Worldwide tank building applications using PP-Sheets: The effect of Foaming on properties Marcus Hoffmann 1, Dominic Müller 1, Marco Stallmann 1, Matt Curtis 2 1 Simona AG Teichweg 16, 55606 Kirn, Germany Tel.: +49 (0) 67 52 14-729, Mob.: +49 (0) 17 17 17 31 87, marcus.hoffmann@simona.de and 2 SIMONA America Inc. 64 N Conahan Drive Hazleton, PA 18201 ABSTRACT For more than 30 years chemical and physical foaming of thermoplastics is a well established technology in the plastic sheet industry. Starting with PVC and other amorphous polymers the general focus of foaming was and still is of course to receive weight reduction and consequently material savings. PVC-foam as an example has been an excellent sheet material for the signage and printing industry. While compact polyolefin and especially polypropylene sheet and pipe materials are very well known for their different applications in the chemical process industry as well as for thermoforming, an increasing pressure on costs in tank building can be observed. In uncritical applications material efficiency and related material and cost savings are one key to success. In addition life cycle analysis and sustainability and therefore material efficiency are gaining more and more importance in today s applications. To reflect these trends, SIMONA decided to start a new foam product line based on high end polypropylene raw materials for tank building applications. The presentation will give insight into the principles and basics of tank building technology which includes long-term material properties like welding and static tank calculation. The worldwide qualities and standards will be discussed and the presentation will end with a discussion of the impact of foaming on sheet properties for tanks.
INTRODUCTION Chemical foaming of thermoplastics is nowadays a well established technology for more than 30 years in the plastic sheet industry. In general the focus of foaming is weight reduction. As an example PVCfoam has been an excellent sheet material for the signage and printing industry. While compact polyolefin sheet materials are very popular for their applications in the chemical process industry as well as for thermoforming, an increasing pressure on costs in tank building can be observed. In uncritical applications material efficiency and related material and cost savings are one key to success. In addition life cycle analysis and sustainability and therefore material efficiency are gaining more and more importance in today s applications. To reflect these trends, SIMONA decided to start a new foam product line based on high end Polypropylene and Polyethylene. As it comes to the Worldwide technical standards in semi-finished products based on PP Based on the technical codes on plastics joining technologies [DVS 2011] and the ISO standards for PP sheets [ISO 15013], which have to be fulfilled in the market for chemical tank building, there are strong requirements for the usage of the relevant raw materials. As it comes to the standard ISO 1873- Part 1 (Plastics - Polypropylene (PP) moulding and extrusion materials - Part 1: Designation system and basis for specifications (ISO 1873-1:1995) a testimony 3.1 according to DIN EN 10204 for a extruded sheet with a typical material used in Europe can be designated as: ISO 1873 - PP-H,ECH,16-09-003 Data block 1 PP H Polypropylene Homopolymer Data block 2 e extruded c coloured h heat stabilized Data block 3 16 MFR 230 C/2,16 KG (0,2-0,4 g/10 min) 09 Tensile Modulus (1200-2000 MPa) 003 Charpy impact (6-12 kj/m 2 ) An optional data block 4 does not apply for tank building materials, but normally contains type and volume of reinforcing fillers. Data block 2 contains the information, if the raw materials contains heat stabilizer, but does not quantify these findings. In the application of heavy gauge sheets the presence of long-term heat agents is of critical importance, especially if it comes to high temperature applications, where PP- Homopolymer is often the material of choice due to its increased crystallinity and therefore consequently its favorable temperature resistance compared the PP copolymers, PVC and HDPE which can act as competitive material in these market segments. In ISO 15013 (Plastics - Extruded sheets of polypropylene (PP) - Requirements and test methods (ISO 15013:2007)) there are additional requirements defined for PP sheets. The highest requirements for PP-H can be found in sheet group 1.1: Material according to ISO 1873- part 1
Dimensions and Tolerances Mechanical and thermal properties PP- H Stress at yield 30 MPa Charpy-impact 6 kj/m 2 Tensile modulus 1200 MPa MFR 230 C/2,16 kg 0,2-0,7 g/10 min Thermal oxidative stability 100 days Shrinking behavior dep. on thickness Sheet group 2 is based on impact PP-copolymer and sheet group 3 describes PP-random copolymers. It has to be pointed out that only a very limited number of raw materials in world comply to sheet group 1.1 in order to make sure that the desired long-term heat ageing performance can be achieved. Thermal oxidative stability can be measured with ISO 4577 (Plastics -- Polypropylene and propylenecopolymers -- Determination of thermal oxidative stability in air), the oven method. Figure 1 shows typical samples from heat oven tests. Figure 1: Heat oven test samples Left part of the picture : Sample at the beginning of the test Right part of the picture: Samples with starting and final degradation Additional standards for raw materials and semi-finished products in Germany The world-wide highest requirements for chemical tanks can be found in Germany. These standards are set by the federal institute for building technologies (Deutsches Institut für Bautechnik, DIBt Berlin). The standards are build up like the value chain in tank building and consequently start with the raw material standards, and follow the properties of pipes, fittings and sheets. The regulations also contain the construction and processing procedures [DVS standards] for building the correctly designed tank. Additional Requirements according to besides the mechanical behavior defined in ISO 15013: Short-term welding factor (DVS 2203-part 2) Long-term welding factor (DVS 2203-part 4) Thermal oxidative stability 150 C (DIN EN ISO 4577) Stress cracking behavior [FNCT] Chemical resistance DIBt Media list PP Creep rupture strength (Pipe) ISO 1167 DIN 8078
SIMONAs PP-DWU AlphaPlus based on homopolymer polypropylene is the only material which has been approved from the DIBt and includes as well the raw material and the semi-finished products.it also has to be pointed out that this standards reflect especially the approved long-term values of the materials, like long-term welding factor and creep rupture strength, which e.g. also has to be approved for the sheet material. The german association of welders (DVS: Deutscher Verband für Schweißtechnik und verwandte Verfahren) has also published a number of well respected standards and guidelines in the tank building community. The technical code DVS 2205 shows how to do Calculation of tanks and apparatus made of thermoplastics Characteristic values. As it comes to the correct processing of the corresponding PP materials the DVS code 2207-part 11 Welding of thermoplastics Heated tool welding of pipes, piping parts and panels made of PP is of great importance to produce long-term reliable systems based on PP. For example for PP the MFR 190 C/5kg has to be in accordance to DVS 2207 part 11 for PP between 0,4 and 1,0 g/10min. These high viscosity materials have to be processed on machines with adequate designed processing technology in order to reach the desired dispersion of the relevant additives, which include anti-oxidants and long-term heat agents [ISO 15013]. Based on these engineered raw materials there are a number of reasons for the use of polypropylene in chemical tank building. High chemical resistance and stress crack resistance High impact strength Good processing properties Excellent efficiency Another famous standard is ASTM D-4101. Typically according to this standard the material properties of sheets found in the US can be designated as ASTM D-4101 Group I Class I Grade II The material is described is general purpose Polypropylene Homopolymer with the following minimum values: MFR 230/2,16 (0,2-1 g/10min) Density max.0,91 g/cm 3 Strength at yield 27 MPa Bending modulus min. 1050 MPa Izod impact 32 J/m HDT (1,8 Mpa) 81 C In that standard there is no reference for tank building applications. As it comes to long-term properties, like thermal oxidative stability, welding factor and creep rupture strength there is no assessment possible for these properties. In direct succession one has to assume that no calculation, no chemical resistance evaluation and no lifetime prediction is possible based on this standard. Polypropylene Applications for compact sheet- state of the art tank building technology Figure 2 shows typical applications of these compact PP sheets. In the left picture a cathodic electrocoating bath with a metal shell is presented. The steel bath was equipped with an internal lining using the loose-shirt method. The right picture shows pickling line where sulphuric acid and other aggressive chemical might be used at high service temperatures and high mechanical loads. Very often in these applications PP-H is the material of choice due to its high continuous operation temperature (100 C) compared to 80 C for the PP Copoplymers (PP-R and PP-B) or HDPE (PE 80 or PE 100).
Figure 2 Left side: Cathodic electro-coating bath with a metal shell, by courtesy of G&H Kunststofftechnik, Sprockhoevel, Germany, [SIMONA 2009-2] Right side Sulphuric acid hot strip pickling line, by courtesy of Kunststoffbau Langschede GmbH, Unna, Germany, [SIMONA 2009-1] It is also found that the higher crystallinity of PP-H leads to a better chemical resistance, which can be explained -depending on the application- by an improved stress crack resistance, a reduced swelling behaviour or a reduced tendency to creep as well as a reduced permeation of critical substances. With respect to these strong requirements towards the materials SIMONA developed PP-DWU AlphaPlus, a homopolymeric polypropylene with an improved performance in these applications. With these environmental issues gaining more and more importance, one focus in the development an alphanucleated material was held in the field of improving the welding quality, short-term and long-term according to the standards of DVS 2203-part 4 [DVS 2203-4] and part 5 [DVS 2203-5]. Improve material efficiency for uncritical applications Besides these developments there is also a strong marketplace in apparatus and tank building, where the chemical resistance is not the first concern. For example as water storage tanks or air ducts. These containments which transport or store liquids and / or other media, which are not harmful for the environment and consequently the DVS rules are not mandatory. So there is a chance to add value by innovation. Figure 3 shows the A-B-A structure of SIMONA PP FOAM
Different weight saving cores can be extruded to reduce density, while maintaining the mechanical and physical properties of the sheet. Using high-end tank building raw materials with low viscosities [MFR 190 C/5kg = 0,4 1,0 g/10 min] and their associated defined welding and processing technology, the coextrusion technology gives perfect rise to a new class of material: PP FOAM. The sheet is produced by using the coextrusion technology, which gives the possibility to tailor-made a thermoplastic coextruded A-B-A sheet for tank building applications. Extruding compact and in thickness A layers is typically based on the high-end material PP-DWU AlphaPlus which is well known for its high quality standards and chemical resistance. If additional functions in the A layer is desired, e.g. like UV-resistance, anti-static, these layers can be customized. In order to foam the core layer down to densities use typically chemical blowing agents to foam the core layer. Coextrusion furthermore increases the functionality of an article significantly. By foaming for example improved heat- and airborne sound insulation properties compared to compact parts can be produced. The internal stresses, sink-marks and warpage-effects can be reduced by a foam structure in the core of the article. A cellular structure may also be used as a design-tool in certain applications e.g. soft touch effect in thermoformed trays. Very often in semi-crystalline materials due to their shrinking behavior, especially if heavy-gauge sheets are concerned, one can observe high internal stresses. These stresses can be reduced immediately by foaming the core. In this context a crucial issue is the performance of the foamed structure with respect to welding. Test that can be done with these joints are a technological bending test and or a short-term welding factor in accordance with DVS. Table 2 finally concludes the mechanical properties, and shows that an adaption of tailor-made parameters makes it possible to fulfil the high-end welding DVS-standards for tank building materials. The bending angle (DVS 2203-part 5) and the short-term welding factor (DVS 2205-part2) can be fulfilled for PE and PP foam [DVS book 2008].. For PP a favourable joining pressure is also twice as high as the DVS standard and can was determined at 0,2 MPa. Property Tensile modulus of elasticity [MPa] ISO 527-1 Stress at yield [MPa] ISO 527-1 PE-FOAM (PE compact) 700 (900) 17 (22) PP- FOAM (PP-H compact) 1700 (1250) 22 MPa (> 32 MPa) Short-term Welding factor [DVS 2203-part2] Bending angle [DVS 2203-part5] > 1, 0 >1,0 fulfilled. fulfilled Table 2 material Typical properties of PE-and PP-Foam in comparison to the corresponding compact
5. References [Hoffmann 2008] Hoffmann, Stallmann, Paul Improved performance of thermoplastic tanks, WJS/DVS Conference on Joining Plastics, 19-20 November 2008, TWI, Cambridge, UK [DVS 2203-4] Technical Code DVS 2203-4 Testing of joints between thermoplastic plates and tubes Tensile Creep test- [DVS 2203-4-2] Technical Code DVS 2203-4 - Supplement 2 Testing of joints between thermoplastic plates and tubes Tensile Creep test- Testing the resistance to slow crack growth using the Full Notch Creep Test (FNCT) [DVS 2203-5] Technical Code DVS 2203-5 Testing of joints between thermoplastic plates and tubes Technological bending test [DVS book 2011] DVS Technical Codes on Plastics Joining Technology, ISBN 978-3-8155-982- 2, English Edition, DVS Media GmbH [ISO 15013] Plastics- Extruded sheets of Polypropylene (PP) Requirements and test methods [SIMONA 2009-1] Praxisstudie 17 - Beizstraße aus PP-DWU AlphaPlus [www.simona.de] [SIMONA 2009-2] Praxisstudie 11 - PP-DWU AlphaPlus - Der Vorteil im Behälter- und Apparatebau [www.simona.de]
Applications of PP FOAM Apparatus components Encasements Linings Transport containers Small sewage treatment Packaging systems Insulation components Reusable containers Cover of tanks
Acknowledged as one of the world s leading manufacturers of semi-fi nished plastics, SIMONA is able to offer you an end-to-end consulting service covering all aspects of tank engineering. We look forward to advising you on: _ the selection of tank and mesh materials as well as reaction resins _ the general design as well as the use of materials and welding methods _ structural calculations according to DVS 2205 and EN 12573 www.simona.de mail@simona.de Phone +49 (0) 67 52 14-0