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July 24, 2017
Viega LLC Moves to New Headquarters in Colorado
PEX tubing manufacturer Viega LLC announced the relocation of the company’s headquarters from Wichita, Kansas, to a brand-new, $12 million facility located in Broomfield, Colorado. The new facility will feature both corporate offices and an educational facility in which they will offer various PEX training courses. Additionally, Viega will be able to show off some of their PEX technology by using it in the heating and cooling systems of their new HQ and in the snow melt system outside of the facility. The company noted fast growth in their sales for plumbing and other water uses as the reason for their expansion.
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July 6, 2017
Using Melt Flow Rate to Determine Change in Molecular Weight - by Rich Geoffroy
If there is one key property for polymers, it is molecular weight --- actually it’s the presence of the very-high-molecular weight fraction. It’s these very long molecules which give the polymer its high elongation, toughness, impact strength, long-term creep resistance and resistance to stress cracking. In semi-crystalline polymers, these long-chain molecules get captured in one or more adjacent crystalline sections and act as links (tie molecules) between the crystallites. In amorphous polymers, the chains are so long that they get severely entangled with the other molecules. Unlike short chains that can easily slip through the entangled mass (a term we define as flow), the long chains are “tied” together such that pulling on one causes all the others to resist the movement. These long chains form the “mortar between the bricks” which gives the strength to the plastic part. Of course, it’s the high molecular weight fraction which is also responsible for high resin viscosity which shows up as low extrusion rates, short injection flow lengths, and poor knit-line strengths. Also, when you “force” the material to flow, these long molecules which are carrying a disproportionate amount of the load, tend to break, therein, slightly reducing the overall molecular weight average.
When there is a failure, one often wants to determine if the molecular weight of the material is the same as that which was specified, or has it been altered during processing or in use. After all, small reductions in average molecular weight can be responsible for significant reduction in tie-molecule density, i.e., performance. There are a number of methods by which one can determine different average molecular weights --- melt rheology, solution viscosity, membrane osmometry, gel permeation chromatography (also called size exclusion chromatography), and light scattering techniques. Each has its own advantages as well as limitations, however, the one most widely used is also the simplest and often the most sensitive measurement --- melt flow rate.
As discussed earlier, a very small change in molecular weight can result in a very significant alteration of a material’s properties. Most of the other methods measure properties of the polymer which are directly proportional to the average molecular weight. Small changes in molecular weight therefore can be lost in the normal variability of the measurements. Melt flow rate, on the other hand, is exponentially related to the average molecular weight of the material such that Melt Flow is approximately equal to Molecular Weight raised to the 3.4 power. The power factor makes melt flow rate an extremely sensitive tool for measuring small changes in molecular weight.
One way to get an indication of molecular weight distribution is to measure the MFR at two or three different conditions. Melt flow rate of polyethylene is generally measured under ASTM D1238 Condition E (190°C/2.16 Kg load) --- commonly called the “melt index”. However, the MFR of polyethylene can also be measured at different conditions like Condition F (190°C/21.6 Kg load) --- the so-called “high load melt index” --- or Condition N (190°C/10.0 Kg load). By monitoring the ratio of the Condition N or F to Condition E, one can develop an index which measures the breadth of the molecular weight distribution --- the higher the ratio the broader the MWD.
Manufacturers generally “tune” their products to fall within a narrow range of melt flow rate. As we all know, MFR is a poor indicator of how the resin will actually “flow” in the machine --- products with the same MFR can result in molding difficulties on the floor. However, by measuring the MFR at these different conditions (effectively at different shear rates), one can measure differences in different batches of resins. With experience, you can set up a specification, within which the resin will be suitable for your molding. Don’t overlook the power of simplicity.
Viega LLC Moves to New Headquarters in Colorado
PEX tubing manufacturer Viega LLC announced the relocation of the company’s headquarters from Wichita, Kansas, to a brand-new, $12 million facility located in Broomfield, Colorado. The new facility will feature both corporate offices and an educational facility in which they will offer various PEX training courses. Additionally, Viega will be able to show off some of their PEX technology by using it in the heating and cooling systems of their new HQ and in the snow melt system outside of the facility. The company noted fast growth in their sales for plumbing and other water uses as the reason for their expansion.
Click to Learn More
July 6, 2017
Using Melt Flow Rate to Determine Change in Molecular Weight - by Rich Geoffroy
If there is one key property for polymers, it is molecular weight --- actually it’s the presence of the very-high-molecular weight fraction. It’s these very long molecules which give the polymer its high elongation, toughness, impact strength, long-term creep resistance and resistance to stress cracking. In semi-crystalline polymers, these long-chain molecules get captured in one or more adjacent crystalline sections and act as links (tie molecules) between the crystallites. In amorphous polymers, the chains are so long that they get severely entangled with the other molecules. Unlike short chains that can easily slip through the entangled mass (a term we define as flow), the long chains are “tied” together such that pulling on one causes all the others to resist the movement. These long chains form the “mortar between the bricks” which gives the strength to the plastic part. Of course, it’s the high molecular weight fraction which is also responsible for high resin viscosity which shows up as low extrusion rates, short injection flow lengths, and poor knit-line strengths. Also, when you “force” the material to flow, these long molecules which are carrying a disproportionate amount of the load, tend to break, therein, slightly reducing the overall molecular weight average.
When there is a failure, one often wants to determine if the molecular weight of the material is the same as that which was specified, or has it been altered during processing or in use. After all, small reductions in average molecular weight can be responsible for significant reduction in tie-molecule density, i.e., performance. There are a number of methods by which one can determine different average molecular weights --- melt rheology, solution viscosity, membrane osmometry, gel permeation chromatography (also called size exclusion chromatography), and light scattering techniques. Each has its own advantages as well as limitations, however, the one most widely used is also the simplest and often the most sensitive measurement --- melt flow rate.
As discussed earlier, a very small change in molecular weight can result in a very significant alteration of a material’s properties. Most of the other methods measure properties of the polymer which are directly proportional to the average molecular weight. Small changes in molecular weight therefore can be lost in the normal variability of the measurements. Melt flow rate, on the other hand, is exponentially related to the average molecular weight of the material such that Melt Flow is approximately equal to Molecular Weight raised to the 3.4 power. The power factor makes melt flow rate an extremely sensitive tool for measuring small changes in molecular weight.
One way to get an indication of molecular weight distribution is to measure the MFR at two or three different conditions. Melt flow rate of polyethylene is generally measured under ASTM D1238 Condition E (190°C/2.16 Kg load) --- commonly called the “melt index”. However, the MFR of polyethylene can also be measured at different conditions like Condition F (190°C/21.6 Kg load) --- the so-called “high load melt index” --- or Condition N (190°C/10.0 Kg load). By monitoring the ratio of the Condition N or F to Condition E, one can develop an index which measures the breadth of the molecular weight distribution --- the higher the ratio the broader the MWD.
Manufacturers generally “tune” their products to fall within a narrow range of melt flow rate. As we all know, MFR is a poor indicator of how the resin will actually “flow” in the machine --- products with the same MFR can result in molding difficulties on the floor. However, by measuring the MFR at these different conditions (effectively at different shear rates), one can measure differences in different batches of resins. With experience, you can set up a specification, within which the resin will be suitable for your molding. Don’t overlook the power of simplicity.
Discussion of melt flow rate and its impact on polymer molecular weight
July 5, 2017
ASTM Emerging Professionals Program
ASTM International is looking to help foster career growth for up-and-coming professionals through their Emerging Professionals Program. Members of ASTM technical committees have the opportunity to nominate and mentor these individuals for work on the committee. ASTM covers the expenses of airfare and lodging for the nominees, and also invites them to their Emerging Professionals Workshop, which covers essential knowledge on ASTM. Committee members interested in this should nominate candidates with 1-5 years of experience with ASTM standards who are either employed at a job that uses or develops ASTM standards or is a graduate student working with ASTM standards. Nominations for the first workshop are due by August 10th.
June 29, 2017
Bryan Hauger Quoted in ASTM Standardization News
The article is titled "Go with the Flow" and highlights how "ASTM committees make an impact on water systems and safety". Bryan is quoted as a representative of F17 for plastic piping alongside industry leaders for other pipe materials including clay pipe and concrete. Dr. Hauger notes the reliance of public water standards including AWWA C906 for Polyethylene Pressure Pipe and Fittings on ASTM standards for "all sorts of details, from the dimensional and performance requirements of pipe and fittings to the testing used to demonstrate conformance". Monthly readership for ASTM Standardization News exceeds 25,000 professionals distributed across all sectors of industry. Bryan added "I was really pleased that ASTM asked for my comments for their article. I have been a strong supporter of the ASTM process for standards development for more than 15 years as a highly inclusive process that creates consensus standards that are fair to industry while protecting public safety". Dr. Hauger participates in a number of North American standards writing organizations relating to plastic pipe including API, CSA Z662, CSA B137, and ASME for his company in Longmont, Colorado.
Click Here for Link
ASTM Emerging Professionals Program
ASTM International is looking to help foster career growth for up-and-coming professionals through their Emerging Professionals Program. Members of ASTM technical committees have the opportunity to nominate and mentor these individuals for work on the committee. ASTM covers the expenses of airfare and lodging for the nominees, and also invites them to their Emerging Professionals Workshop, which covers essential knowledge on ASTM. Committee members interested in this should nominate candidates with 1-5 years of experience with ASTM standards who are either employed at a job that uses or develops ASTM standards or is a graduate student working with ASTM standards. Nominations for the first workshop are due by August 10th.
June 29, 2017
Bryan Hauger Quoted in ASTM Standardization News
The article is titled "Go with the Flow" and highlights how "ASTM committees make an impact on water systems and safety". Bryan is quoted as a representative of F17 for plastic piping alongside industry leaders for other pipe materials including clay pipe and concrete. Dr. Hauger notes the reliance of public water standards including AWWA C906 for Polyethylene Pressure Pipe and Fittings on ASTM standards for "all sorts of details, from the dimensional and performance requirements of pipe and fittings to the testing used to demonstrate conformance". Monthly readership for ASTM Standardization News exceeds 25,000 professionals distributed across all sectors of industry. Bryan added "I was really pleased that ASTM asked for my comments for their article. I have been a strong supporter of the ASTM process for standards development for more than 15 years as a highly inclusive process that creates consensus standards that are fair to industry while protecting public safety". Dr. Hauger participates in a number of North American standards writing organizations relating to plastic pipe including API, CSA Z662, CSA B137, and ASME for his company in Longmont, Colorado.
Click Here for Link
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