WO2009077860A2

WO2009077860A2 - Surface treated inorganic particle additive for increasing the toughness of polymers

Info

Publication number: WO2009077860A2
Application number: PCT/IB2008/003774
Authority: WO
Inventors: Patrick C. Wernett
Original assignee: Specialty Minerals (Michigan) Inc
Priority date: 2007-12-17
Filing date: 2008-12-16
Publication date: 2009-06-25
Also published as: KR20100117566A; EP2231764A2; CN101918485A; WO2009077860A3; BRPI0820846A2; JP2011510106A; CA2709269A1

Abstract

A bioplastic composition comprising a biopolymer containing from 10 - 40 wt% of coated inorganic particles; the particles being coated with one or more of fatty acids, fatty acid derivatives, rosins, rosinates, polyolefin based waxes, oligomers and mineral oils, and combinations thereof has improved stiffness and toughness and also has improved crystallisation kinetics rendering it useful for extrusion, injection moulding and thermoforming.

Description

SURFACE TREATED INORGANIC PARTICLE ADDITIVE FOR INCREASING THE

TOUGHNESS OF POLYMERS

The present invention relates to improvements in or relating to polymer compositions. In particular the invention relates to bioplastics systems which contain biopolymer materials that are biodegradable and or derived from renewable resources and have sufficient improved strength. The improved strength is manifest by a combination of stiffness and toughness. In one embodiment the improved strength allows the polymers to be processed as films and used at economically attractive reduced thicknesses; it also allows the production of thermoformed articles such as food trays from thinner materials. Plastic films have many uses and the economics of film manufacture and use are frequently governed by the thickness of the film that is required to provide certain mechanical properties. The thinner the film to provide the desired properties the better. The invention can also improve crystallisation kinetics of the biopolymer which can improve the processability of the polymer in techniques such as extrusion, injection moulding and blow moulding.

Disposal of plastics is increasingly of concern and biodegradability is important to reduce the amount of non-disposable plastic waste. Biodegradability can take various forms such as compostable perhaps with the aid of chemicals, films are also produced from polymers which have a natural biodegradation as can occur if a film, such as an agricultural mulching film, is dug into soil after use. Various polymers have been developed for their biodegradability, however the polymers tend to have poor mechanical strength rendering them unsuitable for certain uses or, for example requiring an undesirably thick film to achieve reelability and processing without fracture. Impact resistance, tear resistance and mode of failure are all important properties of films, thermoformed and injection moulded parts. In particular the biodegradable polymers with which this invention is concerned tend to be brittle due to an inherent low toughness as expressed as their ability to absorb energy before fracture; this brittleness can lead to fracture and splintering upon impact which can result in polymer fragments from packaging materials in products such as foods. In one embodiment the invention provides bioplastics having a ductile failure mechanism useful as films, for thermoforming and injection moulding applications.

Examples of biopolymers with which the present invention is concerned are polylactic acid sometimes known as polylactide (PLA), polyglyconate, poly (dioxanone), polyhydroxy alkanoates (PHA), particularly polyhydroxybutyrates and polyhydroxy vatarates, polymeric thermoplastic starches (amylose levels above 60%) and combinations thereof, collectively known as biopolymers. Polylactides have been proposed as biodegradable replacements for polypropylene and polystyrene but they have not had sufficient strength. The present invention provides polylactides with such strength and also enables polylactides to compete as a biodegradable replacement for polycarbonates.

These polymers, particularly uncrystallised PLA have a low heat deflection temperature (HDT) which limits its use in high temperature applications. In addition they may have a slow crystallisation kinetics requiring lengthy moulding cycle times particularly in injection moulding.

An aim of the present invention is therefore to increase the strength of bioplastics to shorten moulding cycle times and to improve the crystallisation kinetics without any substantial decrease in biodegradability. It has previously been proposed to include rubbers with polyactides to improve their toughness, however although toughness is improved the stiffness of the polyactide is reduced and the conventional rubbers are not biodegradable. The biodegradable rubbers more recently available are considerably more expensive.

The inclusion of fillers in polymeric materials for various reasons is well known. Fillers are generally included to provide strength and/or reduce the cost of articles made from the polymeric material; fillers may be included in mouldings and extrusions of all shapes and sizes. Calcium carbonate is a well known filler for polymers and it is known that the size and morphology of the calcium carbonate can be tailored to impart certain desirable properties to the polymer in which it is included. It has, for example, been proposed in GB 2336366 A that calcium carbonate may be included in polyethylene, similarly United States Patent 6,911 ,522 describes the inclusion of calcium carbonate in e-caprolactone polymers. An article entitled The Reinforcement of Poly (Lactic Acid) using High Aspect Ratio Calcium Carbonate based Mineral Additive¹ by Zhiyong Xia, Dennis, Prendes and Patrick Wernett describes the inclusion of a calcium carbonate additive EMforce. Bio with polylactic acid in order to improve toughness and stiffness.

It is also known that calcium carbonate may be coated to improve its compatibility with the polymers with which it is used. For example GB 2336366 fills polyethylene with calcium carbonate coated with stearic acid to avoid die lip build up when the polymer is extruded and United States Patent 6,815,479 discloses the use of calcium carbonate coated with from, 2.50 to 4.00 wt % stearic acid as a filler for the polymer Capron nylon to improve the impact strength of the polymer.

It has been found that the use of certain fillers in bioplastics enables an increase in strength to be obtained without impairing the biodegradability of the bioplastics and in particular improves impact resistance and ductability without impairing the stiffness of the polymer. Ductability is indicated by the shape of the stress strain curve and an indication that the bioplastic is ductile if the area under the curve up to the maximum peak is greater than 35% of the total area under the curve the material can generally be regarded as having a ductile failure mode. This has been found to be particularly useful when the biopolymer containing the filler is used to produce films as it enables the production of thinner films having desirable mechanical properties without impairing their biodegradability. It is especially useful for the production of agricultural films and refuse sacks which may be dug into the soil and composted after use. It is also useful in thermoforming and injection moulding applications where the ductability and reduced brittleness reduces splintering of the bioplastic.

One embodiment the present invention therefore provides a bioplastic containing from 10-40 wt % of a coated filler, said coated filler containing less than 1 wt % water as measured by the weight loss when heated at 200⁰C to constant weight.

In a further embodiment the invention provides a bioplastic containing from 10 - 40 wt% of an inorganic particle coated with about 2.3 wt% or more of a fatty acid, fatty acid derivative, rosin, rosinate, polyolefin based waxed, oligomers and minerals oils and combinations thereof.

In a further embodiment the invention provides the use of an inorganic particle coated with one or more of a fatty acid, fatty acid derivative, rosin, rosinate, polyolefin based wax, oligomers and mineral oils to improve the impact resistance of a bioplastic without sacrificing the stiffness of the bioplastic.

In a further embodiment the invention provides the use of an inorganic particle coated with one or more of a fatty acid, fatty acid derivative, rosin, rosinate, polyolefin based wax, oligomers and mineral oils to accelerate the crystallisation kinetics of a biopolymer from the melt. It has been found that the combination of the coating on the filler and the low water content is important in enabling the production of high strength biodegradable materials and also to accelerate crystallisation from the melt, one function of the

coating is to operate as a dispersant and it is preferably a molecule with a polar head that will attach to the filler particle so that the coating is not removed by the biopolymer when it is in the molten state, preferably it is also provided with substantially non polar tail that will integrate with the polymer structure to aid the dispersion of the filler within the polymer. Examples of suitable dispersants are fatty acids and their derivatives (such as fatty acid amides and fatty acid esters) and also their alkali metal salts. For example, C₁₀ to C₂₂ saturated and unsaturated carboxylic acids and their alkali metal salts such as stearic, palmitic, myristic, oleic, linoleic, linolenic acids and their sodium salts are particularly useful. Rosins and rosinates and materials based on abietic acid are other suitable materials that may be used. Other less preferred coating materials that can be used include polyolefin based waxes, oligomers and mineral oils and combinations thereof.

It has been found that the amount of the coating used is important to obtain the improvement in the properties of the bioplastic. The amount required will depend upon the nature of the biopolymer and the particular property or properties with which the bioplastic user is concerned. We have found that with polylactides preferably the coating should be present in an amount of at least 2.3 wt % of the filler material and up to 10.0 wt% may be used, l-polylactides can typically be up to about 40 wt % crystalline material with the remainder being amorphous. The coated filler used in the present invention is believed to serve two functions particularly in polylactic acid, firstly it will nucleate the crystallisation of the polymer speeding up crystallisation rate and producing more uniform crystallites and secondly it will debond from the amorphous phase of the polymer when subject to impact thus absorbing energy so increasing the strength of the material whilst reducing crack propagation and rendering the polymer less brittle. If the polymer is poly-3-hydroxy butyrate which has a higher crystallinity, a lower amount of the dispersant may be required.

The preferred filler is calcium carbonate which may be precipitated calcium carbonate (PCC) or ground calcium carbonate (GCC). Precipitated calcium carbonate is preferred and it is preferred that the calcium carbonate have an acicular morphology with an aspect ratio (length : width) greater than 4, preferably greater than 5. The aspect ratio of GCC is typically about 1. The aspect ratio of the filler particles were determined by using a injection moulded polymer-mineral composite piece. The polymer was plasma etched revealing the mineral particles which were removed from the surface using 2-propanol. The collected mineral particles were analyzed by transmission electron microscopy (TEM) using a JOEL LTD. JEM 1200 EXII instrument. Digital images were collected with an Advanced Microscopy Techniques, Incorporated digital camera system and the filler dimensions were measured using ImagePro Plus^® software. Twenty-four TEM images were collected and analyzed for each sample. The average aspect ratio value was then derived by curve fitting the long versus short dimensions of the particles (aspect ratio) distribution data.

It is also preferred that the calcium carbonate whether it be PCC or GCC has a 95% particle size as measured by a micrometrics 5001 sedigraph and it is particularly preferred that 90% of all particles are no more than 20 microns in size as measured by the sedigraph, more preferably no more than 18 microns and most preferably no more than 2 microns. The particle size measurement is performed using 2g of the uncoated calcium carbonate in 50 ml of a 0.2% DAXAD solution and sonicating the slurry at a 3.5 (out of 5) power setting for 5 minutes prior to introduction into the Sedigraph instrument..

It is important that the water content of the filler be no greater than 1 wt % based on the weight of the filler, more preferably the water content is below 0.5 wt % at the processing temperature of the biopolymer, the water content is measured by Karl Fischer titration of a sample when heated to 200⁰C. The biopolymers with which the present invention is concerned are biodegradable and compostable and tend to decompose in the presence of moisture and the decomposition tends to be accelerated at the elevated temperatures that are typically used for processing the biopolymers. For example, polylactic acid is typically processed at temperatures between 180⁰C to 210⁰C and the presence of water can cause rapid degradation of the polymer at these temperatures.

According to a preferred embodiment of this invention therefore, inorganic additives such as calcium carbonate (CaCO₃) particles coated with a fatty acid greatly improve the mechanical properties such as toughness of polymers and particularly biopolymers such as biodegradable or compostable polylactide (PLA) polymers without hindering the polymer's compostability. Toughness is a material's ability to absorb energy during fracture and biodegradable polymers such as PLA are brittle because of their inherent low toughness. This property of biopolymers has limited their use but when enhanced with inorganic additives according to the present disclosure, the biopolymers' toughness is substantially improved and the usefulness of the biopolymers enhanced. The fatty acid coated inorganic additives such as fatty acid coated calcium carbonate can be used for enhancing the toughness or impact resistance of biopolymers such as PLA, polyglyconate, poly(dioxanone), polyhydroxyalkanoates (PHA) particularly polyhydroxbutyrates and thermoplastic polymeric starches such as those containing more than 60% amylose, and combinations thereof.

Biopolymers as referred to herein includes polymers derived from natural renewable resources and/or those that are generally compostable or generally biodegradable polymers. Bioplastic materials contain these biopolymers. According to this invention the toughness of bioplastics is improved by incorporating an additive comprising inorganic particles that are coated with a coating material such as one of fatty acids, fatty acid derivatives (such as fatty acid amides and fatty acid esters), rosins, rosinates, oligomers, polyolefin based waxes and mineral oils. The inorganic particles are preferably coated with the coating material at a coating level of about 2.3 wt % or more per weight of the inorganic particles. Bioplastics according to the present invention have improved physical properties (including toughness, ductility, and/or stiffness) and may be incorporated into various products, including automotive, electronics and appliance components (e.g., bumpers, dashboards, computer/cell phone housings, etc.), consumer goods (e.g., credit card stock, eating utensils, cups, food trays, fast food containers, plateware, etc.), and packaging products (e.g., food containers, bottles and films such as agricultural films and refuse sacks, etc.).

It has also been found that the incorporation of the coated filler into the bioplastics according to the present invention improves the crystallisation kinetics of the biopolymer. The faster crystallisation enables shorter moulding cycles in operations such as injection moulding and thermoforming where the time required particularly for moulding PLA has been considerably long.

The filler is typically inorganic particles and can be one of a carbonate, silica, kaolin, talc, fine metal particles, wollastonite and glass microspheres, and combinations thereof.

According to one preferred embodiment, the inorganic particles are calcium carbonate particles coated with a C₁₀ to C_2∑ fatty acid or its derivatives to the coating level of between about 2.3 - 10 wt % per weight of calcium carbonate. The calcium carbonate can be any type of calcium carbonate such as precipitated calcium carbonate ("PCC"), ground calcium carbonate ("GCC"), and blends thereof. In one preferred embodiment for enhancing the toughness of PLA polymers, the inorganic additive can be calcium carbonate additive material in particle-like form such as PCC, GCC, or blends thereof. Some examples of calcium carbonate additives in which the present disclosure can be implemented are Omyacarb UFT product available from OMYA Inc. North America, and Superfil® product available from Specialty Minerals Inc. The calcium carbonate particles can be coated with a fatty acid such as stearic acid, which is one of the useful types of saturated fatty acids that comes from many animal and vegetable fats and oils.

The enhanced polymers described above can be prepared by compounding the coated calcium carbonate particles into the polymer resin precursor for the bioplastic material and forming the composite material into a desired form. The coated calcium carbonate particles can be compounded into the polymer resin precursor by melt compounding using a twin screw extruder or similar equipment. An example of such an extruder is a twin screw extruder manufactured by the Leistritz Corporation. As an additive to enhance the toughness of a PLA polymer, the calcium carbonate particles coated with about 2.3 wt % up to about 10.0 wt % preferably up to about 6.0 wt%, more preferably up to about 4.0 wt% of fatty acid can be compounded into PLA at a loading level between 15 to 30 wt % per weight of PLA polymer.

Coating the mineral particles according to the method of the present disclosure has resulted in unexpectedly significant increase in the toughness of the bioplastic system. It is generally known that surface treatment of mineral filler particles in polymer systems improve mechanical properties of the polymer somewhat by reducing absorbed moisture on the particles and lowering the surface energy of the mineral particles. This results in better dispersion of the mineral particles in the polymer system. But, with previously known surface treatments to the mineral filler particles, only minor increase in toughness of the polymer systems were observed.

With the coating of the mineral particles according to the present disclosure, substantial enhancement of the bioplastic composite's toughness is achieved. This appears to be attributed to the coated mineral particles in the resulting polymer composite matrix absorbing energy through debonding at the particle-to-polymer interface more efficiently than in conventional surface treated mineral fillers in other polymer systems. The debonding at the particle-to-biopolymer interface absorbs energy of a crack propagating through the polymer composite. It is believed that this is particularly the case with polymers such as PLA which contain substantial amounts of amorphous regions. The bioplastic containing the coated filler may be processed to produce a wide range of articles traditionally made from plastics. They may be injection moulded, extruded, thermoformed or blow moulded according to the nature of the articles to be produced. For injection moulding we prefer that the composition contain from 10 to 40 wt % of the coated filler, more preferred from 15 to 30 wt %, particularly 20 to 30 wt %. For extruded materials up to 40 wt % of the coated filler should be used. -The materials may be used to produce moulded components for the transportation industry, household goods, packaging materials, construction materials and the like. One particular use is in the production of films particularly films that are compostable and may be used as agricultural films and refuse bags. Here we have found that the use of the additive of this invention allows the production of thinner films with the desirable mechanical properties. For example, compostable agricultural films of polylactic acid may be obtained that have the required mechanical properties such as impact strength, tear resistance and ductile failure at a thickness below 50% of comparable film without filler, in some instances the properties may be obtained at a thickness of 30% or even 25% of the thickness of one unfilled film. These films may be produced by the bubble expansion process or a stenter process. The polymers may also be thermoformed to produce biodegradable food trays.

In the processing of other polymer systems it is usually necessary to include various additives into the polymer to aid processing. Examples are slip agents, antistatic agents, viscosity modifiers and the like. An additional benefit of the present invention is that the biopolymers with which the invention is concerned may be processed without the need for any additional additives. Accordingly in a further embodiment the present invention provides a bioplastic composition of the invention substantially free from additional additives.

The invention is illustrated by reference to the following examples:

Example 1

In a laboratory experiment, the inventor was able to demonstrate the beneficial effect of a fatty acid coated calcium carbonate additive in improving the toughness of PLA polymer. Specifically, the improvement in room and low temperature impact toughness as well as improvement in the stiffness of PLA was demonstrated. The properties of PLA polymer can be controlled by controlling the ratio of the stereoisomers comprising the PLA. For example, the polymerization of predominately the L-form with greater than about 15 mole % of either the D or meso lactide will generate an amorphous PLA random copolymer. Whereas, the polymerization of the L- form of lactic acid will lead to poly-L-lactide (PLLA) which is a semicrystalline polymer with the crystallinity of up to 40 % or more.

The inventor used a number of different calcium carbonate based additives and coated them with stearic acid and compounded into PLLA polymer samples to confirm the beneficial effects of stearic acid coated calcium carbonate on the mechanical properties of PLA. The particular calcium carbonate additive samples utilized as the starting materials were Specialty Minerals Inc.'s EMforce® Bio, Superfil®, OMYA's Omyacarb UFT, and a 50:50 blend of EMforce® Bio and Superfil®. Specialty Minerals Inc.'s EMforce® Bio is an engineered calcium carbonate filler additive that is coated with greater than 2.7 wt % of fatty acid as-manufactured and is intended for reinforcing biopolymers. The samples of the other calcium carbonate additives were coated using a laboratory Henschel mixer to each coating level concentration (0.0 to 4.0 wt %). Each calcium carbonate additive material was compounded into PLLA resin at a target concentration of about 25 wt % level.

The compounding of calcium carbonate additive into PLLA can be carried out by melt compounding using a twin screw extruder. In this example, a Leistritz twin screw extruder was used having an L/D ratio of 40, a diameter of 27mm and 10 independent heating zones was used to compound all formulations. The extruder was operated in a co-rotating mode to ensure good dispersion of calcium carbonate in the PLLA. The PLLA resin was introduced into the feed throat of the extruder (at ambient temperature) using a K-TRON hopper-fed loss on weight feeder. All fillers were side-fed via a K- TRON loss-on-weight feeder into zone 5 of the extruder.

The EMforce® Bio material was produced at a Specialty Minerals Inc.'s manufacturing facility and has an as-manufactured coating level of 3.3 wt % and a water content below 0.5 wt %. The other calcium carbonate additive samples were prepared in the laboratory to a total coating level of 3.3 wt %. EMforce® Bio produced the greatest impact/stiffness balance compared to the other fillers but at the 3.3 wt % coating level, all of the fillers increase the PLLA toughness similarly (including the OMYA UFT product). A 50:50 blend of EMforce® Bio and Superfil® produced properties that were intermediate between the two pure components and is a viable option as a "next generation" EMforce Bio product as a potential reduced cost product. The addition of 3.3 wt % fatty acid to the PLLA resin without a calcium carbonate additive showed no improvement in the mechanical properties compared to the unfilled resin.

The calcium carbonate additives were melt compounded in PLLA (Natureworks 4042D) on a Leistritz 27-mm twin screw extruder operating in co-rotating mode at target concentrations of 20, 25 and 30 wt %. 3.3 wt % fatty acid was also compounded with PLLA to determine if the fatty acid alone could improve PLLA toughness. Composite samples were dusted with an aluminium stearate antiblocking agent prior to injection moulding on an Argburg 88-ton Allrounder machine. Test specimens were conditioned in a controlled temperature and humidity environment (23°C and 50% R. H.) for 3 days prior to mechanical testing.

The particle size distribution of the calcium carbonates used in this study is presented in Table 1 and the plot shown in Figure 1. Samples plotted are Superfil® calcium carbonate coated with stearic acid to 3.3 wt % level 11; UFT calcium carbonate coated with stearic acid to 3.3 wt % level 12; EMforce® Bio (Pallet #12) having as-manufactured

3.3 wt % coating level 13; and a 50/50 blend of EMforce® Bio/Superfil® 14. The

Superfil® 11 had the largest topsize and median particle size while EMforce® Bio 13 had the lowest topsize and median particle size.

Table 1. Particle Size Distribution of the Calcium Carbonate Additives (μm).

Figure 2 shows the flexural modulus of the various polymer samples measured at 23⁰C (room temperature). As discussed above PLLA resin samples were compounded with calcium carbonate to target concentrations of 20, 25 and 30 wt % . The respective line plots shown are PLLA filled with Superfil® (3.3 wt % coating level) 21; PLLA filled with UFT (3.3 wt % coating level) 22; PLLA filled with EMforce® Bio (3.3 wt % coating level) 23; PLLA filled with 50/50 EMforce® Bio/Superfil® blend (3.3 wt % coating level) 24. In addition, control samples of an unfilled PLLA control 25 and PLLA with just 3.3 wt % (based on total weight of the polymer composite) of stearic acid 26 were also prepared and measured. Because the two control samples are not filled with calcium carbonate their additive concentration levels are 0.0 wt %. All calcium carbonate additives significantly increased the flexural modulus compared to the unfilled PLLA 25 and stearic acid-PLLA resin mix 26. EMforce® Bio filled PLLA 23 produced the greatest increase in flexural modulus'. Superfil® filled PLLA 21 produced the lowest increase in flexural modulus of all the calcium carbonate containing composites and the 50/50 EMforce® Bio/Superfil® blend 24 yielded intermediate results as expected.

Figure 3 shows the results of the Dynatup multi-axial impact energies at 23⁰C (room temperature). The EMforce® Bio filled PLLA composite 33 produced the greatest room temperature toughness compared to the other calcium carbonate filled PLLA composites 31 and 34 with the exception of the UFT filled PLLA 32 at 30 wt % loading which had a comparable toughness. Previous studies have shown that a minimum of 20 wt % EMforce® Bio is required to substantially increase the PLLA composite toughness compared to the unfilled control PLLA 35. A maximum toughness is achieved around 25 wt % loading of EMforce® Bio and the toughness begins to decrease above 30 wt.%. This is the same trend observed for the Superfil® filled PLLA 31 and the EMforce® Bio/Superfil® blend 34.

Figure 4 shows the results of the Dynatup multi-axial impact energies at O⁰C. All of the PLLA composites failed in a brittle mode (or nearly all brittle failures, see Table 2). In this case, the Superfil® filled PLLA 41 produced the greatest toughness to which the

UFT filled PLLA 42 matched at the 30 wt % concentration. This is likely due to a surface area-coating level effect, Superfil® having the lowest surface area. The lower surface area of Superfil® product would require less stearic acid molecules to encapsulate the particle compared to the higher surface area particles. This would be expected to produce a thicker coating level around the Superfil® particles. Previous studies in

Natureworks 4032D PLLA indicated that EMforce® Bio can greatly increase O⁰C impact energy of PLLA and provide a ductile failure mechanism at coating level concentrations of about 3.5 wt % or greater.

Table 2 also includes the heat deflection temperature ("HDT") data. All of the mineral fillers at every concentration examined in this study had no effect on increasing the HDT of the PLLA. The addition of stearic acid in the absence of a mineral filler showed a significant decrease in the HDT of the PLLA.

Table 2. Multi-Axial Impact Failure Mechanisms and the Heat Deflection Temperature of PLA and PLA Composites

Figure 5 shows the room temperature notched Izod impact test results performed on the polymer samples. All of the stearic-coated calcium carbonate filled PLLA composites were slightly better than the unfilled and stearic acid-PLLA controls and similar to one another. The plot lines shown are Superfil® filled PLLA 51, UFT filled PLLA 52, EMforce® Bio filled PLLA 53, 50/50 EMforce® Bio/Superfil® blend filled PLLA 54, unfilled PLLA control 55 and PLLA with stearic acid control 56.

The experiment discussed above show that at 3.3 wt % coating level, no further improvement on the mechanical properties of the PLLA, such as the impact toughness, is observed over the performance achieved with 2.7 wt % coating level. Example 2

Figure 6 shows the results of a coating level study on an uncoated EMforce® Bio calcium carbonate precursor particle to determine the optimal coating level. Falling weight impact energy was measured for PLA polymer samples prepared from polymer resin compounded with calcium carbonate particles at various coating levels. The calcium carbonate precursor samples were dry-coated using a laboratory Henschel mixer to each coating level concentration (0.0 to 4.0 weight %). However, the coating process is not limited to a dry-coating process. A wet-coating process can also be used. Each calcium carbonate material was compounded into PLLA at a target concentration of 25 wt %. The measurement of toughness in this test is a falling weight. The resulting plot of Figure 6 shows a classic "S-shaped" curve 60 demonstrating a minimum coating level required to improve impact toughness of the PLLA. From the steep part 62 of the "S-curve," a minimum coating of about 2.3 wt % is estimated to be required to greatly improve the impact toughness of a PLLA composite to about 25 ft. lbs. or better. Tables 3A-3C show the underlying data for the plot of Figure 6.

Table 3A

Table 3B

Table 3C

Note: All samples were evaluated unannealed in 5 Ib batches.

According to the above data, at room temperature, the brittle-ductile transition occurs above 2.0 wt % coating level. The falling weight failures remain ductile at all values above 2.5 wt % and the beneficial effect appears to flatten out somewhat above 3.0 wt % in room temperature applications. This transition point will most likely change if the test conditions are changed. Thus at least for room temperature applications, in PLA polymer systems, the coating level can be controlled to between about 2.3 - 4.0 wt % to minimize the amount of coating. As shown in the curve of FIG. 6, the Dynatup drop energy has just begun to improve above 2.0 wt % coating level, in another preferred embodiment, the coating level can be controlled to between about 2.5 - 4.0 wt %. A higher impact velocity, or lower temperature, should require a higher coating level to produce a ductile failure. It appears that a coating level greater than 3.5 wt % coating is required to produce ductility at a test temperature of zero degrees centigrade.

The notched Izod impact strength increased linearly with coating level. Flexural modulus was not affected by coating level while tensile modulus decreased as coating level increased. This is because the coating decreases the bond strength between the filler and the polymer. It is easier for the filler particles to "pull out" of the polymer when a tensile stress is applied. Note that the tensile strength also decreases with an increase in coating level. The "pull out" forces are lower in flexural testing and therefore the flexural modulus is not affected.

It appears that a coating level of about 3.0 - 4.0 wt % would be a preferred coating range to ensure improvement in the impact toughness of the PLLA resin. The impact toughness balance improves with an increase in coating level but there is a trade-off with tensile strength and tensile modulus. By using the coated calcium carbonate filler of the present disclosure, the toughness of the PLA resin can be improved by as much as 1Ox that of the unfilled resin. Stearic acid as the coating material for the calcium carbonate filler is an example only and other fatty acid coatings would be expected to provide similar improvement in the resin's toughness.

Example 3

Test strips of PLA of variable thickness and containing variable amounts of coated calcium carbonate were produced on a Brabender Intellitorque using a single screw extruder with a variable gap die and a variable speed strip puller. The mechanical properties were measured using a Gardner impact test at 23⁰C, and an Elmendorf Tear test. The results are shown in Figures 8 and 9 and shows that the filler has a significant increase on Gardner Impact resistance. Figure 8 shows the average drop height required for failure of samples of PLA containing varying amounts of coated filler.

Figure 9 shows the force required to propagate a tear according to the Elmendorf tear test of the various samples of PLA containing the coated filler and shows a significant increase in tear strength in the filled samples.

The aspect ratio distribution of the material was measured by TEM micrographs as explained earlier in the text and is shown in Figure 7.

Example 4

PLA containing the coated additive were prepared as in Example 1. Test strips were produced as in Example 3 with target thickness of 4 mil (0.102 mm); 9 mil (0.229 mm) and 15 mil (0.381 mm).

The Gardner impact strength of the strips is shown in Figure 10 and the Elmendorf Tear strength in Figure 11. The figures show that the additive increases toughness with increasing sheet thickness as opposed to the decrease in toughness that is experienced in the absence of the additive. The increase in Gardner Impact strength allows a 3 to 4 times reduction in thickness to achieve comparable mechanical properties. Example 5

The compounds obtained according to the process set out in Example 1 containing various amounts of filler were injection moulded in an Arburg Allrounder 370c Injection Moulder to produce samples conforming to ASTM. The Flexural modulus of the samples is shown in Figure 12, the room temperature multiaxial impact total fracture energy as measured by an lnstron Corporation Dyanatup 9250 HV instrumented multiaxial impact tester is shown in Figure 13 showing the improvement in ductability and impact energy required for fraction achieved when from 15 wt% to 35 wt% of the coated filler is used.

The Figures show that the additive significantly improves the toughness and stiffness of polylactides and, furthermore the addition of the additive converts a brittle failure to a ductile failure.

Example 6

The crystallisation kinetics of a sample of PLA containing 30 wt% EMforce^® Bio at various temperatures were compared with an unfilled PLA sample.

The crystallisation half time from the melt was measured by differential scanning calorimetry and the results are shown in Figure 14 which shows that a significant reduction of the crystallisation half time from the melt can be achieved according to the present invention.

Example 7

The melt viscosity of PLA containing 0, 10, 15, 20, 25, 30 and 40 wt% of EMforce® Bio were measured using a Dynisco lncorpoated LCR 7001 capillary rheometer and the results are shown in Figure 15 showing that the additive significantly reduces melt viscosity.

Claims

1. A bioplastic composition comprising a biopolymer containing from 10 - 40 wt% of coated inorganic particles; the particles being coated with about 2.3 wt% or more of, based on the weight of the particle one or more of fatty acids, fatty acid derivatives, rosins, rosinates, polyolefin based waxes, oligomers and mineral oils, and combinations thereof.

2. A bioplastic composition containing from 10-40 wt% of a filler consisting of inorganic particles coated with a dispersant said filler coated with the dispersant containing less that 1 wt% water at 200⁰C.

3. A bioplastic of Claim 1 or Claim 2 wherein the coating material is stearic acid or a derivative thereof.

4. A bioplastic of any of the preceding claims wherein the inorganic particles are calcium carbonate.

5. A bioplastic of Claim 4 wherein the calcium carbonate particles are selected from the group consisting of precipitated calcium carbonate, ground calcium carbonate, and blends thereof.

6. A bioplastic of any of the preceding claims wherein the inorganic particles comprise one of a carbonate, silica, kaolin, talc, wollastonite, fine metal particles and glass microspheres, and combinations thereof.

7. A bioplastic of any of the preceding claims wherein the coating level is between about 2.3 to 10.0 wt%.

8. A bioplastic according to Claim 7 wherein the coating level is between about 2.3 to 4.0 wt %.

9. A bioplastic composition according to any of the preceding claims wherein the biopolymer is a polylactide.

10. A bioplastic composition according to any of the preceding claims wherein the biopolymers selected from a polylactide (PLA)₁ polyglyconate, poly(dioxanone), polyhydroxyalkanoates (PHA) and polymeric starch polymer resins, and combinations thereof.

11. A bioplastic composition according to any of the preceding claims wherein the filler is precipitated calcium carbonate having acicular morphology with an aspect ratio greater than 4.

12. A bioplastic composition according to Claim 1 1 in which the aspect ratio is greater than 5.

13. A bioplastic composition according to any of the preceding claims in which the filler is calcium carbonate in which at least 90% of the particles have a size no greater than 20 microns.

14. A bioplastic composition according to Claim 13 in which at least 90% of the particles have a size no greater then 18 microns.

15. A bioplastic composition according to Claim 13 or Claim 14 in which at least 90% of the particles have a size no greater than 2 microns.

16. A bioplastic according to any of the preceding claims substantially free of other additives.

17. Automotive components comprising a bioplastic of any of the preceding claims.

18. Appliance components comprising a bioplastic of any of Claims 1 to 16.

19. Electronic components comprising a bioplastic of any of Claims 1 to 16.

20. Consumer goods comprising a bioplastic of any of Claims 1 to 16.

21. Packaging products comprising a biopolymer of any of Claims 1 to 16.

22. Food trays and containers according to Claim 21.

23. Film and bags comprising a bioplastic of any of claims 1 to 16.

24. Film according to Claim 23 comprising an agricultural mulching film.

25. A refuse sack comprising a bioplastic according to any of Claims 1 to 16.

26. A method of enhancing toughness of a bioplastic comprising: providing a biopolymer in resin form; and compounding inorganic additive particles coated with a coating material at a coating level of about 2.3 wt% or more into the biopolymer resin, wherein the coating material is selected from fatty acids, fatty acid derivatives, rosins, rosinates, polyolefin based waxes, oligomers and mineral oils, and combinations thereof.

27. The method of Claim 26, wherein the inorganic additive particles are calcium carbonate particles.

28. The method of Claim 27, wherein the calcium carbonate particles are selected from the group consisting of precipitated calcium carbonate, ground calcium carbonate, and blends thereof.

29. The method of any of Claims 26 to 28, wherein the coating material is stearic acid or its derivatives.

30. The method of any of Claims 26 to 29 wherein the coating level is between about 2.3 to 10.0 wt%.

31. The method of Claim 30 wherein the coating level is between about 2.3 and 4.0 wt %.

32. The method according to any of Claims 26 to 31 in which the coated inorganic additive particle contains less than 1 wt% water at 200⁰C.

33. A method according to any of Claims 26 to 32 wherein the biopolymer is a polylactide.

34. A method according to any of Claims 26 to 33 in which the compounded material is processed by injection moulding or extrusion

35. A method according to Claim 34 in which the material is extruded to produce film.

36. A method according to any of Claims 32 to 35 in which the compounded material is processed at a temperature in the range 180°C to 210⁰C.

37. A method according to any of Claims 26 to 36 in which the material is thermoformed.

38. The use of an inorganic particle coated with one or more of fatty acids, fatty acid derivatives, rosins, rosinates, polyolefin based waxes, oligomers and mineral oils and combinations thereof to improve the toughness and ductability of a bioplastic.

39. The use according to Claim 38 of from 10 to 40 wt% of the inorganic particles based on the combined weight of the coated inorganic particles and the biopolymer.

40. The use according to Claim 38 or Claim 39 of from 2.3 to 10 wt % of the inorganic particle coated based on the combined weight of the coated inorganic particle and the biopolymer.

41. The use according to any of Claims 38 to 40 in which the inorganic particle is calcium carbonate and the coating is a C₁₀ to C₂₂ fatty acid or a derivative thereof.

42. The use according to Claim 41 in which the calcium carbonate is an acicular precipitated calcium carbonate having an aspect ratio greater than 4.

43. The use according to Claim 41 or Claim 42 in which at least 90% of the calcium carbonate particles have a size no greater than 20 microns.

44. The use according to Claim 43 in which at least 90% of the calcium carbonate particles have a size no greater than 2 microns.

45. The use according to any of Claims 38 to 44 in which the coated inorganic particles have a moisture content below 1 wt % at 200⁰C.

46. The use of an inorganic particle coated with one or more of fatty acids, fatty acid derivatives, rosins, rosinates, polyolefin based waxes, oligomers and mineral oils and combinations thereof to speed up the crystallisation from the melt of a biopolymer.

47. The use according to Claim 46 of from 10 to 40 wt % of the inorganic particle based on the combined weight of the coated inorganic particle and the biopolymer.

48. The use according to Claim 46 or Claim 47 or from 2.3 to 10 wt % of the inorganic particle coated based on the combined weight of the coated inorganic particle and the biopolymer.

49. The use according to any of Claims 46 to 48 in which the inorganic particle is calcium carbonate and the coating is a C₁₀ to C₂₂ fatty acid or a derivative thereof.

50. The use according to Claim 49 in which the calcium carbonate is an acicular precipitated calcium carbonate having an aspect ratio greater than 4.

51. The use according to Claim 49 or Claim 50 in which at least 90% of the calcium carbonate particles have a size no greater than 20 microns.

52. The use according to Claim 51 in which at least 90% of the calcium carbonate particles have a size no greater than 2 microns.

53. The use according to any of Claims 46 to 52 in which the coated inorganic particles have a moisture content below 1 wt% at 200⁰C.