The use of plastic mulch in agriculture has increased dramatically in the last 10 years throughout the world. This increase is due to benefits such as increase in soil temperature, reduced weed pressure, moisture conservation, reduction of certain insect pests, higher crop yields, and more efficient use of soil nutrients. However, disposing of used plastic films, which cause pollution, has led to development of photodegradable and biodegradable mulches. Here we review the use of plastic mulches in agriculture, with special reference to biodegradable mulches. Major topics discussed are (1) history of plastic mulch and impact on crop yield and pest management, (2) limitations of polyethylene mulches and potential alternatives, (3) biodegradable and photodegradable plastic mulches, (4) field performance of biodegradable mulches, and (5) use of biodegradable plastic mulches in organic production. We found that (1) despite multiple benefits, removal and disposal of conventional polyethylene mulches remains a major agronomic, economic, and environmental constraint; (2) early use of photodegradable plastic mulch during the 1970s and 1980s, wrongly named biodegradable mulch films, discouraged adoption of new biodegradable mulch films because they were too expensive and their breakdown was unpredictable; (3) biodegradable plastic films are converted through microbial activity in the soil to carbon dioxide, water, and natural substances; (4) polymers such as poly(lactic acid), poly(butylene adipate-coterephthalate), poly(e-caprolactone), and starch-based polymer blends or copolymers can degrade when exposed to bioactive environments such as soil and compost; (5) with truly biodegradable materials obtained from petroleum and natural resources, opportunity for using biodegradable polymers as agricultural mulch films has become more viable; and (6) the source of polymer and additives may limit use of some biodegradable mulches in organic production. More knowledge is needed on the effect of biodegradable mulches on crop growth, microclimate modifications, soil biota, soil fertility, and yields.

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Polyethylene and biodegradable mulches for agricultural applications: a review

Biodegradation of poly(vinyl alcohol) based materials

The use of calcines of natural limestones as CO2 regenerable sorbents is investigated in this work by studying the decay of the maximum carbonation conversion during many carbonation/calcination cycles. New experimental information is complemented with a compilation of previously published data on this subject. The observed conversion limits in the reaction of CO2 with lime are interpreted in terms of a certain loss in the porosity associated with small pores and a certain increase in the porosity associated with large pores. In the carbonation part of every cycle, the CaCO3 fills up all the available porosity made up of small pores plus a small fraction of the large voids, limited by the thickness of the product layer that marks the onset of the slow carbonation rate. A simple model based on textural changes, observed by scanning electron microscopy, fits equally well all the data from this work and from other authors. The two model parameters are consistent with known mechanism occurring during calcinat...

Conversion Limits in the Reaction of CO2 with Lime

A new kind of Ca-based regenerable CO2 absorbent, CaO/ Ca12Al14O33, was synthesized on the basis of the integration of CaO, as solid reactant, with a composite metal oxide Ca12Al14O33, as a binder, for applying it to repeated calcination/carbonation cycles. The carbonation reaction can be applied in many industrial processes, and it is important for practical calcination/carbonation processes to have absorbents with high performance. The cyclic carbonation reactivity of the new absorbent was investigated by TGA (thermogravimetric analysis). The effects of the ratio of active material to binder in the new absorbent, the mechanics for preparation, and the reaction process of the high-reactivity CaO/Ca12Al14O33 absorbent have been analyzed. The results obtained here indicate that the new absorbent, CaO/Ca12Al14O33, has a significantly improved CO2 absorption capacity and cyclic reaction stability compared with other Ca-based CO2 absorbents. These results suggest that this new absorbent is promising in the ap...

Synthesis, experimental studies, and analysis of a new calcium-based carbon dioxide absorbent

Composite particles (10) made of a binder (15) and filler material (20) are provided for use in subterranean formations. The filler is typically finely divided mineral and optional fiber. The particles are useful as proppants to prop open subterranean formation fractures. The particles are also useful for water filtration and artificial turf for sports fields. Methods of making the composite particles are also disclosed.

Composite proppant, filtration media, gravel packing media, and sports field media, and methods for making and using same

Stable, water soluble, sulfonated melamine-formaldehyde and sulfonated melamine-urea-formaldehyde resin solutions are prepared in a four stage procedure, wherein (1) melamine or melamine and urea are condensed with formaldehyde in an aqueous medium at a relative low temperature and a pH of 10-13, followed by (2) the addition of a sulfonating agent, such as sodium metabisulfite, and continued reaction without pH adjustment, followed by (3) lowering the temperature of the reaction medium to 40°-60° C., adjusting the pH to 2.5-4 and continuing the reaction for about 5-150 minutes, and finally followed by (4) adjusting the pH to 6.5-9, heating the reaction medium to 70°-100° C. for 30-180 minutes, adjusting the final solids content to a predetermined value, such as 20%, and adjusting the pH to 8-11. The resulting aqueous solutions are suitable for use as superplasticizer additives to hydraulically settable cementitious materials.

Process for the synthesis of highly stable sulfonated melamine-formaldehyde condensates as superplasticizing admixtures in concrete

A degradable agricultural mulch film as disclosed herein includes a plurality of layers for the controlled release of plant nutrients The first layer is formed from a water-soluble synthetic resin, a releasable form of nitrogen and a releasable form of a plant nutrient in addition to nitrogen A second layer includes a water-soluble synthetic resin having an average molecular weight which is greater than the average molecular weight of the water-soluble synthetic resin in the first layer and a releasable form of nitrogen admixed therein The second layer also includes a thin film of water-resistant polymer to retard the degradation rate of the second layer and to slow the release of nitrogen in the second layer And in the preferred embodiment of the invention a second film of water-resistant polymer which is relatively thin with respect to the first film separates the first and second layers

Multilayer degradeable and controlled release multinutrient mulch film, and process for preparing same

An agricultural mulch film is prepared by mixing conventional plant nutrients with a water-soluble polymer such as polyvinyl alcohol. The mixture is cast in the liquid form and allowed to dry to form a thin film. The dried film is then coated with a thin layer of a water-resistant resin such as polyvinyl acetate to form a composite mulch film. The release of the nutrients contained in the mulch film is controlled by the addition to the water-soluble polymer mixture of either (1) a nitrification inhibitor along with urea, or (2) a water-soluble urea-formaldehyde condensation product. The release of the nutrients is also controlled somewhat by the water-resistant resin coating. Other additives may be added to the mulch film to produce a multi-purpose product.

Degradable agricultural plastic articles, e.g., mulching film, comprising slowly released multinutrients in matrix of thermoplastic, and process for preparing same

Shawqui Lahalih

Papers

Process for the synthesis of highly stable sulfonated melamine-formaldehyde condensates as superplasticizing admixtures in concrete

Multilayer degradeable and controlled release multinutrient mulch film, and process for preparing same

Degradable agricultural plastic articles, e.g., mulching film, comprising slowly released multinutrients in matrix of thermoplastic, and process for preparing same

Development of degradable slow release multinutritional agricultural mulch film

Polymer Compositions for Sand Consolidation in Oil Wells