Blog | TBL Performance Plastics

Blog

How do we Achieve Exacting Tolerances with Plastic Tubing? Lasers.

For many critical applications, it is essential that plastic tubing is produced within strict dimensional tolerance limits. Spatial measurements of a tube, such as inside diameter (ID), outside diameter (OD), wall thickness, concentricity, and overall length all play separate roles in ensuring a tube performs up to intended standards. For example, Peristaltic-pump tubing is especially susceptible to performance flaws when tubing is manufactured out of specification.

The following are three common instruments employed for measuring tubing dimensions: pin gauges, comparators, and ultrasound/ laser systems.

 

 

 

Pin Gauges

Pin gauges are metal pins of strictly calibrated diameter. When measuring a tube with pin gauges, the pin with the lower limit diameter should fit effortlessly through the inside diameter of the tubing, while that of the upper limit should not. Pin gauges are inferior as a sole means of dimensional analysis as they can not be used for continuous in-process control nor do they imply any information about a tubes outside diameter or concentricity. Samples need to be taken, and statistical methods are employed to determine the likelihood that the ID of a particular length of tubing will be within specification. Pin gauges are better utilized as a tool for post-manufacturing quality control.

Comparators

Optical comparators display an enlarged shadow image of the tubing on a display screen. The tubing is placed in a fixed position in the comparator, illuminated with light sources, and the image projected onto a display. Computer software is used to convert the coordinates of the tubing on the screen to measurements of the internal and external diameter, etc.. Comparators are not normally used on the factory floor, but are useful instruments for examining samples in the QC laboratory. Again, statistical methods are needed to determine the probability that a particular length of tubing will be within specification..

Ultrasound/ Laser Measurement Systems

A laser , such as the technology utilized by TBL Performance Plastics, allows for continuous “real time” measurement of extruded tubing as it is produced. The instrument will continuously measure and record the ID, OD, wall thickness, and concentricity, with high accuracy to ensure all critical dimensions remain within specification. In practice, the sensor output can be fed directly to the servo drive motors in the extruder, so any deviations can be immediately corrected.
Typically, a laser system consists of a controller linked to the following devices:

  • “UltraScan” Gauge – This gauge uses ultrasound to determine the wall thickness and concentricity of the extruded tubing. The ultrasound is reflected from the inner and outer tube surfaces.
  • “LaserSpeed” Detector: This is a non-contact unit, which measures the speed of the extruded tubing using lasers, from which the length produced can be calculated.

Data from the whole of the production run can be collected, and retained for subsequent audit if necessary.

Conclusions

Continuous laser measurement devices are superior to pin gauges or comparators as an in-process measurement device. However, pin gauges and comparators are valuable quality-control tools for carrying out a final check of the tubing dimensions, and to analyze which materials have a tendency to expand or shrink after they are allowed to set over time. A robust quality control system will utilize several of such methods to ensure that tubing is manufactured consistently and within specification.

So, which is better, Platinum or Peroxide?

Silicone tubing has many beneficial properties and has been utilized in medical and pharmaceutical applications for over 50 years. It is made from silicone polymers that are extruded then crosslinked and “cured” in to solid form using an assortment of curing methods. The two most common of these methods are platinum-catalyzed addition polymerization (platinum curing) [see Figure A] or peroxide-initiated free-radical polymerization (peroxide curing) [see Figure B]. Platinum-cured silicone tubing is widely accepted in applications where purity is a concern, where peroxide-cured silicone tubing typically exhibits enhanced mechanical strength.

Byproducts

It is important to note platinum curing has no byproducts. Peroxide curing does result in byproducts, which tend to be volatile organic acids [1]. Although a high-heat post-curing method can be employed to drive out many of these impurities, they are a major reason why platinum-cured silicone is often preferred for medical and FDA applications. In addition to its purity, it is sometimes favored for its inherent optical clarity, as peroxide-cured varieties tend to be a bit hazier in appearance, interfering with a user’s ability to visually inspect the contents of the tubing. The tear strength of platinum-cured silicone is usually higher due to the nature of its crosslinks.

A benefit to peroxide-cured silicones is that they typically have superior mechanical properties. In addition, they are generally less expensive. However, their use in the life-sciences industries are limited because of potential liability due to toxicity. To meet the mechanical-performance characteristics of peroxide-cured products, some manufacturers are using platinum-cured low hysteresis silicone, resulting in pump life similar to that seen with peroxide-cured tubing and high-accuracy dosing for peristaltic-pump applications.

Effect of Sterilization Methods on Mechanical Properties

There are four methods most commonly employed for sterilizing non-reinforced silicone tubing. They are electron beam (e-beam) irradiation, gamma irradiation, autoclave (steam sterilization), and treatment with ethylene oxide (EtO) gas.

Irradiation

With respect to e-beam and gamma irradiation, a study done by Adamchuk et. Al. [2] showed peroxide-cured silicone, in particular, exhibited a very significant drop in tensile strength and increase in hardness and tensile modulus (resulting in decreased flexibility), while there was a relatively small change in these values for the platinum-cured sample. Tear strength decreased significantly for platinum and peroxide cured samples, but much more so for the peroxide cured sample. According to the Second Edition of Effect of Steriliaztion Methods on Plastics and Elastomers, some grades of platinum-cured silicone can withstand up to 9 megarads radiation and not experience a significant change in mechanical properties, while peroxide-cured silicone is usually limited to less than 5 megarads [3].

Ethylene Oxide

In the same study, when treated with EtO gas, both samples actually showed an increase in tensile strength and negligible changes in tensile modulus, hardness, and tear strength.

Autoclave

In a separate study, three platinum-cured silicone samples were autoclaved 25 times using three different methods. The methods: flash autoclave (10 minutes at 132°C, at 30psi), standard gravity autoclave (30 minutes at 121°C, at 15psi), and pre-vacuum high-temperature autoclave (30-35 minutes at 121°C). No significant change in physical properties was noted [3].

Summary

For applications where high purity, critical dosing, or repeated sterilization is required, platinum-cured silicone is often the material of choice. Peroxide-cured silicone is a common choice for less demanding (in terms of purity) applications. It is commonly, but not universally, a less expensive alternative to platinum-cured silicone, and often exhibits longer pump life in peristaltic-pump applications.

Figures:

Figure A: Platinum Curing of a Silicone Polymer

platinum-cured silicone

Figure B: Peroxide Curing of a Silicone Polymer

peroxide-cured-silicone

 


Sources

1. dowcorning.com/content/publishedlit/52-1077-01.pdf

2. medical.saint-gobain.com/en/pdf/Saint-Gobain_Silicone_Sterilization_White_Paper.pdf

3. books.google.com/books?id=cvdMtLVeRq4C&pg=PA265&lpg=PA265&dq=autoclave+silicone&source=bl&ots=lggHkGLafR&sig=2ddh8ENuiOLra2d0EOFUZ9wL57Y&hl=en&sa=X&ei=6u12Ud_8MJLE9gTnioHYCA&ved=0CGQQ6AEwBw#v=onepage&q=autoclave%20silicone&f=false

Photos: Silicones-Science.com

 

 

 

 

Custom Plastic Fabrication Center Open for Business!

 

Custom Plastic Tank for Bio-Pharmaceutical

TBL Performance Plastics is pleased to announce the opening of our new corporate headquarters and our world class, expanded facility. Today we want to spotlight our high-purity custom plastics fabrication division.

Our fabrication area has been designed as a white room environment with no corrugate, cutting oils, or metal cutting allowed. The utilities that support the division exceed industry standards for purity

Over 20 Years of Plastic Fabrication Experience

The team heading up our new division has over a combined twenty years of high purity, plastics fabrication experience and are very skilled in machining, forming and advanced welding techniques. In addition, we have added to our mechanical design department to support our customers for timely concept and design approval drawings. We offer this service at no charge for qualified customers.

  • TBL maintains a wide range of stock, polyethylene, PTFE, polypropylene, and PVDF in sheet and rod.
  • Most of our stocked materials are certified to pass USP Class VI and are free of animal derivatives (ADIF).
  • We also, stock PVC and Acrylic for industrial applications.
  • TBL maintains a wide range of stock, polyethylene, PTFE, polypropylene, and PVDF in sheet and rod.
  • Most of our stocked materials are certified to pass USP Class VI and are free of animal derivatives (ADIF).
  • We also, stock PVC and Acrylic for industrial applications.

Our Capabilities Include:

 

  • Cleanroom Assembly (ISO Class 7) of Custom Carboy Tops.
  • Custom Adapters and Fittings
  • Sanitary Welds
  • 3-D Tote Carts
  • Custom Carboys/ Carboy Tops.
  • Rectangular Tanks
  • Deployment Carts
  • Funnels

 

Oina Peristalitc Pumps

TBL Plastics is proud to announce our partnership with Oina, an industry leading manufacturer and developer of peristaltic pumps. As the master distributor for our tubing products in Northern Europe, Oina has validated all of our pump-grade tubing in their pumps. With their technical knowledge and experience in the medical, diagnostic, industrial, and OEM markets. Oina is ideally suited to represent our products in these markets.

A Quote from Oina CEO, Anders Lovas:

“We have during the last year conducted TBL tube tests in multiple pump configurations and applications for several different tube dimensions with very satisfactory results. We have started selling and distributing TBL Pharm-A-Line tubes in analytical instruments, bio-reactors, process industries and pharmaceutical applications.”

Visit Oina.se or Contact Us for application assistance.


Oina Peristaltic Pumps

PVC Tubing and REACH

 

What is REACH?

The European Union has lead the way in “phasing out” many hazardous chemicals from consumer products. The vehicle for this legislation is known as REACH.

Most PVC Tubing is NOT REACH Compliant

Flexible PVC tubing, also commonly known as flexible vinyl tubing is used widely in everything from medical devices to soda and beer tubing in restaurants.

What is DEHP?

PVC tubing is made flexible by adding chemicals known as plasticizers. A phthalate compound known as DEHP remains the most common plasticizer for flexible PVC, with approximately 258 million pounds of DEHP being produced in 1994.

DEHP and Your Health

The amount of DEHP we encounter every day has compelling implications in regards to public health. In a study by the EPA, unusual lung disorders and reduced bile flow in children and infants were attributed to the use of DEHP-containing medical devices. In male rats, various problems with anatomical development of reproductive organs occur as well as decreased testosterone levels and sperm production. Also, prenatal exposure of rats to DEHP resulted in several problems including decreased birth rates and skeletal malformations.

DEHP has been classified by the EPA as class B2, a probable human carcinogen, since 1986.

REACH Compliant Since 2010

Since 2010, We have lead the industry with our REACH compliant line of ClearGreen® tubing. We lead the industry in manufacturing REACH compliant – non DEHP PVC (Vinyl) tubing.

> Get a Sample <

Silicone Sterilization

Silicone is used in a variety of medical instruments and equipment which must be sterilized before use. Three main methods of sterilization can be considered: steam sterilization (autoclave), irradiation and ethylene oxide.

Steam Sterilization by Autoclave

Steam sterilization is typically carried out in an autoclave at 121°c (250°F) for 15 minutes, although other conditions are often used (Rogers, W., 2005). Silicone tubing may start to become gummy after having being steam sterilized several times and should then be replaced.

Irradiation:

Gamma Iradiation

Gamma irradiation is widely used for sterilization of silicone tubing. However, some changes are produced in the silicone, principally an increase in cross-linking, causing an increased hardness and shape memory (Rogers, W., 2005). The latter effect may make kinking of tubing more likely. The tensile elongation of platinum and peroxide cured silicones has been shown to decrease after gamma sterilization, while the tensile strength of platinum cured silicone remains nearly the same.

Electron Beam Irradiation

Electron Beam Irradiation is an alternative to gamma rays. The physical effects are similar, but somewhat less, to those found with gamma irradiation. Again greater degradation was noted with peroxide-cured silicone than with platinum-cured silicone (Gautriaud, E.).

Ethylene Oxide

Ethylene oxide (EO) is a very effective sterilizing method for most silicone materials (Rogers, W., 2005). The ethylene oxide is adsorbed by the silicone and must be removed by post-cycle aeration before the equipment is used. Appropriate testing is required to ensure that removal has occurred. A study (McGunnigle, R.G., 1975) showed that silicone tubing adsorbed about 85% less ethylene oxide than PVC tubing or polyester / polyurethane tubing. Also, desorption of the ethylene oxide was much faster for the silicone tubing than for the other two polymers. Ethylene oxide sterilization was found to have no significant adverse effects on platinum or peroxide cured silicone (Gautriaud, E.), so it is recommended in most cases for these materials. Since ethylene oxide is a toxic, carcinogenic gas, appropriate safety measures should always be in place.

Other Methods

Liquid sterilizing chemicals such as glutaraldehyde are sometime used. It is not clear if these are suitable in general for silicone medical equipment. Also, ozone is a highly toxic gas that can be used for silicone sterilization, but it can be less penetrating than ethylene oxide, only sterilizing surfaces.

Conclusions

Ethylene oxide is widely recommended to sterilize platinum and peroxide cured silicone. Irradiation or steam are also commonly used, but these methods should be considered on a case by case basis in order to not risk compromising critical material properties which ensure capabilities such as critical dosing in peristaltic pumps. Platinum-cured silicone is widely preferred to peroxide cured silicone where purity is a concern. However, peroxide cured silicones tend to have longer life in certain peristaltic pump applications. From the most exacting critical dosing to not so critical applications there are several types of silicones availabe to meet your specific needs. Contact your TBL Plastics representative for tailored recommendations about your process and technical information about our platinum cured silicone tubing or platinum cured silicone gaskets.

References

McGunnigle, R.G. et al (1975), “Residual ethylene oxide: levels in medical grade tubing and effects in an in-vitro biologic system”, Journal of Biomedical Materials Research, 9 (3), p.273-283. Palsule, A.S., Clarson,

S.J. & Widehouse C.W., (2008), “Gamma Irradiation of Silicones”, Journal of Inorganic and Organometallic Polymers and Materials, 18 (2), p.207-221. Rogers, W. (2005), Sterilisation of Polymer Healthcare Products, Shrewsbury: Rapra Technology.

Gautriad, E. et al. “Effect of Sterilization on the Mechanical Properties of Silicone Rubbers”

Difference Between LDPE and LLDPE Tubing

 

What is the Difference Between LDPE and LLDPE?

Low Density Polyethylene (LDPE) and Linear Low Density Polyethylene (LLDPE) are both inexpensive polymers with widely favorable mechanical and chemical resistance properties. Tubing made from both polymers is broadly used, particularly for water, chemicals and gases. Unlike with many other plastics, plasticizers are seldom necessary to obtain flexible products, such as tubing. Both plastics are highly stable with low toxicity. In fact, many grades can even be used for food-contact and medical applications.

LDPE is a homopolymer constituted by ethylene monomers. LLDPE is a copolymer of ethylene and another longer olefin, which is incorporated to improve properties such as tensile strength or resistance to harsh environments. One of four α-olefins (1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene) is commonly polymerized with ethylene to make LLDPE. The amount of the α-olefin is typically low compared to the amount of ethylene.

Which Makes Better Tubing?

LLDPE tends to have greater environmental stress-crack resistance ESCR than LDPE. It has been reported (Wypych, G., 2003) that outdoor LDPE pipes are readily affected by environmental stress cracking. It is stated that the resistance of LDPE can be “improved by a substantial addition of LLDPE (30-40%).” LLDPE also has a higher tensile strength than LDPE and greater puncture resistance (Robertson, G.L., 2006). Since LDPE is a weaker tubing than LLDPE a thicker wall grade can be chosen to compensate, but this has cost implications if a large amount of tubing is required. Flexibility is also affected negatively by a greater wall thickness.

LDPE also has advantages as it is more transparent than LLDPE (Robertson, G.L., 2006), which may be advantageous if visualization of the conveyed fluid is important. It also tends to be more flexible. The performance of LDPE can be greatly improved by incorporating it into a two-layer tube. A flexible polymer such as EVA can be used as the outer layer, while the chemically inert LDPE makes up the inner layer. We have taken advantage of such a “co-extrusion” in our Pharm-A-Line VI & Pharm-A-Line XL Polyethylene-Lined EVA tubing.

Read more about our LDPE and LLDPE tubing.

Conclusions

For most applications LLDPE tubing is preferred, as it is stronger than LDPE. LDPE may often be chosen where flexibility is a factor or if a more transparent tube is needed. LDPE performance is greatly improved when it is used as an inner layer with a more flexible polymer as the outer layer.

References

Robertson, G.L (2006). “Food Packaging, Principles and Practice”, Boca Raton: CRC Press.

Wypych, G. (2003). “Handbook of Material Weathering” 3rd ed. Toronto: ChemTec Publishing.