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OPTICAL PROPERTIES

OPTICAL PROPERTIES. CONTENTS. Introduction Refractive Index Transmission & Haze Specular Gloss Colour Birefringence Clarity Photoelastic Property. INTRODUCTION.

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OPTICAL PROPERTIES

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  1. OPTICAL PROPERTIES

  2. CONTENTS • Introduction • Refractive Index • Transmission & Haze • Specular Gloss • Colour • Birefringence • Clarity • Photoelastic Property Corporate Training & Planning

  3. INTRODUCTION • The application of plastics is increasing day by day due to its unique properties such as excellent clarity & transparency, good mechanical strength, easy process-ability & low cost. The plastics are widely used in transparent & translucent applications .The optical properties of a substance mainly depends on the Molecular structure, morphological characteristics type and amount of additives, processing conditions and post processing operations. • Knowledge of these optical properties is needed for several reasons: (a)Technical use is made of polymers as optical materials in lenses or light fixtures. (b)The relatively large change of refractive index with deformation Corporate Training & Planning

  4. Degree of transparency of commercial polymeric materials may be classified according to the following:- (a)Highly transparent materials (b) Semitransparent materials (c) Opaque materials Corporate Training & Planning

  5. REFRACTIVE INDEX DEFINITION:- It corresponds to the ratio of the speed of light in a vacuum (in practical terms air) to its speed in the object (material) and can be calculated from the sine of the angles of incidence (i) and refraction (r) beams, respectively. n = sin i / sin r Corporate Training & Planning

  6. REFRACTIVE INDEX SIGNIFICANCE: It is a fundamental property used for control the purity of the product and for optical parts design. Its values are used in designing lenses for cameras, microscope & other optical instruments. TEST METHOD: - * ASTM D 542 * ISO 489 SPECIMEN & CONDITIONING:- • The size of the test specimen will correctly fit on the face of the fixed half of the refractometer prisms. A specimen measuring 6.3 mm X 12.7 mm on one face is usually satisfactory. • Test conditioning at 23 + 2oC and 50 + 5% relative humidity. Corporate Training & Planning

  7. REFRACTIVE INDEX EQUIPMENT:- * The apparatus for this test method consists of an Abbe’ refractometer, a suitable source of white light and a small quantity of a suitable contacting liquid. Corporate Training & Planning

  8. REFRACTIVE INDEX PROCEDURE:- * Two procedures are normally used to measure the index of refraction of plastic materials,one refractometer method and the other Microscopical method. • OBSERVATION, CALCULATION & RESULT:- • The value of Refractive index is calculated by dividing the actual thickness of the specimen to apparent thickness of the specimen. • Index of refraction = Actual thickness of the specimen Apparent thickness of the specimen Corporate Training & Planning

  9. REFRACTIVE INDEX FACTOR INFLUENCING:- • Medium used • Wave length of light • Temperature SAFETY PRECAUTIONS:- • Specimen surfaces must be parallel to each other and perpendicular to the direction of orientation. • Specimen must be free from dust & dirt. Corporate Training & Planning

  10. LIGHT TRANSMITTANCE & HAZE DEFINITION:- • Total Transmittance is defined as the ratio of transmitted light to the incident light. The unit of Transmittance is expressed in terms of percentage (%). • The total transmittance light is consists of the direct transmitted and diffused components which are depending on the angular distribution of light. There are two types of angle distribution. • Wide angle scattering (Haze) • Narrow angle scattering (Clarity or Transparency) • Haze is defined as the cloudy appearance on the surface of specimen . Its measured by quantity of light deviates by more than 2.5° from the incident beam. Its unit in percentage (%). • Transparency is defined as the light diffused in a small angle range within 2.5° from the incident beam with high concentration. Corporate Training & Planning

  11. LIGHT TRANSMITTANCE & HAZE SIGNIFICANCE :- • Haze and Luminous Transmittance values are used in Quality Control and specification purpose and to measure colour and visibility in products. TEST METHODS:- • ASTM D 1003 for transparent plastics products • ASTM D 1746 for transparent plastics sheets • ASTM D 1494 for reinforced plastics panels SPECIMEN & CONDITIONING:- • Test specimen must be large enough to cover the aperture and small enough to be tangent to the wall. The size of specimen is approximately 50mm in diameter. • The test specimen is conditioned at 23 + 2oC and 50 + 5% relative humidity for 40 hrs prior to test. . Corporate Training & Planning

  12. TRANSMISSION OF LIGHT & HAZE EQUIPMENT:- * The instrument used for measurement is hazemeter. A Schematic diagram of optics & hazemeter is shown in the figure. Corporate Training & Planning

  13. TRANSMISSION OF LIGHT & HAZE PROCEDURE:-Light beam strikes the specimen through condenser and lens, and enter into the integrating sphere. The sphere’s interior surface is coated uniformly with a matte white material to allow diffusion. A detector in the sphere measures the total transmittance and haze. The ring sensor mounted at the exit port of the sphere detects narow angle scattered light (clarity). SAFETY PRECAUTIONS:- * Specimen size must be within range. * Specimen must be free from dirt & dust. * No hindrance should be there on Entry port. Corporate Training & Planning

  14. SPECULAR GLOSS DEFINITION:- • Specular Gloss is defined as the relative luminous reflectance factor of a specimen at the specular direction. SIGNIFICANCE:- • Specular gloss is used primarily as a measure of shiny appearance of films and surfaces. • All specular gloss values are based on a primary reference standard .A polished black glass with an assign specular gloss value is 100. TEST METHOD:- • ASTM D 523 • ASTM D 2457 Corporate Training & Planning

  15. SPECULAR GLOSS SPECIMEN & CONDITIONING:- • Specimen surfaces must have good planarity free from warpage, waviness, or curvature.The test specimen is conditioned at 23 + 2oC and 50 + 5% relative humidity for not less than 40 h prior to test. EQUIPMENT :- Corporate Training & Planning

  16. SPECULAR GLOSS PROCEDURE:- • The instrument is turned on and placed on a black glass primary standard. • The control knob is adjusted so that the meter indicates the value assigned to the primary standard. • Next, the sensor is placed on the specimen surface and the gloss value is read directly from the analog or digital display. • OBSERVATION, CALCULATION & RESULT:- • The instrument is calibrated during the operation at sufficiently frequent intervals to assure that the instrument value is practically constant. If at any time an instrument fails to repeat readings of the standard to within 2 percent of the prior setting the intervening result should be rejected. The gloss value is directly read on the instrument. Corporate Training & Planning

  17. SPECULAR GLOSS FACTOR INFLUENCING:- • Surface property • Temperature • Humidity • Polymer molecular weight, Melt pressure, injection pressure & mould temperature also influences the gloss of a product. SAFETY PRECAUTIONS:- • Specimen surfaces must be free from dirt and other foreign particles.The specimen surface must be free from surface warpage, waviness, or curvature. Corporate Training & Planning

  18. COLOUR DEFINITION : - • Colour is one small part of the appearance. The variables of appearance include glossiness or matness, opacity or transparency, smoothness or roughness, and metallic reflection or diffusion surfaces of parts of its rays. Colour is measured by a particular wavelength of light reflect and producing sensation in the observer (eye). SIGNIFICANCE:- • It used in part identifications, Quality Control, Product Development and Classification of Products. • There are following terminology to understand the colour theory. • Value: - It is color range from dark to light in which black being darkest and white being lightest. • Hue:- Color has basic difference appearance such as red differ form blue green or yellow these distinctions as called Hue. • Chroma:- Chroma is defined as the attribute of color perception that express the degree of departure from gray of the same lightness Corporate Training & Planning

  19. COLOUR EQUIPMENT:- TEST METHOD:- • ASTM D 2244 • ASTM D 1925 • ASTM D 1729 • ASTM E 308 • ISO 3557 • ISO 4582 SPECIMEN & CONDITIONING:- • The test specimen is conditioned at 23 + 2oC & 50 + 5% relative humidity . Corporate Training & Planning

  20. COLOUR PROCEDURE: - • VISUAL ASSESSMENT OF COLOUR & APPEARANCE: - • The visual examination and evaluation of colour is the most commonly used technique in the plastics industry. • The two essential elements of visual colour evaluation are: - • The viewing of both the sample and a standard by an experienced observer. (2) The use of a predetermined light source at a fixed distance. (b) INSTRUMENTAL METHODS OF COLOUR MEASUREMENT:- Two methods are used for colour measurement: - • Spectrophotometer • Calorimeters • The instrument is calibrated against standard. • A relatively flat, colored specimen is placed in a specimen holder. • A light source is illuminated. • The CIE Lab Colour Scales are displayed on the instrument. • The L, a, b values are noted down. • The L, a, b values are correlated with L, a, b Chart. Corporate Training & Planning

  21. COLOUR Corporate Training & Planning

  22. COLOUR COLOUR SCALES:- • The mathematical relationship between these L scales and the CIE X, Y, Z scale is as follows: -L, a, b (Hunter – Square Root) L=10Y½ ----- (1) aL =17.5 (1.02X – Y) /Y½ ----- (2) bL = 7.0 (Y – 0.8467Z) / Y½ ----- (3)L, a, b (Glasser, et al – Cube Root) L=25.29G1/3 ----- (4) aL =106.0 (R1/3 – G1/3) ----- (5) bL =42.34 (G1/3 – B1/3) ----- (6) Where, G = Y R = 1.02 X B = 0.8467Z Corporate Training & Planning

  23. COLOUR CIE L*, a*, b* (1976) (CIELAB) L*= 116 (Y / Y0) 1/3 – 16 ----- (7) a*= 500 (X / X0) 1/3 – (Y / Y0) -----(8) b*=200 (Y / Y0) 1/3 – (Z / Z0) 1/3 -----(9) Where, X / X0, Y / Y0, Z / Z0 > 0.01 & X0, Y0, Z0 define the colour of the nominally white object-colour stimulus. Corporate Training & Planning

  24. COLOUR OBSERVATION, RESULT & CALCULATION : • Colorimeters & spectrophotometers calculate yellowness index as well as whiteness index and is directly read by instrument. FACTOR INFLUENCING:- • Type of illuminant • Wave length of light • Particle size • Angle of illumination SAFETY PRECAUTIONS  :- • Observation zone area must be free from dust and dirt. • Surface test areas shall be free from abrasion and warpage. Corporate Training & Planning

  25. BIREFRINGENCE DEFINITION:- • It is defined as the maximum algebraic difference between two refractive indices measured in two perpendicular directions. • Birefringence is referred to as stress birefringence and its contributions are:- • Orientation of the amorphous chains between crystallites. Orientation of the crystallites and the form birefringence arising from the interfaces between crystalline and amorphous regions. SIGNIFICANCE :- • Birefringence is a conveniently handled tool for determining orientation in materials. From the orientation of the molecules further conclusions regarding the material properties can be derived. Corporate Training & Planning

  26. BIREFRINGENCE TEST METHOD:- • ASTM D 4093 SPECIMEN & CONDITIONING:- • The specimen is conditioned at 23 + 2 0C and 50 + 5% relative humidity. EQUIPMENT:- • The most common way to determine birefringence is based on the interference method, using a Babinet compensator and polarised light. PROCEDURE:- • The birefringence of flat sample is measured under uniaxial tension using a Babinet compensator & polarised light. PROCEDURE:- • The monochromatic parallel light generated in the light source is plane polarized in the polarizer (a Nicol prism or Polaroid plate), passes through the stressed sample, and then passes through the Babinet compensator. Another Polaroid plate, the analyzer, follows, being rotated 900 with respect to the polarizer. • The light is travelling in the direction perpendicular to the plane of the paper. Since the refractive indexes nx and ny indirections x and y of the stressed polymer are different, the wavelengths of the two wave components tx and tyare also different, therefore the two waves will be out of phase when leaving . Corporate Training & Planning

  27. BIREFRINGENCE OBSERVATION, CALCULATION & RESULT: - Different refractive indexes nx & ny of the sample shows the principle stresses x & y at x & y plane. So retardation, R’ of one wave in the respect to another wave determined by R = d (nx – ny) / no FACTOR INFLUENCING:- * Humidity * Degree of cross linking * Temperature SAFETY PRECAUTIONS:- * Incident light direction must be perpendicular to the plane. * Proper intensity of light must be present. * Equipment must be free from dust and dirt. Corporate Training & Planning

  28. CLARITY DEFINITION:- • Clarity is defined as ‘Light flux deviating less than 2.50 from the normal, on the average’. SIGNIFICANCE:- • The Clarity is the distinctness with object appears when viewed through a film. SPECIMEN & CONDITIONING:- • Specimen may be in form of sheet, or film. • The specimen is conditioned at 23 + 2oC & 50 + 5% relative humidity. EQUIPMENT:- • It consists of clarity sensing unit and photometric unit. Clarity sensing unit consist of a light source, focusing lens, specimen holder & test cell. SAFETY PRECAUTION:- • Specimen must be fitted properly in specimen holder. • Specimen must be free from dust and dirt. Corporate Training & Planning

  29. CLARITY PROCEDURE:- • The equipment is turned on. With no sample in position the unit is standardized until a reading of 100.0 relative to air is obtained. • If a calibrated standard is to be used, it is inserted in the specimen holder, and the instrument brought to balance upon the value assigned to the standard. • The beam is blocked completely with a piece of block flet of paper. ‘Zero adj’ knob is then turned until reading of zero is obtained. • The specimen is placed in the specimen holder. • The reading is recorded as percentage clarity directly from the measurement unit. FACTOR INFLUENCING:- • Humidity • Wavelength • Temperature Corporate Training & Planning

  30. DEFINITION:- Photoelasticity is the property exhibited by some transparent isotropic solids of becoming doubly refracting when subjected to the stress. The difference in the two velocities shows up a birefringence. Stress optical sensitivity is define as the ability of some materials to exhibit double refraction of light when placed under stress. PHOTOELASTICITY Corporate Training & Planning

  31. PHOTOELASTICITY SIGNIFICANCE: - • Photo elastic properties of the transparent materials have been used by design engineers for stress analysis and by process engineers for determining residual stress as well as the degree of orientation in molded parts. SPECIMEN & CONDITIONING :- • The test specimen is conditioned at 23 +  2oC and 50 + 5% relative humidity . EQUIPMENT:- • Basically, two types of photoelasticity polariscopes are employed. Corporate Training & Planning

  32. PHOTOELASTICITY PROCEDURE:- • The object to be examined is placed in the center of the polarizing medium. • The object is viewed from the opposite side of the light source • The polarized light indicates the number of fringes or rings, which is related to the amount of stress, if light is used. • Several additional techniques are used in conjunction with the basic photoelastic concept, which make it possible to analyze complex or unusual problems. Briefly, these techniques are- • Stroboelasticity: use of stroboscopic light to observe photoelastic stress patterns on vibrating or rotating parts. This technique is most often used on photoelastic coatings. • Thermophotoelasticity: measurement of thermal stresses by photoelastic means. • Photoviscoelasticity: analysis of rheology of plastics by photoelastic means. • Scattered – light photoelasticity: observation of laterally illuminated transparent • Models to determine stresses inside the model without slicing; integration • Techniques are used. Corporate Training & Planning

  33. PHOTOELASTICITY FACTOR INFLUENCING:- • Mould design, Gate size & location, weld line etc. • Temperature & Pressure SAFETY PRECAUTIONS:- • Incident light direction must be perpendicular to the plane. • Proper intensity of light must be present. • Equipment must be free from dust & dirt. Corporate Training & Planning

  34. THANK YOU Corporate Training & Planning

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