INNOVATIVE PLASTICS HIGH & LOW SHEAR RATE RHEOLOGY

Transcription

1 INNOVATIVE PLASTICS HIGH & LOW SHEAR RATE RHEOLOGY

2 A SABIC COMPANY Innovative Plastics is a strategic business unit of SABIC. Founded in 1976, SABIC is today the first public, global multinational enterprise headquartered in the Middle East. Our products range from bulk commodity chemicals to highly engineered plastics for demanding applications. We are a leading producer of polyethylene, polypropylene, glycols, methanol and fertilizers and the fourth largest polyolefin producer. SABIC s businesses are grouped into Chemicals, Performance Chemicals, Polymers, Innovative Plastics, Fertilizers and Metals. In Saudi Arabia, the Netherlands, Spain, the USA, India, China and Japan, our dedicated Technology & Innovation centers research ways to meet our customers needs with excellence. INNOVATING FOR CUSTOMER SUCCESS We believe that SABIC customers deserve the full benefit of every advantage our enterprise can offer. After all, our success is defined by our customers success. And with more than 70 years of experience pioneering advanced engineering thermoplastics, SABIC s Innovative Plastics business is positioned to help create new opportunities for growth and breakthrough applications. We offer expertise and experience to our customers in a variety of ways: Material solutions to help drive innovation and market leadership. Design, logistics and processing expertise to spark new ideas and better efficiencies. Unwavering commitment to build longterm relationships with ingenuity, trust and continuous improvement. It s what we strive for and work to deliver a mutual benefit. Excellence and nothing less. 2 INNOVATIVE PLASTICS

3 HIGH & LOW SHEAR RATE RHEOLOGY HIGH SHEAR RATE RHEOLOGY (FOR SHEAR RATES GREATER THAN 100 SEC -1 ): Simulates flow in high shear rate processes (i.e. injection molding and extrusion). Indicates the optimum temperature in the polymer melt for processing. Determines a plastic s suitability for high shear processing using a minimum of time and material. Indicates conditions for flow instabilities ( melt fracture, shark skin, etc.) Provides the basic data for all moldfilling programs. High shear rheology testing is performed in a capillary rheometer, which measures viscosity of the resin under high shear rate conditions (>100 sec -1 ). The material is kept at a constant temperature in the barrel as it is pushed by a piston through a capillary die at various rates of shear. The test is performed over a range of temperatures and shear rates that correspond to processing conditions. Viscosity is then calculated. LOW SHEAR RATE RHEOLOGY (FOR SHEAR RATES LESS THAN 100 SEC -1 ): Simulates flow in low shear processes (i.e. compression molding and extrusion blow molding). Low shear rate rheology measurements are very sensitive to changes in molecular weight, degree of branching and filler content. Useful in characterizing the blowmoldability of a resin. Used to define the thermal stability of a resin at any given temperature. A Dynamic Mechanical Analyzer, equipped with parallel plate fixtures mounted between an actuator and a transducer, is a common method of testing low shear rate rheology. The actuator supplies an oscillating force to the sample, located between the plates, at a specific frequency, and the transducer records the sample response. FIGURE 1 CAPILLARY RHEOMETER Piston Pressure Transducer FIGURE 2 DYNAMIC MECHANICAL ANALYZER Transducer Plate Capillary Sample Plate Material Extrudate Actuator INNOVATIVE PLASTICS 3

4 HIGH & LOW SHEAR RATE RHEOLOGY SHEAR RATE A measure of the rate of deformation of a polymer melt. Calculated from the flow rate and the geometry through which the polymer flows, reported in reciprocal seconds (sec -1 ). (Radians/second are analogous to shear rate.) FIGURE 3 SHEAR THINNING BEHAVIOR Stiffer flow in gates SHEAR STRESS A measure of the pressure required to sustain a constant flow rate through a given geometry, reported in Pascals (Pa). VISCOSITY A measure of a material s resistance to flow (η*), reported in poise, centipoise (100 centipoise=1 poise), Pascal. Second (Pa.S) - 10 poise=1 Pa. S. Viscosity Stronger shear thinning behavior Easier flow in gates VISCOSITY = SHEAR STRESS/SHEAR RATE SHEAR THINNING A decrease in viscosity with increasing shear rates due to molecular alignment during flow. (Shear thinning is not to be confused with shear sensitivity, which is caused by a drop in molecular weight due to degradation.) TYPICAL PROCESSING SHEAR RANGES Because of the shear thinning behavior of plastic melts, it is important to measure viscosities at shear rates typical of the process in question. Evaluating a material for thermoforming or compression molding requires low shear rate viscosity values. For injection molding, high shear rate measurements become more important. Typically, the highest shear rates are found in runners and gates. It is critical to understand flow behavior in these regions for proper tool design. Based on internal SABIC test data. FIGURE 4 SHEAR RANGE DURING PROCESSING Viscosity Low shear rate Compression molding Shear rate (sec -1 ) Extrusion blow molding Shear rate (sec -1 ) Extrusion Injection molding High shear rate Runners Small gates 4 INNOVATIVE PLASTICS

5 FIGURE 5 TEMPERATURE DEPENDENCE OF VISCOSITY Material with high temperature sensitivity has a narrow process window Narrow process window Note: Viscosities for flash and short shot are based on tolling geometry VISCOCITY VERSUS TEMPERATURE Figure 5 displays temperature dependence of viscosity, which measures the decrease in viscosity with increasing temperature. Low temperature dependence implies a wide processing window. Viscosity Short shot Short shot Flash Wide process window Flash viscosity Flash Material with low temperature sensitivity has a wide process window Temp. ( C) Short shot viscosity THERMAL STABILITY MEASUREMENTS (CONSTANT TEMPERATURE AND SHEAR RATE) Measuring how viscosity changes with change can determine the stability of a resin. A significant drop in viscosity indicates resin degradation. If viscosity increases, the resin may be crosslinking, resulting in a build in molecular weight. FIGURE 6 VISCOSITY OVER TIME Crosslinking Viscosity (poise) Process window for crosslinking material Process window for degrading material Stable behavior Degradation Residence time INNOVATIVE PLASTICS 5

6 HIGH & LOW SHEAR RATE RHEOLOGY TYPICAL LOW SHEAR RHEOLOGY TRACES FOR LEXAN RESINS In Figure 7, there are three traces of viscosity vs. frequency for LEXAN resins with different behavior. FIGURE 7 TYPICAL LOW SHEAR RHEOLOGY TRACES FOR LEXAN RESINS LEXAN 121 RESIN Low molecular weight = Low viscosity. LEXAN 101 RESIN High molecular weight = High viscosity. LEXAN 151 RESIN Branched resin, which exhibits greater shear thinning behavior. Viscosity (poise) LEXAN 151 resin LEXAN 101 resin LEXAN 121 resin LOW SHEAR RATE RHEOLOGY CURVES Figure 8 is a typical parallel plate rheometry trace defining G (elastic modulus), G (viscous modulus) and η* (viscosity) as a function of frequency (shear rate). G measures the elasticity of the melt and is related to the die swell observed in extrusion Frequency (rad/sec) Based on internal SABIC test data. FIGURE 8 LOW SHEAR RATE RHEOLOGY CURVES Higher G = Higher melt elasticity. Higher melt elasticity = Higher die swell NORYL HS2000X resin G measures the viscous component of flow. Higher G = Lower melt elasticity. Lower melt elasticity = Less die swell Viscosity (poise) G G η* 235 C Frequency (rad/sec) 6 INNOVATIVE PLASTICS

7 FIGURE 9 HIGH SHEAR RATE RHEOLOGY CURVES Viscosity 10 4 FIGURE 10 R* TECHNIQUE FOR RATING BLOWMOLDABILITY Viscosity (Poise) ,000 NORYL PX0844 resin High viscosity at low shear rate 270 C Low viscosity at high shear rate 300 C 285 C Shear rate (sec -1 ) R* = 1 (rad/sec) 20,000 Poise HIGH SHEAR RATE RHEOLOGY CURVES Figure 9 shows typical capillary rheometry curves defining melt viscosity over a range of shear rates. This trace of NORYL PX0844 resin is typical of the data obtained from the Engineering Data and Tools for any SABIC resin. Each line represents the material s behavior at a specific temperature. A molder uses these traces to determine a plastic s flow under the temperatures and shear rate conditions of the process. R* TECHNIQUE FOR RATING BLOWMOLDABILITY Low shear rate rheology is used for calculating both the process temperature and the melt strength of blowmoldable resins. Process temperature is identified as the temperature that gives a viscosity of 20,000 poise at 100 rad/sec. R* is then calculated by a ratio of viscosities at 1 and 100 rad/sec (at the defined process temperature). High R* (shear thinning behavior) means that the resin flows easily during extrusion and also has sufficiently high melt strength to support the parison when the shear is removed Shear rate (rad/sec) INNOVATIVE PLASTICS 7

8 CONTACT US Americas SABIC 1 Plastics Avenue Pittsfield, MA USA T F Technical Answer Center T Asia Pacific SABIC 1266 Nanjing Road (W) Floor 16, Plaza Shanghai China T F Europe SABIC Plasticslaan 1 PO Box AC Bergen op Zoom The Netherlands T F Technical Answer Center T (0) T E webinquiries@sabic-ip.com Middle East/Africa SABIC Corporate Headquarters PO Box 5101 Riyadh Saudi Arabia T +966 (0) F +966 (0) productinquiries@sabic-ip.com THE MATERIALS, PRODUCTS AND SERVICES OF SABIC INNOVATIVE PLASTICS HOLDING BV, ITS SUBSIDIARIES AND AFFILIATES ( SELLER ), ARE SOLD SUBJECT TO SELLER S STANDARD CONDITIONS OF SALE, WHICH CAN BE FOUND AT AND ARE AVAILABLE UPON REQUEST. ALTHOUGH ANY INFORMATION OR RECOMMENDATION CONTAINED HEREIN IS GIVEN IN GOOD FAITH, SELLER MAKES NO WARRANTY OR GUARANTEE, EXPRESS OR IMPLIED, (I) THAT THE RESULTS DESCRIBED HEREIN WILL BE OBTAINED UNDER END-USE CONDITIONS, OR (II) AS TO THE EFFECTIVENESS OR SAFETY OF ANY DESIGN INCORPORATING SELLER S PRODUCTS, SERVICES OR RECOMMENDATIONS. EXCEPT AS PROVIDED IN SELLER S STANDARD CONDITIONS OF SALE, SELLER SHALL NOT BE RESPONSIBLE FOR ANY LOSS RESULTING FROM ANY USE OF ITS PRODUCTS OR SERVICES DESCRIBED HEREIN. Each user is responsible for making its own determination as to the suitability of Seller s products, services or recommendations for the user s particular use through appropriate end-use testing and analysis. Nothing in any document or oral statement shall be deemed to alter or waive any provision of Seller s Standard Conditions of Sale or this Disclaimer, unless it is specifically agreed to in a writing signed by Seller. No statement by Seller concerning a possible use of any product, service or design is intended, or should be construed, to grant any license under any patent or other intellectual property right of Seller or as a recommendation for the use of such product, service or design in a manner that infringes any patent or other intellectual property right. SABIC and brands marked with are trademarks of SABIC or affiliates Copyright by SABIC. All Rights Reserved. SABIC-PLA-6056-EN