FIELD OF THE INVENTION

The present invention refers to a method for increasing the melt flow rate in a polycaprolactone thermoplastic composition, said method comprising the step of adding 0.5- 20.0 % by weight of calcium carbonate to said polycaprolactone thermoplastic composition.

The present invention also refers to an article comprising a thermoplastic composition prepared according to said method and to the use of said article for manufacturing items such as plastic bags and films as well as items produced by casting and molding techniques.

BACKGROUND OF THE INVENTION

Plastic materials that are not recovered through the recycling industry is a worldwide

environmental problem today. These materials will end up in nature causing several

environmental problems. One example is thermoplastic articles like plastic bags and disposable packaging ending up in our oceans where they will be fractioned over time by mechanical forces and to some extent also by UV-light. They will however not degrade completely. Small plastic particles left in the oceans can for example cause clogging of the intestinal tracts as well as of the gills of fish, which are hampered and even suffocated.

Environmental concerns and increased awareness has created an interest in plastic materials that are biodegradable. Polymers of caprolactone have very good biodegradability, aerobically as well as anaerobically, which makes them attractive for various applications in which this property is required. Among the applications that can be mentioned are films for making bin bags, films for agricultural use, wrapping films and films for coating of disposable packaging.

Many biopolymers have a tendency to adhere to processing equipment like die heads and molds. This will inhibit a viscous flow of the composition in the equipment, and needs to be considered in many different processing techniques like extrusion, injection molding and, not at least, film blowing. There is accordingly a need to develop compositions that are biodegradable and that have improved melt flow properties, making them suitable for use in different processing techniques.

It has now quite surprisingly been found that a small addition (up to 20.0 % by weight) of calcium carbonate to a thermoplastic composition of polycaprolactone will increase the melt flow rate (MFR) of the composition, thus facilitating a viscous flow of the composition in the processing equipment. The increased melt flow rate can help in processing by improving the flow of material through dies and molds and preventing clogging or unwanted pressure fluctuations during processing.

DETAILED DESCRIPTION OF THE INVENTION

Polycaprolactone has emerged as a very useful polymer in thermoplastic compositions.

Polycaprolactone thermoplastics can be used in many different types of applications such as packaging, bags and films, paper coatings, adhesives and orthopedic casts. Polycaprolactone polymers have a wide compatibility with other polymers, including other biopolymers, they are non-toxic and readily biodegradable, both aerobically and anaerobically. The Capa™

Thermoplastic grades with two different molecular weights used in this study (Capa™ 6500 and Capa™ 6800 from Perstorp AB) fulfil the requirements of biodegradation stated in EN 13432, that 90 % biodegradation should occur within 180 days. Already after 45 days it is shown that Capa™ 6800 is completely biodegraded. However, processing of biopolymers can sometimes be challenging. Although polycaprolactone is often relatively easy to process in comparison to other biopolymers, its inherent adhesive properties can sometimes prevent an efficient flow through dies, molds and other processing equipment.

The melt flow rate (MFR) is a measure of the ease of flow of the melt of a thermoplastic polymer and is used as a comparative tool to give an indication of the viscosity of the polymer melt. It is defined as the mass of polymer melt that flows through a capillary of a specific diameter and length in ten minutes, a specified load is applied via prescribed alternative gravimetric weights for alternative prescribed temperatures. The method is described in the standard ISO 1133:2005. The present invention refers to a method for increasing the melt flow rate, as determined by ISO 1133:2005, in a polycaprolactone thermoplastic composition. The method comprises the step of adding 0.5-20.0 % by weight of calcium carbonate to the polycaprolactone thermoplastic composition. The calcium carbonate can in this case be seen as a functional additive.

The molecular weight of a polymer has a direct impact on the melt flow properties of the corresponding thermoplastic composition. A higher molecular weight of the polymer will give a higher viscosity of the composition and hence a slower melt flow of the material. A lower molecular weight of the polymer will give a lower viscosity and a better melt flow, but also a decrease in the mechanical strength of the material.

According to one embodiment of the present invention, the polycaprolactone has an average molecular weight of 20 000-100 000 g/mole, preferably 40 000-85 000 g/mole.

According to another embodiment of the present invention, the polycaprolactone has an average molecular weight of 80 000-100 000 g/mole.

The increase in melt flow rate seen with the method according to the present invention will thus also depend on the molecular weight of the caprolactone polymer. At higher molecular weights (about 80 000 g/mole) the addition of up to 20 % by weight of calcium carbonate will increase the melt flow rate. At lower molecular weights (about 50 000 g/mole), an increase in melt flow rate is predominantly seen at additions of up to 10 % by weight of calcium carbonate.

The addition of calcium carbonate to the polycaprolactone thermoplastic composition is preferably in the range 0.5-15.0 % by weight and most preferably in the range 0.5-10.0 % by weight.

According to yet another embodiment of the present invention, the polycaprolactone is crosslinked. The polycaprolactone polymer may be crosslinked with a multifunctional reagent, like a peroxide, that can link the single chains to each other and create an interconnected network. According to still another embodiment of the present invention, the polycaprolactone is copolymerized or grafted with another polymer species. After selective modification many polymer species can be used for copolymerization with polycaprolactone, but it is preferred to use biodegradable polymers. Especially preferred are copolymers of polycaprolactone and polylactide or polycaprolactone and polyglycolide.

The average particle size of the calcium carbonate used is 1-50 μιη, preferably 1-10 μιη. A thermoplastic film is typically below 1 mm in thickness and can be as thin as 5-10 μιη. Hence, for film applications, the average particle size of the calcium carbonate has to be adapted to fit the film.

The calcium carbonate used in the method according to the present invention can be coated or uncoated, but it is preferred to use a coated calcium carbonate. Coating of the calcium carbonate can be an important factor for reducing the risk of particle agglomeration or bad particle dispersion. These problems can often cause damages or inhomogeneity in a film. A thin thermoplastic film, which can be as thin as 5-10 μιη, is extra sensitive to agglomeration problems.

According to one embodiment of the present invention, the calcium carbonate particles are coated with a hydrophobic coating comprising polycaprolactone of average molecular weight 400-40 000 g/mole, preferably 1000-20 000 g/mole.

The present invention also refers to an article comprising a thermoplastic composition prepared according to the method described above. A variety of techniques can be used for preparing such articles. Examples of these techniques are extrusion, blow molding, film blowing, injection molding, stretch-molding, vacuum molding, calendering and/or any type of casting.

An article according to the present invention can also be prepared by technologies within the field of additive manufacturing, such as fused deposition modeling and selective laser sintering.

According to still another embodiment of the present invention, the article according to the present invention is prepared by fiber production through melt spinning.

Different kinds of additives conventionally used in thermoplastics can be used in preparation of an article according to the present invention. These additives include for example dyes, pigments, fillers, defoaming agents, dispersing agents, slip agents, melt strength enhancers, organic or inorganic fibers, antioxidants, stabilizing agents, plasticizers, dispersing agents and compatibilizers.

Additionally, the present invention refers to the use of articles according to the present invention for manufacturing of a variety of items such as plastic bags, bin bags, agricultural films, films for disposable packaging, films for paper coating and/or multi-layer films, but also different casted and molded articles like bottles or pots for young plants.

Further testing of articles according to the present invention has shown that not only the melt flow rate, but also the mechanical strength of the material is improved, as compared to articles prepared according to a method of equal reference, but wherein no calcium carbonate is added.

EMBODIMENT EXAMPLES

The present invention is further explained with reference to enclosed Embodiment Examples, which are to be construed as illustrative and not limiting in any way.

Example 1: Melt flow rate of Capa™ 6800 with calcium carbonate as functional additive

Polycaprolactone was mixed with 0, 10, 30 and 60 % by weight respectively of calcium carbonate in a co-rotating twin screw extruder. The polycaprolactone was Capa™ 6800, which has an average molecular weight of 80 000 g/mole. The calcium carbonate was Omyacarb T2- AV, which is a coated calcium carbonate with an average particle size of 2 μιη. The extrusion was conducted with a temperature profile of 150 °C at the kneading segments and 120 °C closer to the die. The rotation speed of the screws was 450 rpm.

Melt flow rate measurements

4 g of polycaprolactone-calcium carbonate granules were poured into a CEAST Melt flow Junior and the melt flow rates were determined according to ISO 1133:2005 at 160 °C and 2.16 kg weight. Time for preheating was 5 min. The melt flow rates are shown in Figure 1 below. Melt flow rate

10 20 30 40 50 60 70 wt% Calcium carbonate

Figure 1. Melt flow rate of Capa 6800 with calcium carbonate.

The results in Figure 1 show that an inclusion of up to about 20 % by weight of calcium carbonate to Capa™ 6800 will increase the melt flow rate of the polycaprolactone thermoplastic composition. This is quite surprising, since addition of calcium carbonate would in theory cause an increase in the viscosity of the composition, which would be demonstrated as a decrease in the melt flow rate.

This increase in melt flow rate will make the thermoplastic composition according to the present invention flow easier in processes like for example film blowing or injection molding.

Example 2: Comparison of melt flow rates for Capa 6500 with calcium carbonate or talc as functional additive.

The method according to the invention was compared to a method wherein the calcium carbonate was replaced by another mineral additive (talc).

Polycaprolactone was mixed with the two additives respectively in a twin screw extruder. The mineral additives were added in concentrations of 0, 10, 20 and 30 % by weight respectively. The polycaprolactone was Capa™ 6500, which has an average molecular weight of 50 000 g/mole. The calcium carbonate was Omyacarb T2-AV, which is a coated calcium carbonate of particle size 2 μηι. The talc was Luzenac HAR T84. The extrusion was conducted with a temperature profile of 120°C at the kneading segments and 100 °C closer to the die. The rotation speed of the screws was 400-450 rpm.

Melt flow rate measurements

4 g of polycaprolactone- additive granules were poured into a CEAST Melt flow Junior and the melt flow rates were determined according to ISO 1133:2005 at 100 °C and 2.16 kg weight. Time for preheating was 5 min. The melt flow rates are shown in Figure 2 below.

Melt flow rate

5 10 15 20 25 30 35

wt% Additive

— Capa6500 + talc —■— Capa6500 + calcium carbonate

Figure 2. Comparison of melt flow rate of Capa 6500 with two different mineral additives. The thermoplastic composition comprising talc behaves as could be expected from theory: when talc is added to the composition the viscosity increases and the melt flow rate decreases accordingly. However, in the case where calcium carbonate is added to the composition prepared according to the method of the present invention, the melt flow rate increases for calcium carbonate levels up to about 10 % by weight. This means that the composition will flow easier with an inclusion of (in this case) up to about 10 % by weight of calcium carbonate.

The present results prove that a small addition of calcium carbonate will make the composition flow more easily through the die. The calcium carbonate seems to work as a "lubricant" or "fluid enhancer" in the composition. At higher inclusion rates, this effect is surpassed by the increase in viscosity and the melt flow rate will go down. The present invention thus provides a method for increasing the melt flow rate in a polycaprolactone thermoplastic composition by a small inclusion of calcium carbonate to the composition. The method will provide a thermoplastic composition that is easily processed into biodegradable single use products as well as more durable articles.