Selection of Thermotropic Liquid Crystalline Polymers for Rotational Molding

Selection of Thermotropic Liquid Crystalline Polymers for Rotational Molding Eric Scribben Dissertation submitted to the Faculty of Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Chemical Engineering Dr Donald G Baird, Chairman Dr Richey M Davis Dr Garth L Wilkes Dr Peter Wapperom Dr Scott Case Dr Martin Rogers July 19, 2004 Blacksburg, Va Keywords: rotational molding, TLCP, coalescence, sintering Selection of Thermotropic Liquid Crystalline Polymers for Rotational Molding Eric Scribben (ABSTRACT) Thermotropic liquid crystalline polymers (TLCPs) possess a number of physical and mechanical properties such as: excellent chemical resistance, low permeability, low coefficient of thermal expansion, high tensile strength and modulus, and good impact resistance, which make them desirable for use in the storage of cryogenic fluids Rotational molding was selected as the processing method for these containers because it is convenient for manufacturing large storage vessels from thermoplastics Unfortunately, there are no reports of successful TLCP rotational molding in the technical literature The only related work reported involved the static coalescence of two TLCP powders, where three key results were reported that were expected to present problems that preclude the rotational molding process The first result was that conventional grinding methods produced powders that were composed of high aspect ratio particles Secondly, coalescence was observed to be either slow or incomplete and speculated that the observed difficulties with coalescence may be due to large values of the shear viscosity at low deformation rates Finally, complete densification was not observed for the high aspect ratio particles However, the nature of these problems were not evaluated to determine if they did, in fact, create processing difficulties for rotational molding or if it was possible to develop solutions to the problems to achieve successful rotational molding This work is concerned with developing a resin selection method to identify viable TLCP candidates and establish processing conditions for successful rotational molding This was accomplished by individually investigating each of the phenomenological steps of rotational molding to determine the requirements for acceptable performance in, or successful completion of, each step The fundamental steps were: the characteristics and behavior of the powder in solids flow, the coalescence behavior of isolated particles, and the coalescence behavior of the bulk powder The conditions identified in each step were then evaluated in a single-axis, laboratory scale, rotational molding unit Finally, the rotationally molded product was evaluated by measuring several physical and mechanical properties to establish the effectiveness of the selection method In addition to the development and verification of the proposed TLCP selection method, several significant results that pertain to the storage of cryogenic fluids were identified as the result of this work The first, and argueably the most significant, was that the selection method led to the successful extension of the rotational molding process to include TLCPs Also, the established mechanical properties were found to be similar to rotationally molded flexible chain polymers The biaxial rotationally molded container was capable of performing to the specified requirements for cryogenic storage: withstand pressures up to 34 psi at both cryogenic and room temperatures, retain nitrogen as a gas and as a cryogenic liquid, the mechanical preform retaining nitrogen, as both a gas and as a cryogenic liquid, and resist the development of micro-cracks during thermal cycling to cryogenic conditions iii Acknowledgements The author wishes to express his thanks to Professor Donald G Baird for the support and guidance that resulted in the completion of this work In addition, the author would also like to thank each member of his research committee (past and present): Dr Davis, Dr Loos, Dr Rogers, Dr Wapperom, and Dr Wilkes The author would also wish to acknowledge the following persons: His parents and brother for their continuous support throughout this process John D Souder for guidance and the infinite wisdom in initiating interest in engineering and polymer processing Professor Kurt Koelling and all of the members of CAPCE at The Ohio State University for encouragement to pursue a graduate degree Vladimir Kogan and all of the members of the Aerosol Science group at Battelle Memorial Institute for their direction and inspiration to pursue a graduate degree All current and past members of the Polymer Processing Lab that he had the opportunity to serve with: Phil, Mike, Wade, Matt, Quang, Brent, Chris, and Aaron Those members of the department staff who have made this work easier over the years: Diane, Chris, Riley, Wendell, and Mike The group of Buckeyes that have demonstrated unwaivering support throughout this process The following friends for supplying adequate distraction from his research project: Brooks, John & Jen, Maatha, Doug, Mary, Corey, and too many others to list iv Original Contributions The following are considered to be significant original contributions of this research: A clearer understanding of the effect of viscoelasticity on polymer coalescence Representation of the transient rheological response in the coalescence model is essential to predicting the coalescence rates for polymeric materials at times that are less than their characteristic relaxation times Incorporating the transient rheology provides a qualitative picture of coalescence that is consistant with reports that increasing the relaxation time accelerates coalescence It is demonstrated that TLCPs coalesce faster than is predicted by the Newtonian coalescence model, which is in agreement with a viscoelastic coalescence model that uses the transient rheology However, TLCP coalescence rates cannot be accurately predicted by the transient model, indicating that an anisotropic liquid crystalline constitutive model that includes the effect of liquid crystalline structure may be necessary to accurately model the process A novel technique is developed to produce spherical TLCP particles for use in rotational molding This is used to overcome the low apparent density and unacceptable powder flow that results when TLCPs powders are prepared by conventional grinding methods v A selection method is devised to identify viable TLCP candidates and establish processing conditions for successful rotational molding In the development of this method several key results were established The behavior of the shear viscosity at low shear rates can be used to determine thermal and environmental conditions where coalescence occurs Densification is not possible for TLCPs in the rotational molding process by extending the molding cycle time, as is standard practice for densifying flexible chain polymers in rotational molding However, bubble entrapment is eliminated during the neck growth process by optimizing the mold rotation rate vi Table of Contents Introduction 1.1 Thermotropic Liquid Crystalline Polymers 1.2 Rotational Molding 1.3 Polymer Sintering 10 1.4 Research Objectives 13 1.5 References 15 Literature Review 19 2.1 Rotational Molding 21 2.1.1 Powder Properties 21 2.1.2 Coalescence 37 2.1.3 Processing Considerations 66 2.2 Thermotropic Liquid Crystalline Polymers 76 2.2.1 Mechanical Properties 77 2.2.2 Rheology of Thermotropic Liquid Crystalline Polymers 82 2.3 Research Objectives 94 2.4 References 96 Experimental Methods 3.1 Materials 115 116 3.1.1 Polypropylene 117 3.1.2 Thermotropic Liquid Crystalline Polymers 117 3.2 Thermal Analysis 119 3.3 Generation and Characterization of TLCP Powders 119 3.4 Rheological Characterization 122 3.4.1 Polypropylenes Table of Contents 122 vii 3.4.2 3.5 TLCPs Surface Tension Measurement 123 125 3.5.1 Polypropylenes 125 3.5.2 TLCPs 126 3.6 Coalescence Experiments 128 3.7 Densification Experiments 128 3.8 Single Axis Rotational Molding 130 3.9 Mechanical and Physical Property Testing 131 3.9.1 Testing of Samples from the Densification Study 131 3.9.2 Rotationally Molded Samples 132 3.10 Biaxial Rotational Molding 133 3.11 References 135 The Role of Transient Rheology in Polymeric Coalescence 136 4.1 Abstract 137 4.2 Introduction 138 4.3 Experimental 145 4.3.1 Materials 145 4.3.2 Surface Tension Measurement 146 4.3.3 Rheological Characterization 147 4.3.4 Coalescence 148 Numerical Methods 150 4.4 4.4.1 Model Parameter Fitting 150 4.4.2 Solution of the Transient UCM Model 153 4.5 Results and Discussion 155 4.5.1 Newtonian and Steady State UCM Coalescence Models 155 4.5.2 Single Mode Transient UCM Model 160 4.5.3 Multimode Transient UCM Model 162 Table of Contents viii 4.6 Conclusions 164 4.7 Acknowledgements 166 4.8 References 167 The Role of Transient Rheology in the Coalescence of Thermotropic Liquid Crystalline Polymers 169 5.1 Abstract 170 5.2 Introduction 171 5.3 Experimental 174 5.3.1 Materials 174 5.3.2 Differential Scanning Calorimetry 176 5.3.3 Surface Tension Measurement 176 5.3.4 Rheological Characterization 177 5.3.5 Coalescence Experiments 179 5.4 Results and Discussion 180 5.4.1 Rheological Characterization 180 5.4.2 Experimental Coalescence 184 5.4.3 Transient UCM Coalescence Model Predictions 190 5.5 Conclusions 191 5.6 Acknowledgements 192 5.7 References 193 The Rotational Molding of a Thermotropic Liquid Crystalline Polymer 195 6.1 Abstract 196 6.2 Introduction 197 6.3 Analytical Methods 201 Table of Contents ix 6.3.1 Material 201 6.3.2 Generation and Characterization of Powders 202 6.3.3 Coalescence Experiments 205 6.3.4 Thermal Behavior 206 6.3.5 Surface Tension 207 6.3.6 Rheology 208 6.3.7 Densification Experiments 209 6.3.8 Properties of Densification Samples 211 6.3.9 Single-Axis Rotational Molding Experiments 211 6.3.10 6.4 Properties of the Rotational Molded Samples Results and Discussion 212 213 6.4.1 Powder Flow Characteristics 213 6.4.2 Coalescence 218 6.4.3 Densification 223 6.4.4 Single Axis Rotational Molding 227 6.5 Conclusions 233 6.6 Future Work 234 6.7 Acknowledgements 234 6.8 References 235 Recommendations 238 Appendix A Shear Rheological Data 242 A.1 Polypropylene (190k) 243 A.2 Polypropylene (250k) 247 A.3 Polypropylene (340k) 255 A.4 Polypropylene (580k) 263 A.5 Vectra A 950 272 Table of Contents x To address the processing concerns, two readily Rheological results can be seen in Figures and available commercial resins were evaluated: Vectra A 950 Vectra B 950 displays a definite zero shear viscosity at (hydroxy benzoic acid/ 2,6 hydroxynapthoic acid) and both temperatures Vectra B 950 a polyesteramide (60 hydroxy naphthoic approximately 400 Pa s at 320°C and 600 Pa s at 330°C acid/ 20 terephthalic acid/ 20 aminophenol) Vectra A 950 exhibits a low rate viscosity increase at Vectra B reached a plateau of 320°C, reaching values above 10,000 Pa s It has been Apparatus Steady stress growth measurements were performed on a Rheometrics RMS 800 and were complemented with creep measurements obtained from a stress controlled Rheometrics RSR 8600 A 25 mm diameter cone and plate geometry with a 0.1 radian cone angle was used in an inert (N2) atmosphere Higher rates were obtained with the RMS in small strain dynamic mode crystallinity [6] At 330°C, Vectra A appeared to achieve a zero shear value of around 4000 Pa s As mentioned, the viscosity increase at 320°C could translate to incomplete sintering Spherical Particles As previously mentioned, the spherical particles were A 25.4 mm Killion extruder was used to disperse the TLCP in a low molecular weight polypropylene suggested that this behavior is the result of residual The TLCP was then extracted from the polypropylene matrix to obtain the spherical TLCP particles generated by blending the TLCPs with polypropylene and subjecting the mixture to high deformation rates in the extruder Fig is an SEM of the spherical drops as formed in the polypropylene matrix The TLCP was then extracted, and the size distribution was measured As Sintering experiments were performed in a Linkam seen in Fig 5, a fairly wide range of particle sizes is THM 600 heating stage equipped with an optical obtainable It should also be mentioned that mean particle microscope and a camcorder to record high resolution size can be manipulated through extrusion residence time video The hot stage was capable of achieving a heating and cooling rate rate of 90°C per minute and could maintain temperature within 0.1°C making it safe to assume the experiments were isothermal Once again nitrogen was used to ensure an inert atmosphere Results and Discussion Sintering A 250 µm radius was used in every trial At 320°C Vectra B 950 appeared to coalesce within approximately 20 seconds Vectra A 950 was much slower and appeared to stop after two minutes at around 75% of complete neck Rheology Appendix F Publications growth Sintering results and model predictions are 368 For Vecra B 950 the reached In order to obtain a steady value these resins modified Frenkel expression underpredicted the sintering must be deformed for 200 to 800 seconds Fig shows time by almost 10 seconds The experimental points the results of the stress growth experiments for Vectra A appear to initially increase at a constant rate whereas the 950 at 0.1 and 0.01 s-1 Similar results are observed for models proceed with a decaying rate The UCM based Vectra B These times vastly exceed the deformation expression, with an approximate terminal relaxation time time observed during sintering, 10 to 20 seconds Within of 50 seconds, grossly overpredicts the sintering time In that time, the viscosity has only reached approximately the case of Vectra A 950, both models overestimate half of the steady state value at the low rates observed sintering time but this could be influenced by the fact that during sintering pictured in Figures and the true zero shear behavior was not observed At 330°C, the sintering rates Conclusions became Generating spherical particles not only increases bulk indistinguishable between the two resins reaching density and improves granular flow, but it provides an complete sintering within 15 seconds The modified ideal system for studying the sintering of TLCPs Both Frenkel results initially diverge but achieve acceptable TLCPs exhibit zero shear viscosities at 330°C, but at agreement again when the experimental rate begins to 320°C Vectra A 950 viscosity increases for decreasing decline The UCM values, with a relaxation time of shear rates Sintering kinetics were not accurately approximately 100 seconds for Vectra B 950, again captured by either Newtonian or viscoelastic Maxwell underestimated the sintering rate by approximately 35 models This was attributed to the shear thinning and seconds For Vectra A 950, (λ= 2.5 s) both models were almost identical in underestimating the rate transient nature of TLCP viscosity, which might be addressed using Doi’s theory for rigid rod-like polymers These models unsatisfactorily predicted sintering References times for the selected TLCPs This inadequacy could be In both models zero shear behavior is assumed to exist and attributed to several rheological phenomena deformation rates are not great enough to cause shear thinning behavior If deformation rates are great enough this could explain some of the discrepancies Another explanation is that true steady state behavior has not been Appendix F Publications Z Tadmor and C Gogos, Principles of Polymer Processing, Wiley, New York, 1979, pp 305-307 J Frenkel, “Viscous Flow of Crystalline Bodies under the Action of Surface Tension,” J.Phys., 9, pp 385-391, (1945) J.D Eshelby, “Discussion.” in A.J Shuler, ‘Seminar on the Kinetics of Sintering,” Metals Trans., 185, pp 806-807, (1949) O Pokluda, C.T Bellehumeur, J Vlachopoulos, “Modification for Frenkel’s Model for Sintering,” AIChE Journal, 43, 12, pp 3253-3256, (1997) 369 C.T Bellehumeur, M Kontopoulou, J Vlachopoulos, “The Role of Viscoelasticity in Polymer Sintering,” Rheologica Acta, 37, pp 270-278, (1998) K.F Wissbrun, “Rheology of Rod-Like Polymers in the Liquid Crystalline State,” J Rheol., 25, 6, pp 619-662, (1981) Figure SEM of cryogenically Ground Vectra B 950 Figure Rheology of Vectra at 320°C Appendix F Publications 370 Figure Rheology of Vectra at 330°C Figure SEM of Spherical Drops of TLCP in Polypropylene Matrix Appendix F Publications 371 Figrue Sphere Particle Size Distribution Figrue Sintering Experiments and Model Predictions at 320°C Appendix F Publications 372 Figure Sintering Experiments and Model Predictions at 330°C Figure Vectra A 950 Stress Growth Appendix F Publications 373 Performance of a Rotationally Molded Thermotropic Liquid Crystalline Polymer Eric Scribben and Donald Baird, Department of Chemical Engineering, Virginia Tech simultaneously rotating it about two principal axes Heat Abstract Thermotropic liquid crystalline polymers (TLCPs) applied to the external surface conducts to the tumbling have a number of potentially useful physical properties powder, which eventually exceeds its tack temperature for rotational molding: excellent chemical resistance, and adheres to the mold surface good barrier properties, low coefficient of thermal continues, the powder sinters into an evenly distributed expansion, high tensile strength and modulus, and good layer and densifies as the trapped air bubbles diffuse impact resistance However, it is possible that the nature through the melt The mold continues to rotate as it is of the molding process is such that full advantage of these cooled, and once the plastic is sufficiently rigid the properties cannot be obtained To determine how well product is removed [2] While heating TLCPs perform when rotationally molded a commercially Thermotropic liquid crystalline polymers (TLCPs) available TLCP, Vectra B 950, was studied under static are a class of engineering resins that offer some unique conditions as well as with a single axis rotational molding and potentially useful properties to rotational molding unit capable of measuring the internal air temperature They can have a relatively high resistance to solvents and The processing temperature was determined by measuring excellent barrier properties because of their low gas shear viscosity at several temperatures The tensile solubility They may be molded into structures with strength and modulus of both statically molded and extremely accurate dimensions because of their low or rotationally molded samples were measured Samples negligible coefficient of thermal expansion They are also were evaluated for complete densification by inspecting capable of providing high tensile strength and modulus, the fractured surface which are on the order of 102MPa and 101GPa Introduction and Background respectively [3] Rotational molding is a process used to manufacture Unfortunately, some of these properties may become The process begins by a disadvantage in rotational molding For example low loading polymer powder into a hollow mold and then gas solubility may inhibit bubble dissolution and a hollow plastic products [1] Appendix F Publications 374 negligible coefficient of thermal expansion could make it aminophenol) with a melt temperature of approximately difficult to remove the molded product from a 280°C complicated mold In addition some TLCPs not have a Apparatus well defined zero shear viscosity, which can inhibit Stress growth measurements were performed with a coalescence Traditionally prepared TLCP powders are Rheometrics RMS 800 and complemented by creep fibular with poor powder flow characteristics and result in measurements bridging and poor surface quality It would be useful to Rheometrics RSR 8600 evaluate these materials to determine the state of these plate geometry with a 0.1 radian cone angle was used in issues and their implication on performance an inert (N2) atmosphere for both sets of measurements obtained with a stress controlled A 25mm diameter cone and This work identifies problems associated with Higher rates were obtained with the RMS in small strain mechanical performance of rotationally molded TLCPs dynamic mode with a 25mm diameter parallel plate The low shear rate rheology was measured to ensure that geometry a zero shear viscosity exists and identify an appropriate A 25.4 mm Killion extruder was used to disperse the processing temperature A drop deformation technique TLCP in a low molecular weight polypropylene was used to generate spherical particles to eliminate the TLCP was then extracted from the polypropylene matrix low bulk density problem Various sizes and distributions to obtain the spherical TLCP particles The particles were of these spheres were sintered statically A cylinder was sieved to determine their size rotationally more selected along with four distributions Table contains representative of what is currently used in practice sieve information used in size measurement as well as Tensile tests were performed on the specimens to distribution information The 20, 30, 40, 50 mesh sizes determine what influence size and size distribution has on were selected because extremely fine powders typically strength and modulus have poor solid flow characteristics so a mixture Experimental containing a majority of fines is not normally used [2] molded from a distribution Materials The Four mesh sizes were Distributions D1, D2, and D3 were created to investigate A commercially available resin was selected for this the effect of distribution type on mechanical properties set of experiments: Vectra B 950 a polyesteramide (60 and densification while RM is a more typical distribution hydroxy naphthoic acid/ 20 terephthalic acid/ 20 for rotational molding with the majority of the material being between approximately 300 and 600 microns [2] Appendix F Publications 375 The eight samples were statically sintered into tensile Results from the rheological tests are shown in bars and tested All tensile bars were sintered in a 1.27cm Figure Vectra B 950 displays a zero shear viscosity at × 6.35cm mold with an exposed top surface and a both temperatures, but rate independence occurs at 400 Pa thermocouple fixed in the center of the side wall sec at 320°C and 600 Pa sec at 330°C Results for Nitrogen was supplied through a chamber that covered the temperatures below 320°C are not reproducible, behavior mold The entire unit was placed in a pre-heated hot that can be attributed to varying amounts of residual press The heating soak time was 40 minutes and began crystallinity [4] Since the viscosity at 320°C is less than once the maximum temperature (320°C) was reached at 330°C and lower temperatures contain residual The sintered bars were tested with an Instron 4202 using a crystallinity 320°C was selected as the processing crosshead speed of 1.27mm/min and a 30.5mm gauge temperature length to determine strength and Young’s modulus Statically Sintered Tensile Properties according to ASTM Standard D638-01 The results from the tensile measurements are Rotational molding was done using the distribution summarized in Table No clear relationship between RM with a single axis lab scale device The mold was a size or size distribution and modulus was found stainless steel cylinder with a 3.81cm diameter and Excluding the 20 mesh sample, all moduli were within 7.62cm long Both ends were capped One end was fixed standard deviation of each other to a shaft that was driven by an electric motor rotating at reasonable to assume that the modulus remained constant 10rpm with a mean of 1.03GPa The 20 mesh sample should not The other cap had an opening so that a Therefore, it is thermocouple could be installed to monitor the air be completely disregarded temperature within the mold Heat was provided by a understand why its modulus is almost half of the other convection oven equipped with a nitrogen purge and samples The 1.03GPa mean is also significantly below capable of heating rates up to 60°C per minute The the 20GPa that is possible with good molecular alignment heating cycle was designed to mimic the static sintering [3] conditions The molded product was then sectioned and It would be useful to Possible causes for these discouraging results could strips were used for tensile measurements be insufficient global molecular alignment Although this Results and Discussion may be part of the reason, it cannot completely account Rheology for the problem, since poorly oriented samples have moduli around 2.5GPa [3] It could possibly be attributed Appendix F Publications 376 to poor interparticle adhesion due to the lack of molecular the distribution samples diffusion across contact boundaries This possibility is concentration of large voids than D1, making D1 stronger reasonable since it is well documented that weld line D2 is stronger than D3 but it does not contain more voids strength is a problem in the injection molding of these However, it is easier to identify individual particles materials In addition, it is reasonable to speculate that throughout the surface, the result of poor adhesion It is entrapped bubbles were unable to completely densify, apparent that a correlation between the fracture surface possibly the result of low gas solubility in TLCPs and strength exists, but it is not readily quantifiable A trend was observed between strength and size Sample D2 has a higher Rotationally Molded Tensile Properties If It was found that the tensile modulus and strength of densification was incomplete then it is reasonable to the rotationally molded product was higher than statically assume that voids become smaller in finer powders sintered material Decreased void size should mean increased structural strength was 17.50MPa, which is notably higher than the continuity and strength However, the results from modulus and strength (0.930GPa and 10.51MPa) of the samples D1, D2, and D3 not support this because D3 is static sample This suggested that interparticle adhesion composed of a higher percentage of smaller particles than may have improved or the product contained less bubbles D2 Yet D2 was stronger than D3 To explain the results The fracture surfaces not appear to reveal problems the fracture surfaces were inspected (Refer to Figures with adhesion but bubbles are distinguishable, as shown and for the images) in Figure Examination of the void area in the fractured Strength increased as particle size decreased Figure shows that both weld lines and encapsulated bubbles may contribute to part failure It is easier to identify the boundary of the larger particles in the 20 mesh sample and the concentration of large encapsulated bubbles decreases with particle size The 50 mesh sample does appear to contain a large amount of small bubbles, but perhaps they fail to reduce strength because they not disrupt structural continuity to the extent that the larger ones Figure also shows that large bubble concentration and adhesion explain the strength results for Appendix F Publications The modulus was 2.022GPa and surface can partially explain the improvement The rotationally molded samples show that approximately 8% of the total surface area is void while static conditions produced a sample with 13% void After normalizing the strength and modulus for void content the values from static conditions were still not comparable to that prepared from rotational molding Therefore, a change in adhesion did occur In addition to tensile measurements, the surfaces were inspected The quality of the external surface, 377 surface in contact with the mold, was much worse than interparticle adhesion and bubble content, precisely how the internal surface Pitholes were not found on the much each contributed could not be determined It was internal surface but the external surface did contain a also found that porosity decreased and adhesion significant amount of them This undesirable defect can increased, in comparison to static results, when the be seen in Figure The size of the pitholes could be material was rotationally molded decreased by reducing particle size, but it was unable to cylinder contained a significant amount of pitholes completely eliminate them The surface of the References Despite the bubbles reducing the strength and modulus and the pitholes being a cosmetic deterrent to rotational molding, the rotationally molded LCP did exhibit notable mechanical properties The tensile modulus was comparable to that of crosslinked high density polyethylene, which is nominally 17.9 MPa for industrially produced tanks [5] Conclusions It was found that modulus was not affected by particle size or size distribution under static conditions The modulus was higher when the material was Crawford, R.J., Throne, J.L., Rotational Molding Technology, Plastics Design Library, William Andrew Publishing, Norwich, New York, 2002 Kliene, R.I.,‘Rotational Moulding of Polyethylene’ in Rotational Moulding of Plastics second edition, ed Crawford, R.J., John Wiley & Sons inc New York, 1996, pp.32-61 Sawyer, L., Shepherd, J., Kaslusky, A., Knudsen, R., Tech Spotlight: Unfilled liquid crystalline polymers, [Online], Available: http://www.ticonaus.com/literature/documents/LCP_Article_01_351res 72dpi.PDF, June, 2001 10 Wissbrun, K.F., “Rheology of Rod-Like Polymers in the Liquid Crystalline State,” J Rheol., 25, 6, 1981, pp 619-662 11 High Density Crosslinked Polyethylene (HDXLPE) Storage Tanks, [Online], Available: http://www.polyprocessing.com/updates/GenSpecrev 2-HDXLPE.pdf Key Words rotationally molded Strength decreased with increasing particle size and was also improved when rotationally molded Rotational molding, LCP, mechanical properties Although these results can be explained by Table Sieve and Distribution Sizes Sieve Size Gap Opening (microns) 20 840 30 595 40 420 50 297 60 250 70 210 100 149 Pan - Appendix F Publications D1 0.07 0.13 0.27 0.53 - D2 0.53 0.27 0.13 0.07 - D3 0.10 0.40 0.40 0.10 - RM 0.003 0.076 0.476 0.393 0.016 0.019 0.012 0.004 378 Table Statically Sintered Tensile Results Size 20 30 40 50 D1 D2 D3 RM Modulus (GPa) Strength (MPa) 0.598 7.18 1.093 10.08 1.140 11.00 0.964 12.78 1.040 13.48 1.008 9.61 1.066 9.11 0.930 10.51 Figure Vectra B 950 Shear Viscosity Appendix F Publications 379 Figure Fracture Surfaces of 20, 30, 40, and 50 Mesh Tensile Bars Figure Fracture Surfaces of Tensile Bars Appendix F Publications 380 Figure Fracture Surfaces of Rotationally Molded Cylinder Figure External Surface of RM Cylinder Appendix F Publications 381 Vita The author was born in Ashtabula, Ohio on August 23, 1976 After graduating from Pymatuning Valley High School (Andover, Ohio) in the Spring of 1994, he attended The Ohio State University to pursue a Bachelor of Science degree in Chemical Engineering His undergraduate education was supplemented with work experiences at Koch Materials, Kohler Company, Battelle Memorial Institute, and an undergraduate honors research project in polymer processing under the direction of Dr Kurt Koelling Upon graduation, the author to begin his gradute studies at Virginia Polytechnic Institute and State University in August, 1999 Presently, he is a candidate for the Doctor of Philosphy degree in Chemical Engineering under the direction of Dr Donald G Baird Eric Scribben Vita 382 [...]... Tensile Strength 344 E.6 Biaxial Rotational Molded Tank 346 Appendix F Publications 365 Sintering of Thermotropic Liquid Crystalline Polymers 366 Performance of a Rotationally Molded Thermotropic Liquid Crystalline Polymer 374 Vita Table of Contents 382 xii List of Figures Figure 1.1 Friedelian Classes: a Nematic; b Cholesteric; c Smectic A; d Discotic 3 Figure 1.2 SEM images of ground: a TLCP and b HDPE... Properties of a New Thermotropic Liquid- Crystalline ‘Backbone’ Copolyester,” Polymer, 25, 6, 808 (1984) 20 Noël, C., Chapter 2, “Characterization of Mesophases” in Liquid Crystal Polymers: From Structures to Applications, edited by Collyer, A.A., Elsevier Applied Science, New York (1992) 21 Ober, C.K., Weiss, R.A., Chapter 1, “Current Topics in Liquid Crystalline Polymers in Liquid- Crystalline Polymers, ... Comparison of the tensile strength and modulus of sample S3 when molded in the presence of air 227 Table 6.6 The average density, tensile strength, and tensile modulus from the rotationally molded distribution D4 compared the results for the distribution from the densification study List of Tables 230 xviii 1 Introduction 1 Introduction 1 1 Introduction 1.1 Thermotropic Liquid Crystalline Polymers Liquid crystalline. .. rotational molding device The final objective is to establish rotational molding conditions that optimize the physical and mechanical properties The results from each of these objectives should provide a method of screening TLCPs for effective use in rotational molding 1 Introduction 14 1.5 References 1 Baird, D.G., Ballman, R.L., “Comparison of the Rheological Properties of Concentrated solutions of a Rodlike... Physics of Liquid Crystals 2cnd ed., Oxford University Press, New York (1993) 8 Donald, A.M., Windle, A.H., Liquid Crystalline Polymers, Cambridge University Press (1992) 9 Elliot, A., Ambrose, E.J., “Evidence of Chain Folding in Polypeptides and Proteins,” Discussions of the Faraday Society, 9, 246 (1950) 1 Introduction 15 10 Frenkel, J.F., “Viscous Flow of Crystalline Bodies Under the Action of Surface... Although the knowledge base for polymer coalescence and rotational molding is increasing due to a considerable amount of ongoing research, the work does not encompass TLCPs This work represents an effort to extend rotational molding to include TLCPs where the primary goal is to devise a method to select TLCPs suitable for rotational molding The ability to select suitable high performance resins and optimize... 24061 (1985) 33 Wilson, T.S., “The Rheology and Structure of Thermotropic Liquid Crystalline Polymers in Extensional Flow,” Ph.D Dissertation, Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Va 24061 (1991) 34 Wissbrun, K.F, “Rheology of Rod-like Polymers in the Liquid Crystalline State,” Journal of Rheology, 25, 6, 619 (1981) 35 Webster’s 3rd International... accurate dimensions because of their low or negligible coefficient of thermal expansion relative to flexible chain polymers [5] They also exhibit high modulus, strength, and impact properties [18] These properties can be exploited to apply LCPs in applications where flexible chain polymers perform inadequately 1.2 Rotational Molding Rotational molding, also known as rotomolding, is a process used to... discontinuous, resulting in the formation of defects and polydomain textures Two types of defects have been identified for nematic liquid crystalline polymers [7] In thick samples it is possible to observe a system of dark flexible filaments (defined as disclinations) that correspond to lines of singularity in molecular alignment and result in the formation of multiple domain texture The other defect... Figure 6.13 Image of D1 tensile bar fracture surface confirming incomplete densification 224 Figure 6.14 Internal surface of the rotationally molded sample D4 in the 1.59 cm diameter cylindrical mold 228 Figure 6.15 External surface of rotationally molded sample D4, where the width image is 50.8 mm 229 Figure 6.16 Comparison of bubble formation in static bulk powder and in rotational molding 231 Figure