Polyvinyl Chloride - an overview

21 Nov.,2022

 

pvc shrink film

3.3.7 Polyvinyl Chloride

PVC is a flexible or rigid material that is chemically nonreactive. Rigid PVC is easily machined, heat formed, welded, and even solvent cemented. PVC can also be machined using standard metal working tools and finished to close tolerances and finishes without great difficulty. PVC resins are normally mixed with other additives such as impact modifiers and stabilizers, providing hundreds of PVC-based materials with a variety of engineering properties.

There are three broad classifications for rigid PVC compounds: Type I, Type II, and CPVC. Type II differs from Type I due to greater impact values, but lower chemical resistance. CPVC has greater high temperature resistance. These materials are considered “unplasticized,” because they are less flexible than the plasticized formulations. PVC has a broad range of applications, from high-volume construction-related products to simple electric wire insulation and coatings.

PVC is the most widely used plastic resin in medical devices. Approximately 25% of all plastic medical products are made of PVC, according to most market estimates. The main reason is the resin’s low cost, ease of processing, and the ability to tailor its properties to a wide range of applications. The following is a more thorough list of reasons for the popularity of PVC in medical devices:

Used successfully for over 50 years in various medical devices with no known adverse or toxic effects.

Plasticized PVC has good clarity and transparency retention so that tubes and other products allow for continual monitoring of fluid flow.

PVC can be manufactured in a range of flexibilities and its resistance to kinking in tubing reduces the risk of fluid flow being interrupted.

PVC can be used in a wide range of temperatures, and it retains its flexibility, strength, and durability at low temperatures.

PVC formulations exhibit excellent strength and toughness.

PVC exhibits very good chemical resistance and stability and is also biocompatible for applications in blood bags and drug delivery.

Plasticized PVC maintains its product integrity under various sterilization environments like steam, radiation, and EtO.

PVC can be easily welded to various other plastics by a wide range of methods.

Its relatively lower cost and high-performance value maintains its position as the number one plastic used in medical devices.

PVC has safety and cost advantages for a wide variety of medical applications, especially for single-use disposable devices.

A large number of plasticizers have been used with PVC to reduce rigidity, the most common family being the phthalates, especially, di(2-ethylhexyl) phthalate (DEHP). It is sometimes called dioctyl phthalate and abbreviated DOP. These plasticizers are incorporated in amounts ranging from 40% to 65%. There are many other plasticizers used in medical applications.

Heat stabilizers are typically used in medical grade PVC, to protect it against not only the high temperatures the resin might see during processing, but also the high heat it may encounter in storage or autoclaving. Barium–zinc additives are very effective heat stabilizers for PVC but are restricted for medical applications in some countries. Alternatives like calcium–zinc formulations are often used to stabilize medical-grade PVC. Heat stabilizers trap the hydrogen chloride that is generated when PVC decomposes at high temperatures. This prevents discoloration and degradation. Rigid PVC may contain up to 15% by weight of thermal stabilizers. Another additive, Tinuvin®–P, 2-(2H-benzotriazol-2-yl)-p-cresol, is used to provide stability from exposure to UV light.

Sterilization:

Gamma radiation resistance: Gamma-ray sterilization generally uses an energy dose of about 2.5 megarads. Sterilization at excessive dosage rates or with excessive sterilization times can result in discoloration or odor. Rigid PVC suffers more severe adverse effects than flexible PVC when inappropriate procedures of this type are used. Specific gamma radiation-resistant PVC blends are commercially available [20]. PVC degrades by chain scission when exposed to high-energy radiation causing degradation or the radicals can react with oxygen to form oxidized products leading to discoloration.

EtO resistance: EtO sterilization is recommended for PVC. When choosing EtO gas sterilization, a 7- to 14-day quarantine period is necessary to assure that there is no EtO residue [10]. Sterilization using EtO gas is a method which has proven particularly useful for PVC products having a large number of cavities or capillaries [10].

Autoclave sterilization: Steam sterilization in autoclaves is conducted at temperatures from 121°C to 134°C. The temperature used is above the glass transition temperature of PVC. Rigid unplasticized PVC is unsuitable for use in steam and autoclave sterilizations as the material and parts will warp and distort when exposed to that temperature range. The temperature range poses no problem for flexible PVC, which is a rubbery material. Plasticized, flexible PVC can be sterilized using steam or autoclave. Low-temperature steam sterilization (conducted at 60–80°C) can be used for both rigid and flexible PVC.

Low-temperature plasma sterilization: PVC products can also be sterilized using newly developed low-temperature plasma technology (Sterrad® plasma sterilization) [10].

Applications and uses:

Rigid PVC: luer connectors and Y-sites.

Flexible PVC: secondary packaging, blister packs, solution containers, fluid transport tubes, drip chambers, diaphragms, pull rings, oxygen facemasks, and gloves.