CN110423158A - A kind of preparation method of polylactic acid melting cladded type thiourea slow release fertilizer - Google Patents

Abstract

The invention discloses a preparation method of polylactic acid melt-coated urea slow-release fertilizer. The present invention uses fully biodegradable polylactic acid with a low flowable temperature prepared by a special method to realize melt-coated urea in a high-speed mixer to prepare slow-release fertilizers, so as to improve the performance of the existing coated slow-release fertilizers. Coating process. The melting coating of urea is realized below the melting point of urea (132.5 DEG C) and decomposition temperature, so as to achieve the purpose of sustained release. The method of the invention is simple, has no environmental pollution, and has good coating effect.

Description

A preparation method of polylactic acid melt-coated urea slow-release fertilizer

technical field

The invention relates to the technical field of polymer materials, in particular to a method for preparing a melt-coated urea slow-release fertilizer with polylactic acid having a low flowable temperature.

Background technique

At present, the extensive use of chemical fertilizers has not only greatly increased food production, but also caused low utilization rates of chemical fertilizers, soil compaction, soil acidification, lake eutrophication, groundwater Pollution and other serious environmental problems; in order to improve this situation, people began to vigorously develop slow/controlled release fertilizers, and coated slow/controlled release fertilizers are one of the current research hotspots.

The slow-release performance of coated slow/controlled release fertilizers has a lot to do with the properties of the coated materials. So far, many kinds of coated slow/controlled release fertilizers have come out. From the development of early sulfur-coated slow/controlled-release fertilizers to the present, nitrogen-containing compound-type slightly soluble slow/controlled-release fertilizers, thermoplastic resin-coated slow/controlled-release fertilizers, etc. have also appeared. At present, due to environmental protection issues, degradable polymer materials are gradually being paid attention to by researchers. Polylactic acid (PLA), polycaprolactone (PCL), polybutylene succinate (PBS) are mostly used in this type of slow-release materials. ), polyhydroxyalkanoate (PHA, PHB), ethyl cellulose and other materials, so as to achieve the effect of slow release and environmental protection.

The application of polymer slow-release fertilizers has greatly improved the utilization rate of chemical fertilizers, but also caused soil pollution due to incomplete degradation of some polymer materials and long degradation cycles. More importantly, polymer slow-release fertilizers The preparation of polymer materials usually uses volatile solvents to prepare polymer material solutions. Therefore, the production cost and environmental burden are increased due to the complex process and the volatilization of solvents.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing a polylactic acid melt-coated urea slow-release fertilizer with a low flowable temperature. The overlay effect is good.

The present invention is achieved in this way: the preparation method of polylactic acid melt-coated urea slow-release fertilizer with low flowable temperature is characterized in that: calculated in parts by mass, 100 parts of urea are taken, and 10-30 parts are added to the urea Low flowable polylactic acid powder or granules with an average particle size of 3 μm-3 mm, stirring urea and the polylactic acid powder or granules at 110-130° C. for 2-15 minutes at a stirring speed of 100-500 r/min; The polylactic acid with a low flowable temperature refers to polylactic acid with good fluidity at a coating temperature of 110-120°C, that is, the melt flow rate is greater than 5g/10min at 110-120°C, and the weight is 2.16 kg.

The amino group of urea has affinity with the ester group and carboxyl end group of polylactic acid, so polylactic acid forms a good spread on the surface of solid urea particles after melting, so as to realize the complete coating of urea particles. If the stirring speed is too high, the urea particles will be damaged, and if the stirring speed is too low, the coating thickness will be uneven.

Compared with the prior art, the present invention uses fully biodegradable polylactic acid prepared by a special method with a low flowable temperature to realize melt-coated urea in a high-speed mixer to prepare slow-release fertilizers, which has improved the existing Coating process of coated slow-release fertilizer. The urea is melt-coated below the urea melting point (132.5 DEG C) and decomposition temperature, so as to achieve the purpose of sustained release. The method of the invention is simple, has no environmental pollution, and has good coating effect.

Description of drawings

Fig. 1 is the morphology of granular urea after melt coating in Example 1 of the present invention;

Fig. 2 is the morphology of granular urea after melt coating in Example 2 of the present invention;

Fig. 3 is the morphology of granular urea after melt coating in Example 3 of the present invention;

Fig. 4 is the morphology of granular urea after melt coating in Example 4 of the present invention.

Detailed ways

Embodiment 1 of the present invention: the preparation method of polylactic acid melt-coated urea slow-release fertilizer, 12 parts of special polylactic acid coating materials with low flowable temperature, melt flow rate 8g/10min at 120 ℃ (weight Code weight is 2.16kg), its average particle diameter is 1mm, this polylactic acid is mixed with 100 parts of urea granules, stirs 10 minutes under 120 ℃ in high-speed mixer, and stirring speed is 260 rpm.

Embodiment 2 of the present invention: 15 parts of special polylactic acid coating materials with low flowable temperature, melt flow rate 5g/10min (weight weight is 2.16kg) at 110 ℃, and its average particle diameter is 0.1mm, The polylactic acid was mixed with 100 parts of urea granules, and stirred in a high-speed mixer at 125° C. for 15 minutes at a stirring speed of 300 rpm.

Embodiment 3 of the present invention: 18 parts of special polylactic acid coating materials with low flowable temperature, melt flow rate 55g/10min (weight weight is 2.16kg) at 130°C, and its average particle diameter is 0.5mm, The polylactic acid was mixed with 100 parts of urea granules, and stirred in a high-speed mixer at 130° C. for 2 minutes at a stirring speed of 350 rpm.

Embodiment 4 of the present invention: 21 parts of special polylactic acid coating materials with low flowable temperature, at 120 DEG C, the melt flow rate is 15g/10min (the weight of the weight is 2.16kg), and its average particle diameter is 1.5mm. The polylactic acid was mixed with 100 parts of urea granules, and stirred in a high-speed mixer at 120° C. for 8 minutes at a stirring speed of 200 rpm.

test results

The products obtained in Examples 1-4 were observed with a scanning electron microscope, and the tests were carried out at 25 times, 50 times, 100 times, 250 times, 500 times and 1000 times respectively, and the results are shown in Figures 1-4.

Figures 1-4 respectively show that Examples 1-4 can be simply melt-coated below the melting point of urea, while common polymer-coated slow-release fertilizers require the use of solvents. It shows that after the coating material is treated, the urea can be melt-coated below the melting point of urea and its decomposition temperature to prepare slow-release fertilizers.

The slow-release effect of slow-release urea is tested by soil column leaching test, the method is as follows:

In the test, the slow-release fertilizer in 5.2.3 was used as the test sample. Except for the three groups of slow-release fertilizers U61, U62, U63, U71, U72, and U73, 10 g of the prepared samples were weighed. The specific operation is as follows: 1. First seal the lower end of the PVC pipe with nylon gauze, and then use a cotton pad at the bottom to prevent the soil from flowing out. 2. Weigh 25g of stone sand and add it to the bottom, then mix the air-dried soil and stone sand in a ratio of 5:1, then weigh 250g and add it. 3. Weigh 250g of soil: sand = 5:1 mixed sand mixture and weighed slow-release fertilizer (columnar slow-release fertilizer is placed in the middle of the sand mixture) and mix evenly into the tube, then weigh Add 250g of sand and soil mixture mixed according to the ratio of soil: sand = 5:1 into the tube. 4. Cover the upper part with 25g sand. Number the installed elution columns and fix them on the iron stand, install a conical glass funnel at the bottom of the tube, and place a 50ml Erlenmeyer flask under the funnel to collect the liquid. First, add 30ml of distilled water to the tube at intervals of 5 minutes for a total of 5 times. After the soil is saturated with water, add 200ml of distilled water to the tube respectively. Finally, seal with a perforated film. After cultivating at room temperature for 3 days, the liquid was collected and filtered with water-phase filter paper, then the volume of the filtrate was adjusted to 250ml, and the urea content was tested with a UV spectrophotometer. The leaching operation was repeated every three days until the sustained release was completed.

Example soil column leaching test urea cumulative release rate test results are shown in Table 1:

Example soil column leaching experiment test result (cumulative release rate, %)

The results show that the sustained-release effect increases with the increase of the amount of the specially-made polylactic acid coating material with low flowable temperature. When the low flowable temperature polylactic acid coating material exceeds 15phr, the sustained-release effect is very significant.

Although the embodiments of the present invention have been shown and described, those skilled in the art can understand that various changes, modifications and substitutions can be made to these embodiments without departing from the principle and spirit of the present invention. and modifications, the scope of the invention is defined by the appended claims and their equivalents.

Claims (1)

1. a kind of preparation method of the polylactic acid melting cladded type thiourea slow release fertilizer with low flowable temperature, feature exist In: it calculates according to the mass fraction, takes 100 parts of urea, it is the low flowable of 3 μm of -3mm that 10-30 parts of average grain diameters are added into urea Urea and the polylactic acid powder or particle are stirred 2-15 minutes at 110-130 DEG C, are stirred by the polylactic acid powder or particle of temperature Mixing revolving speed is 100-500r/min；The polylactic acid of the low flowable temperature refers to have at 110-120 DEG C of temperature of plate The polylactic acid of good mobility, i.e., melt flow rate (MFR) is greater than 5g/10min at 110-120 DEG C, and counterweight weight is 2.16kg。