemical Engineering Department Polymer Technology (64572) Eng. Shadi Sawalha
To acquire fundamental chemical and physical information on the synthesis, production and characterization of polymer materials To appreciate the breadth of polymer properties and applications, and to learn in depth about polymers in a particular application area Course Objectives
Course contents Introduction to Polymers and Plastics Introduction, Polymer structure and synthesis, Solid properties of polymers, Mechanical properties, Rheological properties, Processing of thermoplastics Thermoplastics Introduction, Polymer categories, Additives, Polymer blends. Thermosets Materials and applications, Processes Elastomers Introduction, Differences and similarities between Plastics and elastomers, Types of elastomers, Properties of elastomers, valcunizable elastomers, thermoplastic elastomers. Plastics Additives Stabilizers, Fillers and reinforcements, Coupling agents, Plasticizers, Lubricants and processing aids, Foaming agents, Flame retardants, Colorants, Antistats, Organic peroxides, Polymer blends, Miscellaneous additives Plastics Recycling Introduction, Recycling collection, Recycling processing, Design issues, Legislation, Biodegradable plastics
Textbook Charles A. Harper, “Handbook of Plastics Technologies”, McGraw-Hill, 2006 Reference Crawford R. J., “ Plastics Engineering”, Butterworth Heinemann, 3 rd edition, 2002
Learning Outcomes and Competences At the end of this course students should be able to; Have a knowledge about polymer definition, structure, properties and types Understand polymerization reactions Identify polymer types ( Thermoplastic, thermoset, elastomers) and their applications Be familiar with polymer processes and utilize the suitable process for needed final product Select appropriate plastic additives according to required functions in the final product Carry out the principles of recycling to protect environment and save money.
CHAPTER 1 INTRODUCTION TO POLYMERS AND PLASTICS Plastics are an important part of everyday life; products made from plastics range from sophisticated products, such as prosthetic hip and knee joints, to disposable food utensils. The reasons for the great popularity of plastics are the wide range of properties and ease of proceesing which may due to: o Varying the atomic composition of the repeat structure o Varying molecular weight and molecular weight distribution o The presence of side chain branching, via the lengths and polarities of the side chains o The degree of crystallinity can be controlled through the amount of orientation imparted to the plastic during processing, through copolymerization
CHAPTER 1 Polymers differ from the other materials in a variety of ways but generally exhibit lower densities, thermal conductivities, and modulii
CHAPTER 1 Polymeric materials are used in a vast array of products: o In the automotive area, they are used for interior parts and in under-the-hood applications
CHAPTER 1 o Packaging applications are a large area for thermoplastics, from carbonated beverage bottles to plastic wrap Application requirements vary widely but, luckily, plastic materials can be synthesized to meet these varied service conditions. It remains the job of the part designer to select from the array of thermoplastic materials available to meet the required demands
CHAPTER 1 POLYMER STRUCTURE AND SYNTHESIS A polymer is prepared by stringing together a low molecular weight species (monomer; e.g., ethylene) into an extremely long chain (polymer; in the case of ethylene, the polymer is polyethylene) much as one would string together a series of bead to make a necklace
CHAPTER 1 The chemical characteristics of the starting low molecular weight species will determine the properties of the ﬁnal polymer When two low different molecular weight species are polymerized, the resulting polymer is termed a copolymer—for example, ethylene vinylacetate
CHAPTER 1 Plastics can also be classiﬁed as either thermoplastics or thermosets Thermoplastic a high molecular weight polymer that is not crosslinked. It can exist in either a linear or branched structure (has Vander Wals bonds between chains) Upon heating, thermoplastics soften and melt, allowing them to be shaped using plastics processing equipment Have ceiling temperature Scrap can be recovered and recycled ( can be reprocessed) Thermoset has all of the chains tied together with covalent bonds in a three dimensional network (crosslinked) will not ﬂow once crosslinked ( formed by chemical reactions) Can withstand high temperatures Can’t be recycled easily ( not by heating
Chapter 1 Polymerization Reactions There are two primary polymerization approaches: step-reaction polymerization and chain-reaction polymerization Polymers synthesized by step reaction typically have atoms other than carbon in the backbone. Examples include polyesters and polyamides Chain-reaction polymers typically contain only carbon in their backbone and include such polymers as polystyrene and polyvinyl chloride.
Chapter 1 Molecular Weights Unlike low molecular weight species, polymeric materials do not possess one unique molecular weight but rather a distribution of weights
Chapter 1 Molecular Weights M w is larger than or equal to M n
Degree of Polymerization, n n = number of repeat units per chain n i = 6 mol. wt of repeat unit iChain fraction
Chapter 1 Viscosity Average One of the oldest methods of measuring the average molecular weight of polymers is by solution viscosity. The viscosity-average molecular weight, M v, lies somewhere between the number average and the weight average Thus we see that for a particular application only a certain molecular weight range is practical for a given polymer. This range is a compromise between optimum properties and ease of processing 1. Most of the practically useful polymers have a DP between 200 to 2000, corresponding to a molecular weight range from 20,000 to 200,000.
1.3 Solid Properties of Polymers Glass Transition Temperature (T g )
Crystallization and Melting Behavior (T m ) In its solid form, a polymer can exhibit different morphologies, depending on the structure of the polymer chain as well as the processing conditions: o Amorphous: Random unordered structure(chains entangled like spaghetti) ex. Polystyrene o Crystalline: ordered regular structure. Ex: polypropylene and polyethylene which are semicrystalline o Crystallininty can be controlled by different synthetic methods ( Zeigler Natta catalyst) The amount of crystallinity actually present in the polymer depends on a number of factors, including the rate of cooling, crystallization kinetics, and the crystallization temperature. Thus, the extent of crystallization can vary greatly for a given polymer and can be controlled through processing conditions
1.4 Mechanical properties The mechanical behavior of polymers is dependent on many factors, including polymer type, molecular weight, and test procedure Polymeric material behavior may be affected by other factors such as test temperature and rates. This can be especially important to the designer when the product is used or tested at temperatures near the glass transition temperature, where dramatic changes in properties occur
Viscoelasticity Polymer properties exhibit time-dependent behavior, meaning that the measured properties are dependent on the test conditions and polymer type
Failure Behavior The design of plastic parts requires the avoidance of failure without overdesign of the part, leading to increased part weight The type of failure can depend on temperatures, rates, and materials Materials that fail at rather low elongations (1 percent strain or less) can be considered to have undergone brittle failure Failure typically starts at a defect where stresses are concentrated. Once a crack is formed, it will grow as a result of stress concentrations at the crack tip. Many amorphous polymers will also exhibit what are called crazes. Crazes appear to look like cracks, but they are load bearing
Ductile failure of polymers is exhibited by yielding of the polymer or slip of the molecular chains past one another This is most often indicated by a maximum in the tensile stress-strain test or what is termed the yield point. Above this point, the material may exhibit lateral contraction upon further extension, termed necking Molecules in the necked region become oriented and result in increased local stiffness Material in regions adjacent to the neck are thus preferentially deformed, and the neck region propagates. This process is known as cold-drawing (see Fig. 1.11). Cold drawing results in elongations of several hundred percent.
Under repeated cyclic loading, a material may fail at stresses well below the single cycle failure stress found in a typical tensile test This process is called fatigue and is usually depicted by plotting the maximum stress versus the number of cycles to failure Fatigue tests can be performed under a variety of loading conditions as speciﬁed by the service requirements Thermal effects and the presence or absence of cracks are other variables to be considered when the fatigue life of a material is to be evaluated