How Flame Retardants Work in Plastics
Flame retardants are chemical compounds added to plastics in order to prevent, delay, or slow down combustion, reduce smoke formation, and/or prevent the material from melt collapse (anti dripping). These additives are common in numerous everyday products to avoid the ignition and burning of plastics.
The most common flame retardants are halogenated compounds, which include brominated and chlorinated types. Halogenated flame retardants are highly effective at relatively low load levels. Non-halogen, or halogen free, flame retardants are increasing in demand and include intumescents (phosphorus-based) and metallic oxides. Non-halogen flame retardants require a higher load level, and often need additional adjustments to maintain the mechanical properties of the plastic.
One must consider several factors when selecting a flame retardant. Getting to the desired performance often requires a tailored solution with several trials.
- What are the test requirements this part needs to pass (burn time, extinguish time, flame spread, smoke development, industry and government regulations, mechanical properties)?
- What polymers and additives are used in the part?
- The design, shape, and surface area of the part also play a critical role in combustion.
Flame retardant additives can be compounded with the base polymer or added during the plastic processing step. Sometimes combustion may be prevented by simply adding the flame retardant to a surface layer finish on the final product.
When plastic burns, long-chain molecules of the polymer chain are degraded into smaller hydrocarbon molecules and flammable gases, such as free radicals – a process called pyrolysis. For a fire to begin, fuel, oxygen, and an ignition source must be present. Flame retardants work by interfering or eliminating one of these key ingredients, either physically or chemically. There are a few common methods that flame retardants employ to inhibit combustion and below is a description of each.
- Gaseous Inhibition: halogenated compounds such as bromines and chlorines are compatible with many base polymers and are the most common flame retardant additives. During pyrolysis, hydrogen and hydroxide free radicals are produced. During a fire, halogenated flame retardants thermally degrade, releasing hydrogen chloride and hydrogen bromide that react with the free radicals in the flame. These newly formed free radicals include the halogens and are less reactive than the original hydrogen and hydroxide free radicals, thus, suppressing the volume of reactive gases available for combustion reactions. Also, this process slows combustion which in turn cools the system, further reducing combustion.
- Solid Char-Formation: this form of flame retardants is often comprised of non-halogen compounds using phosphorous and nitrogen chemistries. During a fire, these types of flame retardants react to form a thick, solid layer of carbon char on the surface of the plastic. This solid layer insulates and shields the plastic, creating a barrier that interrupts the combustion process by hindering the release of more reactive gases.
- Endothermic Cooling: this class of non-halogen flame retardant includes metallic oxides/ hydrated minerals, such as aluminum and magnesium hydroxides. During a fire, these flame retardants use an endothermic reaction to remove heat and release water molecules. The plastic is cooled and limits the amount of reactive gases being formed, thus hindering the combustion process. The use of hydrated compounds as flame retardants is often limited by the low decomposition temperatures of these materials since plastics processing and manufacturing often occurs at high temperatures.
There are many factors to consider when selecting the right flame retardant for a given application including the base polymer being utilized, the specific government and industry regulations and standards that must be met, as well as the desired properties of the polymer such as viscosity and density. Selecting a flame retardant can be a tricky task, which is why it is important to choose a partner, like Amcor, that has extensive expertise in various flame retardants as well as experience with state-of-the-art compounding and blending processes. Amcor will guide you through the selection process to ensure the right additives are chosen for your specific application.
Amcor
Amcor’s flame retardant additives are called “Amout” and include both halogen and non-halogen types.
Amcor is a manufacturer of polyethylene film and bags, as well as polyolefin compounds, additives, blends, and masterbatches. Amcor has grown from a single product line to hundreds of products and five product divisions. In addition to selling products, we also provide tech support, assistance with your equipment, and process recommendations.
Amcor is also a full line distributor of various chemicals, resins, and gases for the plastic industry. With warehousing and distribution facilities across the United States, Mexico, Eastern Europe and China, we service companies of all sizes and locations across multiple industries.
Amcor realizes that on time delivery, a quality product, and personal service are what it is all about. Contact us today to learn how we can assist with your next project!
Blown Film Extrusion Process Explained
Blown films extrusion is one of many polymer manufacturing processes. This method is used to produce commodity and specialized polymer films that are typically used in packaging such as shrink, stretch, barrier films (used to protect deli meat), frozen food packaging, and shopping bags.
There are many types of polymers that can be used in blown film extrusion with the most common being polypropylene and polyethylene (LDPE, HDPE and LLDPE). This method can manufacture monolayer films as well as more complex multi-layer films that involve co-extrusion to combine more than one plastic into a single film.
Process of Blown Film Extrusion
Blown film extrusion can be complex so we will now explain each step of the process in detail! The first step is to melt the polymer in an extruder. Polymer resin, often in the form of beads, is loaded into a hopper and fed into a heated barrel with a screw. The screw is used to transport the polymer down the barrel. The beads are gradually heated to melt the polymer. The heat profile is an important part of extrusion as the polymer may thermally degrade if overheated. When the molten material reaches the end of the barrel, it is extruded through a die. It is at this point that blown film extrusion differs from other extrusion processes.
There are a few different types of dies used in blown film extrusion with the most common being annular, which is a simple circle die. The molten polymer enters the die head and air is injected via a hole in the die center to radially inflate the polymer into a thin tube that is many times its original, extruded diameter. It is this step of the process that can be adjusted to achieve the desired film thickness and width.
The hot tube film is then cooled, typically with high speed air, and pulled upward by equipment called nip rollers. On most medium to large size film lines, this vertical tube may extend several stories into the air. As the film cools it crystallizes at what is called the frost line. As the tube reaches the nip rollers, at the top of the line, the film is now cool enough to flatten and is then referred to as lay-flat or collapsed tubing. The film is then transported downstream by rollers for further processing (e.g. slit, printed, vented, converted into bags) and is eventually wound into rolls.
There are several advantages of manufacturing film using the blown film extrusion process including the ability to manipulate the mechanical properties of the final plastic based on the process conditions and base polymer(s) used. For example, blown film extrusion inflates the polymer radially while at the same time drawing the polymer upward with rollers. These forces stretch the polymer in both the transverse and draw directions, providing strength in the film. The extent of inflating and drawing can be adjusted to achieve the desired strength in the transverse and draw directions of the final product. Blown film extrusion is also versatile and able to manufacture a variety of single or multi-layer films with a range of film thickness and width.
Amcor’s Film Offerings
As a preferred supplier of plastic films and bags, Amcor has eliminated the distribution channel and sells direct to manufacturers. Lead times are typically 50% less than our competitors at around 2-3 weeks versus 4-6 weeks. With a wide range of capabilities and solutions, we are a vital partner in your company’s packaging success. Our film product offerings include:
- Shrink, bags, tubing, sheeting
- Widths up to 240”
- Color and print
- UVI, VCI, Antistat
- Hand and Machine stretch Films
- BOPP/Cast PP Films
- Woven
- Tape
In addition to plastic film and bags, we specialize in polyolefin compounds, additives, blends, and masterbatches. Amcor is also a full line distributor of various chemicals, resins, and gases for the plastic industry. With warehousing and distribution facilities across the United States, Mexico, Eastern Europe and China, we service companies of all sizes and locations across multiple industries. In addition to selling products, we also provide tech support, assistance with your equipment, and process recommendations.
We realize that on time delivery, a quality product, and personal service are what it is all about. Contact us today to learn how we can assist with your next project!