POLYMER MAJOR PROJECT POLYPROPYLENE A VERSATILE POLYMER COURSE INSTRUCTOR ASSISTANT PROFESSOR, CHEMISTRY Dr. SULAFUDIN VUKUSIC SUBMITTED BY AKHIL MAMMOOTTIL ABRAHAM 920018779

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TABLE OF CONTENTS

INTRODUCTION ...................................................................................................................................... 4 STRUCTURE ............................................................................................................................................... 4 METHOD OF SYNTHESIS ................................................................................................................... 5

Gas phase reactor .................................................................................................................................................... 6 Liquid phase polymerization (Slurry process) .............................................................................................. 7 Bulk Polymerization .............................................................................................................................................. 8

PHYSICAL AND CHEMICAL PROPERTIES ............................................................................... 9 APPLICATIONS ....................................................................................................................................... 11

Rigid Packaging ................................................................................................................................................... 11 Polypropylene in Automotive ......................................................................................................................... 12 Polypropylene in Consumer Products .......................................................................................................... 12 Polypropylene Fibres ......................................................................................................................................... 13 Polypropylene in Industries ............................................................................................................................. 13 Polypropylene in medical applications ........................................................................................................ 13

POLYPROPYLENE PROCESSING TECHNIQUE .................................................................... 14 Injection Molding ................................................................................................................................................ 14 Processing of polypropylene fibers by melt blown process .................................................................. 15 Thermoforming .................................................................................................................................................... 15

REFERENCES ........................................................................................................................................... 17

2 LIST OF FIGURES Figure 1: - Monomer propene ............................................................................................ 4 Figure 2: - Polypropylene polymer structure ..................................................................... 4

Figure 3: - Stereospecific Polypropylene ........................................................................... 5 Figure 4: - Metallocene catalyst ......................................................................................... 6

Figure 5: - Zirconium catalyst responsible for syndiotactic polypropylene ...................... 6 Figure 6: - Gas Phase reactor .............................................................................................. 7

Figure 7: - Slurry phase reactor ......................................................................................... 8 Figure 8: - Polypropylene application globally ............................................................... 11

Figure 9: - Injection molding, Polypropylene .................................................................. 14 Figure 10: - Polypropylene fibre production ................................................................... 15

Figure 11: - Thermoforming polypropylene .................................................................... 16

3 LIST OF TABLES

Table 1: - Polypropylene Processing Condittions ............................................................... 9

Table 2: - Polypropylene general properties ..................................................................... 10

4 INTRODUCTION A linear hydrocarbon polymer, which has similar properties to that polyethylene and polybutene is conquering the world of polymers with its wide range of applications. CnH2n is the general expression of this hydrocarbon polymer. Because of its versatility in application as a plastic and a fibre, the plastic market has lot of room for this polymer [5].

STRUCTURE The monomer or the repeating unit is propylene or propene as shown in the figure 1

Figure 1: - Monomer propene [10]

Addition polymerization of propene or propylene results in long chain polypropylene polymer as shown in figure 2.

Figure 2: - Polypropylene polymer structure [10]

Commercially, the repeating unit or the monomer polymerizes in the presence of Ziegler natta catalyst to produce a stereospecific polypropylene as shown in the figure 3. The position of methyl group determines the stereo regularity of the polymer formed [10]. If the substituent methyl group is on the same side, we get a isotactic polypropylene, if the methyl groups are alternating, a syndiotactic polymer. If the substituent is irregularly arranged we get an atactic polymer.

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Figure 3: - Stereospecific Polypropylene [10]

The stereospecific isotactic and syndiotactic structures are crystalline because the structure has a regularity in its packing. Hence of its regularity in structure polymer is found to be hard, a rigid material and in its pure form the melting point is found to be 440K [10]. However the non-stereospecific atactic polypropylene donot crystallize and high molecular weight atactic polypropylene is rubbery [10]. Commercially available polypropylene is isotactic about 1-5% of atactic content [10].

METHOD OF SYNTHESIS Slurry, solution or gas phase polymerization could be employed for the manufacture of polypropylene. Repeating unit or the monomer is propylene, which is pressurized and heated in the presence of catalyst. Polymerization happens at relatively low pressure and temperature, because of the presence of Ziegler-natta catalyst. Upon changing the conditions used and catalyst employed, the property of the polymer could be varied [10]. Polypropylene production takes place either in a gas phase (fluidized bed or stirred reactor) or a liquid phase reactor (slurry or solution).

6 Gas phase reactor Gas phase reactor is often employed in the production of polypropylene with the help of following catalyst.

1. Ziegler Natta 2. Metallocene

Stereospecific Ziegler-Natta catalyst was a revolution indeed in the manufacture of polypropylene, as polymerization could be carried out at a lower pressure and temperature. The polymer manufactured in the presence of Ziegler-natta catalyst would be isotactic polypropylene. Before we dispatch the final product, which is in the pellet form, the catalyst has to be destroyed. This could be done by addition of water or alcohol. Hence gas phase process could be completed with out much residues in the final product [10]. Metallocene is being used these days for the manufacture of polypropylene. Metallocenes are transition metals forming ligands with cyclopentadienyl [10], one such example is metallocene based on zirconium as shown in the figure 4.

Figure 4: - Metallocene catalyst [10]

The specific orientation of zirconium, facilitate the production of isotactic polypropylene. However once we employ a different zirconium compound as shown in figure 5 syndiotactic polypropylene could be produced, which is the only way of producing syndiotactic polypropylene [10].

Figure 5: - Zirconium catalyst responsible for syndiotactic polypropylene [10]

7 Figure 6 and 7 demonstrates both the process (gas phase and slurry phase respectively).

Figure 6: - Gas Phase reactor [7]

Fig above is a flow sheet for gas phase reactor. We have Ziegler Natta as the catalyst along with the monomer in the gas-phase reactor, where the reactor is operated at 70-800C and at a pressure of 8-35atm [10] [7]. Propylene, nitrogen and hydrogen contribute the inlet stream. They act as heat transfer medium and reactants for the growing polypropylene chain in the fluidized bed reactor. Co-catalyst is continuously supplied into the reactor to activate the reactants and produce polymer particles. Another function of co-catalyst is to ensure that moisture stays below 2ppm and keep the catalyst activated, which is required for the production of industrial grade polypropylene. Once the bed is fluidized, disengaging section of the plant separates the left over gases, which is recycled and combined with the initial feed consisting of propylene, nitrogen and hydrogen. Heat exchanger is employed to remove the excess heat in the recycle stream. The propylene conversion to polypropylene per pass is 2-3%, while the overall conversion can sum up to 98%. The whole plant is designed to run at 30bar [7].

Liquid phase polymerization (Slurry process)

Liquid phase polymerization happens in a slurry reactor, which consist of a pipe usually in the form a loop. Propene and catalyst are fed into the reactor, which is filled with diluent such as isobutene. Polypropylene produced in small pellet circulates around the loop as slurry where the loop reactor is operated at 75-1100C and 8-35 atm [10]. Slurry is continuously removed and the polypropylene pellets removed are dried and transported to the extrusion area.

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Figure 7: - Slurry phase reactor [4]

The only difference from the gas-phase reactor is the introduction of a loop reactor. In other words a semi-plug flow reactor. Catalyst is added to the reactor with the diluent. The purpose of loop reactor is to avoid deposits, provide high surface to volume ratio enhancing heat removal and provides shorter residence time. Gas phase reactor follows the loop reactor, polymerization happens in the following reactor at certain temperature and pressure and the product is dispatched. Copolymerization of polypropylene is carried out in the gas phase reactors.

Bulk Polymerization Monomer and solvent is liquid propene itself. Polymerization happens at a temperature of 340-360K and at a pressure of 30-40atm. The high pressure is because; propene has to be in liquid state. After polymerization solid particles are collected, and liquid separated is recycled [10].

9 Polypropylene processing conditions are as shown in table 1

Parameters Homopolymer Polypropylene

Copolymers of polypropylene

Melt temperature (0C) 210-290 210-290

Mould temperature (0C) 20-60 20-60

Pre-drying Not required Not required

Typical Mould Shrinkage (%)

1.5 2

Reactor Operating temperature (0C)

70-80

70-80

Operating pressure (atm)

8-35

8-35

Table 1: - Polypropylene Processing Condittions [5] [10]

PHYSICAL AND CHEMICAL PROPERTIES Commercial polypropylene is a semi-crystalline polymer, as the polymer structure is isotactic. The crystallinity of the polypropylene lies between low-density polyethylene (LDPE) and high-density polyethylene (HDPE). When copolymerized with ethylene, the polymer has extra toughness and flexibility, hence polypropylene find lot of applications in engineering plastic, and has the potential to replace material like acrylonitrile butadiene styrene (ABS) [8]. Polypropylene is economical and is not as transparent as polymers like polystyrene, acrylic or other plastics. It shows good fatigue resistance, Perfect isotactic polypropylene has melting point around 1700C, depending on the tacticity commercially available polypropylene has melting point ranging from 160 to 1660C. Molecular weight is a function of Melt Flow Index (MFI), enabling us to determine the flow of polymer melts while processing. Polypropylene having high MFI , would have less impact strength [8]. Polypropylene shows moderate barrier resistance to moisture, gases and odours. Though its flexibility is less than of polyethylene, it finds similar application of that of low-density polyethylene (LDPE) [5] [8] [10].

10 Polypropylene has no stress-cracking issues and shows good chemical and electrical resistance. Though the properties of polypropylene are similar to polyethylene, there some differences as well, one such is softening point; polypropylene has a higher softening point than polyethylene making it rigid and hard. Additives are often used for better end-use performance [8]. Polypropylene properties are summarized in table 2. Properties homopolymer Co-polymer

Density (kg/m3) 905 905

Tensile strength (Mpa) 33 25

Tensile Modulus (Gpa) 1.4 1

Elongation at break (%) 150 300

Heat distortion temperature @ 1.8 Mpa/0C

65 60

Volume Resistivity (logUm) 19 19

Oxygen Index (%) 17 17

Table 2: - Polypropylene general properties [5]

11 APPLICATIONS Crates, toys, medical equipments, bottle caps and many day-to-day products are made of polypropylene. Propylene film in package industry, fibres in clothing and carpet are all made of polypropylene [10] [3]. Figure 8 shows the applications of polypropylene in the global market

Figure 8: - Polypropylene application globally [10]

As observed from figure 8, major portion of the polypropylene is used in the manufacture of crates, CD and DVD covers etc , which comes under the roof of rigid packaging (28%), Followed by textile (21%) and technical industries (20%). 15% of polypropylene produced is used as consumer products and 16% in food packaging respectively Superior puncture resistance, low sealing threshold and competitive price has benefited and helped Polypropylene gain ground over cellophane, metals and paper in the manufacture of material to be used in film extrusion. Available polypropylene films are Cast or bi-axially oriented. Film market has three divisions [5].

1. Food and confectionaries 2. Tobacco 3. Clothing

Tobacco products contribute major share for polypropylene after food and confectionaries. Food and confectionaries holds the film market with applications ranging from confectionaries to crisps and biscuits. Another market polypropylene holds share is rigid packaging, which is subdivided into applications varying from caps to crates [5]. Various applications in detail are discussed below.

Rigid Packaging Polypropylene packaging is efficient because of the following properties it possesses [3].

12 Polypropylene in natural state doesnt violate FDA regulations for food contact

applications

Good mechanical and barrier properties

As the product are thin walled, the raw material can be saved, hence reducing the cost.

Good impact resistance at lower temperatures.

Simple and safe storage of products without affecting the features of the product is definitely the primary concern. Reusable and stackable crates made of Polypropylene provide excellent application in transport and storage products without disturbing the content inside [5] [1]. Hence very good solution for storage and transport of products as polypropylene posses good mechanical and barrier properties [1], which has attracted supermarkets, groceries and automotive supply chain as well Blow moulded polypropylene bottles are employed for the packing of condiments, detergents and toiletries. Yoghurt pots available in the market are made of thin-walled polypropylene containers, because of its inherent properties, which helps in preserving the yoghurt [5].

Polypropylene in Automotive In the field of automotives, polypropylene materials are used in interior designing, especially as a monomaterial solution. For example mono material dashboards are very popular in the house of automotives, polypropylene film cushioning, film skins and powder slush moulding integrated with polypropylene textile covers are gainig ground in automotive industries [5]. Now moving to the outer body of the automotives, parts such as bumpers, exterior trim and cladding are all made of polypropylene. Because of the properties listed below, it is gaining ground in such applications [5].

Low coefficient of linear thermal expansion and specific gravity. High chemical resistance and good weatherability. Processability and impact balance.

Pre-colored polypropylene is readily available, avoiding painting of products in some applications [5].

Polypropylene in Consumer Products Properties that make polypropylene a good consumer product are [3].

High stiffness and durability. Good heat resistance and stack strength Outstanding performance and lightweight A very good cycle time.

13 Housewares, luggage, toys, battery cases, furniture, appliances and other durable products for garden and leisure use come under this title. The moulding technique that prevails in this sector is Injection moulding [5].

Polypropylene Fibres Products such as tapes, bulk continuous filaments, staple fibres, spun bound and continuous filament find very much useful for lots of applications that we come across. Polypropylene fibres are used in the manufacture of above-mentioned commodities [5]. Following properties make polypropylene a good non-woven fabric [3]

Lightweight. Good resistance to chemicals, weather, mildew, insects etc. Good abrasion resistance. Sunlight resistance. Good wash ability, quick drying and unique wicking. Low moisture absorption.

Polypropylene in Industries

Polypropylene is a) chemically stable b) When heated only carbon dioxide and water vapor is produced c) Calorific value same as of oil d) Abrasion resistance and light weight [3], hence used in industries for applications mentioned below. Different varieties of sheets, pipes, Returnable Transport Packages (RTP), which constitutes the major portion of the industries are manufactured from polypropylene. Extrusion moulding is, the technique employed in the manufacture these products, except RTP, where Injection Moulding is used. Construction sectors, especially domestic drainage pipes are made of polypropylene [5].

Polypropylene in medical applications As a cost effective and environmentally friendly alternative, polypropylene is conquering the market of medical equipment. Its resistance to a) cleaning agents, b) disinfectants and c) many solvents makes it apt for the manufacture of surgical trays, syringes and lab equipment such as pipette tips, centrifuge and blood collection tubes [5].

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POLYPROPYLENE PROCESSING TECHNIQUE

Injection Molding Standard screw molding equipment is employed without much alteration. Pre-drying is not required but filled resins may require. Feed is fed into the hopper thereafter feed enters the heating phase in the cylindrical section where cylinder temperature is maintained at 400-5700F. The reciprocating motion of the screw pushes the melt forward and then to the mold through nozzle at a pressure of 1000-1500 psi, the frictional motion of the screw also heats polymer. The hopper or feed section is maintained at 30-500F. Good results are obtained at 75% of press capacity. Pressure has to be maintained if not can result in flashing, burning and can stick inside the mold. Mold temperature is kept at 60-1500F. Other parameters that affect the processing are injection time, cure time, back pressure, and screw speed [6].

Figure 9: - Injection molding, Polypropylene [11]

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Processing of polypropylene fibers by melt blown process Initially the polymer is melted in an extruder and it is done through a spinneret, which contains 200-1000 holes at a spinning rate of 800-4000rpm, followed by quenching filaments for spin-finished applications. The drawn filaments are then heated, stretched, crimped and cut for various applications [9].

Figure 10: - Polypropylene fibre production [9]

Extruder which operates at 430-4900F (1) pushes the melt polymer into the spinning pack (2) where polymer melt is homogenized and fed to the roller at constant spinning rate. The melt is cooled inside the quench (3). New filaments are stretched and fed into box (5) for abrasion resistance and to improve thermo-physical properties. Finally step (7) and (9) for stabilizing and crimping respectively. Final product is cut using cutter (10) [6] [9].

Thermoforming The steps involved in thermoforming are [2]

Heating Vacuum forming Cooling Trimming

16 Figure 11 depicts a flow diagram of thermoforming of polypropylene.

Figure 11: - Thermoforming polypropylene [2]

Polypropylene sheets are heated on the clamp, once the polypropylene reaches the thermoforming temperature (170-1850C). The polypropylene gets molded onto the mold by applying vacuum pressure. Once the polymer is molded cooling and trimming would be the concern [2]. The mold temperature determines the appearance, the length of forming cycle and stability of the polymer. Usually the polypropylene molds are maintained at 30-650C. Trimming the polymer from mold depends on the sheet temperature and the equipment employed. With adequate cooling time of 1-2 minutes sheets of thickness less than 1mm could be generated. Cooling for long time generates sheets of thickness greater than 3mm [2].

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REFERENCES [1]Allahvaisi , S. (2012). Polypropylene in the Industry of Food Packaging. In D. Dogan , Polypropylene (pp. 3-21). Croatia: INTECH. [2]CPC Congdon Plastics Consulting LLC. (n.d.). A Guide to Thermoform Processing of Polypropylene . Retrieved April 15, 2015, from http://congdonplasticsconsulting.com/:http://congdonplasticsconsulting.com/ts/sheet/PP%20Thermoforming.pdf [3]ExxonMobil. (n.d.). polypropylene. Retrieved April 17, 2015, from http://www.exxonmobilchemical.com/:http://www.exxonmobilchemical.com/Chem-English/productsservices/polypropylene.aspx [4]Guichon Valves. (1921). PP Polypropylene Manufacturing process of PP . Retrieved April 9, 2015, from http://guichon-valves.com/: http://guichon-valves.com/faqs/pp-polypropylene-manufacturing-process-of-pp-polypropylene/ [5]Hindle, C. (1933). British Plastic federation. Retrieved April 7, 2015, from bpf.co.uk: http://www.bpf.co.uk/plastipedia/polymers/PP.aspx#properties [6]Ineos olefins and polymers USA. (2007, March). Polypropylene processing guide. Retrieved April 8, 2015, from http://www.ineos.com/: http://www.ineos.com/global/olefins%20and%20polymers%20usa/products/technical%20information/ineos_polypropylene_processing_guide.pdf [7]Khan , M. H., Hussain , M. A., & Mujtaba , I. M. (2014, March 27). Polypropylene Production Optimization in Fluidized Bed Catalytic Reactor (FBCR): Statistical Modeling and Pilot Scale Experimental Validation . materials , 2441-2458. [8]Maier, C., & Calafut, T. (1998). Morphology and Commercial forms. Bromley, United Kingdom: Elsevier. [9]Rong, H., & Kannadaguli, M. (2004, April). Olefin Fiber. Retrieved April 2016, 2015, from http://www.engr.utk.edu/: http://www.engr.utk.edu/mse/pages/Textiles/Olefin%20fibers.htm [10]The university of york. (2014, january 2). The essential chemical industry online. Retrieved April 4, 2015, from http://www.essentialchemicalindustry.org: http://www.essentialchemicalindustry.org/polymers/polypropene.html [11]AV Plastics. (1977). What is injection molding? Retrieved April 4, 2015, from http://www.avplastics.co.uk/about-av-plastics: http://www.avplastics.co.uk/what-is-injection-moulding

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