February 2009

The South Texas Section of the Society of Plastics Engineers

Announcement of the International Conference on Polyolefins 2009

The South Texas Section of the Society of Plastics Engineers announces that it will hold the 21st International Conference on Polyolefins, “Polyolefins 2009,” in Houston, Texas at the Hilton Hotel North on February 22, 23, 24 and 25th, 2009. This is the twenty-first in a series of Topical Conferences sponsored by the South Texas Section of the SPE focusing on technical topics in the polyolefins industry. The 2009 conference is expected to have over 600 attendees, including international attendees. There will be thirteen sessions with about 84 papers given in the three days of the conference. There will also be a tutorial session held on Sunday, February 22nd. Presentations will cover a wide variety of topics ranging from globalization, markets, catalysis and polymerization process technology, characterization and testing, nanotechnology, advances in stabilization and polymer modification, process advances in film extrusion and extrusion coating and applications of polyolefins including packaging, films, wire and cables, pipe, emerging energy applications, sustainability and source reduction.

For further information please contact one of the following:

Don Witenhafer, General Chair, Polyolefins 2009 Committee
Phone: 614-657-3895
Email: witenhaferd@cs.com

Tom Walsh, Publicity Chair, Polyolefins 2009 Committee
Phone: 281-493-2344
Fax: 281-493-3537
Email: t.s.walsh@earthlink.net

President’s Message

Sold out! We had a great turn out for the January program Basics of Extrusion seminar hosted by Killion Laboratories. We had to close the registration at 50 people. Tom Butler of BlownFilm Technologies did an excellent job covering the basics of extrusion. We had a very diverse group that included students, resin suppliers, processors and PhD chemists.

February is upon us and our focus is on the International Polyolefins Conference 2009 February 22–25 at the Hilton Houston North. Program Co-Chair’s Don Witenhafer and Robert Portnoy have worked extremely hard to put together a fantastic technical program and group of presenters. I want to thank our sponsors for their support and making this event such a great success. Beyond the technical programs we will enjoy a fun time at the golf outing on Sunday and award cash prizes to students entering the South Texas Section poster contest. The proceeds from this conference provide funding to further our mission of supporting education. The South Texas Section of the Society of Plastics Engineers provided $85,000 in funding and professional liaisons for Society of Plastics Engineers Student Sections at Lamar University, Texas A&M, University of Houston, Texas Tech, University of North Texas and other emerging programs in 2008- 2009. We are proud to promote the education of plastics in these student sections and for the work that these student sections are producing. Should you want to be involved as a sponsor or participate in our exhibition, please contact Brandon Cleary at (281)229-4049.

There are many opportunities to be involved in the South Texas local section. To serve our large geography and busy schedules each month we host a number of informal events. Our monthly technical programs are usually hosted in the evenings at the HESS Club the second Monday of the month. We have an informal breakfast the first Tuesday of each month at 7:00 a.m. on the west side and a lunch meeting the third Friday of each month in The Woodlands. Information about all our events can be found on our website www.spe-stx.org.

February is a busy month for our section and a great time find a place to plug in and meet some friendly people, learn something new, support education and possibly find new business opportunities. If you need more information on any events, want to volunteer in the section or have someone to personally welcome you and introduce you to others at a meeting please feel free to contact anyone in leadership listed on our website. They will be happy to help you get involved.

All the best!

Jeff Applegate
SPE South Texas President 2008-2009

http://www.facebook.com/group.php?gid=35280334773&ref=ts

Join the South Texas Section of the Society of Plastics Engineers on Facebook. Click on the above link and you will be directed to our group page. We hope that this will serve as another communication tool for our Professional Section and be a familiar platform to welcome and inform the Student Sections. It is easy and free, so join in.

International Polyolefins Conference

February 22-26, 2009
North Houston Hilton Hotel

(make room reservations SPE rate directly with hotel at 281-875-2222)

On-line Conference Registration is now open at South Texas Section web site (http://www.spe-stx.org/PolyolefinsRegistration.cfm) or at www.4spe.org

Features and Activities:

• Over 80 peer reviewed papers Feb. 22-25
• 70 Booths with the latest commercial developments.
• SPE International Seminars Feb. 25-26 giving full day instruction on important related topics
• Monday evening networking reception sponsored by PMC Group
• Sunday afternoon golf outing
• Sunday afternoon tutorial on Fundamentals of Polyolefins
• Extensive program and scholarships for students

Sponsored by South Texas Section, Flexible Packaging Division, Thermoplastic Materials and Foams Division, Polymer Modifiers and Additives Division.

SPE Polyolefins Preliminary Program

As of December 1, 2008

February 22-25, 2008
Hilton Hotel North Houston, Houston, Texas, USA
To register go to the following website: http://www.spe-stx.org/PolyolefinsConference.htm

Bulletin Board

Plastics Information: Check it Out

The Houston Public Library on McKinney has resources on plastics and polymers. Check out their catalog at www.hpl.lib.tx.us. If you are not near the McKinney location, you can arrange to pick up your books at your local branch.

The Fondren Library at Rice University has the most complete collection of books on plastics and polymers. This is also a prime resource for patent and trademark information, as well as other US Government documents. You cannot check out books there unless you join Fondren Library [$50], but you can arrange for books to be sent to your library by inter-library loan. Use their catalog at http://library.rice.edu/.

The next best place to browse is at the MD Anderson Library at the University of Houston central campus. South Texas Section has donated many plastics books to this library. If you plan ahead, you can get a TexShare library card from a library where you are a member, which will allow you to check out books from any U of H library. Their catalog is at www.library.uh.edu/.

Book Bag

	Special Effect Pigments Gerhard Pfaff, 2008, 218 pages Price: $195.00 Color designers, product developers, and application technologists in the coatings, plastics, printing inks, and cosmetics industries, and marketing and salespeople seeking to impart knowledge of coatings and pigments to their customers will find useful information in this book. Readers will learn about properties, manufacturing processes, and specific application areas of special-effect pigments that satisfy the demands of the market. The latest advances in colorimetry ensure that products containing special-effect pigments are subjected to state-of-the-art quality assurance methods. Contents Include: History of pearl lustre pigments Optical specialties, manufacture and properties Pearl lustre pigments in paints Pearl lustre pigments in plastics Applications with pearl lustre pigments in printing inks Pearl lustre pigments in cosmetics Colorimetry of pearl lustre pigments General Information Impact of pearl lustre pigments Proof of physiological compatibility
	Biodegradable Polymer Blends and Composites From Renewable Resources Long Yu, 2008, 487 pages Price: $125.00 This reference provides a comprehensive, current overview of biopolymeric blends and composites and their applications in various industries. It is organized according to type of blend or composite. The relationship between the structure of the blend or composite and its respective properties is explored, with particular focus on interface, compatibility, mechanical, and thermal properties. By exploring this relationship, the book helps readers design their own materials. In addition to standard techniques, readers learn several innovative, advanced techniques for improving the interfaces between hydrophilic natural polymers and hydrophobic biodegradable polyesters. The book also explains the latest techniques for analyzing and working with biodegradable nanocomposites. Combining fundamental science with applications that either have been commercialized or show great promise for commercialization, this book is ideal for material and polymer scientists and for students who are interested in bringing new environmentally friendly products to market.
	Extrusion: The Definitive Processing Guide and Handbook Harold F. Giles, Jr., John R. Wagner, Jr., Eldridge M. Mount, III, 2005, 600 pages Price: $315 Why is it important to get to equilibrium and how long does it take? Are there problems running polypropylene profiles on a single screw extruder? Does the job involve compounding color concentrates on a corotating twin screw extruder? This unique reference work is designed to aid operators, engineers, and managers in quickly answering practical day-to-day questions in extrusion processing. This comprehensive volume is divided into 7 Parts. It contains detailed reference data on such important operating conditions as temperatures, start-up procedures, shear rates, pressure drops, and safety.

Thank You from Holmes Scholarship Recipients

Thank You from Johnson Scholarship Recipients

SPE-STX Board Meeting

Location: via Teleconference
Date: December 8, 2008

Continuous Dispersion of Carbon Nanotubes in Polymers Using Ultrasound Assisted Extrusion Process

Rishi Kumar, Todd Lewis and Avraam I. Isayev
Institute of Polymer Engineering
The University of Akron
Akron, Ohio 44325-0301

Abstract

The unique morphology and strong intertube attraction between carbon nanotubes (CNTs) makes the dispersion of CNTs a big challenge and hence limits its effective use. A novel method for the continuous dispersion of carbon nanotubes in a polymer matrix for manufacturing high performance nanocomposites was developed using an ultrasonically assisted twin screw extrusion process. The effect of ultrasound on die pressure, electrical conductivity, rheological, morphological and mechanical properties of polyetherimide filled with 1-10 wt% MWNT was studied. Ultrasonic treatment caused a reduction in die pressure with a permanent increase of viscosity of treated samples.

Introduction

Fiber-reinforced composites have been widely used in the area of aerospace and military due to their light weight and improved mechanical properties. Till date, graphite fiber composites dominate the aerospace industry. There are some problems associated with the conventional fiber reinforced composites such as the accumulation of electrostatic charge on their surface which can cause the local heating resulting in the catastrophic failure of the surrounding materials. In recent years [1], the polymer/carbon nanotube composites have gained tremendous attention both in academia and industry. While the first image of tubes resembling nanotube was published in 1976 [2], major advances in the area happened after the formation of CNTs was published by Iijima in 1991[3]. Because of the exceptional mechanical, thermal and electrical properties along with their light weight [4,5], carbon nanotubes have the potential to surpass graphite fiber composites and overcome the problem associated with the conventional fiber-reinforced composites. Due to the high aspect ratio (100-1000) of CNTs, it is possible to achieve the percolation threshold at very low loading of CNTs [6]. The biggest challenge in effective use of CNTs is their lack of dispersion in a polymer matrix. During synthesis of CNTs, nanotubes easily aggregate or form bundles due to strong intertube van der Waals attraction and hence limit the effective use of their exceptional properties obtained at the individual nanotube level. Many researchers [7, 8] have tried different routes to disperse CNTs, however, successful dispersion still remains a challenge as can be seen from the various review papers on dispersion of CNTs in a polymer matrix [9, 10]. Current commonly used methods for dispersion of nanotubes in polymer matrix are: in-situ polymerization, mechanical and chemical treatment [10]. Among these methods in-situ polymerization and chemical modification may not be commercially viable due to their limitation in scale up and their negative environmental impact. Prolonged sonication of the CNTs in an ultrasonic bath using solvent is one of the most commonly used methods to disperse nanotubes, however, it introduces defects in CNTs and results in reduced aspect ratio which is basis for many of their attractive properties [11]. Melt processing, being more efficient, rapid and environmentally friendly method to disperse CNTs in a polymer matrix, is one of the most preferred techniques from industrial application point of view because of its easiness in scale up. However, a limited number of studies have been done on melt processing/extrusion of polymer/carbon nanotube composites [12-16].

In this study [12], a miniature mixer molder to mix PMMA with up to 26 wt% MWNT was used. The extruded melt was compression molded to make thin films. Dynamic mechanical behavior shows a significant increase in the storage modulus of thin film samples. Morphological, rheological and electrical studies on the PC/MWNT composites were carried out indicating low electrical percolation at loading between 1 and 2 wt% [13, 14]. Also, PE/MWNT composite were studied and electrical percolation near 7.5 wt% loading was found which is usually higher than what observed for other polymers. However no significant improvement in mechanical properties was observed. Functionalized nanotubes were prepared and mixed with Nylon 6 and then further processed in an internal mixer [16]. A significant improvement in the Young’s modulus and tensile strength of Nylon 6 was observed at a 2 wt% MWNT loading. In another study [17], PEI/SWNT composites were prepared in single screw extruder. No significant improvement in mechanical properties was observed for thin film samples; however, significant increase in the tensile modulus was observed when extruded melt was drawn to thin fibers. From the above discussion, there is a clear need to develop a new method which is rapid, clean and commercially viable.

Over the past decade extensive work has been done to develop a novel extrusion process with the aid of high power ultrasound [18-22]. A number of studies on the effect of ultrasound on polymers have been published and reported in various review articles and books. It was shown that ultrasonic oscillations can breakdown the 3-D network in vulcanized rubber within seconds. Ultrasound was found to improve the compatibilization of immiscible plastic blends, plastics/rubber and rubber/rubber blends during extrusion process [23]. In recent years, use of ultrasound to disperse nanofiller in a polymer matrix is gaining attention. Ultrasound helps in rapid exfoliation and intercalation of nano-clay in a polymer matrix [24].

To our knowledge, there has been no work done to improve the dispersion of carbon nanotubes in polyimide matrix with the help of ultrasound assisted extrusion process.

This work presents a novel method for the continuous dispersion of carbon nanotubes in a polymer matrix. Ultrasound assisted twin screw extrusion of polyetherimide (PEI)/MWNT has been carried out. PEI was chosen because of its extensive use in composites for aerospace applications due to its desirable combination of mechanical and thermal properties. They have outstanding dimensional and thermo-oxidative stability with desired processability required for space applications. The effects of ultrasound on die pressure, electrical conductivity, rheological, morphological and mechanical properties were studied.

Experimental

Materials
Polyetherimide (PEI) in powder form made by GE plastics under trade name ULTEM 1000P was used as received. The multiwalled carbon nanotubes (MWNT) were provided by Nanostructured & Amorphous Materials, and were used as received. The MWNT had an outside diameter of 10-20 nm and length varied from 0.5 – 200 µm.

Nanocomposite Preparation
The PEI powder was mixed with 1, 2, 5, and 10 wt% MWNT loading by ball milling for 24 hrs. The mixture was then dried for a minimum of 24 hrs at 110°C in a vacuum oven prior to processing. For melt processing, a continuous co-rotating twin screw extruder equipped with high power ultrasonic die attachment was developed as shown in Figure 1. The micro-extruder (PRISM) has diameter of 16 mm with L/D=25. Two pressure transducers were placed in the die zone immediately before and after the ultrasonic treatment zone. Two horns oscillating at a frequency of 40 kHz were attached to the die zone with a 4mm gap size and molten compound was continuously subjected to amplitudes from 0-6.0 µm. The temperature in the barrel section was set from feed zone to die zone as 280°C, 340°C, 350°C, 360°C, 360°C. The screw speed was set at 50 rpm and 0.5lb/hr feed rate was used.

Tensile bars according to ASTM D-638 were prepared using the HAAKE mini-jet piston injection molder at a temperature of 360°C and mold temperature of 130°C. The injection pressure was 740 bars in each case. Prepared nanocomposites were compression molded into discs of 25 mm diameter and 2.2 mm thickness at 300°C using the Carver 4122 compression molding press, for the rheological measurements. The samples for electrical conductivity measurement were also compression molded into discs of 90 mm diameter and 1 mm thickness.

Rheological Measurements
The rheological properties of the nanocomposites were studied using an ARES, TA Instruments. A 25 mm parallel plate geometry in oscillatory shear mode with dynamic frequency sweep test was used at 340°C for a fixed strain amplitude of 2%.

Electrical Resistivity
A Keithley electrometer (Model 6517A) equipped with an 8009 test fixtures was used to measure the volume resistivity of the nanocomposites in accordance with the ASTM D257 method using applied voltage of 0.1V.

Mechanical Properties
Tensile measurements on injection molded samples were carried out using an Instron test machine Model 5567, Instron Corp. Tests were carried out on minimum five samples according to ASTM D 638 test method at cross head speed of 5mm/min using a 30 kN load cell and an extensometer. The highest value of deviation for tensile strength and Young’s modulus was around 3% and 10% respectively.

Morphological Study
Surface morphology and dispersion of CNTs was investigated on cryofractured injection molded impact bar samples using a field emission HRSEM (Model JEOL JSM-7401 F).

Results and Discussion

Process Characteristics
Fig. 2 shows the entrance die pressure and power consumption for various wt% loadings of CNTs as a function of ultrasonic amplitude. The measured pressure is before the ultrasonic treatment of PEI/MWNT composites. A continuous decrease in pressure with increasing ultrasonic amplitude was observed. This is from a combination of heating from dissipated energy from ultrasound, cavitational effect from ultrasonic waves leading to some thixotropic and permanent changes in polymer, reduction in friction at die walls and horn surfaces due to ultrasonic vibrations and possible shear thinning effect created by ultrasound waves. The die pressure increases with the increase of CNT loading. The measured power consumption is the total power consumption during the treatment of nanocomposites, a part of which is dissipated as heat whereas the rest is being utilized to disperse nanotubes in melt and increasing the polymer-nanotube interaction. It was observed that power consumption increased with the increase of ultrasound amplitude indicating more energy was transmitted from horns to polymer melt.

Rheology
The effect of ultrasound on the complex viscosity of nanocomposites as a function of frequency at different CNT loadings is shown in Fig. 3. There is a tremendous increase in the complex viscosity with the increase of loading of CNTs. It was observed that ultrasonic treatment increased the complex viscosity of nanocomposites and the effect is more pronounced at low frequency. The increase in complex viscosity due to ultrasound was attributed to better dispersion of nanotubes in a polymer matrix with enhanced polymer-nanotube interaction. Storage modulus (G’) of nanocomposites increased by orders of magnitude with the increase in CNT loading (Fig.4). It was observed that at higher loadings, G’ vs. frequency curve is almost reaching a plateau at low frequency indicating the existence of interconnected structure of anisotropic filler [13,15]. The increase in storage modulus with ultrasound further indicates improved polymer-nanotubes interaction as result of better dispersion of CNTs. The effect of CNTs loading and ultrasound on nanocomposites can be seen from the plot of G’ vs. G” in Fig. 5. At a given G” value, the G’ increased significantly with nanotube content and is in accordance with the behavior reported for PC-MWNT composites [13]. It was observed that ultrasonic treatment increases G’ at given G” for nanocomposites at all loadings. The effect of ultrasound and nanotubes loading on damping characteristics of the nanocomposites is shown in Fig. 6. As the nanotube content increases the tan δ decreases and the curve becomes more flat in the low frequency region [15]. A further decrease in tan δ was observed on the ultrasonically treated nanocomposites indicating the improved interaction between nanotubes and polymer matrix.

Electrical Resistivity
The volume resistivity results of nanocomposites as a function of CNTs loading are plotted in Fig. 7. The volume resistivity decreased by 107 Q-cm with 10 wt% loading. A sharp reduction in resistivity is observed between 1 and 2 wt% nanotubes content indicating the percolation threshold between 1 and 2 wt% nanotube loading which is in accordance with the percolation threshold reported for PC/MWNT nanocomposites prepared by melt processing method [13]. No significant change in resistivity occurred with further increasing the nanotube loading upto 10 wt% and with ultrasonic treatment. The enhancement of dispersion of nanotubes in ultrasonically treated samples should lead to reduction of number of contacts between the nanotubes, therefore, causing an increase of the resistivity. However, since percolation threshold, where the volume resistivity varies many decimal orders, was already achieved, minor changes in the electrical conductivity due to improved dispersion cannot be detected. Apparently, rheological properties are more sensitive to variation of CNT dispersion than the electrical conductivity.

Mechanical Properties
The ultrasonic treatment and addition of nanotubes has a significant effect on the mechanical properties of nanocomposites. From Fig. 8, it is seen that there is nearly an increase of 70% in the Young’s modulus for nanocomposites at 10wt% CNT loading as compared to the virgin PEI. The difference in values of Young’s modulus for treated and untreated samples are in experimental error range. The tensile strength increased from 107 to 115 MPa for untreated sample and to 123 MPa for treated samples as shown in Fig. 9, clearly indicating that ultrasonic treatment results in increasing the interfacial interactions between polymer matrix and CNTs. On increasing the CNT content the material becomes more rigid [25], however, in this case both the yield strain and elongation at break was not affected much, in fact for certain conditions treated sample had more elongation at break than untreated samples.

Morphology
Fig. 10 shows HRSEM micrographs of treated and untreated nanocomposites filled with 2wt% CNTs. All images have clearly distinguished nanotubes that are randomly oriented and uniformly dispersed. The images show that the nanotubes were dispersed to a level of 50 nm diameter, which is close to the range (10-20nm) of as received CNTs. It is clearly seen that untreated samples shows the presence of some CNTs bundles whereas samples treated ultrasonically at 6.0µm do not show even a single CNTs bundle.

Conclusions

A new ultrasound assisted melt extrusion process was developed for manufacturing PEI/MWNT nanocomposites. The ultrasonically treated nanocomposites show significant changes in the rheological behavior with tremendous increase in the viscosity, storage modulus and reduced damping characteristics’ of nanocomposites as compared to the untreated ones indicating the better dispersion of nanotubes. As a result of ultrasonic treatment the tensile strength increased without effecting elongation at break and yield strain of nanocomposites.

Acknowledgement

The authors are grateful for the financial support provided by NASA Headquarters.

Keywords

Ultrasound, Multiwalled carbon nanotubes, Polyetherimide nanocomposites, melt processing.

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