EXPERIMENT 3INVESTIGATING POLYMERSSafety information-The chemicals listed below will be used in this experiment. The likely hazardsssociated with each of the chemicals are noted and recommended procedures for~andling are given. You must read this page and the experimental descriptioncarefully before starting the experiment and before coming into the laboratory. Noteany potential hazards and adopt precautions as your safe lab practice. When you aresatisfied that you understand any possible difficulties that might arise and therecommended procedures for dealing with them, sign the declaration and have itinitialled by a demonstrator. This must be done prior commencing lab work. At thebeginning of the lab session demonstrators will quiz you about the safety informationand experimental procedure in order to identify your ability to work safely andefficiently. If you fail to prove ability for safe and efficient work you will not beallowed to start lab practical. Please note, that it is your own responsibility tocomplete the lab practical during time that is allocated to you. Be sure to requestinformation or help if you are in doubt on any point. ChemicalPoly (ethylene glycol)(PEG)Not classified ashazardous materialDo not ingest, avoidskin/eye contact, wear glovesPrecautionsPoly(N-vinyl-2-pyrrolidone) (PVP)Not classified ashazardous materialDo not ingest, avoidskin/eyecontact, wear glovesGlycerolNot classified ashazardous materialskin/eyecontact, wear gloves Hazard Do not ingest, avoidDeclaration – I have -read and understood the contents of the safety information sheetand the script for the·experimentSigned (student~->—~.. ..Checked (demonstrator): __”4_/~-~—~——————– Date: ___}~~:_29EXPERIMENT 3INVESTIGATING POLYMERSLEARNING AIMS• To determine the viscosity of ma~erial f ol mer on their ownTo understand rheolog~cal behav~our Of p lyymer as a function of addedTo understand rheological behavwur O poplasticizer.INTRODUCTION· d · h ” 1 t1·on of products ranging from paintsPolymers are extensively use m t e 1orm~ a . . . ,plastics and inks, to gels, creams and thin films. Differen~ formulat10?s use differentpolymers that act in different ways depending on the desire? properti~s for the finalproduct. Viscosity is an important characteristic for all matenals, e_sp~cially polymers.For liquids (solution or melt), viscosity influences flow charactenstics, heat transfer,and mass transfer. The flow behaviour of a solution or melt is also responsive toproperties such as molecular weight and molecular weight distribution.Viscosity is defined by Webster’s Dictionary as “the study of the change in form andthe flow of matter, embracing elasticity, viscosity and plasticity.” It can also bedescribed as “the internal friction of a fluid caused by molecular attraction, whichmakes it resist a tendency to flow” (Brookfield). A viscometer measures the frictionthat is created when an external object (spindle) attempts to cause a fluid to flow(stirring). The friction is between the ‘layer’ of a fluid that is made to move in relationto another ‘layer’.When investigating viscosity, the following key terms need to be considered (Table3).Table 3 Key parameters for the viscosity investigation Shear Ratey~easure . of change m speed at whichmtermediate layers move with respect to eachotherShearStresstdynes/cm2 orN/m2force. per unit area required to produce thesheanng actionViscosityTlmilli-pascal-seconds(mPa) ·shear stress/ shear rateUnitsDescription centipoise (cps) orA matenal requiring a shear stress of 1 drate of one reciprocal second has a vis ~ne per square centimetre to produce a shearPascal-second is · equal to one centipoise. COSity of one pOise · or 100 centipoise. One milli-30The 2 main classificatio?s of polymer behaviour are Newtonian and non-Newtonian.Newtonian fluids, at a given temperature, have a viscosity that remains constant whenshear rate is v~ed. ‘:- n_on-Newtonian fluid is one where the relationship betweenshear rate and v1scos1ty 1s not constant. In practice, most fluids fall into this lattercategory.Non-Newtonian ~uids may be rurt_her su~divided into 3 categories: pseudoplasticwhere the viscosity ~ecre~se~ with mcre_as1~g shear or show shear thinning i.e paint,dilatant where the v1scos.1ty m~reases with mc~easing shear or show shear thickening• sand/water and plastic which acts as a sohd under static conditions and a certain~~unt of stress mus~ be _applied to the ~uid to induce flow i.e. tomato ketchup.Another factor to consider is that some flmds will display a change in viscosity witht’me under conditions of constant shear rate. Fluids that undergo a decrease in:iscosity with time are termed thixot~opic and those that undergo an increase inviscosity with time are termed rheopectic.The use of hydrogel membranes usually demands polymers capable of forming filmswith high elastic and flexible properties besides having high water absorption. Intenns of improvements of polymer plasticity, addition of specific plasticizers topolymers can produce promising results. The objective of this study is to evaluateeffect of poly(ethylene glycol) (PEG) and glycerol as plasticizers on hydrogelmembranes synthesized from poly(N-vinyl-2-pyrrolidone) (PVP) in aqueouspolymeric solutions.PVP is a highly hydrophilic polymer, biocompatible, and has considerably lowtoxicity. Throughout decades this polymer has been utilized in numerous applicationsin medicine, pharmacy, biotechnology, food, cosmetics and other industries. Forexample, its use as a synthetic blood plasma comes from World War II. Mixtures orblends of PVP-agar -PEG-water and PVP-agar-glycerol-water have been used inhydrogel preparation for diverse applications. Lower-molecular weight PEGs andglycerol are well-known plasticizers for various natural and synthetic polymers, forexample, chitosan, poly(vinyl alcohol) (PVA), PVP etc. Incorporation of a plasticizerin a given polymer mainly aims to lower the glass transition temperature (Tg).Plasticization of a polymer can impart improvements or adjustments in its originalphysical properties (film formation, higher elasticity and elongation at the rupture,more softness, etc.) and enables it to be used in various applications.METHODThe mixtures of PVP-PEG-water, PVP-glycerol-water and PVP-PEG-glycerol-waterwill be prepared using conventional method. Prepare 10 g of following solutions byw~ighing each component (PVP, PEG and glycerol) and dissolving them in water. Stirwith a glass rode to obtain transparent solutions.1. Prepare 10 % (w/w) PVP solutions2. Prepare 10 % (w/w) PVP solutions+ 5 % (w/w) PEG3. Prepare 10 % (w/w) PVP solutions+ 10 % (w/w) PEG4– Prepare 10 % (w/w) PVP solutions+ 5 % (w/w) Glycerol5. Prepare 10 % (w/w) PVP solutions+ 10 % (w/w) Glycerol6– Prepare 10 % (w/w) PVP solutions+ 5 % (w/w) Glycerol+ 5 % (w/w) PEG-…………__31·3jII-.,Draw a table in the lab 1,ook and note weights and solvent volumes.Transfer I.5 ml from prepared solution to lower GeomettY and examine polymerviscosity as a function of shear rate from O.l•I00 s’ using 4 nun GeomettY at 25 °C.You will be required to plot following graphs:• Viscosity as a function of shear rate for each sa~ple.• Viscosity as a function of plasticizer concentrauon. Your graph should contain3 data points (5%, JO% and IO% combined) and 2 data series (PEG andGlycerol).QUESTIONS• What is the rheological behaviour on polymer alone and after addition of• List plasticizer? formulations in which plasticizer is incorporated and its role infonnulation?• hnagine you are preparing a polymer gel formulation to treat mouth ulcers.Descnbe what _types of ingredient you would need to consider incorporatingand why. Obtain the ingredient list of a commercially available mouth ulcertreatment and describe the role of each of the ingredients.32
