When it comes to 3D printing, the sky is the limit. As 3D printing technology continues to advance, applications can be as far reaching as airplane and automobile parts to medical devices and even anatomically correct, biocompatible models. Although 3D printing technology is developing at a rapid pace, the technology itself is not new. It emerged in the 1980s as a means of creating rapid prototypes. In recent years the applications for 3D printed models have evolved with the available hardware, software, and printable materials. Evolving technology, paired with the creative and innovative minds of scientists, engineers, and physicians, has been the launching pad for developments within 3D printing technology specific to healthcare. One way 3D printing technology is poised to create better patient outcomes is in creating an anatomically and patient-specific models to aid in surgery and medical procedures. With the capability to 3D ...
Basketball analogies are among Polymer Solution CEO Jim Rancourt’s favorites. Watch for his upcoming post that celebrates science and free throws this March Madness season.
Not all people are the same. Some are tall, some are short, and the rest are somewhere in between. Average heights vary by country. For example, the tallest people come from the Netherlands, with an average height of 6 feet for men, followed by people from Sweden, Norway, Finland, and Estonia. The shortest people live in Indonesia, Cambodia, and the Philippines.
Our height is defined by both genetics and lifestyle, and at some point in our history, people of a certain height had a survival advantage. Nowadays height still matters, for example in sports.
Take horse racing. Most jockeys range from 4 feet, 10 inches to 5 feet, 6 inches. Or take basketball. Male professional players range from 5 feet, 6 inches to 7 feet, 7 inches, with an average of about 6 feet, 7 inches. The average height of the players matters, and so does the height range. But, in a team sport, each player has his role, and even in basketball height is not everything, because what matters is how the team plays together — especially during March Madness!
It’s the Same With Polymers
What does all of this have to do with polymers? Polymers also play as a team, although most often there are no roles assigned (unless we think of composite materials). In homogenous polymer materials, each polymer chain does the same thing as the next. The length of a polymer chain is defined by molecular weight, and the range of various lengths is characterized by molecular weight distribution.
Many properties of polymers depend on their molecular weight, with high molecular weights resulting in extremely tough and inert polymers, such as ultra high molecular weight polyethylene (UHMWPE), which is used for medical implants and armor. On the other end, low-molecular weight polymers are often viscous or waxy liquids.
Testing Methods
There are several ways to determine the molecular weight of a polymer, including:
- Gel permeation/size exclusion chromatography, which separates the polymer molecules in solution based on size or hydrodynamic volume, using a chromatography column packed with porous beads. Smaller molecules enter the pores more easily and are retained longer. Larger molecules cannot enter the pores and are eluted quickly. Gel permeation chromatography gives a clear picture of molecular weight distribution, and obviously it can be applied to soluble polymers.
- Dilute solution viscosity, which measures the viscosity of a polymer solution at a certain temperature and is expressed as relative, inherent, or intrinsic viscosity. Viscosity of the polymer solution corresponds to the molecular weight of the polymer.
- Rheology, which is the study of a polymer’s flow. To perform a melt rheology test, the polymer is melted and examined. What is measured? The main parameters measured are viscosity, stress-strain relationship, and elongation. The behavior of polymers as they melt is important to predict extrusion behavior. Rheology behavior can be used as a characteristic of the molecular weight, and to perform quality control and batch analysis.
- Melt flow index, which measures the ease of flow of a melted thermoplastic polymer. Melt flow rate is an indirect measure of molecular weight, with high melt flow rate corresponding to low molecular weight.
Size Matters in Processing
Molecular weight characterization of polymers is important for polymer processing, such as the preparation of fibers and films for extrusion and molding. For polymers of a similar chemical composition, the difference in molecular weight will define their properties, such as impact resistance, tensile strength, or biodegradability rate.
The other important parameter is molecular weight distribution, because if you want the material to be uniform, the polymer chains have to behave as one. Take an example of biodegradable polymers. If you are making an implantable medical deviceand you need it to be structurally stable for a certain length of time to support, for example, a growing bone, you can’t have a mix of faster-degrading short chains and slower-degrading long chains. Why not? Because they play as a team, and every team member matters. If one is weak, the whole structure becomes weaker. How do you make the polymer team stronger and more uniform? Certainly there are ways, such as living polymerization, but this is a topic to be addressed in a separate post!
Comments
Post a Comment