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COMPLETELY MICROBIAL POLYESTERS:  POLYHYDROXYALKANOATES 

Microbial polyesters were mentioned briefly in a post titled BIOBASED FEEDSTOCKS (created 17 November 2018).  The present post will cover one class of these materials, whose importance and range of applications are growing rapidly as the polymer industry continues to strive for increased sustainability, in greater detail.

THERMOPLASTIC ELASTOMER ULTRASOUND TRAINING MODELS

Ultrasound imaging has rapidly become one of the most commonly used diagnostic methods of modern medicine over the last several decades.  The image shown below is reproduced from a radiology information website for patients.  Ultrasound imaging uses sound waves to produce images of the inside of the body.  It is used to help diagnose the causes of pain, swelling, and infection in the body’s internal organs, to examine a baby in pregnant women, and to examine the brain and hips in infants.  It is also used to help guide biopsies, diagnose heart conditions, and assess damage after a heart attack.  It is, therefore, used in many different medical specialties, to test for conditions involving most parts of the human anatomy.  It is safe and noninvasive, and it does not use ionizing radiation.

RESIDUAL STRESS CAUSED BY SHRINKAGE OF THERMOSET POLYMERS

This post is based on the discussion of its topic by J. Bicerano, Prediction of Polymer Properties, third edition, Marcel Dekker, New York, 2002, as supplemented by the additional information and literature cited below.

The coefficient of linear thermal expansion β simply equals one third of the coefficient of volumetric thermal expansion α for an isotropic (non-oriented) material:

SHRINKAGE OF COTTON TEXTILES

More than 90% of a cotton fiber consists of cellulose.  The exact percentage of cellulose in a specific cotton fiber sample depends on whether the fiber is wet or dry, and on how much effort has been made to extract the non-cellulosic components.  For example, when it is equilibrated at 65% relative humidity at 20 oC, cotton contains slightly more than 7% of absorbed water by weight.  Hence the percentage of cellulose in a cotton fiber can range anywhere from just a little over 90% (wet, and with none of its non-cellulosic components extracted) to >99% (dry, with most of its non-cellulosic components extracted). 

SOFTWARE FOR MATERIALS MODELING AND SIMULATION

The multidisciplinary and integrated modeling approach often pursued in industrial modeling and simulation was introduced, and the multiscale modeling paradigm usually preferred for such work was summarized, in a post titled MULTISCALE MODELING AND SIMULATION IN INDUSTRY (created 17 November 2018).

The present post takes the discussion one step further by presenting overviews of the materials modeling and simulation software programs that are commercially available from four leading developers of such software.  The images shown in each section are reproduced from the product literature of the software developer that is being discussed in that section.

SELECTION OF MOLECULARLY IMPRINTED POLYMERS

By definition (see Vasapollo et al.), “Molecular Imprinting Technology (MIT) is a technique to design artificial receptors with a predetermined selectivity and specificity for a given analyte, which can be used as ideal materials in various application fields.  Molecularly Imprinted Polymers (MIPs), the polymeric matrices obtained using the imprinting technology, are robust molecular recognition elements able to mimic natural recognition entities, such as antibodies and biological receptors, useful to separate and analyze complicated samples such as biological fluids and environmental samples.”  Readers interested in gaining a broad general understanding of MIPs are recommended to study this excellent open access review article. 

HALLOYSITE CLAY NANOTUBES

Most natural clays consist of stacks of clay nanoplatelets that can be separated from each other (exfoliated).  A vast amount of literature exists about all aspects of the science, technology, and applications of platy clays.

Halloysite, by contrast, consists of bundles of clay nanotubes that can be separated from each other (exfoliated).  It is found in much fewer locations than platy clays.  It is much less familiar than platy clays.  Its applications are at an earlier stage of development than the applications of platy clays.

CERAMICS DERIVED FROM POLYMERIC PRECURSORS

Most ceramics manufacturing processes involve the step of sintering to densify compacted powder samples (green bodies) to form a continuous 3D structure and thus to get ceramic pieces appropriate for the selected application.  Sintering generally requires the use of extremely high temperatures (>>1000 oC) so that it is energy-intensive.  Hence the production of ceramics from formulations that provide fabricated articles possessing excellent properties without requiring the use of such extremely high processing temperatures is an area at the frontiers of materials R&D.

COMPOSITES REINFORCED BY 3-DIMENSIONAL WOVEN FABRICS

In the vast majority of the fiber-reinforced composites used today, individual layers (plies), where each ply contains unidirectionally oriented continuous fibers in a polymer matrix, are stacked with different angles to form laminates.  There is no reinforcing fiber between adjacent plies in such laminates so that they are held together solely by the matrix polymer.  This conventional laminate layout is illustrated in the image below which is reproduced from slides posted by Professor André Preumont from the Université Libre de Bruxelles, Belgium.

BIOPOLYMER AEROGELS

By definition, “an aerogel is an open-celled, mesoporous, solid foam that is composed of a network of interconnected nanostructures and that exhibits a porosity (non-solid volume) of no less than 50%.”  In practice, an aerogel is the dry, low-density, porous, solid framework of a gel, isolated intact from the gel’s liquid component.  The diameters of the open cells may range from <1 nanometer (nm) up to 100 nm and are usually <20 nm.  Most aerogels exhibit 90% to 99.8% porosity.  Aerogels have been manufactured from silica, metals, metal oxides, semiconductor nanostructures, organic polymers, biopolymers, carbon, and carbon nanotubes.  Silica is used most often as the material in commercially sold aerogel products today.  With a porosity of 99.98% and a density of 0.0011 g·cm-3, a specially formulated silica aerogel is the solid material of lowest density that has ever been produced.

BIOHYBRID WEARABLES AS SMART TEXTILES

By definition (see Syduzzaman et al.), “smart textiles are … textiles that can sense and react to environmental conditions or stimuli, from mechanical, thermal, magnetic, chemical, electrical, or other sources.  They are able to sense and respond to external conditions (stimuli) in a predetermined way.

SELECTION OF DENDRIMERS AND HYPERBRANCED POLYMERS

By definition (see Abbasi et al.), “dendrimers are nano-sized, radially symmetric molecules with well-defined, homogeneous, and monodisperse structure that has a typically symmetric core, an inner shell, and an outer shell.”  Hyperbranched polymers differ from dendrimers by their lack of the perfect branching pattern found in dendrimers.  Dendrons, which are monodisperse molecules that branch out from a single focal point, are used in preparing dendrimers.  An anonymous presentation provides a concise overview.  See also Gupta and Nayak and Agrawal and Kulkarni for additional open access review articles.

PRODUCT DEFORMULATION AND REVERSE ENGINEERING

There are many reasons for which a client may need product deformulation services.  Examples include the desire to learn about a competitor’s product for purposes of reverse engineering, the need to assess whether a competitor may be infringing on one’s composition of matter patents, and even the need to learn about the details of one’s own product so that one can continue manufacturing it after the death of a key employee who knew all the details but did not keep comprehensive and up to date records.

BIOBASED FEEDSTOCKS

Many plants, animals, microorganisms, and fungi are biobased feedstock sources for obtaining and/or deriving monomers, oligomers, polymers, and/or biofibers.

While biobased feedstocks still comprise only a very small percentage of the feedstocks used by the polymer industry, their usage is growing much faster than the usage of petrochemical feedstocks so that they are certain to become increasingly important over the years.  For example, in 2014, it was estimated that the revenues of the global plastics industry had ~2.8% annual growth rate, while its biobased portion comprised less than 0.5% of the total revenues of the plastics industry but had ~15% annual growth rate.

MULTISCALE MODELING AND SIMULATION IN INDUSTRY

New product and process development in an industrial setting requires attention to a variety of sometimes contradictory considerations.  These considerations include formulation design, product performance targets, materials and processing costs, market trends, and governmental regulations.  The relevant materials science also encompasses many phenomena.  Hence a multidisciplinary and integrated modeling approach is desirable.  The multidisciplinary nature of industrial modeling is illustrated schematically in Figure 1, which is reproduced from J. Bicerano et al., "Polymer Modeling at The Dow Chemical Company", J. Macromol. Sci. - Polymer Reviews, 44, 53-85, 2004.   

THERMOSET IN-MOLD FINISHING FILM

In-mold coating (IMC) generally involves the production of a coated molded article by means of a process in which a coating film is inserted into a mold and then a resin is injected into the mold to perform injection molding, thereby transferring the coating resin of a transfer layer provided in the coating film onto a surface of the molded article. 

In-mold decorating (IMD) generally involves the production of decorated molded article by means of a process in which a decorative film is inserted into a mold and then a resin is injected into the mold to perform injection molding, thereby decoratively transferring the pattern of a transfer layer provided in the decorative film onto a surface of the molded article.

LIFE CYCLE ASSESSMENT

Life Cycle Assessment (LCA) is a tool used in assessing the environmental impacts of a new product by considering these impacts through all stages of its life.  It is crucial to perform a comprehensive LCA before introducing a new product if the product is being claimed to be more sustainable and hence more beneficial to the environment than the incumbent products.  While the results of the LCA often validate such claims, in some instances LCA shows that a product that appeared superficially and/or intuitively to be more sustainable is actually less sustainable or at best comparable to the incumbent products. 

TRADEOFFS IN OPTIMIZATION OF PROPERTY COMBINATIONS

The fundamental factors affecting various polymer properties make it difficult to obtain some combinations of properties simultaneously.  For example, requiring a thermoset to have extremely high stiffness, strength, toughness, and heat resistance simultaneously tends to increase its brittleness, so that price-versus performance tradeoffs are often made.

OBJECTIVE EVALUATION OF FABRIC HAND

Subjective sensory perceptions of sheet-type fibrous products (such as woven and knitted fabrics, nonwovens, paper products, leathers, and other such products) in contact with the human skin during use have long been recognized as being among the most important quality attributes for such products.  It has, however, been very difficult to evaluate such perceptions, which often play a decisive role in the extent of customer satisfaction with such products, objectively by using instrumentation.

SOURCING OF MATERIALS AND SUPPLY CHAIN MANAGEMENT

There are three different general approaches for selecting and sourcing materials for use in formulations and compounding: (a) Internal sourcing of materials, (b) sourcing of materials from suppliers, and (c) use of formulation and compounding service providers. 

COMPOSITE REPAIR SYSTEMS FOR FLUID SYSTEM COMPONENTS

Fluid conduit assemblies, such as pipelines and hydraulic circuits, are used to transport an assortment of fluids, such as water, oil, various natural and synthetic gases, sewage, slurry, hazardous materials, and the like.  Similar structures are utilized for transmitting electrical and fiber optic cabling across vast expanses of land in establishing telecommunication networks.  The most commonly used conventional methods for repairing damaged fluid system components, such as carrier pipes, include the replacement of the component or the welding of a repair sleeve over the damaged section of the component.

STRUCTURAL COLORATION

Dyes and pigments are chemical colorants.  They are commonly used to impart color to objects.  The major difference between dyes and pigments is that dyes have much finer particle sizes than pigments.  Dyes, in which the coloring matter is dissolved in liquid, are absorbed into the material to which they are applied.  Pigments, on the other hand, consist of extremely fine particles of ground colorant suspended in a liquid which forms a paint film, with this paint film bonding to the surface to which it is applied.

POLYCARBONATE POLYOLS

The two major components of polyurethane formulations are a polyol component and an isocyanate component.  Polyether polyols and polyester polyols have been used as the polyol component in polyurethane formulations for many decades.  They remain the most commonly used polyols.  Vast numbers of polyether polyols and polyester polyols, optimized to provide different combinations of behavior during fabrication processes and performance characteristics of fabricated articles, are available from many different manufacturers.

USE OF BIOPRINTING IN REGENERATIVE MEDICINE

Additive manufacturing, which is more commonly (but less accurately) known as 3D printing, involves the building of three-dimensional (3D) objects by adding successive layers of materials.  Many different types of materials, including polymers, metals, concrete, and ceramics, can be used in 3D printing processes. The techniques and equipment available to perform 3D printing are improving rapidly as 3D printing progresses towards fulfilling its promise to revolutionize many areas of industry.

OVERVIEW OF PROPERTIES OF POLYMERIC MATERIALS

Predictions of Polymer PropertiesThis post is based on the discussion of polymer properties by J. Bicerano, Prediction of Polymer Properties, third edition, Marcel Dekker, New York, 2002. 

The properties of a polymer fall into two general classes.   Material properties are mainly related to the nature of the polymer itself.  Specimen properties are primarily consequences of the size, shape and layout of the finished specimens prepared from that polymer, and the process used to prepare these specimens.

MATERIAL SELECTION CASE STUDIES

This post provides insights, with the help of three anonymous examples, into how we help clients with challenges involving material selection.  The required behavior during the fabrication process and the end use performance characteristics are defined first.  Price is also usually an important consideration, although in a few instances there have been applications of such high value that material price was not a factor.  Potential candidate materials are selected based on the specified processing, performance, and price criteria.  Samples are then obtained from material suppliers for experimental evaluation.

THERMOREVERSIBLE CROSS-LINKING

Melt processing techniques (such as injection molding and extrusion) are applied readily to thermoplastic polymers, and are in fact the most commonly used thermoplastic polymer processing techniques.  By contrast, melt processing techniques cannot be applied to thermoset polymers, since thermoset polymers comprise a three-dimensional network of covalent bonds so that they are unable to melt and flow.

POLYMER RECYCLING TECHNOLOGIES

Efforts to recycle post-consumer polymer products and factory scraps are gaining momentum worldwide with the growing global emphasis on sustainability.  Work in this area includes not only the collection of growing percentages of post-consumer polymer products and factory scraps but also the development of more advanced recycling technologies.

Most of the technologies for recycling post-consumer polymer products and factory scraps fall into one of four major categories; namely, mechanical recycling, chemical recycling, combined mechanical/chemical recycling, and thermolysis.

SHEAR VISCOSITY OF DISPERSIONS OF PARTICLES IN FLUIDS

The difficulty of processing filled materials is often a limiting factor in advanced materials development because of the large increase that often occurs in the shear viscosity (η) of the starting fluid when fillers are added into it. 

It is widely appreciated that η tends to rise rapidly with increasing filler aspect ratio (Af) and volume fraction (Φ).  Moreover, the increase in η for fluids containing highly anisotropic filler particles is sometimes much larger than the increase in stiffness and strength for the same filler particles dispersed at the same η in a solid polymer matrix, making it difficult to incorporate as much nanofiller as one would wish to incorporate. 

NANOCOMPOSITE BEADS VIA SUSPENSION POLYMERIZATION

Suspension polymerization is the preferred technique for manufacturing spherical polymeric beads ranging from about 50 microns to several millimeters in diameter by starting from many monomers.  Hydrocarbon droplets, containing the monomer(s), are suspended in an aqueous medium and then polymerized, with agitation (usually by stirring) to maintain the two-phase system during polymerization, resulting in spherical polymeric beads.  Hence each hydrocarbon droplet is like a mini-reactor in which bulk polymerization is occurring.  The formulation often also includes one or more oil-soluble initiator(s) as well as one or more additive(s) helping stabilize the suspension and controlling its rheology.

ACTIVE DESIGN OF EXPERIMENTS

Many independently adjustable formulation and processing variables often affect the performance characteristics of a product in a very complex and nonlinear manner.  These dependencies sometimes also feature interactions between different independent variables.  Data mining techniques are rapidly becoming powerful tools in optimizing such systems.  This article introduces one such technique.

COMPATIBILIZATION OF IMMISCIBLE POLYMERS

This post is based on information provided by (1) J. Bicerano, Prediction of Polymer Properties, third edition, Marcel Dekker, New York (2002) which is also the source for the image shown below; and (2) J. Bicerano, A Practical Guide to Polymeric Compatibilizers for Polymer Blends, Composites and Laminates, SpecialChem, December 2005.

The morphology of a polymer blend is the outcome of the competition between the drive towards thermodynamic equilibrium and the kinetic barriers that must be surmounted to achieve thermodynamic equilibrium.  The morphology expected on the basis of the thermodynamic equilibrium phase diagram is attained in many instances.  Kinetic barriers prevent thermodynamic equilibrium from being attained and instead “freeze in” a metastable morphology induced by the processing conditions in many other instances.

A PLANT-BASED RENEWABLE ALTERNATIVE TO PET

The development of biobased versions of or biobased alternatives to major polymers, providing comparable performance, is a major area of research and development in the quest to improve the sustainability of the polymer industry.  A biobased version of a polymer has the same repeat unit structure as the original polymer, but it uses biobased (and hence renewable) monomers rather than fossil fuel based monomers as its materials of construction.  A biobased alternative to a polymer uses biobased monomers as its materials of construction and also has a different repeat unit structure than the original polymer.

PERFORMANCE VERSUS PRICE

This post is based on a section from J. Bicerano, A Practical Guide to Polymeric Compatibilizers for Polymer Blends, Composites and Laminates, SpecialChem, December 2005.  The two figures shown in this post are reproduced from this article.

As an empirical rule, if a polymeric product remains a commodity material competing for use in commodity-type applications, the price that the average customer is willing to pay will only increase proportionally to the logarithm of the improvement in its performance:

Price2 ≈ Price1 + cּ ln(Performance2/Performance1)

In this equation, Price2>Price1, Performance2>Performance1 are the corresponding performance levels, “c” is a positive proportionality constant, and “ln” is the natural logarithm.  See Figure 1 for a schematic illustration.  This equation can be generalized readily to more complex cases where the overall “desirability” for a particular application depends on several performance criteria that have different levels of relative importance.

HEAT DISTORTION TEMPERATURE

The "heat distortion temperature" (HDT) is often used in the product literature of commercial polymers as an indicator of the mechanical softening temperature.  The alternative names “heat deflection temperature” (also represented by the acronym “HDT”), and “distortion temperature under load” (DTUL) are also sometimes used for this property. 

OPTIMUM MOLECULAR WEIGHT RANGE FOR THERMOPLASTICS

The average molecular weight between chain entanglements, Me, of a thermoplastic polymer is of great importance in determining both its melt rheology and its mechanical properties.

The melt viscosity, which determines the ease of processing via fabrication methods such as extrusion and injection molding, increases with increasing Mw/Mcr ratio, where Mw denotes the weight-average molecular weight and Mcr≈2Me is the critical molecular weight.  Increasing melt viscosity means more difficult melt processing.

Call Bicerano & Associates Consulting, LLC at (912) 235-2238 or use our online form or email us at info@polymerexpert.biz today!

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