Introduction

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The agricultural and horticultural industries are emerging as major potential consumers of plastics in the form of film, sheet, pipe, and molded products in such areas as agriculture: disease and pest control, water conservation supply and drainage, fertilizer transport, storage and application, crop conservation, livestock rearing, produce collecting and transportation, tools, machinery and equipment, and buildings and structures.

The energy situation also called for a reappraisal of the role of film plastics for reducing heat loss from both plastics and glass greenhouses. The use of plastics in winter crop storage was a neglected field, but now interest is growing for using insulated double-skinned black plastic constructions similar to those employed in mushroom production. Plastics has been effectively used as aids for fruit and vegetable storage in the form of linings for boxes, bags, and bins. Rigid plastics also have an important role in containers for holding and transporting produce from point of harvest to point of consumption. Use of plastics in netting for crop windbreaks, plant pots and containers, soil conditioners (expanded plastics waste), mulch films, and pipe for drip or trickle irrigation will be increasing in the future all over the world.

Single- as well as multiple-span polyethylene tunnels and a rigid polyvinyl chloride (PVC)-rooted structure covering up to a third of an acre are increasingly being used for agricultural cultivation. Greater economy has been achieved using a single structure consisting of posts and tensioned wires with a polyethylene film roof.

Agriculture, horticulture, and related areas of plastics applications consume 2,250,000 tons/year of plastics worldwide.

Plastics and the Environment, Edited by Anthony L. Andrady. ISBN 0-471-09520-6 © 2003 John Wiley & Sons, Inc.

According to Jean-Claude Garnaud of the International Committee on Plastics in Agriculture [5], in western Europe consumption of plastics in agri-related areas amounts to 700,000 tons/year. Film applications area is dominant in terms of volume usage. Applied Market Information (AMI) estimated that the European market uses about 500,000 tons/year in agricultural films, of which greenhouse films are about 50%, silage and mulch films are 25% each.

The agricultural film market is growing at about 2.5%/year overall, according to Andrew Reynolds of AMI. Greenhouse film applications show the fastest growth because of the demands for early crops of fruits and vegetables. On average 25-37 g of films are consumed per kilogram of produce for crops, melons, strawberries, and tomatoes [44].

Linear low-density polyethylene (LDPE) is the most important polymer, followed by (high-density polyethylene) HDPE. According to Gernaud, western Europe consumes 570,000 tons/year of agricultural LDPE, of which 350,000 tons have been used in films and tubings.

The European Union (EU) countries use 160,000 tons in transparent crop covering, 148,000 tons in black silage film, 60,000 in transparent mulch films, and around 33,000 in stretch films [44].

Low-diameter low-density polyethylene/linear low-density polyethylene (LDPE/LLDPE) based irrigation tubing is another significant agricultural end use. Higher diameter (>32 mm) tubes are usually made with HDPE or PVC. Western Europe uses 100,000 tons of rigid PVC pipes for drainage and 60,000 tons/year of flexible PVC hose piping, though not all can be classified as agriculture end use. Other applications for plastics in agriculture include polypropylene (PP) twine for binding applications and corrugated PP pipes/fittings for irrigation.

High-density polyethylene is currently used in netting applications for tree protection and oyster farming; also HDPE, PP, and polystyrene (PS) foams are used in making packaging crates for vegetable/fruit transportation.

Other polymers find limited agricultural uses. Among these are glass-reinforced plastics (GRP) tanks, silos and vats, polyethylene terephthalate (PET) filament based thermal screens and flat covering sheets. Polycarbonate (PC) and poly-methylmethacrylate (PMMA) are used in limited amounts for double- or triplewall sheets for top of the line greenhouses.

This chapter presents the use of plastics in three major sectors: (i) greenhouses (ii) mulches, and (iii) agricultural irrigation. Since these plastics are meant for long-term usage in harsh outdoor conditions of higher temperatures, ultraviolet (UV) radiations, temperature cycling, and other climatic factors. Therefore, these plastics are stabilized with a number of UV stabilizers including antioxidants, hindered amine light stabilizers (HALS), and Ni quenchers, which provide protection against, heat, UV radiation, temperature cycling during day to night, high wind velocity, high humidity, and other climatic factors that are interacting simultaneously. The most important weather parameter that affects the lifetime of plastics used in agricultural applications are discussed.

Stabilization of plastics, particularly greenhouse films, mulch films, silage, and rigid pipes used in irrigations, are discussed in detail. Some case studies showing the outdoor performance of greenhouse films, mulches, and pipes exposed in near equatorial regions are also discussed in this chapter. The UV stabilizers mentioned in this chapter are state-of-the-art products. Their structures and trade names of these commercial products are shown in the Appendix.

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