Plasticizers

Plasticizers

Abstract

Plasticizers, when added to materials, make them more flexible and pliable as well as making them easier to process. In many medical and life science applications, these materials are vital to the effectiveness of the materials. Throughout these fields, there are many applications for plasticizers. Understanding these applications makes it easier to choose the right plasticizer for each material and application, ensuring more effective materials for use in these industries. 

History

Humans have been adding plasticizers in the forms of oils and waxes to polymers for centuries to improve their flexibility and pliability. Many plasticizers have made incredible advances possible in the field of plastics. When plastics were first produced, they were very hard and inflexible as well as being very brittle. 

Due to the introduction of plasticizers, however, it has become easier than ever to use plastics in a variety of common products. It’s no longer necessary, for example, to purchase milk in glass bottles. Plasticizers have made many common food storage options a reality, from cling wrap to microwaveable containers. 

In addition to improving the flexibility of plastics, plasticizers also make plastics usable at very low temperatures. Plasticizers are also commonly used in photography and a variety of industrial applications. This ubiquitous product is, in fact, so familiar that it is a critical part of many homes and businesses--and many people don’t even realize which plasticizers can be found in the items that they use every day. 

Plasticizer Uses

Plasticizers are used across a wide range of industries. They are typically used to create flexible vinyl products, which may include everything from floor and wall coatings and roofing membranes to cable and wire coverings and medical devices. 

Plasticizers are also widely used in adhesives, sealants, and other commonly-used materials. The use of plasticizers is carefully regulated, particularly in Europe; however, thanks to these stringent regulation requirements, these critical materials come to the companies that use them prepared for the type of hard use necessary in many environments. 

Types of Plasticizers

Primary plasticizers are components that improve the elongation and softness of the plastic. Typically, primary plasticizers are compatible enough with the initial polymer or resin that they can be used on their own in order to create this effect. 

Secondary plasticizers, on the other hand, are usually combined with primary plasticizers in order to enhance the compatibility of the primary plasticizer or improve its effect on the material in question. Secondary plasticizers, which can also be known as extender plasticizers, may not have enough affinity for the resin or polymer in question to act on their own. 

There are several types of plasticizers that are used on a regular basis in many industries, particularly medical devices and life sciences applications. 

Adipates

Adipates are typically food grade and can, therefore, be used in the packaging of foods and other materials intended for consumption. Adipates are often used when low-temperature flexibility is desirable, though they are not as effective as sebacates. They are also resistant to ultraviolet light. They are clear and have an odor that is barely noticeable during production. 

Most adipates do need to be stored in areas free from atmospheric moisture in order to avoid degradation of the product over time. Adipates include: 

  • 79A
  • DOA
  • DIOA
  • DINA

Citrates

Citrate-based plasticizers are rapidly finding a place as a replacement for traditional products which were formerly based on crude oil. They are often suitable for both biobased plastics and traditional plastic products, making them a versatile solution for many applications. Citrates are suitable for a variety of purposes; thanks to their low toxicity, they are often used for medical-grade products, food packaging, and pharmaceutical coating. 

Citrates are also frequently used as sealants and adhesives. When citrates are used as a plasticizer, gamma irradiation can be used to sterilize the products. Citrates include:

  • TBAC
  • TBC
  • GTA
  • TEAC

Phosphates

Phosphate esters are commonly used when additional flame retardation is needed in the finished product. They are frequently used in the adhesive and sealant industry, where this property is of utmost value. Autoclave sterilization is a common method for sterilizing materials made with this plasticizer. Thanks to their high price tag, phosphate esters are not used as frequently in other industries, particularly when their flame retardant properties are unnecessary or other materials are suitable. Common phosphates include:

  • DDP
  • TOF
  • TCP

Phthalates

Phthalates are the most common form of plasticizer. They are also the most cost-effective, which is part of the reason why they are the plasticizer of choice in many medical and surgical materials made of PVC. This common product is used in a wide range of applications, including many in the medical field: pharmaceutical coatings, catheters, blood transfusion devices, lubricants, and more. 

Outside the medical field, phthalate plasticizers can be found in products like caulk, paint, children’s toys, detergents, waxing, inks, and even food products. Many who appreciate cosmetic products will be interested to know that phthalates are often found in eye shadow, moisturizer, hairspray, nail polish, and more. This common additive, in fact, is used nationwide on an incredible level, with high levels of consumption that make it obvious that phthalates are a vital part of many industries. 

Phthalates are typically sterilized using autoclaves, though gamma irradiation is also an effective method for sterilization depending on the other components of the finished material. Common phthalates include:

  • DEHP
  • DINP
  • DIDP
  • DPHP
  • DBP
  • BBP
  • BOP
  • DHP
  • DIHP
  • DOP
  • DIOP
  • DCP
  • DIUP
  • UDP
  • DTDP

Sebacates

Sebacates, which perform even better in low-temperature environments than adipates, are commonly used for materials that will be used in outdoor industries. Thanks to their freeze resistance, sebacates are frequently found in materials that need to be flexible at lower temperatures in addition to synthetic rubbers, food packaging, and medical supplies. Sebacates are used to plasticize PVC, chloroethylene polymer, cellulose nitrate, ethyl cellulose, and synthetic rubber.  This material can be sterilized by using ethanol or through gamma irradiation. Common sebacates include:
•    DMS
•    DBS
•    DOS
•    DIDS

Trimellitates

Trimellitates are known for their low volatility and low migration. This makes them the ideal product for applications in higher-temperature conditions where migration could be a problem. With the right additives, trimellitates can be used to sustain color over a longer period or to increase extraction resistance. 

These bio-based plasticizers are commonly found in automobile interiors, medical tubing, and photograph storage as well as wire and cable insulation, where its low volatility can be of supreme importance. Trimellitates are sterilized by gamma irradiation. Common trimellitates include:

  • NODTM
  • TOTM
  • TIOTM
  • TINTM

Environmental Concerns

In recent years, many individuals have become concerned with the use of plasticizers and their ability to be released both into the environment and into individuals. Thanks to stringent requirements on these products, there is little threat to either the environment or to individuals who have chosen to use these products. Their continued use in medical-grade products continues to be safe for the individuals who have need of those materials. 

Fortunately, there are also more bio-friendly options available for many items using plasticizers, including both citrates and trimellitates. These products are biologically based and may be more comfortable for individuals who are concerned with the properties of other plasticizers. Those plasticizers that have been approved for regular use, including the hotly-contested phosphates, must pass stringent requirements, making most individuals safer than they think. 

Regular investments in research and development in this vital sector have helped make plasticizers safe for use, ensuring that their applications are able to continue. Plasticizers must also meet key availability and cost regulations in order to make their way into the public sector, which is part of the reason these key plasticizers are the most common on the market. Selecting the right one for each application is critical for individuals who want to ensure that they’re getting the best performance out of their plasticizer. 

Phthalates in Medical Applications

When it comes to medical applications, DEHP tops the list. As the only phthalate listed by the European Pharmacopoeia as a recommended substance for a variety of medical uses, DEHP is an incredibly useful phthalate that allows for the production of a variety of items, including:

  • Disposable medical items
  • Blood bags
  • Tubing
  • Devices used for infusion
  • Feeding tubes
  • Urine bags
  • Gloves
  • Catheters
  • Drain tubes and bags
  • Surgical items

In many cases, plasticizers may make up as much as 20-40% of these common medical materials by weight. Feeding tubes, which need to be highly flexible, may have as much as 80% of their weight made up of plasticizers. 

In recent years, several alternatives to DEHP have become available. These alternatives, however, have not been tested as fully as DEHP, leading to reluctance in many production facilities to make the change. The substitution of alternative plasticizers can also lead to a high-cost increase in a variety of products that are currently relatively inexpensive to make and are readily available to many medical professionals. 

In some cases, substitutions may also lead to a less-flexible material that fails to meet the needs of the medical professionals using them. However, DEHP is used as the plasticizer of choice for PVC in the medical device field. Without it, PVC would be hard and brittle. 

Plasticizers in Life Sciences

Plasticizers have a wide range of applications in life sciences, as well. They are found in a number of materials that are used every day, including:

  • Culture dishes
  • Cell culture flasks
  • Bioreactors
  • Chemical and pill containers
  • Pipettes
  • Tubes
  • Hoses
  • Vials
  • Packaging

Plasticizers have a wide variety of uses that make them critical to the current production of many materials. Without them, PVC would simply be too fragile for use in many of its current applications. Other materials might be too brittle, too hard, or impossible to mold. Without plasticizers, it would be impossible to create some of the rubber compounds that are most commonly used in a variety of applications. Realistically speaking, the introduction of plasticizers has had a huge impact on the field of plastics in general, making it possible to use them in a variety of applications that would have otherwise been impossible. 

Plasticizer Migration

One of the biggest concerns with the use of phthalates in many medical devices is the potential for migration. Patients undergoing extended procedures such as multiple blood transfusions or long-term dialysis treatments are at the greatest risk of exposure to DEHP. While studies in lab animals have shown adverse effects in liver toxicity and reproductive systems, the ability of the compound to affect humans is still of great debate within the scientific and regulatory communities. 

Neonatals are assumed to be at heightened risk due to their small size and need for medical care at birth. There have not been adequate studies performed to determine with any degree of certainty if the exposure poses a detriment to their health. Most Neonates receive IV fluids via a syringe infusion pump rather than gravity feed, lessening the possibility of exposure, however. 

DEHP exposure is most common in children sucking, mouthing or chewing on plastic toys. However, it has been assessed to have low acute toxicity and the risk is deemed minimal. 

In addition to toxicity concerns associated with migration, another concern is regarding the migration of plasticizers from flexible PVC material to rigid, non-PVC material, such as from flexible tubing to a connector or fastener. The migration can act as a softener where the two come into contact, causing degradation of the rigid connectors by environmental stress cracking or crazing 

The concern surrounding plasticizer migration continues to receive scrutiny and calls to find a replacement material is coming from medical device manufacturers which may lead to the removal of this material from numerous medical products. Many medical supply production facilities have begun to address the need to replace DEHP with a plasticizer that can perform similarly without adverse health risks. In order to fully weigh the risk of migration, however, there are several things that must be considered:

  • Many phthalates are known not to cause damage over short-term use, especially the type of short-term use that is common in common medical settings.
  • There is a wide range of products available that are not currently regulated, including phthalates that will continue to produce the effects many companies need in their plasticizers without using DEHP or other plasticizers that are currently subject to regulation. 
  • Only in huge doses in rodent trials have phthalates been shown to cause the development of cancerous and precancerous cells. 
  • Methods have been developed to quantify plasticizers, in order to calculate the amount of these materials that have actually been used in many medical-grade products and rate them accordingly. 
  • DEHP’s migratory effect increases substantially over time, making it a better product for short-term use than long-term. 
  • Long-term exposure to DEHP and other common phthalates used in PVC has been shown in lab studies to cause hormone disruption, most notably affecting reproduction and development. This disruption, however, is most common in individuals who have experienced long-term exposure. 

In most cases, the potential for phthalate exposure is greater from medical supplies than in food storage products. Whether it is of concern depends on the duration and frequency of the exposure. Migration is more common when PVC is exposed to fatty foods, oils, and cheese, and it is advised that a different material is used to store these food items. 

Migration also increases along with temperature and continued exposure. As a result, many companies are currently working to find food-safe and medical-grade alternatives to the phthalates currently used in many common products. These efforts have been successful; there are currently several alternatives available for many products made using plasticizers, including citrates and trimellitates. 

Summary

Plasticizers are commonly chosen by determining the compatibility with the base plastic and the volatility of the plasticizer in question. As concern continues to rise about the use of phthalates in many medical and food-grade devices, it’s likely that citrates and trimellitates, in spite of their higher price point, will move to center stage in the plasticizer industry. 

By carefully examining the qualities of each of the plasticizers currently available on the market, including how they are able to be sterilized and their potential environmental impact, it’s possible to make a wise choice about the material used in the production of food-grade products, life science products, and medical devices. As changes continue to be made across the plasticizer industry, it’s clear that advances in the field will lead to a deeper understanding of how materials impact both the people that use them and the industry as a whole.