HK1192577B - Blends of a polylactic acid and a water soluble polymer - Google Patents

Description

Blends of polylactic acid and water soluble polymers

Technical Field

The present invention relates to water-dispersible biodegradable compositions that can be formed into films and fibers. The invention also relates to a polymer blend comprising polylactic acid and a water-soluble polymer.

More particularly, the present invention relates to the use of graft copolymers (PLA-grafted water-soluble polymers) for compatibilizing PLA and water-soluble polymers. This reactive compatibilization of immiscible polymer blends is achieved in such a way that the main blend components are covalently bonded. Furthermore, such reactive compatibilization can be carried out by reactive extrusion.

Background

For disposable products, it is desirable to use biodegradable and water dispersible materials.

Biodegradable polymers disposed of in a biologically active environment are degraded by the enzymatic action of microorganisms such as bacteria, fungi and algae. Their polymer chains can also be cleaved by non-enzymatic processes, such as chemical hydrolysis. The term "biodegradable" as used herein refers to the aerobic biodegradation of plastics under controlled composting conditions using standard test methods, the composition degrading within a year.

The term "water-dispersible" as used herein means that the composition dissolves or disintegrates into fragments of less than 0.841 millimeters (20 mesh) after immersion in water at room temperature for about 24 hours.

Poly (lactic acid) or polylactic acid (PLA) is an attractive biodegradable and biocompatible polymer. It is derived from renewable resources (e.g., corn, wheat, or rice) and is biodegradable, recyclable, and compostable. In addition, PLA exhibits excellent processability. In fact, PLA has better thermal processability than other biodegradable materials, such as poly (hydroxyalkanoates) (PHAs), poly (-caprolactone) (PCL), etc. It can be processed by injection molding, film extrusion, blow molding, thermoforming, fiber spinning, and film forming. However, the use of PLA may be limited due to the fact that it is a hydrophobic polymer and cannot be dissolved or dispersed in water.

Water-soluble biodegradable polymers can be synthesized by modifying starch and cellulose. For example, carboxymethylcellulose (CMC) with different degrees of carboxymethyl substitution is a class of commercially available water-soluble polymers. Hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), Methyl Cellulose (MC), and Ethyl Cellulose (EC) are used as binders, water retention aids, thickeners, film formers, lubricants, or rheology modifiers. Water-soluble polysaccharides are also produced by microbial fermentation. Xanthan gum is the most widely used microbial polysaccharide. Industrial uses of xanthan gum include oil recovery (viscosity control), paper making, agriculture (stimulating plant growth), and cosmetics. Pullulan (pullulan) also shows a variety of possible uses. For example, its good moisture retention and low oxygen permeability make it useful as an edible film for food packaging.

To date, poly (vinyl alcohol) (PVOH) is the only polymer with only carbon atoms in the backbone that is considered biodegradable. It is currently used in the textile, paper and packaging industries, such as paper coatings, adhesives and films. Importantly, PVOH is water soluble.

One disadvantage associated with water-soluble biodegradable polymers is that they are overly sensitive to water, which limits their use for most conventional polymer applications. It is therefore desirable to provide materials that can be used in the manufacture of disposable articles and that are water-responsive. Such materials should preferably be versatile and inexpensive to manufacture. It is also desirable that the material be sufficiently stable for the intended use, but degrade under predetermined conditions.

The use of polymers to make water-dispersible articles is known in the art. Compositions comprising multilayer polymeric films are mainly reported. There are indeed many examples of multilayer films used in disposable articles. These examples are mostly composed of a film or fiber comprising an outer layer of an environmentally degradable polymer and an inner layer of a water responsive polymer. The purpose of such structures is to adjust physical properties to improve the stability or lifetime of such structures. For example, U.S. Pat. No.4,826,493 describes the use of a thin layer of hydroxybutyrate polymer as a component of a multilayer structure that acts as a barrier film.

Another example of the use of multilayer films is U.S. patent No.4,620,999, which describes the use of water soluble films coated or laminated to water insoluble films as disposable pouches. A similar type of bag is disclosed in JP 61-42127. It is composed of an inner layer of a water-repellent water-dispersible resin (such as polylactic acid) and an outer layer of polyvinyl alcohol. However, these examples are all limited to compositions consisting of layers of different polymers and do not include actual blends of different polymers.

Other water responsive articles are disclosed in U.S. Pat. No.5,508,101, U.S. Pat. No.5,567,510, and U.S. Pat. No.5,472,518. These patents disclose a series of water-responsive compositions comprising a hydrolytically degradable polymer and a water soluble polymer. However, the article is comprised of a polymer that is first formed into a fiber or film and then combined. Thus, although the fibers and films of the polymers of such compositions are in close proximity, they are not actual blends.

Polymer blending is an attractive approach for adjusting the properties of polymeric materials without having to invest in new chemistry. Co-continuous polymer blends exhibit the best performance improvements in different blend morphologies because both components contribute substantially to the properties of the blend. However, poor interfaces between the different polymeric phases of the blend often lead to a significant loss of properties, more particularly a deterioration of the mechanical properties is observed. To overcome this problem, compatibilizers have traditionally been used to strengthen the interface. In this field, reactive compatibilization technology is a very attractive and economical way to obtain stable heterophasic polymer blends.

For most binary polymer blends, no suitable reactive groups are present and functionalization of the blend components is required. However, for some binary polymer blends, a reactive polymer that is miscible with one of the blend components and reactive with the other component may be added as a compatibilizer precursor. This type of blend compatibilization can be advantageously achieved by reactive extrusion.

Reactive Extrusion (REX) is a polymer processing technology that primarily involves the use of an extruder as a chemical reactor. Polymerization and other chemical reactions, such as reactive compatibilization, are performed in situ while processing is ongoing. Thus, REX differs from traditional polymer manufacturing processes in that the synthesis is a separate operation and the extruder only serves as a processing aid.

U.S. patent No.5,945,480 discloses components of a flushable personal care product made using fibers based on a blend of polyvinyl alcohol and polylactic acid. The blend components are compatibilized with polylactic acid modified with 2-hydroxyethyl methacrylate (HEMA). While the disclosed invention is directed to improving the compatibility of polymer blends, no reactive compatibilization is mentioned. In fact, only hydrogen bonding between hydroxyl groups of HEMA and polyvinyl alcohol can be expected. The examples do not describe the formation of any chemical covalent bonds to promote blend compatibility, and do not involve actual reactive compatibilization procedures.

Optimally combined polymer blend compositions for making fibers and films are desirable because they are very stable. Optimal incorporation of the polymer means modification of the polymer interface such that the polymer copolymer exhibits a co-continuous morphology. This can be achieved by means of reactive extrusion. Tailored blend properties can be obtained by judicious selection of reactive compatibilizers. While blended polymer compositions are known, reactively compatibilized co-continuous polymer blends are desirable because the resulting compositions are more stable and versatile.

In view of the foregoing, it would be desirable to produce biodegradable and water-dispersible polymer blends that are preferably easily processed into films and fibers. It is also desirable to provide thermally processable polymer blends with good mechanical and physical properties.

Summary of The Invention

According to a first aspect of the present invention there is provided a water dispersible and biodegradable composition comprising a blend of polylactic acid and a water soluble polymer, wherein the blend further comprises a reactive compatibilizer in an amount sufficient to compatibilize the blend.

In second and third aspects of the invention, there is provided a film and a fibre formed from the water-dispersible and biodegradable composition according to the first aspect, respectively.

In another aspect, there is provided a method of making the composition of the first aspect, the method comprising: preparing a reactive compatibilizer by reactive extrusion of polylactic acid and maleic anhydride, and melt blending the compatibilizer with polylactic acid and a water-soluble polymer.

In another aspect of the invention, there is provided filter material and a filter element comprising fibres according to the third aspect of the invention. Smoking articles comprising such filter materials or such filter elements are also provided.

In a further aspect of the invention there is provided the use of a reactive compatibilizer in the reactive compatibilization of PLA and a water-soluble polymer whereby the PLA and the water-soluble polymer are covalently bonded.

Brief Description of Drawings

FIG. 1 is a series of photographs of pure PLA and a film of PLA and PVOH 50/50w/w blend illustrating the dispersion of the polymer blend of the present invention in water.

FIG. 2 shows a) not compatibilized; and b) a 500 μm film of plasticized PLLA/HEC40/60 blend compatibilized with 10 wt% MA-g-PLLA.

FIG. 3 shows a) not compatibilized; and b) PLLA/PVOH 60/40 (w/w) blends compatibilized with MA-g-PLA¹H NMR spectrum.

Fig. 4 is a series of photographs of pure PLA and monofilaments of PLA and PVOH 40/60 w/w blends illustrating disintegration and dispersion of the polymer blend composition in water.

Detailed Description

The present invention provides polymeric compositions having good mechanical properties, such as strength and good processability, while also being water-dispersible and biodegradable. This means that these compositions can be used to make materials, such as films and fibers, suitable for use in disposable articles that are used for a relatively short period of time and are subsequently disposed of.

The films and fibers are useful as components of disposable products such as packaging films, nonwoven tissues, and the like. The water-dispersible films and fibers of the present invention have the unique advantage of being biodegradable such that the films or fibers and articles made from the films or fibers are readily degradable.

One particular use of such materials is in smoking articles that are stored under relatively stable conditions and then quickly used and disposed of. It is desirable that the remaining elements of the discarded smoking article, particularly the filter element, disintegrate and disperse rapidly under normal environmental conditions and that the component parts are biodegradable.

The composition comprising polylactic acid and one or more water soluble biodegradable polymers can be formed into various products, including films and fibers, using standard methods known in the art. This is made possible by the fact that the polymer blends of the present invention are compatibilized and exhibit excellent processability.

Compatibilization refers to the process of modifying the interfacial properties of immiscible polymer blends. Compatibilization enables the manufacture of immiscible polymer blends with modified interfaces and/or morphologies in which the two immiscible polymers are stabilized by covalent or ionic bond formation between the phases or by attractive interactions between the molecules (e.g., dipole-dipole, ion-dipole, charge transfer, H-bonding, or van der waals forces, etc.). Reactive compatibilization of immiscible polymer blends is a method for obtaining well-dispersed and stable phase morphology. It is based on the in situ formation of block-or graft copolymers at the interface between the phases of the polymer blend during melt blending. In some cases, a third polymer that is miscible with one of the blend components and reactive with the other component can be used to form the compatibilized copolymer at the interface. Reactive compatibilization of immiscible polymer blends is ensured in the present invention by the fact that the major blend components are covalently bonded.

The polylactic acid (PLA) used in the present invention can be manufactured by various synthetic methods such as ring-opening polymerization of lactide or direct polycondensation from lactic acid. One commercially available poly (lactic acid) (PLA, 4032D) useful in the present invention is a commercial grade supplied by NatureWorks LLC (USA) and has a number average molecular weight (Mn (PLA)) of 58,000 g/mol, a D-isomer content of about 1.5% and a polydispersity index of 2.1. Any PLA grade can be selected for use in the present invention, and the molecular weight of the PLA can vary depending on the desired properties and use. Poly (L-lactide) (PLLA) is preferred because its crystallinity facilitates the manufacture of the fiber.

The water-soluble polymer used in the present invention is preferably biodegradable. Biodegradable water-soluble polymers containing reactive groups, such as hydroxyl or amine functional groups, are suitable for use in the present invention. Preferred biodegradable water-soluble polymers include polyvinyl alcohol (PVOH), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), Methyl Cellulose (MC) and Ethyl Cellulose (EC), hydroxyethyl methacrylate (HEMA), xanthan gum and pullulan or blends thereof. More preferably, the biodegradable, water-soluble polymer is PVOH or HEC. A wide variety of biodegradable water-soluble polymers are expected to provide the same effect for PLA as PVOH and HEC and are effective in the present invention.

The polymer blends of the present invention preferably contain 30 to 70% by weight of biodegradable water-soluble polymer. More preferably, the polymer blend contains from 40 to 60 wt%, most preferably from 45 to 55 wt% of the biodegradable water soluble polymer.

By compatibilizing the PLA and the water-soluble polymer using a graft copolymer (PLA-grafted water-soluble polymer), compatibilization is ensured. Indeed, the preferred reactive compatibilizer, maleic anhydride grafted polylactic acid (MA-g-PLA), can react with the hydroxyl groups of the selected water-soluble polymer (e.g., HEC or PVOH) so as to form a PLA-grafted water-soluble polymer that can improve the interfacial quality between the PLA and the selected water-soluble polymer. Thus, such reactive compatibilization of immiscible polymer blends is achieved in a manner that covalently bonds the major blend components.

Most biodegradable water-soluble polymers have hydroxyl groups. Thus, the selected reactive group must be readily grafted onto the PLA and must be reactive with hydroxyl functionality.

The method of making the preferred reactive compatibilizer, maleic anhydride grafted polylactic acid (MA-g-PLA), was demonstrated by a reactive extrusion process. The grafting reaction may also be carried out in other reaction apparatus, as long as the necessary mixing of PLA and Maleic Anhydride (MA) and any other reactive ingredients is achieved and sufficient energy is provided to carry out the grafting reaction. The grafted PLA may contain 0.1 to 5 mole% grafted MA. The grafted PLA preferably contains 0.2 to 1 mole% grafted MA, most preferably 0.3 to 0.6 mole% grafted MA.

Other reactive ingredients that may be added to the compositions of the present invention include initiators, such as Lupersol ® 101 @, liquid organic peroxides available from ElfAtochem North America, Inc. of Philadelphia, USA. Free radical initiators useful in the practice of the present invention include acyl peroxides, such as benzoyl peroxide; a dialkyl peroxide; a diaryl peroxide; or aralkyl peroxides such as di-t-butyl peroxide; dicumyl peroxide; cumyl butyl peroxide; 1, 1-di-tert-butylperoxy-3, 5, 5-trimethylcyclohexane; 2, 5-dimethyl-2, 5-di (tert-butylperoxy) hexane; 2, 5-dimethyl-2, 5-bis (t-butylperoxy) hexyne-3 and bis (a-t-butylperoxyisopropylbenzene); peroxy esters, such as tert-butyl peroxypivalate; tert-butyl peroctoate; tert-butyl perbenzoate; 2, 5-dimethylhexyl-2, 5-di (perbenzoate), di (perphthalic acid) tert-butyl ester; dialkyl peroxymonocarbonates and peroxydicarbonates; hydroperoxides such as t-butyl hydroperoxide, p-menthane hydroperoxide, pinane hydroperoxide and cumene hydroperoxide, and ketone peroxides such as cyclohexanone peroxide and methyl ethyl ketone peroxide. Azo compounds, such as azobisisobutyronitrile, may also be used.

In addition, other components known in the art may be added to the graft polymer of the present invention to further enhance the properties of the final material. For example, polyethylene glycol may be further added to improve the melt viscosity. Other additives may also be incorporated as desired to provide specific properties. For example, antistatic agents, organically modified clays, pigments, colorants, and the like can be incorporated into the polymer composition. Additionally, processing characteristics can be improved by incorporating lubricants or slip agents into the polymer blends of the present invention. All of these additives are typically used in relatively small amounts, typically less than 3% by weight of the final composition.

Melt blending is a preferred method for combining the PLA and the water-soluble polymer according to the present invention. More particularly, reactive melt processing by reactive extrusion is preferred.

The melt blending of polylactic acid and biodegradable polymer is subjected to thermomechanical deformation in a suitable kneader, such as a Bradender-type internal mixer, a roller mill, a single or multiple screw extruder or any other mechanical mixing device which may be used to mix, compound, process or manufacture the polymer. A particularly desirable reaction apparatus is an extruder having one or more ports. In a preferred embodiment, the reaction apparatus is a co-rotating twin screw extruder, such as a ZSE 18 HP twin screw extruder manufactured by Leitritz GmbH, Nuremberg (Germany). Such extruders have multiple feed and discharge ports.

The presence of PLA or modified PLA (which is PLA plasticized with common plasticizers such as triacetin, tripropionin, triethyl citrate, etc.) in the blends used to make films and fibers reduces the water sensitivity of the pure biodegradable water-soluble polymer. Grafted MA-g-PLA is preferably used to enhance the compatibility between PLA and biodegradable water-soluble polymers by means of reactive compatibilization by reactive extrusion. This compatibilization is intended to improve the processability and thermomechanical properties of the final material. The blend may be used to make shapes other than films or fibers and to thermoform the blend into complex shapes.

Examples

The invention is illustrated in more detail by the following specific examples. It is understood that these examples are exemplary embodiments and that the invention is not limited by any of the examples.

Examples 1

Maleic anhydride grafted PLA was made using Leistritz ZSE 18 HP. The dried PLLA pellets were pre-blended with 3 weight percent maleic anhydride and 0.5 weight percent Lupersol 101 prior to introduction into the extruder. Then maleation was carried out at 190 ℃ using low screw speed (50 rpm) to increase residence time.

The MA-g-PLLA thus obtained was purified and the MA amount was evaluated by titration. The MA content was estimated to be 0.45 wt%.

Examples 2

Various PLLA/HEC 50/50w/w compositions were obtained by melt compounding the polymer pellets and additives (plasticizers, compatibilizers) at 30 rpm for 3 minutes followed by 60 rpm for 6 minutes at 190 ℃ using a Brabender mini-kneader (model 50EHT, 80 cm free volume) equipped with cam blades. HEC was obtained from Merck. Glyplast @ was obtained from Condensa Quimaca, Spain. Polyethylene (Mw =200) was obtained from Fluka. The polymer and additives were dried in a vented oven at 80 ℃ overnight prior to processing.

Films with a thickness of 500 μm were then prepared by compression moulding at 190 ℃ using an Agila PE20 hydraulic press (low pressure 120 seconds without degassing cycle followed by high pressure cycle of 150 bar for 180 seconds, cooling with tap water at 50 bar for 180 seconds). The mechanical properties of the PLLA/HEC 50/50 (w/w) blends plasticized with 20 wt.% Glyplast were evaluated by tensile testing. MA-grafted PLLA was used as a compatibilizer. The results are reported in table 1 below.

TABLE 1

Sample (I)	MA-g-PLA (% by weight)	Young's modulus (MPa)	Breaking stress (MPa)	Breaking strain (%)
					1	0	977 ± 33	15.3 ± 0.5	3 ± 1
3	4	817 ± 68	12.8 ± 1.0	22 ± 4
					4	8	878 ± 99	13.7 ± 0.7	23 ± 4

As observed, the blend is quite brittle in the absence of the compatibilizer. Addition of MA-g-PLLA improved ultimate elongation but did not change tensile strength. The best results were obtained with 4 wt% MA-g-PLLA.

Examples 3

Plasticization of Hydroxyethylcellulose (HEC) is considered. For this purpose, the production processes customary for starch plasticization were successfully adapted.

A mixture of HEC and plasticizer was prepared at room temperature and for some compositions, water was added. These premixes were allowed to swell overnight on standing. Next, the composition was melt processed through a Brabender at 110 ℃ for 6 minutes. Various compositions were prepared to investigate the effect of water and plasticizer content. The prepared samples are listed below:

-HEC/Glycerol 60/40

-HEC/Glycerol 70/30

-HEC/glycerol/water 60/30/10

-HEC/glycerol/water 60/25/15

-HEC/PEG 200/Water 60/30/10

-HEC/PEG 400/Water 60/30/10

-HEC/glycerol/water 60/30/10.

For each composition, a gel-like structure was obtained, which appears to indicate efficient HEC plasticization.

Examples 4

Plasticized HEC was used to prepare PLLA/HEC blends. Plasticized PLLA/HEC40/60 compositions were prepared by melt blending in a Brabender at 190 ℃. An uncompatibilized blend and MA-g-PLLA based composition were prepared and a 500 micron thick film was obtained by compression molding.

FIG. 2 shows the films thus produced and reveals the effect of MA-g-PLLA on their morphology. It was observed that a non-uniform surface was obtained in the absence of the compatibilizer.

The mechanical properties of these films were investigated by means of tensile tests and the limiting properties of the uncalendered and MA-g-PLLA-based blends were characterized. It was shown that the addition of MA-g-PLLA increased the tensile strength of the blend by about 30% and doubled the strain at break. These results show the effect of the compatibilizer on the mechanical properties of the PLLA/HEC blends. Compatibilization with MA-g-PLLA did improve young's modulus and tensile strength compared to the uncalibrated blend.

Examples 5

Various PLLA/PVOH 50/50w/w compositions were obtained by melt compounding the polymer pellets and additives (plasticizers, compatibilizers) at 30 rpm for 3 minutes followed by 60 rpm for 6 minutes at 190 ℃ using a Brabender mini-kneader (model 50EHT, 80 cm free volume) equipped with cam blades. PVOH (grade Mowiol @ 23-88) is supplied by Kuraray GmbH, Germany. Glyplast @ was obtained from Condensa Quimica, Spain. Polyethylene (Mw =200) was obtained from Fluka. The polymer and additives were dried in a vented oven at 80 ℃ overnight prior to processing.

Films with a thickness of 500 μm were then prepared by compression moulding at 190 ℃ using an Agila PE20 hydraulic press (low pressure 120 seconds without degassing cycle followed by high pressure cycle of 150 bar for 180 seconds, cooling with tap water at 50 bar for 180 seconds).

The mechanical properties of the PLLA/PVOH 50/50 (w/w) blends were evaluated by tensile testing. MA-grafted PLLA was used as a compatibilizer. The results are reported in table 2 below.

TABLE 2

Sample (I)	Plasticizer (20 wt%)	MA-g-PLLA (% by weight)	Young's modulus (MPa)	Breaking stress (MPa)	Breaking strain (%)
						1	Is free of	0	2723 ± 162	35.0 ± 4.2	2 ± 1
2	Is free of	8	2679 ± 157	50.3 ± 4.6	3 ± 1
						4	Glyplast®	8	1169 ± 103	15.5 ± 2.1	16 ± 6
5	PEG	8	877 ± 81	13.1 ± 1.8	4 ± 1

Thus, the addition of MA-g-PLLA enhances the tensile strength of the blend while not affecting the ultimate elongation. The addition of Glyplast improved the elongation, while PEG was not effective.

Examples 6

MA-g-PLLA was used as a compatibilizer for the PLLA/PVOH blend. This enhancement in compatibility is attributed to the formation of covalent bonds between PVOH and PLA, so that the graft copolymer can improve the interface quality.

Evidence of efficient manufacture of these copolymers during melt processing of the blends has been provided by dissolution testing. For this purpose, consider the uncompensated and MA-g-PLA-based PLLA/PVOH 60/40 blend. They were immersed in water and the water soluble fraction was recovered after filtration and drying. Next, these fractions were immersed in chloroform and NMR characterization considered only the soluble fraction. This method enables the isolation of the copolymers which may be formed (since these are the only components soluble in both water and chloroform).

¹The H NMR spectrum is shown in fig. 3. As can be observed from the "b" spectrum shown in fig. 3, the presence of PLA signal (mainly at about 5.3 ppm) confirms the formation of the graft copolymer.

Examples 7

Plasticization of PVOH was performed using a leiritz ZSE 18 HP twin screw extruder. Glycerol was used as plasticizer. Glycerol was obtained from Sigma-Aldrich. PVOH was processed at 210 ℃ using a screw speed of 30 rpm. Glycerol was introduced via the second barrel zone and the feed was controlled by a liquid feeder. In this manner, a PVOH composition plasticized with 33.3 wt.% glycerin can be prepared.

The plasticized PVOH thus obtained was used to prepare a PLLA/PVOH 50/50w/w blend. These compositions were prepared in the absence of a compatibilizer and in the presence of 8 wt% MA-g-PLA as a compatibilizer. The polymer blend was processed at 190 ℃ using a screw speed of 50 rpm. Next, fibers of the polymer blend were obtained using a DSM mini-extruder equipped with a fiber spinning device. Only compositions containing MA-g-PLA could be fiber processed, confirming that MA-g-PLLA can improve polymer blend processability.

Examples 8

Monofilaments based on PLLA and PVOH were produced. For this purpose, a DSM vertical micro-extruder equipped with a dedicated monofilament die was used. The composition was prepared at 190 ℃ using a screw speed of 120rpm and a mixing time of 4 minutes. The samples prepared were:

PLLA (pure Polymer)

PLLA/PVOH 50/50 (w/w) + 10% by weight of MAGPLA

PLLA/PVOH 40/60 (w/w) + 10% by weight of MAGPLA.

The use of a circular die (0.5 mm diameter) and DSM spinning unit enables the production of approximately 0.4 mm diameter monofilaments.

Table 3 reports the tensile properties of the monofilaments. It is noteworthy that the test conditions used are similar to those considered for the film test (crosshead speed: 20mm. min.)^-1Gauge length 25.4 mm).

As observed, PLLA-based monofilaments exhibited higher stiffness than PBS-based samples. In both cases, an increase in PVOH content improves tensile strength and ultimate elongation.

TABLE 3 tensile Properties of PVOH-based monofilaments

^a The MAgPLA content is 10 wt%.

Fig. 4 is a series of photographs of pure PLA and monofilaments of PLA and PVOH 40/60 w/w blends illustrating disintegration and dispersion of the polymer blend composition in water.

To address the various problems and advance the art, the present disclosure sets forth, by way of example, various embodiments in its entirety in which one or more of the claimed inventions are practiced and provide superior polymer compositions. The advantages and features of the present disclosure are merely representative of examples of embodiments and are not exhaustive and/or exclusive. They are merely intended to assist in understanding and teaching the claimed features. It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects of the present disclosure are not to be considered limiting of the disclosure as defined by the claims or limitations of equivalents to the claims, and that other embodiments may be employed and modifications may be made without departing from the scope and/or spirit of the present disclosure. Various embodiments may suitably comprise, consist of, or consist essentially of various combinations of the disclosed elements, components, features, components, steps, means, and the like. Moreover, this disclosure includes other inventions not presently claimed, but which may be claimed in the future.

Claims (21)

1. A filter element for a smoking article comprising a fiber formed from a composition comprising a blend of polylactic acid and a water soluble polymer, wherein the blend further comprises a reactive compatibilizer in an amount sufficient to compatibilize the blend.

2. A filter element as claimed in claim 1, wherein the water soluble polymer is selected from: polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose and ethyl cellulose, xanthan gum and pullulan or blends thereof.

3. A filter element as claimed in claim 2, wherein the water soluble polymer is polyvinyl alcohol or hydroxyethyl cellulose.

4. A filter element as claimed in any preceding claim, wherein the water soluble polymer is included in an amount in the range 30 to 70% by weight of the blend of polylactic acid and water soluble polymer.

5. A filter element as claimed in claim 4, wherein the water soluble polymer is included in an amount in the range 40 to 60% by weight of the blend of polylactic acid and water soluble polymer.

6. A filter element as claimed in claim 4, wherein the water soluble polymer is included in an amount in the range 45 to 55% by weight of the blend of polylactic acid and water soluble polymer.

7. A filter element as claimed in claim 1, wherein the reactive compatibilizer is a graft copolymer.

8. A filter element as claimed in claim 7 wherein the graft copolymer is a copolymer of polylactic acid and a compound reactive with hydroxyl groups.

9. A filter element as claimed in claim 8 wherein the graft copolymer is maleic anhydride grafted polylactic acid.

10. A filter element as claimed in claim 1 wherein the composition further comprises other reactive ingredients.

11. A filter element as claimed in claim 10, wherein the other reactive component is an initiator.

12. A filter element as claimed in claim 11, wherein said initiator is selected from Lupersol 101, acyl peroxides, aralkyl peroxides, peroxy esters, dialkyl peroxymonocarbonates, peroxydicarbonates, hydroperoxides, ketone peroxides and azo compounds.

13. A filter element as claimed in claim 1, wherein the composition further comprises one or more additional components selected from: an agent that improves the melt viscosity of the composition, an antistatic agent, an organically modified clay, a colorant, a lubricant, or a slip agent.

14. A filter element as claimed in claim 13 wherein the additional component is included in an amount of less than 3% by weight of the final composition.

15. A method of making a filter element as claimed in any one of the preceding claims, the method comprising forming fibres from a composition comprising a blend of polylactic acid and a water soluble polymer, the method comprising: reactive extrusion of a blend of polylactic acid, a water-soluble polymer, and a reactive compatibilizer.

16. A method as claimed in claim 15, wherein the polylactic acid, the water-soluble polymer and the reactive compatibilizer are melt blended.

17. A method as claimed in claim 15 or 16, wherein the reactive compatibilizer is a maleic anhydride grafted polylactic acid made by reactive extrusion of polylactic acid and maleic anhydride.

18. A process as claimed in claim 17 wherein the maleic anhydride grafted polylactic acid comprises 0.1 to 5 mole% grafted maleic anhydride.

19. A process as claimed in claim 18 wherein the maleic anhydride grafted polylactic acid comprises 0.2 to 1 mole% grafted maleic anhydride.

20. A process as claimed in claim 17 wherein the maleic anhydride grafted polylactic acid comprises 0.3 to 0.6 mole% grafted maleic anhydride.

21. A method as claimed in claim 15, wherein the compatibilization involves the formation of chemical covalent bonds.