The useful life of an agricultural plastic

In addition to deciding the type of plastics that agricultural producers will use to enhance their different crops, one of the most important aspects to consider is the durability of agricultural plastic since that will determine, to a large extent, that the crops produce more and better fruits at the end of the season. For this reason, we will talk about the useful life of agricultural plastic in this post.

The durability or lifetime of an agricultural plastic will depend on several factors such as:

• The climate of the area where the crop is located
• Terrain conditions
• Geographical context
• Type of solar radiation you receive

Likewise, extending or shortening their useful life will depend on the use and treatment that is given to these plastics. Plastic durability is understood as the time during which the film maintains its properties, including optical, mechanical, and physical properties.

In general, the useful life of an agricultural plastic is between two or three years, depending on the quality and materials that have been used to create it, as well as the techniques implemented by the manufacturer.

It’s worth mentioning that in addition to the incidence of climatic factors such as rain, high or low levels of solar radiation, wind, and high or low temperatures, other factors directly influence the durability of an agricultural plastic such as chemicals used in crops, whether fertilizers or pesticides.

It also negatively influences the durability of agricultural plastics if the films are not properly tensioned during their installation causing them to tear or dent prematurely or if they are overworked to make them “fit” in a certain perimeter.

Thus, the factors that can affect the shelf life of agricultural plastic can vary between external and internal.

According to the publication “Plastic Films in Agricultural Production” (Díaz, t., et al, 2001), in the case of external factors the most common are:

• Storage conditions
• Processes and raw material used in its manufacture
• How the agricultural plastic is installed

External factors also play a role during use:

• Greenhouse structure
• Climatic conditions
• Phytosanitary products – agrochemicals

Regarding the internal factors, the following stand out:

• Plastic thickness
• Stabilizers and other additives
• Base polymer type (LDPE, LLDPE, EVA)
• Type of plastic (monolayer or multilayer)

Below, we explain in more detail the external and internal factors that influence the durability of agricultural plastic.

External factors affecting the useful life of an agricultural plastic

• Manufacturing processes

At this point, agricultural producers should take into consideration what process was used to manufacture the film to be used on their crops. For example, if there was adequate management of the temperature at the moment of melting the raw material to preserve its properties, as well as if there was an adequate tension of the film to avoid the appearance of wrinkles or the consistency in maintaining formulations and thicknesses throughout the production.

• Storage

Ideally, to guarantee the useful life of agricultural plastic, when not in use it should be stored preferably in a dry place, free of humidity, and away from direct sunlight.

Temperatures must be adequate (neither too high nor too low) to prevent them from starting to degrade, even before being used. The recommendation is to pay attention to the date of manufacture and, once acquired, avoid storing it for a long time before installation, as this may compromise its durability. The recommended time is 6 months in season and avoid using plastic from one year to another in case of long duration applications.

• Installation

Once it has been decided to install the film, it is best to do the work preferably in the early hours of the morning when the weather is still cool and without strong winds.

In this way, the risk of warm temperatures directly affecting the material is minimized, causing it to expand or stretch, thus compromising its integrity and, therefore, its useful life.

Most of the time, when installing a plastic film, it is common for installers to apply a small tension to ensure that it is well-positioned on the metal structure and thus prevents it from slipping because of winds. However, the degree of tension applied to them can have a direct impact on the useful life of agricultural plastic and must be carefuly applied.

For example, experts in the field recommend that the stress applied to roof materials should not exceed 1%, so if you have a 200m plastic roof, it is best to apply a maximum stress of 2m to avoid compromising the integrity of the roof.

The most important thing is to know what type of plastic you have and to follow the installation instructions carefully to avoid installing it incorrectly.

There are external factors that take place specifically during the installation of plastics:

• Climate impact

The climatic conditions of each area must certainly be considered since the useful life of agricultural plastic will never be the same in all crops and geographical areas. For example, in the case of the sun radiation, these won’t be the same everywhere because the distribution of the light spectra will vary depending on the location of the crop.

“The percentage of UV radiation increases with altitude, therefore, the radiation will be more aggressive for a plastic in a high-altitude area than at sea level; and the material would require a higher content of UV additive since this additive is responsible for degradation” (Díaz et al, 2001).

When high or low temperatures are added to radiation, the durability of agricultural plastic is likely to be affected.

Rainfall, and hail, also has a direct impact, so it’s essential to know how to place the films so that the water drains properly and thus avoid stagnation in the plastic or, on the contrary, that ends up flooding the crop field.

There are areas where frost usually occurs and a lot of snowfalls, so it’s essential to try to place strong structures that allow placing plastics with an adequate thickness that manage to tolerate the weight of the snow.

The World Bank has a global solar radiation atlas that can be used as a reference to having a better orientation of your needs depending on the installation area of your crop.

• Type of structure

The service life of an agricultural plastic will depend to a large extent on the type of structure in which it is installed, such as greenhouses, as well as the materials used for its construction.

The structures can be plastic, metal, or wood, so each one will require special care when placing the plastics.

In the case of metallic structures, their temperature generally tends to increase when they receive direct sunlight and when in contact with the plastic, it begins to degrade more rapidly. In this case, it’s recommended to paint the metallic structure with a special white paint for reflection of sunlight or to cover with insulating tape the areas where it comes into contact with the plastic to attenuate the degradation process of the film.

When crops are grown in structures made of wood, it often happens that some acidic components of the wood migrate towards the plastic, causing the material to be compromised. To prevent this from happening, it’s essential to study which type of wood is the most recommendable and, if necessary, immunize it so that it causes the least possible damage to the plastic.

There are structures such as tunnels and greenhouses where special care must be taken to ensure that the height is adequate because if it is too low there will probably not be much ventilation and some products such as pesticides will come into almost direct contact with the plastic film, causing it to begin to degrade sooner than expected.

 

 

• Products used

It is crucial to review the type of substances or agrochemicals that are used in each crop because, depending on their composition, they could shorten the useful life of agricultural plastic. Most harmful chemicals are sulphur and chlorine.

There are some cases where agricultural producers use chemicals to disinfect and prepare the soil before cultivation, which can cause damage to the plastics used in greenhouses.

To avoid this, it is best to try to use another plastic that serves as a barrier to cover the ground where the substances were applied and thus prevent the gases from leaving and affecting the other films. Another option is to use double chamber or double skin on the roofs to avoid direct fixation of the chemicals on the more important outer skin.

In this case, agricultural producers must analyze very well the properties and tolerance to chemicals that the plastics they are going to acquire have by reviewing their letter of guarantee.

Internal factors affecting the useful life of an agricultural plastic

• Plastic film thickness

The thickness of the agricultural plastic is another factor that will determine whether the useful life of an agricultural plastic is greater or lesser.

In this case, the larger the caliber or thickness of a plastic film, the longer it will last, and the thinner it is, the shorter it will last.

This is because very thin plastic sheets have a lower level of UV additive, which makes them more prone to breakage, while thicker ones have higher UV additive points, which gives them greater stability. It is therefore essential for agricultural producers to define very well the type of agricultural plastic they will need according to the requirements of their crops.

• Base polymer

At this point, it is preferable to acquire plastics that have been manufactured with quality resins that have a traceability to the supplier and also must be free of contaminating agents, in this way the final result will be a much more stable and durable film capable of withstanding external attacks.

• Plastic layers

Agricultural plastic sheets have layers, whether they have one, three, five, or seven layers. These multi-layered plastics tend to last longer since there are companies dedicated to making better combinations of specialty additives to create increasingly stronger and more resistant agricultural plastics.

The Armando Alvarez Group is one of those plastics manufacturers that have the necessary technology to manufacture agricultural films of up to seven layers that are much more resistant and durable.

• Stabilizers

According to the information reflected in the Plasticulture Workshop held between Earth University and the Armando Alvarez Group, there are at least two stabilizers on the market: Nickel, which allows manufacturing yellow-green plastics with greater resistance to agrochemical applications; and Hals, which allows achieving a transparent shade in plastics.

Although the agricultural plastics used in structures such as greenhouses or tunnels have made significant technological advances, it’s now common to have doubts about their specific applications and useful life.

Agricultural producers will always be looking for new alternatives to protect their crops and thus achieve higher levels of productivity and yield, to learn more about it, we recommend watching our webinar on polyethylene covers and specific applications in greenhouses.