Plastics offer several advantages for outdoor containers. This is due to factors such as their inability to withstand outdoors conditions without rust like metals. The processibility of plastics means they can be made into diverse geometry and sizes to meet diverse outdoor demands. In the outdoor environment, plastics get exposed to UV radiation, rain, dust, puncture, microbes, extreme temperatures and more. In this article we discuss how plastic containers used outdoors are made weatherproof and UV stable.
Outdoor Applications of Plastic Containers
When used in outdoor conditions plastics might not only be required to withstand all sorts of weather conditions, they are also often expected to last for several years, even decades. This could be due to the cost of replacement and installation. It is also more sustainable to extend the use of containers as much as possible in order to keep them out of the waste stream. The cost of disposal also needs to be considered; both environmental as well as financial cost.Some of the common outdoor application of plastic containers include:
- Water storage tanks
- Plastic barrels
- Intermediate Bulk Containers
- Planters
- Bird feeders
- Watering cans
- Fuel storage tanks
- Plastic gas cans
- Refuse bins
- Outdoor fish tanks
- Outdoor storage boxes
- Shipping crates
- Chemicals storage
Types of Plastics Used in Outdoor Applications
HDPE, PP, ASA and PC are good candidates commonly used for production of plastic containers for outdoor application. These plastics have relatively stable structures, they are relatively easy to process into containers and have considerable durability. They have well documented use in outdoor application and well established known additives to enhance their performance.Other plastics such as PVDF, acrylics, PTFE have inherent UV stability and can be used for outdoor application in specialty applications or applications requiring high performance materials. These plastics are generally priced higher than commodity plastics such as PP and HDPE.
Plastics that Should Not be Used in Outdoor Application
It is important here to mention plastics that are not recommended for outdoor applications due to their inherent properties. Even the common plastics used for outdoor containers as discussed above require additional technology and additives to protect them in the outdoor environment. Some plastics even with such modification still are not suited for outdoor application for reasons such as
Poor moisture resistance or hydrophilic plastics Plastics with poor thermal resistance
UV sensitive plastics
Plastics that are prone to leaching toxic chemicals
Examples of plastics that fall into one or all of these categories include polystyrene, polyvinyl chloride (PVC), polyethylene terephthalate and most biodegradable plastics such as PHB, PLA and PCL.
Weatherproofing Outdoor Plastic Containers
Protecting plastics in outdoor application from sunlight, heat, moisture, dust, microbes and other elements that may weaken it and affect its durability requires a combination of approaches.
Surface finish
A glossy finish prevents dust, moisture and microbes from settling on the surface. When rain pours on a smooth glossy surface there is less chance of some moisture being retained on micro crevices and serving as a host for microbes or causing oxidation or degradation. A glossy surface also partly reflects some of the UV radiation reaching the plastic container
Impact Modifiers
In harsh weather conditions such as storms and tornadoes, outdoor containers can get blown over. They must be made out of materials that won’t shatter. UV stabilized polycarbonate (PC) is often used as an alternative to glass for outdoor application where the container needs to be transparent. Adding Impact modifiers like EVA and EPDM also improves the impact resistance of the plastic. The impact resistance of other plastics like LDPE, HDPE, PP and PET is also improved using these impact modifiers.
Reinforcement
Metals, glass, and ceramic, have more weight per volume than plastics. While the lightweight attribute of plastics might be desirable in many applications, In outdoor application, to weatherproof the plastic container against heavy winds, it becomes necessary to make it heavier. Adding reinforcements that increase the density of the material might be more cost saving than increasing the wall thickness.
Overmolding
Plastic can be overmolded on a heavier material like metal. This gives a container with all the advantages of plastic but can be heavy enough to withstand heavy winds in outdoor conditions.
Thick Wall Injection Molding
The plastic container can be manufactured with thick walls to improve their resistance to outdoor conditions. Injection molding of thick walled containers poses specific challenges. We discussed this in previous article .
Carbon black Additive
The first defence for protecting plastics from UV damage is to prevent the UV radiation from reaching the plastic in the first place. As black materials tend to absorb UV radiation while lighter colors reflect it, the use of carbon black as pigment works by absorbing the UV radiation and preventing it from penetrating into the polymer. This way the plastic is shielded physically from UV radiation
Nanotechnology
Use of nanoparticles as additives can have a wide range of impact on weatherability of plastic containers. Examples are carbon nanoparticles which can significantly improve the toughness of plastics like HDPE, and titanium oxide nanoparticles that can improve thermal stability and protect against UV radiation.
UV stabilizers used in Outdoor plastic containers
The exposure to sunlight is the greatest factor that causes plastic deterioration in outdoor application. Sunlight causes heat and UV radiation which can trigger degradation of the plastic. This degradation occurs in the form of breaking down long chain polymer structure into shorter chains and/or weakening or breaking the secondary bonds between the polymer chains or between the polymer and other components of the formulations such as fillers, plasticizers, pigments and other additives. This overtime leads to brittleness, yellowing, loss of color and loss of mechanical properties.UV stabilizers have proven very useful in extending the lifespan of plastics in outdoor applications. Companies such as Curbel Plastics have manufactured and supplied brands of UV stable plastics for decades.There are different types of UV stabilizers in the market. Choosing the right one can make a difference in the lifespan of your plastic container of up to decades. This requires understanding which types are best suited for outdoor application. Some UV stabilizers may offer protection against mild UV exposure such as that experienced by plastics used for storage of drinks and food. There are also limits on which stabilizers can be used in some applications such as food contact and products used in healthcare.The exposure to sunlight is the greatest factor that causes plastic deterioration in outdoor application. Sunlight causes heat and UV radiation which can trigger degradation of the plastic. This degradation occurs in the form of breaking down long chain polymer structure into shorter chains and/or weakening or breaking the secondary bonds between the polymer chains or between the polymer and other components of the formulations such as fillers, plasticizers, pigments and other additives. This overtime leads to brittleness, yellowing, loss of color and loss of mechanical properties.UV stabilizers have proven very useful in extending the lifespan of plastics in outdoor applications. Companies such as Curbel Plastics have manufactured and supplied brands of UV stable plastics for decades.There are different types of UV stabilizers in the market. Choosing the right one can make a difference in the lifespan of your plastic container of up to decades. This requires understanding which types are best suited for outdoor application. Some UV stabilizers may offer protection against mild UV exposure such as that experienced by plastics used for storage of drinks and food. There are also limits on which stabilizers can be used in some applications such as food contact and products used in healthcare.
| UV Stabilizer | Mechanism of Action |
|---|---|
| Hindered Amine Light Stabilizers HALS | Act as free radical scavengers. Commonly used with PE and PP |
| Titanium dioxide TiO2 | Inorganic pigment. Acts by reflecting and scattering UV rays, exceptional heat and water resistance. Also gives a bright clean white color |
| Lightfast Organic Pigments | Carbon based pigments. Act by reflecting broad spectrum of the UV, mainly to retain color of product under sun exposure |
| UV absorbers UVA | Act by blocking the UV radiation from reaching the plastic. They convert the radiation to heat |
Variables to Consider when Designing Outdoor Plastic Containers
The containment requirement
What is going to be stored in the container? The thickness of the container, the size and geometry of the container.
Location and Climate
The environmental conditions the plastic container is exposed to will vary significantly with location. It is therefore important to consider the target market where the container will be applied. This could mean having different formulations for different geographical locations. For example an outdoor water tank that will be used in Iceland will experience significantly lower temperatures and sunlight than that to be used in Senegal.
Compatibility of plastics and UV stabilizers
The activity of a UV stabilizer might be enhanced by using other additives to boost the effect. This helps you get the best out of the UV stabilizer. A common example of this is the use of HALS in PE and PP. The UV scavenging activity of HALS is significantly enhanced in the presence of UV absorbers such as benzophenones and Benzotriazoles.Conversely, other additives may also hinder the activity of UV stabilizers. It is therefore important to consider the combined effects of all the compounds when designing plastic containers for outdoor use.
Conclusion
While some plastics may have inherent UV stability and weatherability, using UV stabilizers and implementing technologies to improve weather resistance can significantly extend the lifespan and durability of plastic containers in outdoor applications. Factors such as location, design, and application requirements should be considered while choosing the types of additives or technologies to implement for improving the UV stability and weather resistance of a plastic container.