What is Polyvinyl Chloride ( PVC ), and What is it Useful for?
What you need to Be familiar with PVC Plastic
Polyvinyl Chloride ( PVC ) is one of the most frequently used thermoplastic polymers on the planet (next to only a few extensively used plastics like PET and PP). It is a naturally white and extremely brittle (prior to the additions of plasticizers) plastic. PVC has existed longer than most plastics having been first synthesized in 1872 and commercially manufactured by B.F. Goodrich Company in the 1920s. In comparison, various other common plastics were first synthesized and became commercially viable only in the the 1940s and 1950s. It is used most commonly in the construction industry but can be used for signs, healthcare applications, and as a fiber for clothing.
PVC is produced in two general forms, first as a rigid or unplasticized polymer (RPVC or uPVC), and second as a flexible plastic. Flexible, plasticized or regular PVC is softer and much more amenable to bending than uPVC as a result of addition of plasticizers like phthalates (e.g. diisononyl phthalate or DINP). Flexible PVC is often used in construction as insulation on electrical wires or in flooring for homes, hospitals, schools, and other areas where a sterile environment is a priority, and in some cases as a replacement for rubber. Rigid PVC is also used in construction as pipe for plumbing and for siding which happens to be commonly referred to by the term “vinyl” in the United States. PVC pipe is commonly known as by its “schedule” (e.g. Schedule 40 or Schedule 80). Major differences between the schedules include things like wall thickness, pressure rating, and color.
Some of PVC plastic’s most significant characteristics include its relatively low price, its resistance to environmental degradation (and also to chemicals and alkalies), high hardness, and outstanding tensile strength for a plastic when it comes to rigid PVC. It is easily available, frequently used and easily recyclable (categorized by resin identification code “3”).
What are the Characteristics of Polyvinyl Chloride (PVC)?
Some of the most significant properties of Polyvinyl Chloride (PVC) are:
Density: PVC is very dense in comparison to most plastics (specific gravity around 1.4)
Economics: PVC is easily available and economical.
Hardness: Rigid PVC is quite hard.
Strength: Rigid PVC has fantastic tensile strength.
Polyvinyl Chloride is a “thermoplastic” (compared to “thermoset”) material which has to do with just how the plastic reacts to heat. Thermoplastic materials become liquid at their melting point (a range for PVC between the really low 100 degrees Celsius and higher values like 260 degrees Celsius dependent upon the additives). A major useful attribute about thermoplastics is that they may be heated to their melting point, cooled, and reheated again without significant degradation. Rather than burning, thermoplastics like polypropylene liquefy, which enables them to be easily injection molded and then subsequently recycled. By contrast, thermoset plastics can only be heated once (typically during the injection molding process). The first heating causes thermoset materials to set (similar to a 2-part epoxy) resulting in a chemical change that cannot be reversed. When you attempted to heat a thermoset plastic to a high temperature a second time it will simply burn. This characteristic makes thermoset materials poor candidates for recycling.
Why is Polyvinyl Chloride (PVC) used so frequently?
Rigid PVC in particular has extremely high density for a plastic making it extremely hard and customarily very strong. It is also readily available and really economical which combined with the long-lasting characteristics of most plastics allow it to be a simple selection for many industrial applications like construction.
What Are The Different Types of PVC?
Polyvinyl Chloride is widely available in two broad categories: rigid and flexible.
How’s PVC made?
Polyvinyl Chloride is made from one of three emulsion processes:
Suspension polymerization
Emulsion polymerization
Bulk polymerization
Polyvinyl Chloride for Prototype Development on CNC Machines, 3D Printers, & Injection Molding Machines: There are two main issues working with PVC which makes it fairly problematic and not generally recommended for use by non-professionals. The first is the emission of toxic and corrosive gases when melting the material. This takes place to some degree or another while 3D printing, CNC machining, and injection molding. We suggest you take a look at the MSDS data sheets for different chlorinated hydrocarbon gases like chlorobenzene and discuss the production process with a professional manufacturer. Second is the corrosive nature of PVC. This is problematic when PVC is repeatedly coming into contact with metal nozzles, cutters, and/or mold tools that happen to be made from a material other than stainless steel or some other similarly corrosion resistant metal.
3D Printing:
Polyvinyl Chloride is available in filament form as a plastic welding rod (the material used in welding) but it is not presently retrofit for specific use in 3D printing. Even though there certainly are a growing number of plastics and plastic substitutes available for 3D printing, by far the two most common are still ABS and PLA. At Creative Mechanisms we typically 3D print with ABS.
The biggest challenge with PVC for 3D printing is its corrosive nature (potentially compromising the functionality of typical machines if it were used over a extended period period). There was an intriguing kick starter to develop a PVC capable 3D printing nozzle (extruder head) put forward by engineer and entrepreneur Ron Steele that unfortunately closed missing the interest in 2014.
CNC Machining:
Polyvinyl Chloride may be cut on a CNC machine but any machinist who’s tried has probably experienced degradation in the cutter depending on the material it is manufactured from. PVC is very corrosive and abrasive and cutters that aren’t made from stainless steel or a comparably corrosive resistant material will probably deteriorate with time.
Injection Molding:
Polyvinyl Chloride may be injection molded just like other plastics however the inclusion of chlorine in the material complicates the procedure. This is due to melted PVC can give off a corrosive toxic gas. Accordingly, shops need to be equipped with sufficient ventilation systems. Those that aren’t are likely to be reluctant to work with the material. Additionally, special corrosive resistant materials like stainless steel or a chrome plating are needed for the mold tool when injection molding PVC plastic. Shrinkage in PVC is frequently between 1 and 2 percent but can vary based on a variety of factors including material durometer (hardness), gate size, holding pressure, holding time, melt temperature, mold wall thickness, mold temperature, as well as the percentage and type of additives.
Is PVC Toxic?
PVC can cause a health hazard when it’s burned as it emits hydrogen chloride (HCl) fumes. In applications where the likelihood of fire is high, PVC free electrical wire insulation is oftentimes preferred. Fumes can also be emitted when melting the material (such as during prototyping and manufacturing processes like 3D printing, CNC machining, and injection molding). We recommend you take a look at the Material Safety Data Sheets (MSDS) for different chlorinated hydrocarbon gases like chlorobenzene and discuss the production process with a professional manufacturer.
What are the Advantages of Polyvinyl Chloride?
Polyvinyl Chloride is readily available and relatively inexpensive.
Polyvinyl Chloride is very dense and therefore very hard and resists impact deformation very well when compared with other plastics.
Polyvinyl Chloride has very good tensile strength.
Polyvinyl Chloride is incredibly resistant to chemicals and alkalies.
What are the Disadvantages of Polyvinyl Chloride?
Polyvinyl Chloride has very poor heat stability. Because of this additives which stabilize the material at higher temperatures are typically included with the material during production.
Polyvinyl Chloride emits toxic fumes when melted and/or subject to a fire.
Although there are a few shortcomings, Polyvinyl Chloride is an excellent material overall. It has a unique blend of qualities that make it particularly useful for the construction business.
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