Characteristics of PETThe critical parameters for PET resin quality are Intrinsic Viscosity (IV), Residual Acetaldehyde (AA) content, Color (L, a & b), Crystallinity and Dust content. Brief description of each Property and its significance is given below: Intrinsic Viscosity (IV) PET resins are classified on the basis of IV which is a measure of average length of polymer molecular chains or molecular weight. It influences the melt viscosity and processing behavior of PET and properties of the end products. It is used by most PET producers to control the polymerization process, to assist customers in the selection of PET for specific application and to control the preform moldings process. Generally if an application requires higher strength/ESCR, a high IV is recommended. The IV of PET is determined from the flow times of polymer solution and pure solvent in a viscometer at a designated temperature. The IV value will vary depending on the type of solvent used and temperature conditions. Residual Acetaldehyde (AA) Content Acetaldehyde (CH3CHO) is generated during poly condensation process as a by-product of thermal degradation and gets entrapped in PET resin when molten polymer is cooled. Acetaldehyde is a harmless chemical but it does have a flavor. Since it has low Boiling Point (21°C) and sweet fruity odour, it can influence taste of packed products, if present in excessive amounts. The technology used by Reliance ensures that AA content is controlled below 1 ppm in all RELPET resins. AA also gets generated during processing of PET in to preforms/ bottles. Thus it is important to take utmost care while producing PET preforms / bottles (particularly for applications like water and soft drinks) to control generation of AA during perform molding. The type of machine/mould and processing parameters used for PET have a major influence on AA level in molded performs/bottles. At room temperature AA is a colorless vapor, which is soluble in water and most common organic solvents. When PET preform is made, the AA generated gets entrapped in a glassy matrix; i.e. it gets “dissolved” in the solidified PET. Over long time periods, Reflected/ transmitted color.e. it indicates Red & „-ve‟ Indicates Green. by three components. yellowness and haze affect the appearance of a bottle. ‘L’ denotes . The color should be as close to neutral as possible. ‘a’ denotes – Red to Green. light source or aperture. By such perception an observer may distinguish between two objects of the same size. so that the chips do not soften and form agglomerates during drying prior to molding. Black to White goes through „Grey‟. 50%. dust content is kept less than 100ppm.Black to White. In case of RELPET. When „b‟ value is „+ve‟. shape and structure.Color It is the visual sensation produced by light of different wavelengths throughout the visible region of the spectrum. i. Crystallinity should be above 50%. Crystalline It is a measure of the degree of orderliness of PET molecule. and the other two together define the chromaticity. PET bottle producers are constantly striving to manufacture high quality products where appearance is an equally critical factor like any other property. b scale. The most widely used technique in PET industry is the color metric spectrophotometer. a. which measures the wavelength distribution of light reflected or transmitted by a sample and uses this to calculate comparative color values. It is a three-dimensional characteristic of the appearance of an object. Polymer Dust content: It is essential that the „Dust‟ content in PET polymer is minimal in order to have trouble free processing. good clarity and no specks/marks in the finished container. When L value is „0‟. L*. a*& b*. it indicates Black & „100‟ Indicates White. ‘b’ denotes – Yellow to Blue. The color values are generally measured on an L. RELPET chips are supplied with crystallinity value of min. When „a‟ value is „+ve‟. . The crystallinity is directly related to the density of polyester and is normally derived from the density value. it indicates Yellow & „-ve‟ Indicates Blue. One dimension usually defines the lightness. ppm 0 to –2.0 max.Pet resin Grades and their applications Based on the above parameters PET resign is available in four grades – G5761. 0 to –2.0 max.02 1.0 CIE > 50 0 to -4 > 50 Crystallinity ] Melting Point % = 247 = °C = 247 > 50 = 247 = 247 Flatwater EdibleOil NonFood products Small Jars CSD Carbonated Water Water Edible oil Alcoholic Beverages Agrochemicals Pharmaceuticals Non-food products Wide mouth jars APET Sheet Strapping Hot Fill CSD particularly for tropical conditions Carbonated water Agrochemicals Large bottles/jars APET Sheet Strapping CPET Carbonate d water .84+0.02 1. G5841 and G5821QH. The specifications of these grades and their applications are shown in the “Selector Guide Table” given below: Parameters Intrinsic Viscosity (IV) Acetaldehyde (AA) b‟ Colour Unit dl/g G5761 0.84+0. 0 to –4.0 max. G5801.0 > 50 G5841 0.02 1.82+0.02 1.0 max.0 G5821 QH 0.82+0. G5801 0.