March 2009

March Meeting
PVC Polymerization, Compounding, and Processing

Remember our section golf outing, Monday, April 20th at Timber Creek Golf Course in Friendswood. For details and reservations go to www.spe-stx.org

President’s Message

Dear SPE South Texas Section members:

On behalf of the Board members of the South Texas Section of the Society of Plastics Engineers, I want to congratulate Don Witenhafer and his committee for all the hard work to host a successful 2009 International Polyolefins Conference and exhibition. This conference requires a significant amount of time and effort to put together and I want to recognize all of the committee members that worked to make this year’s event successful. Bill Diecks, Glenn Rasberry, Suzanne Biggs, Tom Walsh, Renee Colyer, Emery Jorgenson, Jill Martin, Brandon Cleary, Paul Zerfas, Martin Husti, Robert Portnoy, Lan Nguyen, Donna Davis, Paul Banks, Terry Vermas, Bill Talbott, Davit Diesberg.

What a difference a year makes. Last year we were talking about the emergence of the Middle East and Asia as suppliers and consumers of plastics, a 5 year average global GDP growth of 3.5% and 5 year average domestic GDP growth of 2.9%, we talked about the impact of high energy cost on the markets and industry consolidation. This year we find a steep decline in energy cost in the face of a significant global and domestic economic contraction. Industry consolidation has picked up the pace and we continue to find the world is indeed flat.

The funds from the International Polyolefins conference are the primary resource used to promote the scientific and engineering knowledge relating to plastics by the South Texas section. The South Texas section of the SPE supports the education of plastics in local K-12 schools as well as supporting 10 college and University Society of Plastics Engineers student chapters.

I would like to specifically thank our sponsors that make this conference possible. Without their support the conference and all the activities to promote the education of plastics the SPE South Texas Section would not be possible. THANK YOU!

Platinum Sponsor

PMC Group Inc. was this years Platinum Sponsor and hosted the welcome reception at the Hilton Houston North hotel. PMC Group, Inc. is a privately held global manufacturer of specialty chemicals and plastics, founded in 1994 by Dr. PM Chakrabarti, former chief of technology at PPG Industries, with a vision to create an organization capable of sustaining growth through innovation. PMC Group operates manufacturing facilities in North America, Europe and Asia. The company is headquartered in Mt. Laurel, New Jersey.


Gold Sponsors
          

Silver Sponsors

Bronze Sponsors

Again, thank you to all sponsors, committee members, speakers and attendees that make this conference the worlds largest and best managed technical conference specializing in Polyolefins.

Respectfully yours,

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.

Summit with RTP Company

Explore material technologies with our experts!
Join us for a one-day Imagineering Plastics Workshop where our most experienced experts will equip you with technical information that will help increase your competitive edge!

March 31
Dallas, Texas

April 1
Houston, Texas

April 3
Monterrey, Mexico

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

	Essentials of Polymer Science and Engineering Paul C. Painter & Michael M. Coleman, 2009, 525 pages This book is both an introduction to polymers and an imaginative invitation to the field of polymer science and engineering as a whole, including plastics and plastics processing. The text explains and helps students as well as professionals appreciate all major topics in polymer chemistry and engineering: polymerization synthesis and kinetics, applications of probability theory, structure and morphology, thermal and solution properties, mechanical properties, biological properties, and plastics-processing methods. Designed to supersede many standard texts (including the authors’), Essentials of Polymer Science and Engineering is unique in a number of ways. Special attention has been paid to explaining fundamentals and providing high-level visuals. In addition, the text is replete with engaging profiles of polymer chemists and their discoveries. The book explains the science of polymer engineering and tells the story of the field from its beginnings to the present, indicating when and how polymer discoveries have played a role in history and society. In addition it contains study questions and problems. Contents: Microstructure and Molecular Weight Polymer Synthesis Polymerization Kinetics Polymerization Probability and Statistics Copolymerization Spectroscopy and the Characterization of Chain Microstructure Structure and Morphology Natural Polymers Crystallization, Melting and the Glass Transition Polymer Solutions and Blends Molecular Weight and Branching Mechanical and Rheological Properties Processing
	Polyolefin Blends Edited by Domasius Nwabunma, Thein Kyu With an emphasis on nano- and micro-structures of crystals and phase morphology, this reference condenses and consolidates current information on polyolefins so that the reader can compare, select, and integrate a material solution. It includes chapters covering formulation design, processing, characterization, modeling and simulation, engineering performance properties, and applications. Miscibility, phase behavior, microstructure, crystallization, hierarchical morphology, and physical and mechanical properties are also discussed. And new research trends, including in-situ reactor blending and reactive processing, are reviewed. Contents: Overview of Polyolefin Blends, Miscibility and Characteristics of Polyolefin Blends, Miscibility, Morphology and Properties of Polyethylene Blends, Miscibility and Crystallization of Binary Polyethylene Blends. Microscopically Viewed Structural Characteristics of Polyethylene Blends between Deuterated and Hydrogenous Species: Cocrystallization and Phase Separation, Thermal and Structural Characterization of Binary and Ternary Blends based on Isotactic Polypropylene, Isotactic Poly (1-Butene) and Hydrogenated Oligo (Cyclopentadiene), Morphological Phase Diagrams of Blends of Polypropylene Isomers and Poly(ethylene octene) Copolymer, Structure, Morphology and Mechanical Properties of Polyolefin Based Elastomers, Morphology and Mechanical Properties in iPP/Polyolefin-Based Copolymer Blends, Functionalization of Olefinic Polymer and Copolymer Blends in the Melt
	Advancing Sustainability Through Green Chemistry and Engineering Edited by Rebecca L. Lankey, Paul T. Anastas, 2005, 264 pages Explores the frontiers of pollution prevention through technologies that are at the forefront of green chemistry and engineering. Topics covered include environmentally benign synthesis, pharmaceuticals, greener solvents, and bio-based synthesis and processing. Each chapter provides an in-depth treatment of the technical aspects of a specific green chemistry and engineering innovation. It shows how research can be used in practical industrial applications, such as decreasing energy consumption, decreasing the use of toxic and persistent materials, and decreasing the consumption of non-renewable resources.

Education Committee Announcement

Rebecca Tadesse – PO2009 Scholarship Announcement

Rebecca Tadesse, from Houston, is an undergraduate senior at Baylor University. Her major is Mechanical Engineering with a Minor in Math. She is going to graduate this coming May. She plans to pursue a career in polymers at Dow Chemical in Freeport upon graduation.

She is currently involved in the expansion of the polymers lab at Baylor. Prof. Walter Bradley has begun to further focus on polymer properties as part of the ME degree, and Rebecca is working as a Professor's Assistant to this end.

She has worked summer internships at Dow Chemical, and Halliburton Energy Services both in Houston. She has done volunteer work at Texas Children's Hospital, and The Museum of Health and Medical Science – again both in Houston.

Professional organizations are numerous, including American Society of Mechanical Engineers, Society of Women Engineers, Engineers with a Mission and The National Society of Black Engineers of which she is currently serving as President. To round this all off, she also received the Tennis Team Player Award.

I suspect, based on her academic achievement, extracurricular and work related studies, as well as athletic abilities, that Baylor is going to miss her after graduation. It is obvious that their loss will definitely be the polymer industries gain.

Please join us in welcoming Rebecca as a South Texas Section, PolyOlefins 2009 Scholarship recipient.

Sean Conroy – PO2009 Scholarship Announcement

Sean Conroy, a Pennsylvania native, did his undergraduate studies at Carnegie Mellon University, graduating in 2007 with a degree in Physics. He is pursuing a Masters Degree at Baylor and will be working on polymeric composites – exploring natural reinforcement materials.

Over a three year period, while at Carnegie Mellon, he spent summers as an intern at Sandia National Laboratories in Livermore, CA. Upon graduation from Carnegie Mellon he spent a year in Iraq as an English instructor and international relief worker.

He has been an International Science and Engineering Fair winner, Vice President of the Carnegie Mellon Society of Physics Students, recipient of the Bechtel Bettis Undergraduate Scholarship and a Carnegie Mellon Student Undergraduate Research Grant, as well as being on the Mellon College of Science Dean’s List.

Just listening to his achievements has most folks seeing that he is a pretty smart fellow. If there are any doubters then his decision to come to Baylor, and discover the good life in Texas, surely dispels them.

Please join us in welcoming Sean as a South Texas Section, PolyOlefins 2009 Scholarship recipient.

SPE-STX Board Meeting Minutes

Because of the Polyolefins Conference, the board of directors did not meet this month. Minutes from January’s meeting are not yet approved and will be included in next month’s newsletter.

Designing Injection Molded Bioplastics Products

Rolf Koster, Bregtje van Dijken and Lobke van Erve, Faculty of Industrial Design Engineering, Delft University of Technology, Delft, The Netherlands

Abstract

The ongoing need to keep reducing trial-and error in product design definitely applies to plastics products, and perhaps even more to bioplastics. It remains essential to optimize unavoidable weak spots in injection molded products, such as flow weld lines. Critical product properties were investigated for a poly-hydroxybutyrate, an experimental wood fiber-filled poly-hydroxybutyrate, and a general purpose polystyrene for comparison. Specimens from products molded with poly-hydroxybutyrate were found to have quite good impact strengths in weld line regions. Certain non-trivial injection molding settings, which reduce the impact strength in neat product regions, were found beneficial for weld line properties.

Introduction

Application of bioplastics, however limited, is rapidly growing. Much of this growth in the recent past can be attributed to packaging applications, particularly foils, and short-lived products for immediate disposal. Injection molded bioplastics applications have been less numerous until now, partly because bioplastics are not yet applied in large production volumes which injection molding is traditionally most suited for.

One of the Delft Faculty of Industrial Design Engineering research programs has the objective to develop design guidelines and methods for engineering design of reliable and durable products, focussing on he opportunities offered by new materials and technologies and on dealing with their challenges of novelty. As part of this program, several research activities have been and are being conducted. One such activity is to investigate the application potential of some bioplastics and other new materials for injection molded products. A few molds are available for experimental work. One of these molds is for a part containing a weld line.

The benefits of new materials will only be fully expressed in products if weak spots, such as weld lines in injection molded products, can be properly addressed. Weld lines may be critical with regard to product quality for some thermoplastics. Therefore, research into the effects of variations in injection molding settings, combined with mechanical testing, will be helpful for developing design guidelines for injection molded bioplastics products.

This paper reports results obtained with a neat polyhydroxybutyrate (PHB) and a wood fiber-filled PHB. The work was a BSc credited research project performed by two of us (Bregtje van Dijken and Lobke van Erve).

Background

Bioplastics
Oil-based plastics are of organic origin. Their rates of production and of breakdown are generally not in balance with each other, as is the case for most natural organic matter [1]. Most societies have not shown their capability to deal with this imbalance, as demonstrated by large waste volumes occupied by discarded products. One of the possible solutions to match production and breakdown rates is to utilize biodegradability, which can be achieved with most bioplastics. Another trigger to explore applicability of bioplastics is the uncertainty about future availability and price of oil for oil-importing countries.

Essential success factors for bioplastics products include processability, predictability and achievement of desired product properties based on material properties and processing parameters, material stability during product life, and rapid product biodegradation when desired after the end of product life.

It should be noted that bio-based materials are based on renewable resources, but generally these resources need to be synthesized into materials suitable for conversion into products. Biodegradable materials and materials based on renewable resources are two different categories that do not always overlap [2].

The rate of product degradation does not only depend on the material’s capability of biodegradation, but on product geometry as well, since biodegradation acts through product surfaces [1].

Injection Molding of PHB
PHB is a fully biodegradable material, fully based on renewable resources. It is a high molecular mass energy storage product of bacteria and algae [3]. In the synthesized form it is highly crystalline, unlike the natural state.

The injection molding processing window is rather narrow, and special melt processing and processing parameters are needed to avoid brittleness and achieve acceptable properties. It is necessary to minimize the combined effect of melt residence time and elevated temperatures in the plasticator. This is best achieved by a reverse temperature profile [4]-[5].

Weld Lines
Flow weld lines are formed during molding if two melt flows converge or reunite. A weld line region of a product may be mechanically weakened due to limited molecular chain diffusion across the weld line interface (particularly near the cooler skin), stress concentrations at the bottom of the V-shaped notches at the product surfaces, and different orientations of macromolecules near weld lines caused by the fountain flow at the melt front [6]-[8].

For amorphous materials or materials with a significant amorphous fraction, weld line strength may benefit from molding settings that increase temperatures or decrease melt viscosities near the skins in a weld line region.

For semicrystalline thermoplastics the degree of crystallization has an important effect on weld line properties since crystal growth is not hindered by a weld line butmay even be preferential in the direction perpendicular to the fountain flow. The higher the degree of crystallinity, the less a weld line is weakened.

Weld lines will remain a subject of concern for materials with a tendency towards brittle behavior as well as for materials with micro-scale reinforcements.

Experimental

The part with weld line is shown in Figure 1 (left). Four or five of these parts can be assembled to form a coffee cup carrier (Figure 1 right). Materials used for molding this part were general purpose polystyrene (PS) grade 638 by Dow for reference, PHB grade P226 by Biomer, and an experimental grade P226 filled with 25% wood fibers in such a way that the manufacturer expected the fibers to act as nucleants for crystallization.

Molding the wood fiber-filled PHB was somewhat challenging since the heat input from the plasticator could not be too high to avoid over-heating of the wood, whereas lower temperatures did not enable proper mold filling for this specific narrow-gated mold. The amount of material was not enough for extensive experimentation, and therefore the properties of the molded parts may not have been optimum.

Molding the neat PHB was less challenging, although overheating of the melt did occur particularly during the startup runs.

Specimens from the parts were impact tested in a pendulum impact tester with maximum fracture energy equal to 4J. Figure 2 shows the locations where impact specimens were taken from the parts (left), and the positioning of the specimens in the impact tester for sideways impact (right). Ten specimens were tested for each combination of material and molding parameter settings, both without and with weld line.

Results

The average impact strengths for all combinations of material and molding parameters settings, both without and with weld line, have been summarized in Figure 3. Figure 4 shows the 95% confidence intervals for most impact test results, and the 68% confidence intervals for cases in which the 95% confidence did not enable distinction of differences.

For the PS specimens the only significant difference between molding parameter effects, as concluded from the 95% confidence intervals, was caused by the setting with higher plasticizing temperatures. The higher plasticizing temperatures were favorable for the weld line, as expected, and unfavorable for the specimen without weld line, as expected too because less molecular orientation is to be expected in the tensile direction.

For the PHB specimens the lowest injection speed was most favorable for weld line strength. No significant distinction through the 95% confidence intervals could be made between all other molding settings. The specimens without weld line exhibited the lowest impact strength at the lowest injection speed, together with the specimens molded with higher injection pressure and higher mold coolant temperature; a significant difference between these three settings could not be distinguished.

It is clearly seen that the wood fiber filling causes a decrease of impact strength. The decrease is less dramatic, however, for the weld line impact strength, indicating enhanced crystallization across the weld line. Even the 68% confidence intervals for the wood-filled specimens were rather wide and no significant effect of the molding parameters could be distinguished.

Unfilled PHB specimens exhibited superior impact strength as compared to the PS specimens, both without weld line and, to a lesser extent, with weld line. Nearly all wood-filled PHB specimens had impact strength values similar to the PS specimens.

Concluding Remarks

The most notable conclusions from the experimental results are:
• neat PHB has a better impact strength than PS, also at the weld line;
• the molding settings for best weld line impact strength in both PS and neat PHB give the lowest impact strength in other areas;
• the (relative) weld line factor for this geometry and type of test is lower for PHB, however (about 0.2-0.3 for PHB, versus 0.2-0.55 for PS);
• some of the results obtained with neat PHB may be less than achievable because of over-heating of the melt during injection molding;
• the results obtained with fiber-filled PHB are likely to be less than achievable because of over-heating of the wood fibers during injection molding;
• wood fiber filling in PHB reduces impact strength;
• no major effect of molding settings was found for wood fiber-filled PHB (perhaps the non-optimum processing was dominating);
• wood fiber filling in PHB appears to promote crystallization (less weld line strength reduction).

Acknowledgments

Dr Urs Hänggi at Biomer, Germany, provided all materials free of charge, data and processing guidelines, as well as participated in extensive e-mail communication during our injection molding experiments, to assist us in process optimization.

References

[1] R. Jongboom and M. Dartée, Lecture handouts of Workshop “Product Development with Bioplastics”, Delft Faculty of Industrial Design Engineering, 11 May 2006
[2] Tech Focus, Plastics Engineering Magazine, October 2006
[3] G.F. Moore and S.M. Saunders, Advances in Biodegradable Polymers; RAPRA Publication, ISBN 185957-118-2
[4] Processing of Biomer^®P-series (PHB); from web site of Biomer: http://www.biomer.de/VerarbPE.html (consulted Winter 2005)
[5] J. Zhang, S. McCarthy and R. Whitehouse, Reverse Temperature Injection Moldingof Biopol™ and Effect on Its Properties; Journal of Applied Polymer Science, 94, 483-491 (2004)
[6] S. Fellahi et al., Weld lines in Injection Molded Parts: A Review, Adv. Polym. Technol. 14:3 169-195, 1995
[7] R. Seldén, Effect of Processing on Weld Line Strength in Five Thermoplastics, Polym. Eng. Sci. 37:1 205-218, 1997
[8] Dealy & K.F. Wissbrun, Melt Rheology and its Role in Plastics Processing, ISBN 0-442-22099-5, Van Nostrand Reinhold, New York, 1990