In the case of photoinitiated degradation light is absorbed by photoinitiators, which are photocleaved into free radicals, which further initiate degradation in nonphotochemical processes of the polymer macromolecules. These polymers are found in nature, example plants and animals. The degradation of polymers usually starts at the outer surface and penetrates gradually into the bulk of the material blaga. Ultraviolet rays interact with these bonds to form free radicals, which then react further with oxygen in the atmosphere, producing carbonyl groups in the main chain. The most important feature of the book is the physical. Cutright, colonel, dc, usa, bienvenido perez, lieutenant colonel, dc, usa joe d. By way of example, consider a polymer such as polyethene which, in a normal commercial sample, will be made up of molecules having to 2000 ch, groups in continuous chains. Uv radiation causes photooxidative degradation which results in breaking of the polymer chains, produces free radical and reduces the molecular weight, causing deterioration of mechanical properties and leading to useless materials, after an unpredictable time. Major industrial polymers major industrial polymers fluorinated polymers.
The book covers occurrence, synthesis, isolation and production, properties and applications, modification, and the relevant analysis methods to reveal the. Biopolymers are polymers produced by living organisms. The wellknown natural polymers used in pharmacy and other fields are chitosan1, carrageenan2, is paghula3, acacia5, agar9, gelatin8, shellac, guar gum and gum karaya. Method 3b residual hydrocarbon in solution polymers by capillary. Posey, lieutenant colonel, dc, usa united states army institute of dental research, walter reed army medical center. Photodegradation takes place when uv or vis radiation breaks down the chemical bonds in a polymer, ultimately causing cracking, chalking, color changes and the loss of physical properties. Polyethylenes, with linear structures, can pack together easily and are referred to as high density polyethylenes. One of the most useful of the natural polymers was rubber, obtained from the sap. On this basis they are classified in two types a addition polymers the polymers formed by the addition of monomers repeatedly without removal of by products are called addition polymers.
Polymerization is the process in which monomer units are linked by chem ical reaction to form long chains. Types of polymers polymers can be separated into plastics and rubbers as engineering materials, it is appropriate to divide them into the following three categories. Common synthetic polymers that can be attacked include polypropylene and ldpe, where tertiary carbon bonds in their chain structures are the centres of attack. Condensation polymers undergo chain scission by hydrolysis eg. Nanoporous linear polyethylene from a block polymer precursor. Polymer can be destroyed by a variety of environmental agents. Biodegradation or biotic degradation is a specific property of certain plastic materials that is, of the polymers these materials are made of. The strain hardening nature of polymers is necessary for the processability at the time of film blowing and fiber spinning process.
New polymers offering properties, one of which is true susceptibility to. Such polymers exhibit mechanical strength only when macromolecules have a chain length greater than about 150 to 200 atoms in line. There are two different mechanisms of degradation of polymers. These polymers contains all the atoms of monomers hence they are integral multiple of monomer unit. Biodegradable polymers are a special class of polymer that breaks down after its intended.
The contributions describe approaches for conjugating proteins and peptides to polymers, generating complex macromolecular architectures via orthogonal and selective cycloadditions, fabricating alkyne and azide functionalized surfaces, and designing multifunctional network polymers. Sun light accelerates the rate of oxidation which may be accelerated by atmospheric pollutants capable of. Stabilization of polymers against photodegradation exposure of polymers to sunlight or t o artificial light sources results in a more or less rapid deterioration of their physical and mechanical properties as a consequence of either primary and secondary photochemical processes or of subsequent photoinitiated thermal reactions. Madorsky and sidney straus august 3, 1959 work on thermal egradation of polymers has previously been carried out al lempcm t ures up to about 500 g. Macromolecules or polymers are found in the human body, animals, plants, minerals and manufactured products. Typically, the term refers to the combined action of sunlight and air.
In thermoplastic polymers, both ductile and brittle fracture are possible. Unsaturated molecules are more reactive hydrocarbon molecules ii. Addition and condensation polymers can exist with a crosslinked network, depending on the monomers used in the synthesis. Fracture strengths of polymers are low compared to metals and ceramics.
Hourston department of materials, loughborough university, uk this article is a revision of the third edition article 18. Astm d 640099 references a number of other astm documents including. Thermaloxidative degradation of polymers most polymers will undergo significant changes over time when exposed to heat, light, or oxygen. Synthetic polymers have been widely used in making various medical devices, such as disposable supplies, implants, drug delivery systems and tissue engineering scaffolds. Introduction to polymers by case western reserve university file type. Thermal degradation of polymers at high temperatures 1 samuel l. Polymers that are not highly crosslinked have properties that depend greatly on the forces that act between the chains. The examples are high density polythene, polyvinyl chloride, etc. Chapter 3 photodegradation of polymers sciencedirect.
Synthesis, properties and biodegradability of the main classes and new families of synthetic polymers are discussed below. Stabilization and degradation of polymers advances in. Ptfe was discovered serendipitously in 1938 by a dupont chemist, roy plunkett, who found that a tank of gaseous tetrafluoroethylene cf2cf2 had polymerized to a white powder. Crosslinked polymers are formed when long chains are linked in one gigantic, 3dimensional structure with tremendous rigidity. These changes are the result of lightinduced homolytic fission of chemical bonds photolysis and photooxidation. Photodegradation and photostabilization of polymers. These different structures of a polymer, despite having the same overall composition, can directly influence accessibility of the material to the enzymecatalyzed polymerchaincleavage,andalsohaveacrucial impact onhigherordered structures ofthe polymers crystals, crystallinity, glass tran. The ductility of thermoplastic polymers is reduced upon cooling 5. Review the full course description and key learning outcomes and create an account and. Major industrial polymers fluorinated polymers britannica. Polymers polymers are the giant molecules of chemistry. Synthetic polymers are a mainstay of modern life, but nature also makes polymers.
Due to their various qualities, such as lightness, chemical and microbial stability, nondegradable polymeric materials are routinely. The effect of strain hardening needs to be controlled to ensure film and fiber thickness tolerances thereby stabilizing the filament and the bubble during the elongation process. Cellulose, starch, chitin, proteins, peptides, dna and rna are all examples of biopolymers. A variety of synthetic polymers as plastic polythene, synthetic fibres nylon 6,6 and synthetic rubbers buna s are examples of manmade polymers extensively used in daily life as well as in industry. Melting point and glass transition temperature of polymer. Network polymer article about network polymer by the. If a large number of monomers a are linked together then the polymer is represented as a n a a a a a n. Elastomers where 1 and 2 are plastics and 3 are rubbers. Photodegradation of polymers 148 exposure to sunlight and some arti. The exposed surfaces of products may then discolour and crack, and in.
Polymers usually contain many more than five monomers, and some may contain. Fracture is initiated at stress concentrators scratches, notches, etc. The lower molecular weight polymers are quite soft and gummy resins, but they are brittle to impact at fairly low temperatures. Photodegradation chain scission andor crosslinking occurs by the activation of the polymer macromolecule provided by absorption of a photon of light by the polymer. Linear polymers these polymers consist of long and straight chains. Natural polymers from the greek poly meaning many and meros meaning parts are found in many forms such as horns of animals, tortoise shell, shellac from the lac beetle, rosin from pine trees, asphalt, and tar from distillation of organic materials. Photodegradation is usually oxidation and hydrolysis. Introduction to materials science, chapter 15, polymers. The process by which the polymers are formed is called polymerisation. Nanoporous linear polyethylene from a block polymer.
Thermal degradation of polymers at high temperatures. Hightemperature plasticity due to the ability of the molecules to slide past one another thermally activated or arrhenius process 4. Cellulose, starch and chitin, proteins and peptides, dna and rna are all examples of biopolymers, in which the monomeric units are sugars. Classification of polymers presented by devansh gupta m. Polymer degradation can be caused by heat thermal degradation, light photodegradation, ionizing radiation radio degradation, mechanical action, or by fungi, bacteria, yeasts, algae, and their enzymes biodegradation. Method 3b residual hydrocarbon in solution polymers by. Often photodegradation is avoided, since it destroys paintings and other artifacts. Deteriorative reactions occur during processing, when polymers are subjected to heat, oxygen and.
Porous polyolefin membranes play an integral role in lithiumion battery technology as the barrier preventing direct anode and cathode contact. What are polymers and classification of polymers notes pdf ppt 19092014 18022017 shiva 1 comment addition polymers, chain growth polymerisation, condensation polymers, crosslinked polymers, elastomers, linear chain polymers, step growth polymerisation. A survey of supramolecular materials prepared via click chemistry is nicely complemented by a chapter on. The small buildingblock molecules are called monomers. Radiation processing of polymers pdf radiationinduced degradation of natural polymers is a promising application of ionizing radiation to develop natural bioactive agents. Sep 23, 2016 classification of polymer on different basis 1. Most polymers polyalkenes are nonbiodegradable and take many years to break down. These natural polymers are widely used in pharmaceutical industry as emulsifying. Probing glasstransition dynamics in liquid polymer using xrays. The advantages of using polymers, as biomaterials, are their manufacturability. Shorter chains produce oils or crystalline solids, such as paraffin. The unit substance or substances from which the polymer is obtained is called a monomer. Block polymers containing a sacrificial component have proven to be attractive precursors for nanoporous polymer membranes stemming from their unique ability to selfassemble into mesoscopically organized structures. Structure of polymers the time has come, the walrus said, to talk of many things.
Introduction to materials science, chapter 15, polymer structures university tennessee, dept. Polymer degradation and stability deals with the degradation reactions and their control which are a major preoccupation of practitioners of the many and diverse aspects of modern polymer technology. Larson, lieutenant colonel, dc, usa, and william r. Polymers being adaptable can be easily moulded as per requirement, are used extensively in various fields including household, food industry, medical, packaging and transport wnek, 2008. What are polymers and classification of polymers notes. Photodegradation is the alteration of materials by light. Linear polymers including those that are branched but not crosslinked 3. Familiar examples of crosslinked polymers are bakelite, rubber, and casting boat resin. Degradation rates of polymers and copolymers of polylactic. The potential of an xray spectroscopy technique to shed light on the mysterious. The macromolecule can have different end units, branches in the chain, variations in the sequence. Branched chain polymers these polymers contain linear chains having some branches, e. Exposure to ultraviolet uv radiation may cause the significant degradation of many materials. Polymerization technology laboratory thermal degradation of polymers reactions where the degree of polymerization of polymers decreases without changing the chemical constitution of the monomers are called degradation reactions.
In norrish type ii mechanism, the close approach of the excited carbonyl group to a h atom, forming a 6 membered ring is a prerequisit and. Electronic structures, equilibrium geometries, and energetics of the ground states of polyenyl cations and neutral polyenes. The uv resistance of unprotected polymers varies widely and depends on the structure and composition. The polymers obtained by simple chemical treatment of natural polymers to change their physical properties like starch, silicones 3. Overview of nmr of bulk polymers university of akron. It is however partly responsible for remineralization of biomass and is used. In the present work the range has been extendcd to 8500 c. Physical aspects of the photodegradation of polymers. Polymers, liquid crystals, polymer liquid crystals, polymer dispersed lcs, polymer stabilized lcs, lyotropic lcs and ferroelectric lcs. Of shoesand shipsand sealingwax of cabbagesand kings lewis carroll, through the looking glass 1872 shoes, ship, sealing wax, cabbage, and a king the many things listed by the walrus are actually very similar in chemical composition. Contents some basic definitions classification of polymers 1.
Since the beginning of radiation processing of polymers almost half a century ago, radiation crosslinking technologies have been extensively developed. Photodegradation of polymers 153 light absorption by ketone chromophores can induce bond cleavage by either norrish type i or type ii mechanisms. Examples are proteins, cellulose, starch, resins and rubber. There are three different types based on the structure of the polymers. Nmr of polymers pdf characterization of polymers by nmr. A polymer is a high molecular mass compound ranging from 5000 to one million and they are formed by the combination of a large number of one or more low molecular weight compounds.
The commodity polymers with which we are most familiar were developed to provide. These changes will have a dramatic effect on the service life and properties of the polymer and can only be prevented or slowed down by the addition of uv stabilizers and antioxidants. Polyamides and cellulose and starch based polymers to improve rates of decomposition. Low density polyethylenes consist of branched chain molecules, with some cross. You may need a pdf reader to view some of the files on this page. During world war ii it was applied as a corrosionresistant coating to protect metal equipment used in the production of radioactive material. Degradation rates of polymers and copolymers of polylactic and polyglycolic acids duane e. According to indian express, which has accessed documents submitted to the andhra pradesh environment impact assessment authority seiaa. Na description this note covers the following topics. Glass transition temperatures of some polymers polymer t g.
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