FIELD OF THE INVENTION:
The present invention relates to partially bio-based and bio-compatible polyurethane microcapsules. More particularly, the present invention relates to partially bio-based and bio-compatible polyurethane microcapsules for sustained release of the active ingredient and the process for the preparation thereof.
BACKGROUND AND PRIOR ART:
Bio-based polymers are materials which are produced from renewable resources. The synthesis of polymers from renewable resources has attracted the attention of researchers throughout the globe because of the escalating cost of petrochemicals, increasing demand and concern regarding depletion of the mineral oil sources along with political and environmental concerns. Most of the polymeric shell materials used for encapsulation of active core by interfacial polymerization are based on petroleum feed stock.
Article titled “Isosorbide-based microcapsules for cosmeto-textiles” by N Azizi et al. published in Industrial Crops and Products; 2014, Volume 52, pp 150-157 reports New microcapsules based on renewable materials and containing perfume designed for cosmeto-textile application. Such microcapsules contained the neroline fragrance as core material and bio-based polyurethane as wall material. The polymer wall was synthesized by interfacial polycondensation of isosorbide and methylene bis(phenyl isocyanate). The chemical structure of the microcapsules was confirmed by IR and 1H NMR spectroscopies. The encapsulation efficiency of perfume was determined using 1H NMR analysis technique accounts for 30% which is very low for commercial viability.
Polyurethane microcapsules by interfacial polymerization of toluene 2,4-diisocyanate (TDI) or 4,4-diphenylmethane diisocyanate (MDI) with diol for encapsulation of water-borne polyurethane (PU) paint is disclosed in “The synthesis of polyurethane microcapsules and evaluation of self-healing paint protection properties” by Sooyoul, Park et.al published in 21st International Conference on Composite Materials in 2017.
Aromatic diisocyanates such as methylene bis(phenyl isocyanate) or toluene diisocyanate are routinely used in synthesis of polyurethanes, the major limitation in the use of aromatic diisocyanates in the field of microencapsulation is the toxicity of degradation products causing harm to environment. However, polyurethanes based on aliphatic diisocyanates are considered as more biocompatible than polyurethanes based on aromatic isocyanates because the products of degradation of aromatic isocyanates are toxic, such as aromatic amines (Chem. Eng. Trans. 2016, 49, 349-354).
The Research article titled ‘Tuning Controlled Release Behavior of Starch Granules Using Nanofibrillated Cellulose Derived from Waste Sugarcane Bagasse’ by Parshuram G. Shukla et.al published in ACS Sustainable Chem. Eng in May, 2018 provides controlled release formulations (CRFs) to encapsulate agrochemicals for sustained release, wherein the CRFs are prepared from cellulose nanofibres (CNFs) derived from waste sugarcane bagasse mixed with gelatinized maize starch and urea formaldehyde to yield nano composite granular formulation. Dimethyl phthalate (DMP) is used as model encapsulant. In recent years, nanoparticulates such as nanoclay (J. Text.App.2016, 26, 180-188.), nanocellulose (Langmuir 2017, 33, 1521-1532, ACS Appl. Mater. Interfaces2017, 9, 31763-31776) and nanosilica (Front. Chem. 2015, 3, 42, 1-15) have been employed to enhance the barrier properties and attain further reduction in release of active ingredient from CRFs. These investigations have mainly focused on core shell nanocomposite microcapsules having non-biobased polymer wall made of polyurea or polyurethane.
Owing to increasing environmental awareness and rapid oil feedstock depletion, the exploitation of renewable resource materials for the synthesis of polymeric shell materials is the current need in the field of microencapsulation.
Therefore, thus there is a still need in the art to provide bio-based polyurethane microcapsules that can achieve high encapsulation efficiency and sustained release rate using bio-sourced materials.
OBJECTIVE OF THE INVENTION:
The primary objective of the present invention is to provide a partially bio-based and bio-compatible polyurethane microcapsules having polymeric wall made up of bio-based diol and aliphatic diisocyanate.
Another objective of the present invention is to provide a process for the preparation of partially bio-based and bio-compatible polyurethane microcapsules by using simple, interfacial polymerization which is relatively cost effective and conducive to scale up.
SUMMARY OF THE INVENTION:
Accordingly, the present invention provides a partially bio-based and bio-compatible polyurethane microcapsules for sustained release of the active ingredient comprising;
i) a core containing at least one active ingredient;
ii) a bio-compatible polymeric shell of (a) bio-based diols, (b) aliphatic diisocyanate(s), (c) a cross-linker and (d) an additive;
wherein, the partially bio-based and bio-compatible polyurethane microcapsule has high encapsulation efficiency of 70-95% and sustained release rate of the active ingredient.

The active ingredient is selected from the group consisting of perfumes, biocides, pharmaceuticals, pesticides, enzymes, chemical reagents, self-healing agent and the like in an amount ranging from 30 to 80 % w/w based on the total weight of microcapsules. In preferred embodiment, the active ingredient is selected from dimethyl phthalate, N,N-Diethyl-meta-toluamide (DEET), Ibuprofen, Diuron, Zinc Pyrithione, Irgarol, and 4-Anisaldehyde.
The aliphatic diisocyanate is selected from the group consisting of Isophoronediisocyanate (IPDI), pentamethylenediisocyanates (PDI), 1,6 Hexamethylenediisocyanates (HMDI) and 4,4’-Diisocyanatodicyclohexylmethane (H12 MDI).
The bio-based aliphatic diol is selected from the group consisting of isosorbide, 1,3-propane diol, 1,4-butane diol, 2,3-butane diol, and 1,6-hexane diol.
The mole ratio of diisocyanate to hydroxyl groups used is 1.2: 1.
The cross-linker is selected from the group consisting of glycerol, trimethylol propane (TMP), triethylenetetramine (TETA) and trimethylol ethane (TME) in an amount of 5 to 20 wt % based on the weight of diol.
The additive is selected from nanoparticulates such as nanocellulose, nanoclay, nanosilica and carbon nanotube (CNT) in an amount ranging from 2 to 6 wt % based on total weight of monomers.
In another aspect, the present invention provides a general interfacial polymerization process for the preparation of partially bio-based and bio-compatible polyurethane microcapsules comprising the steps of:
a) preparing the additive solution in water by overnight stirring followed by homogenization;
b) adding the dispersion prepared in step (a) to the solution of surfactant in water followed by sonicating the mixture;
c) emulsifying the solution of diisocyanate and active ingredient in the continuous phase prepared in step (b);
d) preparing the solution of diol, cross-linker and catalyst in water;
e) adding the mixture prepared in step (d) drop-wise to the mixture prepared in step (c); and
f) stirring the reaction mixture of step (d) followed by centrifugation and filtration to obtain partially bio-based and bio-compatible polyurethane microcapsules.
The surfactant in the process is selected from the group consisting of polyvinyl pyrrolidone (PVP K-90), polyvinyl pyrrolidone (PVP K-30), Polyvinyl alcohol (PVA), Tween 80, sodium lignosulphonate (SLS) and sodium dodecyl sulfate (SDS) in an amount of 3 to 5 % (w/v) based on the continuous medium.
BRIEF DESCRIPTION OF THE DRAWINGS:
Fig. 1: Optical micrograph of Example 1
Fig. 2: Optical micrograph of Example 2
Fig. 3: Optical micrograph of Example 3
Fig. 4: Optical micrograph of Example 4
Fig. 5: SEM image of Example 2
Fig. 6: SEM image of Example 3
Fig. 7: SEM imageof Example 4
Fig. 8: Release rate study of Example 2, Example 3 and Example 4.
Fig. 9: Optical micrograph of Example 5
Fig. 10: Optical micrograph of Example 6
Fig. 11: Optical micrograph of Example 7
Fig. 12: SEM image of Example 5
Fig. 13: SEM image of Example 6
Fig. 14: Optical micrograph of Example 8
Fig. 15: Optical micrograph of Example 9
Fig. 16: Optical micrograph of Example 10
DETAILED DESCRIPTION OF THE INVENTION:
The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.
The present invention provides polyurethane microcapsules for controlling the release of the active ingredient wherein the polymeric wall of the microcapsule is formed using bio-based diols and aliphatic diisocyanates. The polyurethane microcapsules of the present invention are biocompatible thereby eliminating the toxic products formed after degradation of the bio-based polymeric wall. Further, the polyurethane microcapsules are prepared by simple, cost effective interfacial polymerization which ensures direct control of the mean size and thickness of the capsules and high active loading with tunable delivery processes.
In an embodiment, the present invention discloses partially bio-based and bio-compatible polyurethane microcapsules for sustained release of the active ingredient comprising;
i) a core containing at least one active ingredient;
ii) a polymeric shell consisting of (a) bio-based diol, (b)aliphatic diisocyanate, (c) a cross linker and (d) an additive;
wherein the bio-based polyurethane microcapsule has high encapsulation efficiency of 70-95% and sustained release rate of the active ingredient.

The monomer aliphatic diisocyanate is selected from the group consisting of isophorone diisocyanate (IPDI), pentamethylene diisocyanates (PDI), 1, 6 Hexamethylene diisocyanates (HMDI) and 4,4’-Diisocyanatodicyclohexylmethane (H12 MDI).
The bio-based aliphatic diol is selected from the group consisting of isosorbide, 1,3-propane diol, 1,4-butane diol, 2,3-butane diol, and 1,6-hexane diol.
The molar ratio of diisocyanate to hydroxyl groups used is 1.2: 1
The active ingredient is selected from the group consisting of perfumes, biocides, pharmaceuticals, pesticides, enzymes, chemical reagents, self-healing agent and the like in an amount of 30 to 80 wt % based on total weight of microcapsules. In preferred embodiment, the active ingredient is selected from dimethyl phthalate (DMP), N,N-Diethyl-meta-toluamide (DEET), Ibuprofen, Diuron, Zinc Pyrithione, Irgarol, and 4-Anisaldehyde.
The bio-based cross linker of the present invention is selected from the group consisting of glycerol, trimethylol propane (TMP), triethylenetetramine (TETA) and trimethylol ethane (TME) in an amount ranging from 5 to 20 wt % based on the weight of diol.
The additive is selected from bio-based nanoparticulates such as nanocellulose, nanoclay, nanosilica and carbon nanotube (CNT) in an amount ranging from 2 to 6 wt % based on weight of polymer wall.
In another embodiment, the present invention provides a general interfacial polymerization process for the preparation of bio-based polyurethane microcapsules comprising the steps:
a) preparing the additive solution in water by overnight stirring followed by homogenization;
b) adding the dispersion prepared in step a) to the solution of surfactant in water followed by sonicating the mixture;
c) emulsifying solution of diisocyanate and active ingredient in the continuous phase prepared in step b);
d) preparing the solution of diol, cross-linker and catalyst in water;
e) adding the mixture prepared in step d) drop-wise to the mixture prepared in step c) and
f) stirring the reaction mixture followed by centrifugation and filtration to obtain partially bio-based and bio-compatible polyurethane microcapsules.

The additive is selected from nanocellulose, nanoclay, nanosilica and carbon nanotube (CNT).

The aliphatic diisocyanate is selected from the group consisting of isophorone diisocyanate (IPDI), pentamethylene diisocyanates (PDI), 1,6 Hexamethylene diisocyanates (HMDI) and 4,4’-Diisocyanatodicyclohexylmethane (H12 MDI).
The bio-based diol is selected from renewable resource material such as isosorbide, 1,3-propane diol, 1,4-butane diol, 2,3-butane diol, and 1,6-hexane diol.
The surfactant is selected from the group consisting of polyvinyl pyrrolidone (PVP K-90), polyvinyl pyrrolidone (PVP K-30), polyvinyl alcohol (PVA), Tween 80, sodium lignosulphonate (SLS) and sodium dodecyl sulfate (SDS).
The cross-linker is selected from the group consisting of glycerol, trimethylol propane (TMP), triethylenetetramine (TETA) and trimethylol ethane (TME).
The catalyst is selected from a group consisting of 1,4-Diazabicyclo[2.2.2]octane (DABCO), DibutyltinDilaurate (DBTDL).
The active ingredient is selected from the group consisting of perfumes, biocides, pharmaceuticals, pesticides, enzymes, chemical reagents, self-healing agent and the like. In preferred embodiment, the active ingredient is selected from dimethyl phthalate, N,N-Diethyl-meta-toluamide (DEET), Ibuprofen, Diuron, Zinc Pyrithione, Irgarol, and 4-Anisaldehyde.
Accordingly, the solution of additive in water was prepared by overnight stirring followed by homogenization and was added to the solution of surfactant in water. To this continuous phase, solution of diisocyanate and active ingredient was added and stirred at 1000 rpm and 27oC. The solution of diol, cross-linker and catalyst in water was prepared separately and added drop-wise to the continuous phase containing diisocyanate and active ingredient at 1000 rpm and 27oC and continued to stir for 4 hours at 30oC. After continuing the stirring at 50oC at 500 rpm for 2 hours, the reaction mixture was centrifuged and the obtained polyurethane microcapsules were filtered and dried.
In a preferred embodiment, the present invention discloses partially bio-based and bio-compatible polyurethane microcapsules for sustained release of the active ingredient comprising;
i) a core containing dimethyl phthalate as active ingredient in an amount ranging from 30 to 80 wt % based on total weight of microcapsules and
ii) a polymeric shell consisting of isophorone diisocyanate and a bio-based isosorbide, glycerol as cross linker in an amount of 5 to 20 wt % based on the weight of isosorbide, and nanocellulose as additive in an amount of 2 to 6 wt % based on polymer weight;
wherein, the partially bio-based and bio-compatible polyurethane microcapsule has high encapsulation efficiency of 70-95% and sustained release rate of the active ingredient.
The molar ratio of isophorone diisocyanate to hydroxyl groups used is 1.2:1.
In another preferred embodiment, the process for the preparation of bio-based polyurethane microcapsules by using interfacial polymerization is depicted in Scheme 1 below:

Scheme 1: Synthesis of polyurethane by interfacial polymerization

In an embodiment, the polyurethane microcapsules loaded with 50% DMP and 2-4 wt % of the additive i.e. nanocellulose of the present invention are spherical in shape with average size of 2-25µ.
The partially bio-based and bio-compatible polyurethane microcapsules of the present invention containing nanocellulose shows sustained release rate of the active ingredient DMP, in comparison to the pristine microcapsules (MIC’s).The microcapsules containing 2% nanocellulose exhibited significant reduction in the release rate of DMP in the first 500 min as compared to MICs containing 4 % nanocellulose (Fig 8).
EXAMPLES:
The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.
Materials: Dimethyl phthalate (99%), Isophorone diisocyanate (98%) (IPDI), 1, 4-Diazabicyclo (2, 2, 2) octane (98%) (DABCO) were purchased from Sigma Aldrich, USA. Methanol (HPLC grade, 99.7%) and Glycerol were purchased from Merck Ltd, India. Polyvinyl pyrrolidone (K90, LR) (PVP) was obtained from S. D. Fine Chemical Ltd, India. Isosorbide was a gift sample obtained from Reliance Company. Nanocellulose fibrils were isolated from waste sugarcane bagasse in the laboratory. Distilled water was used as a continuous medium. All other chemicals were used as received.
Example 1: Preparation of blank microcapsules
1.25 g of surfactant PVP K90 (5 % w.r.t continuous medium) was dissolved in 25 mL of distilled water in a 250 mL beaker by sonicating the mixture for 30 minutes. To this surfactant solution, 2.7 g of IPDI was added while stirring the mixture at 1000 rpm (revolutions per minute) using turbine type stirrer at 27 °C. Then the mixture of 1 g of isosorbide, 0.2 g of glycerol and 0.022 g of DABCO in 4 mL of distilled water was added drop wise over a period of 10 min. The reaction mixture was continued to stir at 30 °C for 4 hours at 1000 rpm and at 50°C for 2 hour at 500 rpm. The dispersion was centrifuged and filtered and the obtained residue was dried in air draft oven at 45 °C. The yield of microcapsules obtained was 89 %.
Example 2: Preparation of polyurethane microcapsules (pristine microcapsules) containing dimethyl phthalate (DMP) with 50 % loading:
2.0 g of surfactant PVP K90 (5 % w.r.t continuous medium) was dissolved in 40 g of distilled water in 250 mL beaker by sonicating the mixture for 30 minutes. To this surfactant solution, mixture of 3.45 g of DMP and 2.7 g of IPDI was added while stirring the mixture at 1000 rpm (revolutions per minute) using turbine type stirrer at 27 °C. Then the mixture of 1 g of isosorbide, 0.2 g of glycerol and 0.022 g of DABCO in 4 mL of distilled water was added drop wise over a period of 10 min. The reaction mixture was continued to stir at 30 °C for 4 hours at 1000 rpm and at 50°C for 2 hour at 500 rpm. The dispersion was centrifuged and filtered and the obtained residue was dried in air draft oven at 45 °C. The yield of microcapsules obtained was 66.32 %.
Example 3: Preparation of polyurethane microcapsules containing nanocellulose (2 % NC) as an additive and dimethyl phthalate (DMP) with 50 % loading:
0.078 g of nanocellulose (2 % w.r.t. polymer wall) was dispersed in 10 mL of distilled water and was added to a surfactant solution of PVP K90 (5 % w.r.t continuous medium) prepared by adding 2.0 g of surfactant in 30 g of distilled water in 250 mL beaker. To this solution, mixture of 3.45 g of DMP and 2.7 g of IPDI was added while stirring the mixture at 1000 rpm (revolutions per minute) using turbine type stirrer at 27 °C. Then the mixture of 1 g of isosorbide, 0.2 g of glycerol and 0.022 g of DABCO in 4 mL of distilled water was added drop wise over a period of 10 min. The reaction mixture was continued to stir at 30 °C for 4 hours at 1000 rpm and at 50°C for 2 hour at 500 rpm. The dispersion was centrifuged and filtered and the obtained residue was dried in air draft oven at 45 °C. The yield of microcapsules obtained was 68.58 %.
Example 4: Preparation of polyurethane microcapsules containing nanocellulose (4 % NC) as an additive and dimethyl phthalate (DMP) with 50 % loading:
0.156 g of nanocellulose (4 % w.r.t. polymer wall) was dispersed in 10 mL of distilled water and was added to a surfactant solution of PVP K90 (5 % w.r.t continuous medium) prepared by adding 2.0g of surfactant in 30g of distilled water in 250 mL beaker. To this solution, mixture of 3.45g of DMP and 2.7g of IPDI was added while stirring the mixture at 1000 rpm (revolutions per minute) using turbine type stirrer at 27°C. Then the mixture of 1 g of isosorbide, 0.2g of glycerol and 0.022g of DABCO in 4 mL of distilled water was added drop wise over a period of 10 min. The reaction mixture was continued to stir at 30°C for 4 hours at 1000 rpm and at 50°C for 2 hour at 500 rpm. The dispersion was centrifuged and filtered and the obtained residue was dried in air draft oven at 45 °C. The yield of microcapsules obtained was 62.22 %.

Example 5: Preparation of polyurethane microcapsules (pristine microcapsules) containing dimethyl phthalate (DMP) with 40 % loading: 2.0 g of surfactant PVP K90 (5 % w.r.t continuous medium) was dissolved in 40 g of distilled water in 250 mL beaker by sonicating the mixture for 30 minutes. To this surfactant solution, mixture of 2.30 g of DMP and 2.7 g of IPDI was added while stirring the mixture at 1000 rpm (revolutions per minute) using turbine type stirrer at 27 °C. Then the mixture of 1 g of isosorbide, 0.2 g of glycerol and 0.022 g of DABCO in 4 mL of distilled water was added drop wise over a period of 10 min. The reaction mixture was continued to stir at 30 °C for 4 hours at 1000 rpm and at 50°C for 2 hour at 500 rpm. The dispersion was centrifuged and filtered and the obtained residue was dried in air draft oven at 45 °C. The yield of microcapsules obtained was 64.66 %.
Example 6: Preparation of polyurethane microcapsules (pristine microcapsules) containing dimethyl phthalate (DMP) with 60 % loading: 2.0 g of surfactant PVP K90 (5 % w.r.t continuous medium) was dissolved in 40 g of distilled water in 250 mL beaker by sonicating the mixture for 30 minutes. To this surfactant solution, mixture of 5.17 g of DMP and 2.7 g of IPDI was added while stirring the mixture at 1000 rpm (revolutions per minute) using turbine type stirrer at 27 °C. Then the mixture of 1 g of isosorbide, 0.2 g of glycerol and 0.022 g of DABCO in 4 mL of distilled water was added drop wise over a period of 10 min. The reaction mixture was continued to stir at 30 °C for 4 hours at 1000 rpm and at 50°C for 2 hour at 500 rpm. The dispersion was centrifuged and filtered and the obtained residue was dried in air draft oven at 45 °C. The yield of microcapsules obtained was 71.75 %.
Example 7: Preparation of polyurethane microcapsules (pristine microcapsules) containing dimethyl phthalate (DMP) with 70 % loading: 2.0 g of surfactant PVP K90 (5 % w.r.t continuous medium) was dissolved in 40 g of distilled water in 250 mL beaker by sonicating the mixture for 30 minutes. To this surfactant solution, mixture of 8.06 g of DMP and 2.7 g of IPDI was added while stirring the mixture at 1000 rpm (revolutions per minute) using turbine type stirrer at 27 °C. Then the mixture of 1 g of isosorbide, 0.2 g of glycerol and 0.022 g of DABCO in 4 mL of distilled water was added drop wise over a period of 10 min. The reaction mixture was continued to stir at 30 °C for 4 hours at 1000 rpm and at 50°C for 2 hour at 500 rpm. After the completion of the reaction, free DMP was seen in the dispersion.

Example 8: Preparation of polyurethane microcapsules (pristine microcapsules) from 1,4 butane diol (BDO) and isophorone diisocyanate (IPDI) containing dimethyl phthalate (DMP) with 50 % loading: 2.0 g of surfactant PVP K90 (5 % w.r.t continuous medium) was dissolved in 40 g of distilled water in 250 mL beaker by sonicating the mixture for 30 minutes. To this surfactant solution, mixture of 4.71 g of DMP and 3.51 g of IPDI was added while stirring the mixture at 1000 rpm (revolutions per minute) using turbine type stirrer at 27 °C. Then the mixture of 1 g of 1,4 butane diol, 0.2 g of glycerol and 0.022 g of DABCO in 4 mL of distilled water was added drop wise over a period of 10 min. The reaction mixture was continued to stir at 30 °C for 4 hours at 1000 rpm and at 50°C for 2 hour at 500 rpm. The dispersion was centrifuged and filtered and the obtained residue was dried in air draft oven at 45 °C. The yield of microcapsules obtained was 82.57 %.
Example 9: Preparation of polyurethane microcapsules (pristine microcapsules) from 1,4 butane diol (BDO) and isophorone diisocyanate (IPDI) containing dimethyl phthalate (DMP) with 70 % loading: 2.0 g of surfactant PVP K90 (5 % w.r.t continuous medium) was dissolved in 40 g of distilled water in 250 mL beaker by sonicating the mixture for 30 minutes. To this surfactant solution, mixture of 11.0 g of DMP and 3.51 g of IPDI was added while stirring the mixture at 1000 rpm (revolutions per minute) using turbine type stirrer at 27 °C. Then the mixture of 1 g of 1,4 butane diol, 0.2 g of glycerol and 0.022 g of DABCO in 4 mL of distilled water was added drop wise over a period of 10 min. The reaction mixture was continued to stir at 30 °C for 4 hours at 1000 rpm and at 50°C for 2 hour at 500 rpm. The dispersion was centrifuged and filtered and the obtained residue was dried in air draft oven at 45 °C. The yield of microcapsules obtained was 94.19 %.
Example 10: Preparation of polyurethane microcapsules (pristine microcapsules) from 1,4 butane diol (BDO) + 1,1,1-Tris(hydroxymethyl)propane (as a cross-linker) (TMP) and isophorone diisocyanate (IPDI) containing N,N-diethyl-meta-toluamide (DEET) with 50 % loading: 2.0 g of surfactant PVP K90 (5 % w.r.t continuous medium) was dissolved in 40 g of distilled water in 250 mL beaker by sonicating the mixture for 30 minutes. To this surfactant solution, mixture of 4.53 g of DEET and 3.33 g of IPDI was added while stirring the mixture at 1000 rpm (revolutions per minute) using turbine type stirrer at 27 °C. Then the mixture of 1 g of 1,4 butane diol, 0.2 g of TMP and 0.022 g of DABCO in 4 mL of distilled water was added drop wise over a period of 10 min. The reaction mixture was continued to stir at 30 °C for 4 hours at 1000 rpm and at 50°C for 2 hour at 500 rpm. The dispersion was centrifuged and filtered and the obtained residue was dried in air draft oven at 45 °C. The yield of microcapsules obtained was 70.60 %.

Experimental Data:
Experiment No. DMP % Loading Additive % Particle Size (micron) Yield* Encapsulation Efficiency (%)
Example 1 - - 2-10 89 % -
Example 2 50 % - 2-25 66.32 % 93.24
Example 3 50 % 2 % 2-25 68.58 % 80.28
Example 4 50 % 4 % 2-25 62.22 % 70.26
Example 5 40 % - 2-25 64.66 91.20
Example 6 60 % - 2-25 71.75 86.71
Example 7 70 % - 2-15 # #
* % Yield was calculated by filtration method, # Free DMP seen in the dispersion

? Experimental Details for Examples 8 to 10:
Expt. No. Diol Diisocyanate Active % Loading Cross-linker Particle Size (micron) Yield*% Encapsulation Efficiency (%)
Example 8 1,4 Butane diol IPDI DMP 50 % Glycerol 2-25 82.57 92.24
Example 9 1,4 Butane diol IPDI DMP 70 % Glycerol 2-25 94.19 86.91
Example 10 1,4 Butane diol IPDI DEET 50 % TMP 2-25 70.60 79.81
* % Yield was calculated by filtration method
Characterization of pristine microcapsules (MICs):
Olympus BX-60, USA optical microscope fitted with Olympus SC30 digital camera was used to measure the size of MICs. SEM (E-SEM, Quanta 200-3D) at 15 kV was used to study the morphology of MICs. Samples were drop casted on silicon-wafer and sputter coated with gold prior to imaging to avoid charging. FT-IR spectra were recorded using ATR mode on a Perkin-Elmer Spectrum GX spectrophotometer. 1H-NMR spectra were recorded on a Bruker NMR spectrophotometer (400 MHz) in DMSO-d6 solution at 27°C. UV-visible spectrophotometer (Hitachi model 220) was used to study the release of DMP from MICs.
1. Optical Microscopy and SEM
Obtained microcapsules (aqueous dispersion) were observed through optical microscope to determine their size and size distribution. Optical micrographs of blank polyurethane microcapsules (Example 1), pristine MICs (Example 2) and MIC-NC (2 wt %) (Example 3).Optical micrographs of all the synthesized batches exhibited the spherical shape of the MICs and the average size of all the MICs were in the range of 2 to 25 microns.SEM photographs of (a) pristine MICs (Example 2) (b) MIC-NC (2 wt %) (Example 3) and MIC-NC (4 wt %) has been presented in the figures 4 to 6. The morphology of the polyurethane microcapsules exhibited the spherical shape.

2. FT-IR and 1H-NMR Study:
FT-IR spectra were recorded using ATR mode on a Perkin-Elmer Spectrum GX spectrophotometer. FT-IR spectrum of pristine MICs exhibited the presence of characteristic frequencies of DMP (1722 cm-1 due to -C=O, 1273 and 1121 cm-1 due to ester group) along with urethane characteristics frequencies (3327 cm-1 corresponding to -N-H, 1730 cm-1 due to -C=O, 1070 cm-1 due to –C-O-C ) whereas blank microcapsules of polyurethanes indicated only urethane characteristics frequencies. This indicated the encapsulation of DMP by polyurethane as a wall material.
1H-NMR spectra were recorded on a Bruker NMR spectrophotometer (400 MHz) in DMSO-d6 solution at 27°C.
Example 1 (Blank microcapsules of polyurethane) 1H-NMR (400 MHz, DMSO-d6): d (ppm) 5.77 (d, 1H, -NH), 5.57 (d, 1H, -NH), 3.67 (s, 2H, -CH2-NH), 2.75 - 0.77 (combined signals corresponding to –CH3, -CH2, -CH of isosorbide and IPDI).
Dimethyl phthalate d (ppm): 7.74-7.69 (d, 4 Ar-H), 3.82 (s, 6H, -CH3)
Example 2 (Microcapsules of polyurethane loaded with 50 % DMP) d (ppm): 7.73-7.69 (d, 4 Ar-H), 3.82 (s, 6H, -CH3), 5.77 (d, 1H, -NH), 5.57 (d, 1H, -NH), 2.75 – 0.76 (combined signals corresponding to –CH3, -CH2, -CH of isosorbide and IPDI).
1H-NMRspectrum of polyurethane microcapsules loaded with DMP exhibited the characteristic peaks of the DMP.
3. Extraction Studies:
Extraction of the DMP was carried out to determine the actual loading of DMP in the capsules i.e. encapsulation efficiency. Following procedure was used for the extraction studies: Approximately 0.5 g of sample was taken and transferred to 100 mL round bottom flask. 25-30 mL methanol was added to this flask and refluxed at 60-70°C for 8 h. The mixture was cooled to 27°C and filtered through Grade-3 sintered crucible. The residue was washed with 25-30mL methanol and filtrate was transferred to 100 mL volumetric flask then diluted with methanol. From this 100 mL flask, 1.0 mL of solution was transferred to 25 mL volumetric flask and diluted with methanol. This last dilution was performed thrice. The absorbance of the diluted solution was determined at 276 nm (?maxfor DMP) on UV spectrophotometer (Hitachi-Model 220).
The concentration of DMP determined using calibration slope (0.01) using following formula:

The encapsulation efficiencies of MICs of the types pristine, containing 2 % NC and 4 % NC were found to be 93.24 %, 80.28 %, 70.26 %, respectively. This indicated that DMP content obtained by extraction studies is in good agreement with theoretical loading.
4. Release rate studies
A perfect sink condition was followed to carry out release study of DMP from MICs. A sufficient quantity of MICs was taken in 400 mL distilled water in 500 mL beaker kept in thermostatic bath maintained at 30 ± 0.1 oC. The release mixture was stirred at 200 rpm using over head stirrer fitted with rod having paddle type blades. At a specific time interval, 10 mL aliquots were taken out using graduated 10 mL pipette having cotton plug at the tip to avoid entering of capsules in the aliquot. The amount of DMP release from MICs was determined by measurement of absorbance at the maximum wavelength of absorbance (?max 276 nm). 10 mL of eluting solvent (water) was added to the beaker to make total volume at 400 mL. The release rate experiments for each sample were carried out in duplicate and average of cumulative release obtained from two sets of experiments was noted (Fig 8).
Advantages of invention:
• Use of renewable resource materials for the preparation of bio-based polyurethane microcapsules by using interfacial polymerization.
• Higher encapsulation efficiencies in the range 70- 95 % and lower release rate.
• Use of aliphatic diisocyanate since polyurethanes based on aliphatic isocyanates are considered as more biocompatible than polyurethanes based on aromatic isocyanates because the products of degradation of aromatic isocyanates are toxic, such as aromatic amines.

,CLAIMS:We claim:
1. A bio-based polyurethane microcapsules for sustained release of active ingredient comprising;
i) a core containing at least one active ingredient;
ii) a polymeric shell consisting of (a) bio-based diol, (b)aliphatic diisocyanate, (c) a cross linker and (d) an additive; wherein the bio-based diol is selected from the group consisting of isosorbide, 1,3-propane diol, 1,4-butane diol, 2,3-butane diol, and 1,6-hexane diol and the aliphatic diisocyanate is selected from the group consisting of 1,6 Hexamethylene diisocyanates (HMDI), Isophorone diisocyanate (IPDI), pentamethylene diisocyanates (PDI), and 4,4’-Diisocyanatodicyclohexylmethane (H12 MDI);
wherein, the mole ratio of diisocyanate to hydroxyl groups used is 1.2: 1; and
wherein, the bio-based polyurethane microcapsule has high encapsulation efficiency of 70-95%.
2. The bio-based polyurethane microcapsules as claimed in claim 1, wherein the active ingredient is selected from perfumes, biocides, pharmaceuticals, pesticides, enzymes, chemical reagents and self-healing agents.
3. The bio-based polyurethane microcapsules as claimed in claim 2, wherein the active ingredient is selected further from dimethyl phthalate, N,N-Diethyl-meta-toluamide (DEET), Ibuprofen, Diuron, Zinc Pyrithione, Irgarol, and 4-Anisaldehyde.
4. The bio-based polyurethane microcapsules as claimed in claim 1, wherein said linker is selected from the group consisting of glycerol, trimethylol propane (TMP), triethylenetetramine (TETA) and trimethylol ethane (TME).
5. The bio-based polyurethane microcapsules as claimed in claim 1, wherein an additive is selected from nanocellulose, nanoclay, nanosilica and carbonaotube (CNT).
6. A process for the synthesis of bio-based polyurethane microcapsule by using interfacial polycondensation comprising the steps of:
a) preparing the additive solution in water by overnight stirring followed by homogenization;
b) adding the dispersion prepared in step a) to the solution of surfactant in water followed by sonicating the mixture;
c) emulsifying solution of diisocyanate and active ingredient in the continuous phase prepared in step b);
d) preparing the solution of diol, cross-linker and catalyst in water;
e) adding the mixture prepared in step d) drop-wise to the mixture prepared in step c); and
f) stirring the reaction mixture followed by centrifugation and filtration to obtain partially bio-based and bio-compatible polyurethane microcapsules.
7. The process as claimed in claim 6, wherein said surfactant is selected from the group consisting of polyvinyl pyrrolidone (PVP K-90), polyvinyl pyrrolidone (PVP K-30), polyvinyl alcohol (PVA), Tween 80, sodium lignosulphonate (SLS) and sodium dodecyl sulfate (SDS).
8. The process as claimed in claim 6, wherein said catalyst is selected from the group consisting of 1,4-Diazabicyclo[2.2.2]octane (DABCO), and DibutyltinDilaurate (DBTDL).