Let it shine – light stabilizers extend agricultural film life

Let it shine – light stabilizers extend agricultural film life

9:57 AM, 23rd October 2017
Let it shine – light stabilizers extend agricultural film life
The benefits of greenhouse production are so convincing that vegetables such as tomatoes, peppers, cucumbers and eggplants are already being cultivated largely under polyolefin roofs.

By Hermann Althoff

According to the United Nations estimates, over 9 billion people will be living on Earth by the year 2050. The amount of arable land needed to feed them, however, will not increase at the same rate. Inexpensive greenhouses made from plastic film represent one way to solve this problem: With the aid of such greenhouses, the output per hectare can be increased considerably.

An important market – in several respects

As a result of urban growth, and also because of increased erosion and climate change, the amount of arable land is decreasing. The challenge is how to increase the intensity of agricultural activity while keeping the products affordable.

There is limited scope to increase arable land in Asia Pacific

Greenhouses that can be erected very inexpensively through the use of plastic film are one possible way out of this dilemma: They provide an ideal environment for plants, protect vegetables from the effects of frost, wind and rain, ensure uniformly high quality and help fruit ripen faster. In this way, several crops can be harvested in one year. Moreover, modern plastic film can be tailored specifically to the unique light and temperature requirements of many field-grown fruits. At the same time, they help to use water more economically – a resource that has to be looked after even more closely in the coming years.

The benefits of greenhouse production are so convincing that vegetables such as tomatoes, peppers, cucumbers and eggplants are already being cultivated largely under polyolefin roofs. Currently, about 3,500,000 metric tons of film is produced worldwide every year for the agricultural market. At the same time, the demand for agricultural film for use in greenhouses is foreseen to grow at an annual rate of about four percent. Rising demand in Asia Pacific is the major driver of the greenhouse film market. Other fast-growing greenhouse areas in the world are in the Mediterranean region, South America, and Eastern Africa.

Agriculture has special requirements

Optimized agriculture also includes carefully considered use of agricultural chemicals to prevent harvests from attack by pests or mould. Environmentally friendly solutions are advancing on this front as well. The use of sulphur, for instance, being approved for application on organic produce even in highly regulated German agriculture, is recording noteworthy growth. However, the use of elemental sulphur and other agricultural chemicals places special demands on the film used in greenhouses.

The reason for this lies in the sensitivity of thermoplastic films to UV light. This energy-rich radiation causes plastics to become brittle over the course of time via a complex, multi-step chemical mechanism. Low-cost, thin film, in particular, can become useless after only a few weeks of exposure to the open sky as a result of this effect. Polymer chemistry has, of course, already developed additives that can slow this degradation reaction. However, their suitability for use in agricultural film is rather limited, since their effectiveness is reduced considerably by sulphur and acids stemming from the wooden or iron construction of greenhouses. Halogen-containing chemicals can also contribute to the deactivation of common UV stabilizers.

Special products withstand agricultural chemicals

There are, however, already alternatives in the BASF light stabilizer portfolio, specifically for the agricultural sector. Whenever converters produce a greenhouse film, they have to allow for solar irradiance, expected film durability, type of cultivation as well as type and frequency of agro-chemicals used. Chimassorb®, Tinuvin®, Tinuvin® XT and Tinuvin® NOR® light stabilizers allow converters to match any combination of these conditions.

Through use of Tinuvin® XT 100, it is possible to produce in a very economical manner LDPE (Low-density polyethylene) films that withstand severe agricultural chemicals levels and also assure a service life of two and more years even under intense sunlight. The performance of such stabilized films is also very good when in contact with wood and metal greenhouse structures. Without a light stabilizer, they would not last even one growing cycle.

The capabilities of this UV stabilizer were verified by extensive testing at BASF over several years. This included investigating the ageing characteristics of the stabilized film in detail in the laboratory. They also had to prove themselves in extended field tests in China and India.

BASF plastic additives increase durability of greenhouse film in Yunnan, China

BASF’s plastic additive Tinuvin® XT 100 has been adopted by Yuxi Xuri Plastics Production Co., Ltd, a leading greenhouse film manufacturer in China, to make low density polyethylene (LDPE) film. The film is used to cover a greenhouse for growing grapes in Yunnan province in China.

The requirements for greenhouse films are highly demanding. Greenhouse film manufacturers must allow for solar irradiance, expected film durability, type of cultivation as well as type and frequency of agrochemicals used.

Yuxi Xuri Plastics was struggling to ensure that the greenhouse film did not prematurely break down in the presence of high agrochemicals. Premature failure of the films could result in compensation payouts, and for the farmer: decreased grape yields and reduced income as well as additional costs to reinstall the film. They needed a way to stabilize the film and assure its lifetime prediction.

“With Tinuvin XT 100, it is possible for us to produce LDPE films that withstand even high agricultural chemical levels and assure a service life of up to two years, even under intense sunlight,” said Wang Ming Xian, general manager of Yuxi Xuri Plastics. “Switching to Tinuvin XT 100 helped us to regain our market share in Yunnan.”

Besides, UV absorbers which directly intercept the harmful radiation in the same way as a sun cream, compounds of the sterically hindered amine light stabilizer (HALS) class are important for protecting greenhouse films. These HALS slow down not only the weathering process due to UV radiation but also the degradation of the material caused by heat and chemicals. Because all these trigger factors lead to the formation of free radicals – extremely reactive molecules which destroy the long molecule chains of the polyethylene – the film loses its stretch properties, becomes brittle and decays. The hindered amines of HALS compounds, incorporated in Tinuvin XT 100, intercept the free radicals and make them harmless.

With the aid of inexpensive greenhouses made from plastic film, agricultural output per hectare can be increased considerably. BASF’s light stabilizer Tinuvin® XT 100 protects film made from thermoplastic resins against overly fast degradation when exposed to UV light. It also ensures the efficacy of the films over a longer period even in the presence of high concentrations of agricultural chemicals like elemental sulphur.

Author: Hermann Althoff is Senior Vice President, Performance Chemicals, Asia Pacific, BASF.

© Chemical Today Magazine


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