LDPE Used As Greenhouse Covering Materials: A Study of Degradation dan Stabilizations

Posted on October 30, 2011

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The Kingdom of Saudi Arabia covers a large area of about 2 000 000 km2, which is about 80 % of the total area of the Arabian peninsula. The country is located between 15.2° and 32.6° north and 34.1° and 55.5° east, and the climate is generally mild in the winter, but dry and hot in the summer. Rainfall occurs in the winter but never exceeds 100 mm per year in most regions except for the southwestern mountains of Asir, where it rains more often in the summer.
To reduce dependence on oil exports as the main source of income and to produce more food for the increasing population with a high standard of living, Saudi Arabia has been making intensive efforts through its five-year development plans to develop the agricultural sector. Agricultural exploitation has never happened like this. As a result of government encouragement and financial assistance, cultivated land has increased dramatically from about 435 000 ha in 1980 to more than 1.5 million ha in 1990. Recently, advanced technology and modern machinery were introduced, new crops and varieties were cultivated, industrial greenhouses and agricultural projects were established.
A greenhouse is a building where plants are grown. It has different types of covering materials. The most frequently found are glass and plastic. It has been known that plastics have long been used in agriculture. This is because of the properties of plastics (compared to glass), namely, unbreakability, low price, transparancy, flexibility, ease of forming into various shapes and light weight [1].

Polyethylene (PE) dominates the use of plastic films as greenhouse covering materials. Polyethylene has similar permeability as glass to short wave transmission but much higher permeability to longwave radiation. In addition, polyethylene covers are easy to handle and are the cheapest greenhouse covers [2,3]. Low-density polyethylene (LDPE) is the most widely used polyethylene grade, due to its relatively good mechanical and optical properties. Furthermore, LDPE has availability in large sheets, high light transmission and light weight, but it has also important disadvantages [4].

A common problem with polyethylene is the short shelf life (2-3 years at most), mainly in harsh weather conditions such as high temperature, high solar intensity, and dust, all of which are common in arid regions (e.g. central region of Saudi Arabia). In such conditions, mechanical resistance and light transmission could deteriorate quickly [2-7]. Another drawback is its poor heat retention, allowing some 60-80% of radiant heat (mid infrared) to pass through [4]. Therefore, it is important to investigate how to improve the resistance an durability of this film by adding special additives. In Saudi Arabia, the use of LDPE films in agriculture is not yet widely practised. There is no systematic study to investigate most proper polymer materials and additives appropriate to arid climate in this Kingdom.

REFERENCES
[1] Bualek, S., Suchiva, K., Boonariya, S., Ratana-Arakul, B. “Aging of low density polyethylene films for agricultural use in Thailand.” J.Sci.Soc. Thailand 17, 1991: 103-122.
[2] Alhamdan, A. M., Al-Helal, I. M. “Mechanical deterioration of polyethylene greenhouses covering under arid conditions.” Journal of materials processing technology 209, 2009: 63–69.
[3] Ulrich, H. “Introduction to Industrial Polymers.” New York: Hanser Publisher, 1982.
[4] Dilara, P.A., Briassoulis, D. “Degradation and stabilization of low-density polyethylene films used as greenhouse covering materials.” Journal of Agricultural Engineering Research 79, 2000: 309-321.
[5] Dehbi, A., Mourad, A. I. “Durability of mono-layer versus tri-layers LDPE films used as greenhouse cover: comparative study.” Arabian Journal of Chemistry, 2011.
[6] Al-Helal, I. M., Alhamdan, A. M. “Effect of arid environment on radiative properties of greenhouse polyethylene cover.” Solar Energy 83, 2009: 790–798.
[7] Briassoulis, D., Schettini, E. “Analysis and design of low-density polyethylene greenhouse films.” Biosystems Engineering 84 (3), 2003: 303–314.

Thesis Proposal by Muhammad Abduh Tuasikal
King Saud University
25th October 2011
wwww.polimerabduh.wordpress.com

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