CENTRAL INSTITUTE OF PLASTICS ENGINEERING & TECHNOLOGY
Question Bank
3 MARK --- QUESTION
4/5 MARK ----QUESTION
COURSE : DPMT
SEMESTER : III
SUBJECT : Plastic Materials & Testing
2 MARK ---QUESTION
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1. WHAT IS NUMBER AVERAGE MOLECULAR WEIGHT
Ans:The number average molecular weight is defined as the total weight of polymer divided by the total number of molecules. The number average molecular weight is therefore given by: This can also be written as: where xi is the number fraction (or mole fraction) of polymer with molecular weight Mi.
2. EXPLAIN THE TERM “POLYDISPERSITY INDEX”
Ans: The dispersity index, or formerly polydispersity index (PDI), or heterogeneity index, or simply dispersity (Đ), is a measure of the distribution of molecular mass in a given polymer sample.(PDI) of a polymer is calculated, where is the weight average molecular weight and is the number average molecular weight.
3. NAME A FEW APPLICATIONS OF POLYSTYRENE
Ans:Polystyrene is transparent and used for many applications. A few of the most familiar uses of styrene include: Solid and film polystyrene, used in rigid foodservice containers, CD cases, appliance housings, envelope windows and many other products. Polystyrene foam is also used in food service products and building insulation.
4. WRITE THE STRUCTURE PROPERTY RELATIONSHIP BETWEEN ALIPHATIC AND AROMATIC POLYESTERS WITH MELTING POINT
Ans: Aliphatic Polyesters have a melting point of 85 degree C whereas Aromatic Polyesters have a melting point of 265 degree C. The difference in these two types of Polyester is due to the addition of phenol rings at the open handles of the aliphatic chain, thereby making the chain less movable, and hence there is an increase in its melting point. Thus, change in structure leads to its property change, as in case of melting point of Aliphatic & Aromatic Polyesters
5. GIVE EXAMPLES OF TOUGH AND SOFT PLASTIC MATERIAL
Ans:Examples of Tough Plastics are ABS, polycarbonate, PPSU, and UHMW ETC.
Examples of Soft Plastics include polyethylene (PE), polypropylene (PP) and polyvinyl chloride
(PVC) etc.
6. WHAT IS A STRESS STRAIN CURVE USED, INCASE OF PLASTIC MATERIALS
Ans:The stress-strain curve is for an ideal elastoplastic material which has linear elastic properties up to the yield stress and then ideal plastic properties. It represents shear stress and shear strain, for any plastic material, when it is applied to the torsional loading of a load cell/ shaft.
7. WHAT IS THE FULL FORM OF BIS & ASTM STANDARDS
Ans:BIS - Bureau of Indian Standards
ASTM - American Society for Testing and Materials
8. WHAT IS PRECONDITIONING? WHY DO WE DO IT PRIOR TO TESTING?
Preconditioning covers the treatment of polymers or plastics prior to testing. It is a Thermal treatment to consolidate interatomic bonding within the polymer system. This is done to stabilize the plastic or polymer at the test temperature, as per standards.
9. WHAT ARE THE DIFFERENT TYPES OF POLYMERIZATION
Ans:There are two main types of polymerization, chain-reaction (or addition) and step-reaction (orcondensation) polymerization. One of the most common types of polymer reactions is chainreaction (addition) polymerization.
10. DIFFERENCE BETWEEN HOMOPOLYMER AND COPOLYMER, WITH EXAMPLES
Ans:A homopolymer is a polymer where every mer unit of the chain is the same. Examples:
Polyvinylchloride (PVC) is a homopolymer.A copolymer is a polymer formed when two (or more) different types of monomers are linked in the same polymer chain, as opposed to a homopolymer where only one monomer is used. Eg.ABS
11. DIFFERENCE BETWEEN HETEROCHAIN POLYMER AND HOMO CHAIN POLYMER,
WITH EXAMPLES
Ans: Heterochain polymers are those polymers in which the backbone contains elements such as
oxygen, nitrogen, sulfur, or silicon in addition to carbon. Many of these compounds are complex
in structure. Example: Silicon Polymers ( - Si – O – Si – O – Si - ) Homochain polymers have only one kind of atom in the main chain. Examples are
Polypropylene, Polyethylene, ( – C – C – C – C – C - )
12. DIFFERENCE BETWEEN ORGANIC POLYMERS AND INORGANIC POLYMERS,
WITH EXAMPLES
Ans: Organic polymers are macromolecules composed of many repeating monomer units, mainly
composed of Carbon. Both synthetic and natural polymers can be Organic Polymers. Examples
are Polypropylene, Polyethylene, Polyvinyl chloride etc.
Inorganic polymers are polymers with a skeletal structure that does not include carbon atoms in the backbone. Polymers containing inorganic and organic components are sometimes called hybrid polymers, and most so-called inorganic polymers are hybrid polymers. Examples of inorganic polymers are Silicon Polymers etc.
13. WHAT IS A POLYMER BLEND
Ans: A polymer blend is a mixture of two or more polymers that have been blended together to create
a new material with different physical properties. Also, in Polymer Blends, the mix is in proportion of which the concentration of each polymeric ingredient is above 2 wt.%. Blends are either miscible or immiscible
14. EXPAIN THE TERM “FRP”
Ans: Fibre-reinforced plastic (FRP) (also called fiber-reinforced polymer, or fiber-reinforced plastic) is a composite material made of a polymer matrix reinforced with fibres. The fibres are usually glass (in fibreglass), carbon (in carbon-fiber-reinforced polymer), aramid etc. Rarely, other fibres such as paper, wood, etc have been used. The polymer is usually a matrix that involves plastics like epoxy, vinylester, or polyester thermosetting plastic etc.
15. WHAT ARE PET FIBERS? MENTION TWO APPLICATIONS
PET is produced by the polymerization of ethylene glycol and terephthalic acid. Ethylene glycol is a colourless liquid obtained from ethylene, and terephthalic acid is a crystalline solid obtained from xylene. In this semicrystalline form, PET is made into a high-strength textile fibre, having good stiffness. PET fibres applications are majorly in Fabrics, PET fibers make them highly resistant to deformation, so they impart excellent resistance to wrinkling in fabrics. They are often used in durable-press blends with other fibres such as rayon, wool, and cotton, reinforcing the inherent properties of those fibres while contributing to the ability of the fabric to recover from wrinkling.
16. WHAT ARE KEVLAR FIBER
Kevlar is a heat-resistant and strong synthetic fiber, and used as a replacement for steel in racing
tires. Typically it is spun into ropes or fabric-sheets that can be used as such or as an ingredient
in composite material components.
Kevlar has many applications, ranging from bicycle tires and racing sails to bulletproof vests,
because of its high tensile strength-to-weight ratio, it is also used to make modern marching drumheads that withstand high impact. When used as a woven material, it is suitable for mooring lines and other underwater applications.
17. APPLICATIONS OF ARAMID FIBERS
Ans: Aramid fibers are an aromatic polyamide that is characterized by long rigid crystalline polymer
chains. This class of fibers are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic-rated body armor fabric and ballistic composites, in bicycle tires, marine cordage, marine hull reinforcement, and as an asbestos substitute.
18. NAME ANY FOUR MECHANICAL PROPERTIES FOR TESTNG OF PLASTIC
MATERIALS
Ans: Tensile Strength, Flexural Strength, Impact Strength, Compressive Strength, Hardness
19. WHAT IS GLASS TRANSITION TEMPERATURE
The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials), from a hard and relatively brittle "glassy" state into a viscous or rubbery state as the temperature is increased.
20. WHAT IS Tg GLASS TRANSITION TEMPERATURE?
Ans:Thermoplastic resins melt when its temperature becomes higher than its melting point and becomes liquid, but as it is gradually cooled from the liquid state its viscosity gradually increases, and it goes into a rubbery state and it finally solidifies. The temperature at the border from the rubbery state to the solid state (called the glass state) is called its "glass transition temperature". The glass transition temperature is generally indicated as Tg.
21. WHAT ARE THE APPLICATIONS OF PHENOL FORMALDEHYDE?
Phenol formaldehyde resins (PF) or phenolic resins are synthetic polymers obtained by the reaction of phenol or substituted phenol with formaldehyde. Used as the basis for Bakelite, PFs were the first commercial synthetic resins (plastics). They have been widely used for the production of moulded products including billiard balls, laboratory countertops, and as coatings and adhesives.
22. WHAT IS MELAMINE FORMALDEHYDE?
Melamine resin or melamine formaldehyde is a hard, thermosetting plastic material made from melamine and formaldehyde by polymerization. In its butylated form, it is dissolved in n-butanol and xylene. It is then used to cross-link with alkyd, epoxy, acrylic, and polyester resins, used in surface coatings. There are many types, varying from very slow to very fast curing types of melamine resins.
23. WHY ARE PLASTICS YUSED IN FOOD PACKAGING INDUSTRIES?
Permeability Property for plastic films enables the plastic to be used for packaging industries. The use of different polymers in food packaging industry depends on the properties of the food product. Also, manufacturing, handling, and packaging engineering procedures can influence the final properties of packaging material, especially in terms of barrier properties which are, further, strictly correlated to the intrinsic structure of the polymer such as degree of crystallinity, crystalline/amorphous etc.
24. EXPLAIN MFI. ALSO MENTION ITS UNITS
Melt Flow Index (MFI) is a measure of how many grams of a polymer flow through the die in ten minutes. The test is performed at a given temperature depending on the plastic. The force used to push the plastic through the system is supplied by a weight which sits on top of a ram.
Unit of MFI is gm/ 10 minutes.
25. WHAT IS THE FULL FORM OF NABL & ISO.
National Accreditation Board for Testing and Calibration Laboratories (NABL) is an autonomous body, used for accrediting laboratories. ISO organization is actually called International Organization for Standardization. The International Organization for Standardization (ISO) is an international standard-setting body composed of representatives from various national standards organizations.
26. MENTION THE APPLICATIONS OF PHENOL FORMALDEHYDE
Ans:Used as the basis for Bakelite, PFs were the first commercial synthetic resins (plastics). They
have been widely used for the production of moulded products including billiard balls, laboratory
countertops, and as coatings and adhesives. Additionally, Phenolic resins are also used in the circuit board production that is for making circuit board like PCB
27. WRITE DOWN THE WORKING PRINCIPLE OF DIELECTRIC CONSTANT TESTER
FOR INSULATION RESISTANCE
Ans:Dielectric Constant is used to determine the ability of an insulator to store electrical energy. The
dielectric constant is the ratio of the capacitance induced by two metallic plates with an insulator between them to the capacitance of the same plates with air or a vacuum between them. A sample is placed between two metallic plates and capacitance is measured. A second run is measured without the specimen between the two electrodes. The ratio of these two values is the dielectric constant.
WHAT ARE ATACTIC POLYMER ?
Polymers having randomly arranged functional groups around the main chain are called Atactic
Polymers
Eg.: - [A – B – A – A- -A – B – B – A – B – A – A - ]-
Polymers that are formed by free-radical mechanisms such as polyvinyl chloride are usually atactic. Due to their random nature atactic polymers are usually amorphous. In hemi isotactic macromolecules every other repeat unit has a random substituent. Atactic polymers are technologically very important.
28. WHAT IS DSC. HOW IS IT USEFUL IN FINDING THE PROPERTIES OF POLYMERS?
DSC is Differential Scanning Calorimetry. Dielectric Thermal Analysis. 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. The properties like Melting Point, Glass Transition temperature etc can be determined by DSC.
29. WHAT IS CRYSTALLANITY? NAME AY ONE POLYMER HAVING HIGHEST CRYSTALLINITY?
Ans:Linear chains of polymer which donot branch, or are more precisely compactly kept, are called as
crystalline polymers. Crystalline structures are generally very ordered, which is what gives them strength and rigidity. A crystalline polymer, where the molecular chains are largely locked in place against one another, is similar. On application of load, a crystalline polymer would prefer breaking rather than bend. Example of polymer having highest crystallinity is HDPE (High Density Polyethylene)
30. WHAT DO YOU MEAN BY “SELF EXTINGUISHING IN NATURE”. GIVE ONE
EXAMPLE.
Ans:Polymers are generally termed as Self-extinguishing according to the standard UL94. These polymers find applications in Industries, manufacturing of self-extinguishing and spark-proof
hoses etc. Example of one Self Extinguishing Polymer if PTFE, having UL94 V0
31. WHAT IS LCP? WRITE TWO APPLICATIONS OF LCP POLYMERS.
Ans:LCP stands for “Liquid Crystal Polymer”. They are relatively unique class of partially crystalline
aromatic polyesters based on p-hydroxybenzoic acid and related monomers. Liquid crystal polymers are capable of forming regions of highly ordered structure while in the liquid phase.
Application: Liquid Crystal Polymers find applications in automotive, electronics, medical & healthcare and other industries.
32. WHAT ARE FIBERS? WHICH FIBERS ARE USED FOR HIGH TEMPERATURE
COMPOSITE APPLICATIONS.
Fibers are monofilaments that are spun from polymers, for high modulus and tenacity. They are useful for making composites and Fiber Reinforced Composites in the areas of automotives, aeronautics, defence etc. Carbon Fibers are used for high temperature composite applications.
33. WHY DO THE IMMISCIBLE BLENDS EXHIBIT POOR MECHANICAL PROPERTIES
Ans:Polymer blends & alloys are utilized in various applications based on their properties. If a blend that is immiscible in the thermodynamic sense, it will show a separation phase-out, so that the different polymers do-not blend well. This occurs mainly due to the lack of physical and chemical interaction across the phase boundaries and poor interfacial adhesion Such phase-separated systems exhibit poor mechanical properties.
34. WHAT IS BOPP? EXPALINITS APPLLICATIONS.
BOPP is Biaxially oriented Polypropylene. During manufacturing process, When the polypropylene film is extruded and stretched in both the machine direction and across machine direction it is called biaxially oriented polypropylene. Biaxial orientation increases strength and clarity. Applications include box overwrap applications of tape cassettes and CDs, making of Clear Bags etc.
35. WHAT IS RIM TECHNOLOGY? WHICH THERMOSET RESIN IS IT USED FOR.
Ans:RIM technology is Reaction Injection Moulding (RIM), used for manufacturing of polyurethane
RIM parts having high strength and low weight. Like thermoplastic injection moulding, RIM is a
plastics-forming process that uses moulds to form parts. The thermoset resin that uses RIM technology is polyurethane, as they begin with two liquid components, compared with the pellet form of most thermoplastics. These liquid components - an isocyanate and a polyol - are developed in two-part formulations, which are often called polyurethane RIM systems.
36. WHAT DO YOU UNDERSTAND BY THE APPLICATION OF EPOXY RESING FOR
”POTTING AND ENCAPSULATING MATERIALS”?
Ans:Epoxy resin is used for Potting and Encapsulation applications. In this application, the reusable
mould is made out of “hard to adhere to” materials such as Teflon or Silicone. The purpose of encapsulation is to create a protective “shell” around the assembly. Encapsulation provides resistance to shock and vibration, as well as creating a seal against moisture, solvents, and corrosive agents. They are mainly used for fast curing encapsulating material for mechanical shock resistant systems.
37. EXPLAIN THE PROPORTIONALITY OF MFI TO VISCOSITY.
Melt Flow Index (MFI) is inversely proportional to viscosity. The melt flow index (MFI) is a measure of the ease of flow of the melt of a thermoplastic polymer, which also depends upon the melt conditions of the test. However, the viscosity for any material depends on the applied force (load cell) of the MFI Machine.
38. WHAT IS ASTM STANDARD? EXPLAIN THE ASTM TEST METHOD FOR TENSILE
PROPERTIES
Ans:ASTM is “American Society for Testing and Materials”, it is a non-profit organization that sets and
publishes standards adhering to materials and their testing. ASTM D-638 is the ASTM test method for tensile properties.
39. WHAT IS HDT? DEFINE GIVNG THE DEFLECTION OF STANDARD BAR.
Ans:HDT is a Thermo-Mechanical Property for Plastics, also called as Heat Deflection / Distortion
Temperature. Heat deflection temperature is defined as the temperature at which a standard test bar deflects a specified distance under a load. The deflection of standard bar in HDT test is 0.010 inch.
40. WHAT IS VST? MENTION THE ASTM STANDARD & HEATING RATE FOLLOWED IN
VST TEST.
Ans:VST is also called as Vicat Softening Temperature, and it is used in measuring technology for the
melting point. It indicates the temperature at which a circular indenter with a cross-section of 1 mm² under a standard load of 10 N or 50 N will penetrate the specimen precisely 1 mm deep. The Vicat softening temperature is defined in ISO 306 and ASTM D1525. The heating rate followed in VST test is 50 ± 5 °C/hr
41. WHAT IS IEC? HOW IS IEC RELATED TO PLASTICS?
Ans:The International Electrotechnical Commission (IEC) is an International Standards Organization
that prepares and publishes International Standards for all electrical, electronic technologies, collectively known as "electrotechnology". As plastics are excellent insulators and find applications in the areas of manufacturing of sockets, cables etc, Plastic Moulded products are governed by IEC standards.
42. WHT IS FATIGUE PROPERTY FOR PLASTICS?
Fatigue is a behaviour that the material shows, when subjected to repeated cyclic loading in terms of flexing, stretching, compressing or twisting. During testing, the layers are subjected to severe cyclic bending and twisting deformation, which in turn leads to structural behavioural change of plastic materials.
43. WHAT IS REFRACTION? WRITE THE DIMENSIONS OF REFRACTIVE INDEX.
Ans:Refractive index is the ratio of the velocity of light in vaccum to its velocity in transparent medium.The refractive index or index of refraction of a material is a dimensionless number that describes how light propagates through that medium. It is defined as. where c is the speed of light in vacuum and v is the phase velocity of light in the medium.
44. WHAT IS CAPILLARY VISCOMETER USED FOR?
Ans:The viscosity of Newtonian fluids can be most precisely determined using capillary viscometers.
This method of measurement, measures the time taken for a defined quantity of fluid to flow through a capillary with a known diameter and known length. A viscometer based on Hagen Poisson's (Hagen-Poisculli) rule is obtained by measuring the flow rate of fluid flowing through the capillary, the pressure difference between the capillary outlet and the inlet, and then according to Hagen Poisson's law. Hagen - bershaw leaf formula: ETA = (n R^4Pt) /8VL
Among them:
V--t time flows through the capillary volume
R-- capillary radius
P-- capillary pressure difference at the end of two
L-- capillary length
45. WHAT IS DENSITY? EXPLAIN THE DIFFERENCES IN DENSITIES OF POLYOLEFINS,
PVC AND WATER
Ans:Density is a measurement that compares the amount of matter an object has to its volume. Density is found by dividing the mass of an object by its volume. Polyolefins (PE &PP) is the only type of polymer that has density less than water. For most polymers density is a constant; polypropylene is 0.90 g/cm3, polycarbonate is 1.2 g/cm3, etc.
Density of water is 1 g/cm3, Density of PE/ PP is 0.91 – 0.967 g/cm3, Density of PVC is 1.38 g/cm3
46. EXPLAIN THE DIFFERENCE BETWEEN TENSILE MODULUS AND TENSILE
STRENGTH
Ans:Tensile Strength: it is the limit up to which a material can bear tensile stress without fracture or crack. Young modulus is defined as the ratio of stress to strain within elastic limit. Tensile strength is a 'point' (the highest point) on the Stress-Strain Curve. Young's modulus is a mechanical property that measures the stiffness of a solid material. It defines the relationship between stress (force per unit area) and strain (proportional deformation) in a material in the linear elasticity regime. of a uniaxial deformation.
47. STATE THE ZIGLER NATTA PROCESS FOR MANUFACTURING OF HDPE, IN BRIEF.
Ans:The Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the
synthesis of polymers of 1-alkenes (alpha-olefins).The Ziegler-Natta catalyst, as granules, is mixed with a liquid hydrocarbon (for example, 2- methylpropane (isobutane) or hexane), which simply acts as a diluent. A mixture of hydrogen and ethene is passed under pressure into the slurry and ethene is polymerized to HDPE. The reaction takes place in a large loop reactor with the mixture constantly stirred. On opening a valve, the product is released and the solvent is evaporated to leave the polymer, still containing the catalyst. Water vapour, on flowing with nitrogen through the polymer, reacts with the catalytic sites, destroying their activity. The residue of the catalyst, titanium(IV) and aluminium oxides,remains mixed, in minute amounts, in the polymer.
48. EXPLAIN THE HINGE PROPERTY OF PP
The properties of PP are strongly affected by its tacticity, the orientation of the methyl groups etc. As polypropylene is resistant to fatigue, most plastic living hinges, such as those on flip-top bottles, are made from this material. However, it is important to ensure that chain molecules are oriented across the hinge to maximise strength.
49. ENLIST THE DIFFERENCE BETWEEN HIPS & GPPS
Polystyrene (PS) is made by polymerizing styrene monomer, polymerization by a variety of synthetic methods. PS is a non-crystalline thermoplastic resin, can be divided into general purpose polystyrene (GPPS), high impact polystyrene (HIPS) and expanded polystyrene (EPS). GPPS is a General Purpose Polystyrene, density of GPPS is 1.04 to 1.09, the transparency is up to 88% -92%, refractive index is 1.59 to 1.60, and such a high refractive index made it has a good gloss, and a decorative effect. Good dimensional stability. Common Range: Commodity: cups, all kinds of boxes, toothbrushes, combs, food containers, pens etc. HIPS is high impact polystyrene, polystyrene impact polystyrene products can be produced by adding the polybutyl rubber particles approach. HIPS is a modified material of PS, divided rubber composition containing 5-15%, the toughness of PS increased about four times the impact strength is greatly increased. PS molding and coloring are strong. HIPS water absorption is low, as compared to GPPS
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