Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-02-11
2002-09-24
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S330000, C428S337000, C428S402000, C071S024000, C071S063000, C071S064130, C071S064010
Reexamination Certificate
active
06455149
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to pelletized peat moss that readily degranulates and expands to its original unpelletized (loose) state after contact with water.
BACKGROUND
The unique features of peat moss are well known. Peat moss is a combination of cellulose, lignin, humus acid, waxes, and resins. Peat moss leaves are one cell layer thick and are thin-walled with large cavities that readily absorb and hold water. Peat moss has high water retention and holding capacity, high buffering capacity, high cation exchange capacity, high organic matter, excellent aeration qualities, and high porosity. Clearly, these characteristics set it apart from competing products such as compost, coir, and others.
However, peat is not without its shortcomings. Peat moss is usually packaged in compressed bales at about 15 pound/foot
3
(15 lb/ft
3
, 240 kg/m
3
), and the relatively bulky bales take up considerable storage space. Peat moss is relatively non-free flowing. This makes the removal from the bale somewhat difficult, especially in greenhouses and container growing applications where substrate mixes are commonly prepared. In fact, bale busters have had to be specifically designed to open up compressed bales of peat moss.
Most types of loose peat moss are dusty and somewhat of a burden to use, especially in the small quantities typically used by garden hobbyists. It is common practice for these types of users to try to scoop peat moss from a compressed bale. In this situation the hobbyist is confronted with a hard-to-penetrate mass of packed peat moss, that when removed from the bag, generates significant dust. Workers handling peat often need to wear masks to prevent inhalation of dust particles.
In addition, baled or loose peat moss is difficult or nearly impossible to use in conventional lawn spreading fertilizer equipment. Loose peat moss bridges easily, causing void areas to form in the feed hopper above the spreader, thereby preventing the free flow of peat moss through the spreader. Although the free flow characteristics of peat moss can be improved by lowering its moisture content, it then becomes difficult to rewet and too dusty to use.
SUMMARY OF THE INVENTION
This invention provides water swellable pellets including peat moss, a pH adjusting agent, a wetting agent, and optionally a processing additive. Preferably, the pellets of this invention have a bulk density of about 300 kg/m
3
to about 600 kg/m
3
.
This invention also provides a method for preparing water swellable peat moss pellets. The method includes: preparing a mixture including peat moss and a pH adjusting agent; extruding the mixture through a die to form pellets; and adding a wetting agent to the mixture prior to extruding and/or to the pellets after extruding. Preferably the die has a compression ratio of about 2 to about 4. In a preferred embodiment, the method is a continuous process for preparing peat pellets.
As used herein, “water swellable” means that the pellet has a pellet swell length (PSL) of greater than about 1.2. The “pellet swell length” is defined as the ratio of wetted pellet length to unwetted pellet length after the pellet has been saturated with water. The bulk density is defined as the weight of pellets (kg) required to fill a cubic meter of volume.
It should be understood that where incorporation of an ingredient is specified, either a single ingredient or a combination or mixture of materials may be used as desired. It should also be understood that the specification of a value that includes the term “about” is meant to include both higher and lower values reasonably close to the specified value. For many properties, values either 10% above or 10% below the specified value are intended to be included by use of the term “about”.
DETAILED DESCRIPTION OF THE INVENTION
This invention provides peat moss pellets that readily degranulate and expand back to their original loose and fluffy peat moss state after contact with water. The pellets remain easily and instantaneously wettable after they are produced. Specifically, this invention identifies formulations for peat moss pellets that readily reexpand (degranulate) to a fluffy peat moss-state after wetting. After initial wetting and subsequent drying, the peat readily rewets.
The particle size of the pellets can vary depending on the application. Typical particle sizes are about 1.4 millimeter (mm) to about 4.0 mm for many applications. The bulk density of the pellets is typically at least about 19 pounds per cubic foot (lb/ft
3
) (300 kilograms per cubic meter (kg/m
3
)), preferably at least about 22 lb/ft
3
(350 kg/m
3
), and more preferably at least about 25 lb/ft
3
(400 kg/m
3
). The bulk density of the pellets is typically at most about 37 lb/ft
3
(600 kg/m
3
), preferably at most about 31 lb/ft
3
(500 kg/m
3
), and more preferably at most about 28 lb/ft
3
(450 kg/m
3
). The pellets have good mechanical strength and contain little or no dust. The pellets have long shelf life as evidenced by their relatively stable functional properties (e.g., expansion in length or volume upon wetting) over a period of from about one month to about three months. The pellets are easily handled in bulk or bag form and are easily spread with conventional fertilizer spreading equipment. The pH of the pellets is typically at least about 5.5, preferably at least about 6.0, and more preferably at least about 6.5. The pH of the pellets is typically at most about 8.0, preferably at most about 7.5, and more preferably at most about 7.0.
Pellets can be produced by either batch or continuous methods. For example, a batch method may consist of a single compression stroke operation where the peat is compacted into molds using pressure, followed by removing the pellets produced from the molds. Although pellets can be produced by batch methods without substantial heat buildup, batch methods are labor and time intensive and are not cost effective methods for use in the production of commercial quantities of peat pellets. Continuous extrusion-based pelletizing methods are ideal methods for economically producing commercial quantities of peat pellets. However, extrusion methods suffer from significant buildup of heat that is produced in the extrusion process.
Pelletizing is a processes that utilizes compaction and extrusion to produce pellets. When material is forced through a die to produce pellets, frictional heat is imparted to the material being pelletized. In many cases this is a favorable situation, as the heat can activate some types of binders and increase their effectiveness. However, in the case of peat moss, frictional heat is an undesirable consequence of pelletizing. Heat activates the natural waxes and resins in the peat moss, thereby transforming the surface to essentially a hydrophobic, nonwettable state as evidenced by the small expansion in length and volume observed upon contact with water. The activated waxes act to waterproof the pellet, an undesirable result in the case of the peat pellets of this invention.
The ingredients used to make the peat pellets of this invention are often mixed with a commercially available solids mixer such as the Model S-10 Ribbon Mixer from H.C. Davis Sons Manufacturing Co., Inc. (Davis, Bonner Springs, Kans.). Although conditions may vary depending on the equipment being used and the materials being processed, the mixer is typically run at about 20 revolutions per minute (rpm) to about 30 rpm for about 5 minutes to about 10 minutes to adequately blend the ingredients. Alternatively, the ingredients can be added continuously to ports in a pellet mill with the mixing taking place during the pelletizing process.
The ingredients may then be converted to pellets using a commercially available pellet mill such as those available from California Pellet Mill Co. (CPM, Crawfordsville, Ind.). Although conditions may vary depending on the equipment being used and the materials being processed, the pellet mill is typically run at about 240 rpm with a feed rate of about 300 grams per minute (g/min) to extrude the mixt
Hagen Timothy S.
Malterer Thomas J.
Kiliman Leszek
Mueting Raasch & Gebhardt, P.A.
Regents of the University of Minnesota
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