Japanese　

J. E. Spruiell, Professor and Head, Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996-2200

INTRODUCTION

The University of Tennessee, Knoxville (UTK), is one of the oldest institutions of higher education in the United States of America. It traces its origins back to 1794. In that year the Federal Territory, that was 2 years later to become the State of Tennessee, granted a charter to Blount College, named in honor of William Blount, territorial governor. The institution was renamed The University of Tennessee in 1879 when it was selected by the legislature of the state to be Tennessee’s State University. Currently, the University of Tennessee, Knoxville offers more than 300 degree programs to its 26,000 students.

Polymer science and engineering at UTK began as an organized effort after Professor James L. White joined the faculty of the Department of Chemical Engineering in 1967. Professor White began to develop a major effort in polymer processing and to involve other UTK professors in polymer activity. Among these early investigators were Prof. D. C. Bogue and Prof. J. E. Spruiell. A degree program in Polymer Engineering eventually developed out of these efforts; it became official in 1975. Along the way additional faculty were added in support of the Polymer Engineering Program, including Prof. E. S. Clark and Prof. J. F. Fellers. After Professor White ’s departure to lead the Polymer Engineering program at the University of Akron in 1983, the responsibility for the Polymer Engineering degree program moved to the new Department of Materials Science and Engineering, where it still resides today. This is one of only a handful of polymer engineering degree granting programs in the USA. However, the current polymer science and engineering effort at UTK is not concentrated in one location; it is distributed among at least four departments: Chemistry, Mechanical Engineering and Engineering Science, Materials Science and Engineering, and Textile Science.

The faculty have developed and contribute to the efforts of two major research centers: The Center for Materials Processing and the Textiles and Nonwovens Development Center. The Center for Materials Processing is a State of Tennessee/Industry supported center which covers processing of all types of materials, including metallic and ceramic materials as well as polymers. The Textiles and Nonwovens Development Center carries out research on nonwovens with an emphasis on nonwovens manufactured from synthetic polymers by processes such as “melt blowing” and “spunbonding.” This center is supported by state government and industry, including Exxon Chemical Company and a wide range of nonwovens manufacturers.

Major research Areas

Table 1 lists the primary personnel in each department and gives a very brief description of their primary interests. An examination of this list shows that the program at UTK can be described in terms of four major program areas. These are (1) polymer morphology and crystallization, (2) polymer processing, (3) polymer blends and composites, and (4) nonwovens. There is also overlap among these program areas. For example, there is considerable work being done on processing of melt blown and spunbonded nonwovens which could be classified under either nonwovens or polymer processing. We will now briefly describe some of the current research that is ongoing in each of these areas. These descriptions are not intended to be exhaustive, but merely illustrate the types of activities which are currently ongoing or which have been recently carried out.

Table 1. Polymer Science and Engineering Faculty at UTK and Their Primary Interests

Polymer Morphology and Crystallization

The objective of the work being carried out by Professor Bernhard Wunderlich and a team of several post-doctoral researchers and graduate students is to understand the solid state of linear macromolecules. This involves the analysis of structure, morphology, macroconformation and motion, and thermodynamic and mechanical properties. Of special interest is the study of small-size phase structures in polymers (nanophases) and the understanding of mesophases (liquid crystals, plastic crystals and conformationally disordered crystals). The key instrumentation used in this research is based on calorimetry (temperature-modulated and standard DSC, microcalorimetry based on modulation of AFM-tip temperature and adiabatic calorimetry). Additional techniques involve

solid state NMR, atomic force microscopy, single-molecule analysis and

X-ray diffraction. Mathematical models are developed using irreversible thermodynamics and molecular dynamics simulation. Cooperation exists with the polymer group at

Oak Ridge National Laboratory (Drs. Noid, Sumpter, Habenschuss, and Annis) and with a number of collaborators around the world (with B.V. Lebedev U. Nishny Novgorod, Russia; H. Bu, Fudan University, China; H. Baur, BASF, Germany; and with Dr. Kreitmeier, U. Regensburg, Germany. New developments include: 1) A better understanding of nanophase separation in polymers (a topic that emerged from the research of the last eight years), 2) updates of the ATHAS data Bank of heat capacities of polymers to the year 2000, including a shift to instant access over the internet, 3) analysis of new polymers, including biological molecules, and 4) an improved understanding of the new techniques of temperature-modulated calorimetry and microcalorimetry, where the latter

allows a spacial resolution of less than 1 micrometer.

Professor Paul Phillips has been actively involved in studies of the molecular factors that control the morphology and crystallization kinetics of polymers for more than 20 years. He has also done extensive investigations of the influence of elevated pressure on the process of crystallization. Recent studies have included examining the effect of elevated pressures on the morphology, phase stability, and crystallization kinetics of isotactic polypropylene, determination of the equilibrium melting temperature and morphology of very low density ethylene-octene copolymers (LLDPEs), and the crystallization of random copolymers based on poly(hexamethylene adipamide).

A new technique has been developed by Professor Joe Spruiell and his students which allows studies of crystallization kinetics of polymers at cooling rates as high as 5000 °C/min. This is about two orders of magnitude higher than the maximum cooling rates that can be accurately used for such measurements using standard DSC methods. This technique is based on the well known light depolarizing microscopy technique, but provisions are made so that the sample temperature can be rapidly changed and carefully monitored. This technique has now been applied to a number of polymers to examine crystallization under cooling conditions which approach those found in many processing operations. Polymers studied include a variety of polypropylene homo and copolymers, high density polyethylene, polyamide 6 and 66, and aliphatic polyketones (Shell’s Carillon? resins).

Polymer Processing

The activities in this area range from studies of fiber and film formation, through nonwoven web formation, to on-line monitoring techniques for reactors, extrusion lines and other processes. The latter effort is lead by Professor Marion Hansen. The research of his group is directed at developing ideas for in-line monitoring of chemical and polymeric processes. The goal is to take classical bench top optical spectroscopic characterization methods and, by interdisciplinary engineering research, develop them into molecular-based

in-line process monitors for process feedback control. Over the past decade this research has led to the production of fiber optic probes that can be directly installed in polymer reactors and extruders. These probes have been operated at maximum temperatures and pressures of 325 °C and 2,000 psi. This effort has led to commercial polymerization reactors which are producing copolymers for targeted values of comonomer ratios with closed-loop feedback control. Current research projects include: (1) ultraviolet in-line fiber optic spectrometry of polymer additives in flowing molten polymers, (2) near infrared in-line fiber optic spectrometry of polymer composition and rheological functions of flowing molten polymers, (3) in-line polarized Raman spectrometry of polymer composition and rheological functions of flowing molten polymers, (4) in-line fiber optic Raman spectrometry of batch emulsion polymerization, and (5) in-line fiber optic near infrared spectropolarimetry for polymer composition and rheological functions of flowing molten polymers.

The research of Professor Joe Spruiell emphasizes the relationship between processing conditions and the structure and properties of the resulting products. He is perhaps best known for his on-line studies of structure development in fiber and film processing. Recent activities have included modeling of the blown film process, and an extensive investigation of the differences in processing-structure-property interrelationships between conventional Ziegler-Natta polypropylenes and metallocene catalyzed polypropylenes. This latter effort has examined the nature and causes of melting point differences, crystallization kinetics differences, and differences in melt spun fiber formation and spunbond web formation. Other recent efforts have included (1) detailed studies of high speed melt spinning of poly(L-lactic acid) and (2) studies of melt spinning and drawing of polyketone resins. The work on poly(L-lactic acid) is of interest because this polymer is produced from a renewable resource (corn) and is biodegradable. It therefore has the potential to replace polymers in current use in a number of applications where biodegradability is important. The work on polyketones has concentrated on producing high strength-high modulus fibers and understanding the crystallization process in processes such as injection molding.

Professor R. R. Bresee and Professor M. W. Milligan have teamed up to attack the problem of “shot” formation in meltblown webs. Meltblown webs involve an extrusion process for producing very tiny filaments (typically 1-5 ? m in diameter) which are laid on a collection device to produce the web. The term “shot” refers to undesirable particles of non-fibrous resin that are sometimes present in meltblown webs. Professor Bresee has developed a computer based quantitative microscopy technique for characterizing the size, shape and number density of shot and their location in the web. Professor Milligan has carried out detailed studies of the dynamics of meltblown web formation and evaluation of potential shot formation mechanisms through on-line investigation of the web formation process through high speed photographic and video techniques.

A final example of polymer processing research at UTK is the work of Professor J. F. Fellers to develop new ways to make fiber reinforced thermoplastic resin composite materials. He has recently received a patent on a process wherein a resin impregnated fiberglass bundle is first prepared and then continuously incorporated into a suitable matrix. Initial results have produced reinforced cement structures that have flexure strengths greater than 5000 psi in three-point bend tests. Typical values for the flexure strength of “rebar” reinforced concrete are in the range 500-1000 psi.

Polymer Blends and Composites

Studies of polymer blends are being carried out by Prof. Mark Dadmun and Prof. Roberto Benson. Prof. Dadmun has a substantial group of 6 graduate students and a postdoctoral research associate doing research on polymer blends. One project involves investigating how material properties of polymer blends can be optimized through inducing miscibility between amorphous and liquid crystalline polymers (LCP) using hydrogen bonding as well as interfacial modification of immiscible polymer blends with copolymers of various structures. Utilizing a copolymer as the amorphous polymer, where the copolymer consists of a monomer that can participate in hydrogen bonding and one that cannot, systematically varies the amount of hydrogen bonding. By varying the composition of this copolymer the amount of intermolecular hydrogen bonding changes. Another project involves strengthening the biphasic interface of immiscible polymer blends by a copolymer that acts as a surfactant. Methods of incorporating copolymers into blends include in-situ transreaction between two homopolymers, addition of novel copolymers that are synthesized using ‘living’ free radical polymerization during processing, and reactive engineering. Another area of active research is the use of in-situ shear microscopy and shear light scattering to determine the shear induced structure of polymer blends and solutions.

The research activities in polymer composites are largely in the areas of (a) process development and characterization, process modeling and process optimization for dimensional control, (b) composites durability, (c) fiber-matrix interface mechanics, (d) constitutive modeling, (e) mechanical characterization at room, elevated and sub-zero temperatures, and (f) investigation of damage mechanisms in composites. This research is being done by Professors Madhu Madhukar, Jack Weitsman and Roberto Benson in addition to the work of Prof. Fellers mentioned above.

During a typical cure cycle for a thermoset polymer composite, the polymer volume changes significantly (both expansion and shrinkage) resulting in cure-induced stress development in the embedded fibers. The effect of these stresses is lack of dimensional control of the composite part, fiber waviness, matrix microcracking, etc. A new technique has been developed at UTK which determines the cure induced stress for a given cycle and then determines an optimum cure cycle that minimizes these stresses. This technique has been applied to a variety of aerospace grade material systems, and it has been shown that the cure cycle modification can often reduce these stresses by about 20%.

A recent study modified the commonly used “Single Fiber Fragmentation Method” of studying interface properties to allow the determination of the interface properties at elevated and sub-zero temperatures. Experiments on various fiber-matrix systems show that the interface properties are strong functions of temperature. These studies are allowing better prediction of the composite behavior as a function of temperature.

Other research includes studies of alternative methods of curing such as radiation curing, durability of composites when exposed to hostile environments or complex stress/time histories (fatigue), and development of “swirl mat” composites. These latter materials are fiber glass reinforced composites with a reaction injection molded polyurethane matrix. The fibers are laid approximately randomly into a mat which is then filled by the matrix reactants. The development of swirl mat composites is largely aimed at applications in the automotive industry.

Nonwovens Research

As mentioned above, a major research center called the Textiles and Nonwovens Development Center (TANDEC) exists on the UTK campus. TANDEC has a number of special facilities which are not common on university campuses. Some specific examples include a one meter Reicofil spunbond line, three different lines for producing meltblown webs, a card for producing staple fiber webs, a laboratory scale five roll calendar, and an array of testing equipment for characterizing nonwoven webs. The director of TANDEC is Professor L. C. Wadsworth.

As illustrated in Table 1, a number of faculty are involved in studies of nonwovens. The major focus of the research in nonwovens is investigation of the process-structure-property relationships in the meltblowing and spunbonding processes using polypropylene, polyethylene, polymer blends and other specialty resins. The relationships among polymer properties, extrusion characteristics, quench conditions; web formation and bonding variables are studied. Investigations are also being made of the effects of colorants and other additives on processing conditions and fabric performance properties. As noted above, one of the major issues in meltblowing research is the cause of “shot” formation. Investigation of the thermal bonding process is an important area of research for both spunbonding and staple fiber nonwovens. These studies include efforts to understand the influence of process and molecular variables including fiber orientation and strength on the optimum bonding temperature and fabric strength.

A substantial effort is also underway in applications research for nonwovens. Examples include electrets, filters, improved wetting, dyeability, bondability, sterilization, etc. of nonwovens through plasma and other surface treatments. The plasma work involves the generation of a one atmosphere plasma which allows economical, on-line treatment of webs. Other significant research efforts include development of synthetic leather, development of barrier fabrics for medical applications, stretchable nonwovens and the use of nonwovens in polymer matrix composites.

Closure

Polymer science and engineering is alive and well at UTK. The program has evolved into a multidisciplinary effort with efforts concentrated in four major areas: (1) polymer morphology and crystallization phenomena, i.e. the polymer solid state, (2) polymer processing, (3) polymer blends and composites, and (4) nonwoven fabrics produced largely from synthetic polymers. The next few years will likely entail some major changes as some of the current faculty retire. It will be very important to replace these faculty with energetic and enthusiastic young faculty with a vision of the future and a desire to continue to build the area of polymer science and engineering at UTK.

Over the years a number of Japanese scientists and engineers have either graduated from UTK or have spent some time there as post-doctoral or visiting researchers. We are eager to have other Japanese students and researchers join us in our efforts to continue to build the Polymer Science and Engineeering activity at UTK.