HUP0000723A2 - Thermoplastic composition - Google Patents

Description

^.2. 3 people publishing : - 1 :::· h

10,630 COPIES

PCT/US9724078 I

I

Thermoplastic composition

Kimberly-Clark Worldwide, Inc., NEENAH, US

The present invention relates to a thermoplastic composition comprising an unreacted blend of an aliphatic polyester polymer and a multicarboxylic acid. The thermoplastic composition can be extruded into fibers from which nonwoven structures can be formed that can be used in disposable absorbent products for absorbing liquids, such as body fluids.

Disposable absorbent products are currently widely used in many areas. For example, in the field of infant and child hygiene, diapers and training pants have replaced reusable absorbent garment-type products. Other commonly used disposable absorbent products include feminine hygiene products such as sanitary napkins or tampons, adult incontinence products, and medical products such as surgical masks and wound dressings. A disposable absorbent product generally has a composite structure, i.e. a top layer, a back layer, and an absorbent structure disposed between the top and back layers. Such products generally also have a fastening system by which they can be secured to the wearer's body.

Disposable absorbent products are usually exposed to liquid one or more times during use, where the liquid is water, urine, menstrual fluid, or blood. Therefore,

- 2 The lower layer forming the outer cover of a disposable absorbent product is generally made of a liquid-insoluble, liquid-barrier material, such as polypropylene films, which have sufficient strength and are easy to handle, whereby the disposable absorbent product maintains its integrity during use and prevents leakage of liquid reaching the product.

Although current disposable baby diapers and other disposable absorbent products have been generally accepted, these products still need to be improved in certain areas. For example, many disposable absorbent products are difficult to dispose of as waste. Flushing many absorbent products down the toilet and down the drain usually leads to clogging of the toilet or the pipe connecting the toilet and the sewage system. In particular, the outer cover material of disposable absorbent products does not decompose or disperse after being flushed down the toilet, and therefore disposable absorbent products cannot be disposed of in this manner. While the outer cover materials of the disposable absorbent product are made very thin to reduce the overall weight and thus reduce the likelihood of clogging toilets or sewers, the outer cover material is generally not strong enough to prevent tearing or splitting due to the forces that occur during normal use.

Solid waste disposal is also a growing concern around the world. As landfills continue to fill, there is a growing need to reduce the weight of disposable products, incorporate more recyclable and/or biodegradable components into disposable products, and design products that can be disposed of in ways other than landfills.

- 3 such as by placing in underground storage facilities.

There is a need for new materials that can be used in disposable absorbent products that generally maintain their integrity and strength during use, but can be more efficiently disposed of after use. For example, a disposable absorbent product can be easily and efficiently disposed of by composting. Another option for easily and efficiently disposing of a disposable absorbent product is to dispose of it in a wastewater collection system where the disposable absorbent product can be degraded.

Although fibers made from aliphatic polyesters are known, problems have arisen in their application. In particular, it is known that the crystallization rate of aliphatic polyester polymers is relatively low, for example compared to polyolefin polymers, whereby aliphatic polyester polymers are often poorly processable. In addition, the dimensional stability of aliphatic polyester polymers under heat is generally not good. Aliphatic polyester polymers usually undergo severe heat shrinkage during polymer chain elongation during downstream heat treatment processing, such as heat bonding or lamination, unless an additional step, such as heat setting, is also used. However, such a heat setting step generally limits the application of the fiber in in situ nonwoven production processes, such as spunbonding and meltblown processes, where heat setting is very difficult to perform. In addition, the use of processing additives may reduce the biodegradation rate of the original material, or the processing additives themselves may not be biodegradable.

The object of our invention is therefore to produce a thermoplastic composition that has improved processability, reduced crystal size, improved dimensional stability under heat, and is more biodegradable.

A further object of our invention is to produce a thermoplastic composition that can be easily and efficiently converted into fiber.

It is a further object of our invention to provide a thermoplastic composition which can be used to produce nonwoven structures.

It is a further object of our invention to produce a fiber or nonwoven structure that is readily biodegradable in the environment.

The invention provides a thermoplastic composition that is biodegradable to a desired extent, yet is easily manufactured and easily processed into desired final structures, such as fibers or nonwovens.

One aspect of our invention is a thermoplastic composition comprising a mixture of a first component and a second component.

One embodiment thereof comprises a blend of an aliphatic polyester polymer and a multicarboxylic acid, wherein the multicarboxylic acid has a total carbon number of less than about 30, resulting in a thermoplastic composition having the desired properties.

Another object of our invention is a fiber having desired properties, which was produced from the thermoplastic composition.

A further object of our invention is a nonwoven structure comprising fiber produced from the thermoplastic composition.

One embodiment of such a nonwoven structure is a backsheet for use in disposable absorbent products.

The invention relates to a thermoplastic composition comprising a first component and a second component. In our description, a thermoplastic is defined as a material that softens when heated and returns to its original state substantially upon cooling to room temperature.

The first component of the thermoplastic composition is an aliphatic polyester polymer. Examples of aliphatic polyester polymers that can be used include, but are not limited to, polylactic acid, poly(butylene succinate), poly(butylene succinate-co-adipate), poly(hydroxybutyrate-co-valerate), polycaprolactone, sulfonated poly(ethylene terephthalate), blends and copolymers of these polymers.

In one embodiment of our invention, it is desirable to use polylactic acid as the aliphatic polyester polymer. Polylactic acid polymer is generally prepared by polymerization of lactic acid. However, one skilled in the art will recognize that a chemically equivalent material can also be prepared by polymerization of lactide. As used herein, the term polylactic acid polymer refers to a polymer prepared by polymerization of either lactic acid or lactide.

It is known that lactic acid and lactide are asymmetric molecules that have two optical isomers, which are called the levorotatory (hereinafter referred to as L) enantiomer and the dextrorotatory (hereinafter referred to as D) enantiomer. As a result, by polymerizing a certain enantiomer or by using a mixture of the two enantiomers, different polymers can be prepared that are chemically similar, yet have different properties. In particular, it has been found that a polylactic acid polymer has a stereochemical- 6 -

For example, the melting point, melting point, and crystallinity of the polymer can be controlled by modifying the polymer. If these properties can be controlled, a multicomponent fiber can be produced that has the desired melt strength, mechanical properties, softness, and processability properties, and can thus be used to produce thinned, heat-set, and shrinkable fibers.

It is generally desirable that the aliphatic polyester polymer be present in the thermoplastic composition in an amount that enables the desired properties to be achieved in the thermoplastic composition. The amount of aliphatic polyester polymer in the thermoplastic composition is less than 100% by weight, preferably about 40% to about 100% by weight, more preferably about 50% to about 95% by weight, even more preferably about 60% to about 90% by weight, even more preferably about 60% to about 80% by weight, and most preferably about 70% to about 75% by weight, all values in weight being based on the combined weight of aliphatic polyester polymer and polycarboxylic acid present in the thermoplastic composition.

It is generally desirable for the aliphatic polyester polymer to have a weight average molecular weight that allows the thermoplastic composition to exhibit the desired melt strength, fiber mechanical strength, and fiber twisting properties. Generally, if the weight average molecular weight of the aliphatic polyester polymer is too high, it means that the polymer chains are highly entangled, which may result in the aliphatic polyester polymer being difficult to process in a thermoplastic composition. Conversely, if the weight average molecular weight of the aliphatic polyester polymer is too low, it means that the polymer chains are not entangled. 7 - ........

• · · ··· ··» · · tak enough to result in a thermoplastic composition in which the aliphatic polyester polymer has a relatively low melt strength, making high-speed processing very difficult. Thus, the aliphatic polyester polymers useful in the present invention preferably have a weight average molecular weight of between about 10,000 and about 2,000,000, more preferably between about 50,000 and about 400,000, most preferably between about 100,000 and about 300,000. The weight average molecular weight of the polymers or polymer blends useful in the present invention can be determined by the method described in the test methods section of this specification.

It is also desirable that the aliphatic polyester polymer have a polydispersity index value that enables the thermoplastic composition to have the desired melt strength, fiber mechanical strength, and fiber spinning properties. As used herein, the polydispersity index is the value obtained by dividing the weight average molecular weight of a polymer by the number average molecular weight of the polymer. In general, if the polydispersity index value of an aliphatic polyester polymer is too high, the thermoplastic composition containing this aliphatic polyester polymer may be difficult to process due to the variable processing properties caused by the polymer segments containing low molecular weight polymers exhibiting lower melt strength during spinning, so it is desirable that the aliphatic polyester polymer have polydispersity index values that are preferably between about 1 and about 15, more preferably between about 15 and about 15. 1 to about 4, most preferably between about 1 and about 3. The number average molecular weight of polymers or polymer mixtures can be determined by the method described in the test methods section of this specification.

It is generally desirable that the aliphatic polyester polymer be melt processable. Therefore, it is desirable that the aliphatic polyester polymer preferably has a melt flow rate of between about 1 g/10 min and about 200 g/10 min, more preferably between 10 g/10 min and about 100 g/10 min, and most preferably between 20 g/10 min and about 40 g/10 min. The melt flow rate of a material can be determined, for example, by ASTM test method D1238-E.

It is desirable in the present invention that the aliphatic polyester polymer be biodegradable. As a result, a thermoplastic composition comprising the aliphatic polyester polymer, whether in the form of a fiber or a nonwoven structure, is substantially biodegradable when disposed of in the environment and exposed to air and/or water. As used herein, biodegradable means that a material is degraded by naturally occurring microorganisms such as bacteria, fungi, and algae.

It is also desirable in the present invention that the aliphatic polyester polymer be compostable. As a result, the thermoplastic composition comprising the aliphatic polyester polymer, whether in the form of a fiber or a nonwoven structure, is substantially compostable when disposed of in the environment and exposed to air and/or water. As used herein, compostable means a material that undergoes biodegradation at a composting site in a manner that is indistinguishable from the environment by being degraded to _carbon dioxide, water, inorganic compounds and biomass at ^a rate that is comparable to that of known compostable materials.

The second component of the thermoplastic composition is a multicarboxylic acid. The multicarboxylic acid can be any acid containing two or more carboxylic acid groups. Dicarboxylic acids containing two carboxylic acid groups are preferred for the purposes of the invention. It is generally desirable that the number of carbon atoms in the multicarboxylic acid not be too high, as the crystallization kinetics, i.e. the rate of crystallization, may be less than desired. Therefore, it is desirable that the number of carbon atoms in the multicarboxylic acid preferably be less than about 30, more preferably about 3 to about 30, even more preferably about 4 to about 20, and most preferably about 5 to about 10. Suitable multicarboxylic acids include, but are not limited to, malonic acid, citric acid, succinic acid, glutanic acid, adipic acid, pimelic acid, parafic acid, azelaic acid, sebacic acid, and mixtures thereof.

It is generally desirable for the multicarboxylic acid to be present in the thermoplastic composition in an amount that results in the desired properties of the thermoplastic composition. The multicarboxylic acid is preferably present in the thermoplastic composition in an amount of more than 0 wt. %, more preferably more than 0 wt. % and about 60 wt. %, more preferably about 5 wt. % and about 50 wt. %, even more preferably about 10 wt. % and about 40 wt. %, even more preferably about 20 wt. % and about 40 wt. %, and most preferably about 25 wt. % and about 30 wt. %, all weight values being based on the total weight of aliphatic polyester polymer and multicarboxylic acid present in the thermoplastic composition.

In order to process the thermoplastic _composition of the invention into a product, such as a fiber or nonwoven structure _, having the desired properties, it is generally desirable, in our understanding, that the multicarboxylic acid is preferably present in liquid form during the processing of the thermoplastic composition by heat treatment, but that upon cooling of the processed thermoplastic composition the multicarboxylic acid is converted to a solid or crystalline state before the aliphatic polyester polymer is converted to a solid or crystalline state.

It is believed that the multicarboxylic acid in the thermoplastic composition of the present invention serves two important but distinct functions. First, when the thermoplastic composition is in the molten state, it is believed that the multicarboxylic acid acts as a lubricant or plasticizer, which facilitates processing of the thermoplastic composition and increases the flexibility and strength of the final product, such as a fiber or a nonwoven structure, by internally modifying the aliphatic polyester polymer. While not wishing to be bound by a theory, it is believed that the multicarboxylic acid replaces the secondary bonds holding the aliphatic polyester polymer chains together with bonds between the multicarboxylic acid and the aliphatic polyester polymer, thereby facilitating the movement of polymer chain segments. This effect is demonstrated, for example, by a mixture of polylactic acid and adipic acid, where the melting temperature of the thermoplastic composition shifts towards lower temperatures with increasing mixing ratio of adipic acid to polylactic acid. As a result, the torque required to operate the extruder is generally reduced to a very large extent, compared to the polylactic acid po

- 11 by processing the polymer alone. In addition, the processing temperature required to transform the thermoplastic composition into a final product, such as a fiber or nonwoven, is generally greatly reduced, thereby reducing the risk of thermal decomposition of the polylactic acid polymer. Second, when the final product produced from the thermoplastic composition, such as a fiber or nonwoven, is cooled and solidifies from its liquid or molten state, it is assumed that the multicarboxylic acid acts as a nucleating agent. It is known that aliphatic polyester polymers have a very slow crystallization rate. Traditionally, there are two main ways to address this. One is to change the cooling temperature profile to maximize the crystallization kinetics, while the other is to add a nucleating agent to increase the sites and degree of crystallization.

Cooling of the extruded polymer to room temperature is usually achieved by blowing air at room temperature or colder over the extruded polymer. This can be called quenching or supercooling, since the temperature change is usually greater than 100 °C, and most often greater than 150 °C, in a relatively short time, such as seconds. Further modification of this common method to the required ideal temperature profile - which is the only method to maximize the crystallization kinetics of aliphatic polyesters in a real production process - is very difficult due to the extremely large amount of cooling required within a very short time. However, the conventional cooling methods can also be used in combination with a second modification method. The conventional second method is to mix a nucleating agent, such as solid particles, with the thermoplastic composition,

- 12 to provide sites for initiating crystallization during quenching. However, such solid nucleating agents generally agglomerate very easily in the thermoplastic composition, which can cause clogging of filters and clogging of the spinneret holes during spinning. In addition, the nucleating effect of such solid nucleating agents generally peaks at about 1%. Both of these factors generally reduce the possibility or need to add a larger mass of solid nucleating agents to thermoplastic compositions. However, in processing the thermoplastic composition of our invention, it has been found that the multicarboxylic acid is generally present in a liquid state during the extrusion process, thus acting as a plasticizer and can solidify or crystallize before the aliphatic polyester during cooling, where the multicarboxylic acid acts as a nucleating agent. It is assumed that upon cooling from a homogeneous melt, the polycarboxylic acid will solidify or crystallize relatively quickly and completely as soon as the temperature falls below its melting point, since it is a relatively small molecule. Adipic acid, for example, has a melting point of about 162 °C and a crystallization temperature of about 145 °C.

The aliphatic polyester polymer, which is a macromolecule, has a relatively low crystallization rate, which means that it generally solidifies or crystallizes more slowly upon cooling and this occurs at a temperature lower than its melting point. For example, polylactic acid has a melting point of about 175 °C and a crystallization temperature of about 121 °C. During cooling, the polycarboxylic acid then begins to crystallize before the aliphatic polyester polymer and usually

- 13 act as solid nucleation sites within the cooling thermoplastic composition.

It is generally desirable for a thermoprocessed thermoplastic composition or a product made from such a thermoplastic composition, such as a fiber or a nonwoven structure, to have a crystallite size that enables the thermoplastic composition or product made therefrom to exhibit desired properties. In one embodiment of our invention, it is generally desirable for the thermoprocessed thermoplastic composition or product made therefrom, such as a fiber or a nonwoven structure, to have an average crystallite size of preferably less than about 12.0 nm, more preferably less than about 11.0 nm, even more preferably less than about 10.0 nm, even more preferably less than about 8.0 nm, and most preferably less than about 7.0 nm. The average crystallite size of a material can be determined by the method described in the test section.

The above has described the main components of the thermoplastic composition of the invention, however, the thermoplastic composition is not limited to these components and may also contain other components that do not adversely affect the desired properties of the thermoplastic composition. Other components that can be used include, but are not limited to, pigments, antioxidants, stabilizers, surfactants, waxes, flow improvers, solid solvents, plasticizers, nucleating agents, particulates and materials added to improve the processability of the thermoplastic composition. One example of such optional components is a surface-modified particle, which is available, for example, from

- 14 Burgess Pigment Company (Sandersville, Georgia, US) under the name Burgess Polyclay surface modified particulate or Barretts Minerals, Inc. (Dillon, Montana, US) under the name Micropflex 1200 surface modified particulate. If the thermoplastic composition contains such additional components, it is generally desirable that their amount be preferably less than about 5 wt. %, more preferably less than about 3 wt. %, most preferably less than about 1 wt. %, where all values given in wt. % are based on the total weight of the aliphatic polyester polymer, multicarboxylic acid and additional components present in the thermoplastic composition.

The thermoplastic composition of the present invention is generally simply a mixture of the aliphatic polyester polymer, the multicarboxylic acid, and optionally additional components. It has been recognized that it is critical to achieving the desired properties of the thermoplastic composition of the present invention that the aliphatic polyester polymer and the multicarboxylic acid do not substantially react with each other and form a copolymer that includes both the aliphatic polyester polymer and the multicarboxylic acid. The aliphatic polyester polymer and the multicarboxylic acid remain separate components of the thermoplastic composition.

1- In one embodiment of the invention, after dry blending the aliphatic polyester polymer and the multicarboxylic acid, the resulting thermoplastic composition dry blend is preferably blended to form a substantially homogeneous dry blend of the aliphatic polyester polymer and the multicarboxylic acid. The dry blend can then be melt blended, for example in an extruder, to form a substantially homogeneous melt of the aliphatic polyester polymer and the multicarboxylic acid.

- 15 ·ί. ...* · ··;· form a melt blend. The substantially homogeneous melt blend can then be cooled and pelletized. Alternatively, the substantially homogeneous melt blend can be directly transferred to a spin pack or other apparatus for forming fibers or nonwovens. Another method of blending the components of the invention is to add the multicarboxylic acid to the aliphatic polyester, for example, in an extruder used to blend the components. Additionally, both components can be melt blended simultaneously at the outset. Other methods of blending the components of the invention are possible and will be readily apparent to those skilled in the art. Techniques such as nuclear magnetic resonance and infrared spectroscopy can be used to determine whether the aliphatic polyester polymer and the multicarboxylic acid have remained in substantially unreacted form, and to evaluate the chemical properties of the final thermoplastic composition.

It is generally desirable that the melting or softening temperature of the thermoplastic composition be within the range typically required for most processing. Thus, it is generally desirable that the melting or softening temperature of the thermoplastic composition is preferably between about 25°C and about 350°C, more preferably between about 55°C and about 300°C, and most preferably between about 100°C and about 200°C.

It has been found that the thermoplastic composition of the invention generally exhibits better processability properties than a thermoplastic composition comprising the aliphatic polyester polymer but containing no multicarboxylic acid. The improved processability of a thermoplastic composition is characterized by a reduction in the glass transition temperature (Tg).

- 16 ··· ···* ··:· It is believed that at the glass transition temperature, the polymers in the thermoplastic composition begin to move segmentally, which means that enough energy - usually thermal energy - is available to cause the bulk polymer to flow. A decrease in the glass transition temperature means that less thermal energy is required to induce this segmental movement and the resulting flow. If a thermoplastic composition is processed at a relatively lower temperature, the components of the thermoplastic composition will not be as susceptible to thermal decomposition. Similarly, if a thermoplastic composition has a lower glass transition temperature, the processing equipment - such as an extruder - can typically be operated at a lower power level, so that less torque is required to rotate the extruder screw. In general, a thermoplastic composition that has a lower glass transition temperature generally requires less energy to process and is therefore more economical to use.

In one embodiment of our invention, the thermoplastic composition or product made therefrom, such as a fiber or a nonwoven structure, preferably has a glass transition temperature (Tg) of less than about 55°C, more preferably less than about 50°C, even more preferably less than about 45°C, most preferably less than about 40°C.

In our description, fiber or fibrous is understood to mean a material having a length to diameter ratio greater than about 10. In contrast, non-fiber or non-fibrous is understood to mean a material having a length to diameter ratio of about 10.

- 17 '*·* .:.... * ·.» · ••χιό or less.

Processes for producing fibers are well known and need not be described in detail here. Melt spinning of polymers produces continuous filaments, such as spunbonded or meltblown fibers, and discontinuous filaments, such as staple fibers and structures. Typically, to produce spunbonded or meltblown fibers, the thermoplastic composition is extruded and fed into a distribution system where the thermoplastic composition is fed onto a spinneret plate. The spun fiber is then cooled, solidified, and drawn into a conventional nonwoven fabric by an aerodynamic system. If staple fibers are produced instead of directly forming a nonwoven structure, the spun fiber is cooled, solidified, and drawn to an intermediate fiber diameter, usually by a mechanical roller system, and then wound. The fiber can then be cold drawn at a temperature below its softening temperature to the desired final fiber diameter, and crimped or textured and cut to the desired fiber length. The fibers can be cut into relatively short pieces, such as staple fibers, which are about 25 to about 50 mm long, or chopped fibers, which are even shorter and generally less than 18 mm long (e.g., U.S. Pat. Nos. 4,789,592 and 5,336,552).

A problem that arises in the production of fibers from aliphatic polyester polymers alone is that such fibers often shrink under the influence of heat during processing by down-flow heat treatment. Heat shrinkage occurs primarily due to heat-induced chain elongation of polymer segments in the amorphous phase and in the incompletely crystalline phase. To overcome this problem, it is generally desirable to make the material as crystalline as possible prior to the bonding stage so that the thermal energy is directly used for melting rather than chain elongation and rearrangement of the incompletely crystalline structure. One solution to this problem is to subject the material to a heat setting treatment. When the fibers subjected to the heat setting treatment reach the bonding roller, the fibers do not shrink significantly because they are already fully or largely oriented. However, it is generally very difficult to implement an in-line heat setting process in typical spunbond and meltblown processes. The solution of our invention generally reduces the need for a heat setting step, but does not eliminate its use, since the use of a multicarboxylic acid in the thermoplastic composition generally allows the use of available spunbond and meltblown techniques without major process modifications. Blending the aliphatic polyester polymer with a multicarboxylic acid therefore generally maximizes the crystallization of the aliphatic polyester polymer, thereby minimizing the expected heat shrinkage of the aliphatic polyester polymer.

In addition, in the production of chopped fiber, if inline heat setting is possible, according to one embodiment of our invention, it is advantageous to subject the fibers produced from the thermoplastic composition of the invention to heat setting. It is desirable that such heat setting further reduces the heat shrinkage of the fiber. This heat setting can be carried out so that the

- 19 fibers are subjected to a constant stretch, typically but not exclusively between about 10 and about 20%, preferably at a temperature above about 50°C, more preferably above about 70°C, most preferably above about 90°C. It is generally advisable to use the highest possible values during the heat setting treatment, both in terms of the applied stretch and the temperature, without losing the processability of the fiber. However, too high a heat setting temperature, such as a temperature close to the melting temperature of one of the components of a fiber, can reduce the strength of the fiber and can result in the fiber becoming difficult to handle due to its stickiness.

In one embodiment of our invention, it is desirable that the shrinkage of the fiber made from the thermoplastic composition, as expressed by the Heat Shrinkage value at a temperature of about 100°C and a period of about 15 minutes, is preferably less than about 15, more preferably less than about 15.

1, more preferably less than about 5%, most preferably less than about 25%. The amount of shrinkage is calculated as the difference between the initial and final lengths of the fiber divided by the initial length of the fiber divided by one hundred. The amount of shrinkage of a fiber can be determined by the method described in the test methods section of this specification.

The thermoplastic compositions of the present invention are suitable for producing fibers or nonwoven structures that can be used in disposable products, including disposable absorbent products such as diapers, adult incontinence products and panty liners; menstrual products such as sanitary napkins and tampons; and other absorbent products such as wipes, aprons, wound dressings and surgical caps and masks. Accordingly, another aspect of our invention is a disposable absorbent product comprising the fibers or nonwoven structures of the present invention.

In one embodiment of the invention, the thermoplastic composition is formed into a fibrous matrix for incorporation into a disposable absorbent product. The fibrous matrix may be, for example, a fibrous nonwoven. The fibrous nonwovens may be made entirely of fibers produced from the thermoplastic compositions of the invention or may be blended with other fibers. The length of the fibers used may depend on the intended end use. If the fibers are to be water-soluble, such as in a toilet, it is preferred to choose a length of 15 mm or less.

One embodiment of our invention is a disposable absorbent product comprising a liquid-permeable topsheet, a backsheet attached to the liquid-permeable topsheet, and an absorbent structure disposed between the liquid-permeable topsheet and the backsheet, wherein the backsheet comprises fibers made from the thermoplastic composition of the invention.

Disposable absorbent products are generally described, for example, in US-A 4,710,187; US-A 4,762,521; US-A 4,770,656; and US-A 4,98,603.

All absorbent products and structures of our invention are generally exposed to body fluids multiple times during use. Accordingly, it is desirable for the absorbent products and structures to be capable of being repeatedly exposed to body fluids.

- 21 *”* ·Ι. ··/· absorb body fluids in the amount that the absorbent products and structures encounter during use. Fluid loads do not usually occur at the same time.

Testing procedures

Melting temperature

Melting temperatures were determined using differential scanning calorimetry. Melting temperatures were determined using a differential scanning calorimeter, a Thermal Analyst 2910 Differential Scanning Calorimeter (DSC) manufactured by T.A. Instruments Inc. (New Castle, Delaware, USA), equipped with a liquid nitrogen cooler and operated with Thermal Analyst 2200 analysis software.

The material samples tested were either fibers or resin pellets. It is preferable not to handle the material samples directly, but rather with tweezers and other tools, so as not to introduce anything that would cause erroneous results. The material samples cut from the fibers or resin pellets were placed in an aluminum pan and weighed on an analytical balance to an accuracy of 0.01 mg. If necessary, a lid was placed over the material sample in the pan.

The differential scanning calorimeter was calibrated using an indium metal standard and a baseline correction was performed as described in the differential scanning calorimeter manual. A sample of material was placed in the test chamber of the differential scanning calorimeter for testing and an empty pan was used as a control. All tests were performed with the test chamber operating at 55 cm^/min, industrial grade.

- 22 g nitrogen purge. The heating and cooling program is a two-cycle test that begins with equilibration of the chamber to -75 °C, followed by a 20 °C/min heating cycle to 220 °C, followed by a 20 °C/min cooling cycle to -75 °C, and then another 20 °C/min heating cycle to 220 °C.

The results were evaluated using the analysis software, which identified and quantified the glass transition temperature (Tg) corresponding to the inflection point, the endothermic and exothermic peaks. The glass transition temperature was defined as the area under the line where a distinct change in slope occurred, and the melting temperature was then determined using an automatic inflection calculation.

Apparent viscosity

Among the rheological properties of the material samples, a capillary rheometer (Göttfert Rheograph 2003 capillary rheometer manufactured by Göttfert, Rock Hill, South Carolina, USA) was used to evaluate the apparent viscosity in combination with the WinRHEO (version 2.31) analysis software. The capillary rheometer equipment included a 2000 bar pressure transducer and a 30/1:0/180 round-hole capillary die.

If the material being tested is sensitive to water or is known to be so, the material sample is dried in a vacuum oven at a temperature above its glass transition temperature, i.e. above 55 or 60°C for polylactic acid materials, at a vacuum of at least 381 mmHg at a pressure of at least 30 standard cubic feet per hour.

- 23 with nitrogen gas flushing for at least 16 hours.

Once the equipment is warmed up and the pressure transducer is calibrated, the sample is gradually loaded onto the column, each time introducing resin into the column with a loading rod to ensure constant melting throughout the test. After the sample is loaded, a two-minute melting period precedes each test to allow the sample to melt completely at the test temperature. The capillary rheometer automatically records data points and determines the apparent viscosity (in Pa.s) at seven apparent shear rates (s' ¹ ): 50, 100, 200, 500, 1000, 2000 and 5000. When examining the resulting curve, it is important that the curve is relatively smooth. If there are significant deviations from a general curve between two points, which may be due to air in the column, the test run should be repeated to confirm the results.

The resulting rheological curve, which plots apparent viscosity as a function of apparent shear rate, indicates how the material sample will behave at this temperature in an extrusion process. Of particular interest are the apparent viscosity values obtained at shear rates of at least 1000 s, as these are typical conditions in commercially available filament winding extruders.

Weight/number average molecular weight

The molecular weight distribution of polylactic acid samples with a weight average molecular weight (M _w ) between 800 and 400,000 was determined using a gas permeation chromatography (GPC) method.

- 24 ' ·· · · · ** * * » * a ι» * _Α * »· *ν·

The GPC is equipped with two PLgel Mixed K linear 5 μ 7.5x300 mm analytical columns connected in series. The column and detector temperature is 30 °C. The mobile phase is HPLX grade tetrahydrofuran (THF). The pump speed is 0.8 ml/min with a 25 ml injection volume. The total run time is 30 min. It is important to note that new analytical columns should be set up approx. every four months, a new guard column approx. every month and a new inline filter approx. every month.

Polystyrene polymer standards, purchased from Aldrich Chemical Co., were mixed in a 10:90 mixture of dichloromethane (DCM) and THF solvents (both HPLC grade) to obtain solutions with a concentration of 1 mg/mL. Multiple polystyrene standards may be combined in one standard solution, provided that their peaks do not overlap during chromatography. A series of standards with molecular weights ranging from approximately 687 to 400,000 should be prepared. Examples of standard mixtures prepared with Aldrich polystyrenes of varying weight average molecular weights are: standard 1 (401,340; 32,660; 2,727), standard 2 (45,730; 4,075), standard 3 (95,800; 12,860) and standard 4 (184,200; 24,150; 687).

Next, prepare the strain control standard. Dissolve 10 g of a 200,000 molecular weight polylactic acid standard (#19245, Polysciences Inc.) in 100 mL HPLC grade DCM in a glass jar with a Teflon-lined lid using an orbital shaker (at least 30 min). The mixture is poured onto a clean, dry glass slide and allowed to evaporate first before being placed in a vacuum oven preheated to 35 °C and dried for over 14 h at 25 mm Hg vacuum. The polylactic acid is then removed from the oven.

The samples are immediately ground in a grinding mill (with a 10 mesh screen) taking care not to overfeed or stop the grinder. A few grams of the ground sample are stored in a dry glass jar in a desiccator, while the remainder of the sample can be stored in a refrigerator in a similar type of jar.

It is important to prepare a new control standard before starting each new run, and since molecular weight is greatly affected by sample concentration, great care must be taken in its measurement and preparation. To prepare the control standard, weigh 0.0800 ± 0.0025 g of a polylactic acid control standard with a weight average molecular weight of 200,000 into a clean, dry scintillation vial. Then, using a graduated pipette, add 2 ml of DCM to the vial and screw the cap tightly on. Allow the sample to dissolve completely, if necessary by mixing on an orbital mixer such as a Thermclyne Roto Mix (type 51300) or similar. To determine whether the material is completely dissolved, hold the vial at a 45 degree angle to the light. Rotate slowly and observe the liquid as it drains down the vial. If the bottom of the vial does not appear smooth, the sample has not dissolved completely. It may take several hours for the sample to dissolve. Once dissolved, add 18 ml of THF using a graduated pipette, screw the cap tightly on, and mix.

Prepare a sample by weighing 0.0800 ± 0.0025 g of the material into a clean, dry scintillation vial (great care must be taken in both weighing and preparation). Add 2 ml of DCM to the vial using a graduated pipette and screw the lid on.

- 26 screw the cap tightly. Allow the material to dissolve completely using the same method as described above for the preparation of the control standard. Then add 18 ml of THF using a graduated pipette, screw the cap tightly and mix.

The evaluation begins by injecting a standard preparation for testing to check the equilibration of the system. Once equilibration has been verified, the standards are injected. Once these have run out, the control standard preparation is injected, followed by the samples. The control standard preparation is re-injected after every seven sample injections and at the end of the test. Be careful not to inject more than twice from any one vial, and to perform these two injections within 4.5 hours.

There are four quality control parameters to evaluate the result. First, the correlation coefficient of the fourth-order regression for each standard should be between 0.950 and 1.050. Second, the relative standard deviation of the weight average molecular weight of the control standard preparations should be below 5.0 5 in each case. Third, the weight average molecular weight of the injected control standard preparation should be within 10% of the weight average molecular weight of the first control standard preparation injected. Finally, the lactide response to the 200 pg/ml standard injection should be recorded on an SQC data sheet. The response should be within the specified SQC parameters, considering the control lines on the sheet.

Furthermore, polystyrene standard preparations include:

- Based on a calibration curve constructed from Mark Houwink constants measured for 27 polylactic acids and polystyrene in THF at 30°C, we calculate the molecular statistics, which are as follows: polystyrene (K=14.1*10'', a=0.700) polylactic acid (K=54.9*10 ⁵ ,a=0.639).

Heat shrinkage of fibers

The equipment required to determine heat-induced shrinkage includes the following: a convection oven (Thelco 160DM laboratory oven), 0.5 g (± 0.06 g) sinker weights, 1.27 cm staples, masking tape, chart paper with at least 0.635 cm squares, foam pinboard 27.9 x 35.6 cm (11 x 14 inches) or equivalent means for mounting the chart paper and samples. The convection oven must be capable of operating at 100°C.

Fiber samples are melt spun under appropriate spinning conditions, preferably in bundles of 30 fibers, and mechanically drawn to produce fibers having a jet stretch of 224 or greater. Only fibers with the same jet stretch can be compared with respect to their heat shrinkage. The jet stretch of a fiber is the ratio of the speed of the stretching roller to the linear extrusion rate (distance/time) of the molten polymer leaving the spinneret. The spun fiber is usually wound onto a bobbin using a winder. The wound fiber bundle is separated into 30 filaments, if not previously obtained as a 30 filament bundle, and cut into 22.9 cm (9 inch) lengths.

The chart paper is attached to the pinboard with tape, aligning one edge of the chart paper with the

- 28 to the edge of a pinboard. Tape one end of the fiber bundle (no more than the final 2.54 cm). Clip the taped end to the pinboard at the edge where the chart paper was attached so that the edge of the clip is above one of the horizontal lines on the chart paper, holding the fiber bundle in place (the taped end is just visible under the clip). Pull the other end of the bundle taut and place it parallel to the vertical lines on the chart paper. Then, 17.8 cm (7 inches) down from where the clip secures the fiber, clip the 0.5 g sinker around the fiber bundle. Repeat the attachment procedure for each parallel. Typically, three samples can be attached at a time. Marks can be made on the chart paper to indicate the initial position of the sinking weights. The samples are placed in the oven at approx. 100°C so that they hang vertically and do not touch the pin board. After 5, 10 and 15 minutes, quickly mark the new position of the sinking weights on the chart paper and return the samples to the oven.

After the test is completed, the pin board is removed and the distances between the starting point (where the clip holds the fibers) and the points at 5, 10, and 15 minutes are measured using a ruler graduated to approximately 0.16 cm (1/16 inch). It is recommended that three replicate tests be performed per sample. The means, standard deviations, and percent shrinkage are calculated. The percent shrinkage is calculated by dividing the difference between the initial length and the measured length by the initial length and multiplying the quotient by one hundred. For the heat shrinkage values given in this specification, 15

- Data obtained at 29 minutes were used.

Crystal size determination

The measurement of crystallite size within a fiber sample is performed by X-ray diffraction using an X-ray machine available from Philips Inc. (Mahwah, New Jersey, USA) under the name XRG-3000 x-ray machine. The X-ray machine is equipped with a copper tube. Images are obtained and plotted using a wide-angle goniometer. To determine the effective crystallite size of a fiber sample, a reflection pattern is taken in the equatorial direction of the fiber, scanning through the (hkl) layer line. The (100) plane at approximately 16.4° 2Q is chosen as constant for all size calculations. The average crystallite size perpendicular to the (100) plane is then calculated using the Scherrer equation.

Biodegradability test

The biodegradability of the samples is determined by the Organic Waste Systems (Ghent, Belgium) method using a modified ASTM 5338.92 or equivalent ISO CD 14855 test method. The modification of ASTM 5338.92 consists in maintaining the test chambers at a constant temperature of 58°C throughout the test and not using an increasing temperature profile.

Examples: Example 1

Polylactic acid polymer (PLA) was purchased from Chronopol Inc., Golden, Colorado, USA. The L:D ratio of the polylactic acid polymer was

- 30 100:0, melting point approx. 175 °C, weight average molecular weight approx. 211,000, number average molecular weight approx. 127,000, polydispersity index approx. 1.66 and residual lactic acid monomer value approx. 5.5 wt.

The polylactic acid polymer is mixed with adipic acid in various amounts. When mixing the polylactic acid polymer with adipic acid, the components are first dry mixed and then thoroughly mixed in the melt, which is achieved by a counter-rotating twin-screw extruder. The mixing is carried out either with a BRABENDER™ twin-screw compounder or a HAAKE™ twin-screw extruder equipped with a mixing screw.

The premixes are converted into fibers using an in-house fiber spinneret. The spinneret has a 1.9 cm (0.75) diameter screw with a 24:1 length:diameter ratio and three heating zones. From the spinneret, the material is fed into a 1.6 cm (0.62 inch) diameter Koch® static mixer unit and then into the spinneret (heating zones 4 and 5) through a 15-30 hole pre-spinneret, each hole having a diameter of approximately 500 gm. The temperatures of each heating zone are listed in order in the temperature profile column (Table 1). The fibers are air-quenched using an air temperature of 13-22°C and drawn off by a mechanical draw roller and either passed to a take-up unit (as in the Lurgi spunbonding process). The process conditions for some of the fibers produced are shown in Table 1.

Table 1

Polymer mixture *PLA/Adipic acid (100:0)

PLA/Adipic acid (85:15)

PLA/Adipic acid (75:25)

Temperature profile 160/180/190/190/190

145/155/160/160/160

150/170/165/160/160

Note required to reduce extruder speed, torque and pressure lower heat to maintain extrusion pressure lower heat to maintain extrusion pressure not the sample according to the invention

The heat shrinkage (Tg) and average crystal size of the prepared fibers were then determined. The results obtained are shown in Table 2. The actual percentage of polylactic acid polymer and adipic acid was determined using nuclear magnetic resonance as the ratio between the CH and CH ₂ peaks.

Table 2

Feeded Adipic acid Tg(°C) Medium Percentage adipic acid actual crystallite heat shrinkage quantity amount in the spun fiber t, L(hki) A *0/ 0.0% 63.4 120 16.6% 5% 5.0% 53, 9 - - 10% 9.2% 41, 6 100 8.9% 15% — 45, 0 — — 25% 27.1% 36, 9 60 0%

* not the sample according to the invention

Example 2

Polylactic acid polymer was obtained from Chronopol Inc. (Golden, Colorado, USA). The polylactic acid polymer has an L:D ratio of 100:0, a melting point of approximately 175°C, and a weight percent

- 32 lag has a molecular weight of about 181,000, a number average molecular weight of about 115,000, a polydispersity index of about 1.57 and a residual lactic acid monomer value of about 2.3% by weight.

The polylactic acid polymer is mixed with adipic acid in various amounts. When mixing the polylactic acid polymer with adipic acid, the components are first dry mixed and then thoroughly mixed in the melt, which is achieved by a counter-rotating twin-screw extruder. The mixing is carried out either with a BRABENDER™ twin-screw compounder or a HAAKE™ twin-screw extruder equipped with a mixing screw.

The prepared blends are converted into fibers using an in-house fiber spinneret. The spinneret has a 1.9 cm (0.75) diameter screw with a 24:1 length:diameter ratio and three heating zones. From the spinneret, the material is fed into a 1.6 cm (0.62 inch) diameter Koch® static mixer unit and then into the spinneret (heating zones 4 and 5) through a 15-30 hole pre-spinneret, each hole having a diameter of approximately 500 µm. The temperatures of each heating zone are listed in order in the temperature profile column (Table 3). The fibers are air-quenched using an air temperature of 13-22°C and drawn off by a mechanical draw roller and either fed to a take-up unit (as in the Lurgi spunbonding process). The process conditions for some of the fibers produced are shown in Table 3.

- 33 Table 3

Polymer mixture Temperature profile Note *PLA/Adipic Acid (100:0) 180/207/195/195/195 necessary to reduce extruder speed, torque and pressure PLA/Adip ins av (95:5) 160/185/175/175/175 lower heat to maintain spinning pressure PLA/Adipic Acid (90:10} 160/185/175/175/175 lower heat to maintain spinning pressure PLA/Adipic Acid (85:15) 150/175/170/170/170 lower heat to maintain spinning pressure PLA/Adipic Acid (80:20) 150/175/170/170/170 lower heat to maintain spinning pressure PLA/Adipic Acid Ή E „ E 'J 150/170/168/168/168 lower heat to maintain spinning pressure PLA/Adipic Acid <70:30) 150/170/165/165/165 lower heat to maintain spinning pressure

* not the sample according to the invention

The heat shrinkage (Tg) and biodegradability of the prepared fibers were then determined. The results obtained are shown in Table 4. The actual percentage of polylactic acid polymer and adipic acid was determined using nuclear magnetic resonance as the ratio between the CH and CH peaks.

- 34 « a · ··· ··· ··· · ···· · ····♦ • ······ ··· · . table

Feeded Adipic acid Tg(°C) Medium crystal- Percentage adipic acid actual size, L _(h w) A heat shrinkage quantity quantity of in woven fiber *0% 0.0% 56, 5 7 6.1% 34% 5% 5.2% - — 40% 10% 9.2% 49, 5 92.5% 10% 15%. 18.3% 50, 9 - 7% 20% 12.1% - - 14% 2 5% 19.7% 49.4 100% 12% 30% 21.6% 49, 4 — 0%

* not the sample according to the invention

It will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from the spirit thereof. Accordingly, the detailed description and the above examples are intended to be illustrative only and are not intended to limit the scope of the claims.

Claims (27)

- • « « · · ·· ··/· • «·· · ·· ·· * PATENT CLAIMS 1. A thermoplastic composition comprising a mixture of the following components: a) an aliphatic polyester polymer having a weight average molecular weight of from about 10,000 to about 2,000,000, wherein the aliphatic polyester polymer is present in the thermoplastic composition in an amount of from about 50 to about 95 wt. %; and b) a polycarboxylic acid having less than about 30 carbon atoms, and wherein the polycarboxylic acid is present in the thermoplastic composition in an amount of from about 5 to about 50 wt. %, wherein all weight values are based on the total weight of the aliphatic polyester polymer and polycarboxylic acid present in the thermoplastic composition. 2. The thermoplastic composition according to claim 1, characterized in that the aliphatic polyester polymer comprises one of polylactic acid, poly(butylene succinate), poly(butylene succinate-co-adipate), poly(hydroxybutyrate-co-valerate), polycaprolactone, sulfonated poly(ethylene terephthalate), or mixtures or copolymers of these polymers. 3. A. Thermoplastic composition according to claim 2, characterized in that it contains polylactic acid as aliphatic polyester polymer. 4. The thermoplastic composition of claim 1, wherein the aliphatic polyester polymer is present in an amount of from about 60 to about 90% by weight of the thermoplastic composition. 5. The thermoplastic composition according to claim 1, characterized in that it contains as multicarboxylic acid one of malonic acid, citric acid, succinic acid, glutanic acid, adipic acid, pimelic acid, parafic acid, azelaic acid, sebacic acid or mixtures thereof. 6. The thermoplastic composition according to claim 5, characterized in that it contains adipic acid as the multicarboxylic acid. 7. The thermoplastic composition of claim 1, wherein the multicarboxylic acid is present in an amount of from about 10 to about 40% by weight of the thermoplastic composition. 8. The thermoplastic composition of claim 1, wherein the multicarboxylic acid comprises a multicarboxylic acid having a total carbon number of from about 3 to about 30. 9. The thermoplastic composition of claim 1, characterized in that it has a glass transition temperature of less than about 55°C. 10. The thermoplastic composition of claim 9, characterized in that it has a glass transition temperature of less than about 50°C. 11. The thermoplastic composition according to claim 1, characterized in that the aliphatic polyester polymer is polylactic acid, - 37 poly(butylene succinate), poly(butylene succinate co-adipate), poly(hydroxybutyrate co-valerate), polycaprolactone, sulfonated poly(ethylene terephthalate), or mixtures or copolymers of these polymers; and the multicarboxylic acid is malonic acid, citric acid, succinic acid, glutanic acid, adipic acid, pimelic acid, parfumic acid, azelaic acid, sebacic acid, or mixtures thereof; and has a glass transition temperature of less than about 55°C. 12. The thermoplastic composition according to claim 11, characterized in that it contains polylactic acid as the aliphatic polyester polymer and adipic acid as the multicarboxylic acid. 13. The thermoplastic composition of claim 12, characterized in that the polylactic acid polymer is contained in an amount of between about 60 and about 90 weight percent and the adipic acid is contained in an amount of between about 10 and about 40 weight percent. 14. Fiber produced from a thermoplastic composition, which thermoplastic composition contains a mixture of the following components 2 : a: a) an aliphatic polyester polymer having a weight average molecular weight of from about 10,000 to about 2,000,000, wherein the aliphatic polyester polymer is present in the thermoplastic composition in an amount of from about 50 to about 95 wt. %; and b) a multicarboxylic acid having less than about 30 carbon atoms, and wherein the multicarboxylic acid is present in the thermoplastic composition in an amount of from about 5 to about 50 wt. %, wherein all weight average molecular weights are in the thermoplastic composition. - 38 - , . ...» » «... *ζ*· *’f* refers to the total weight of aliphatic polyester polymer and multicarboxylic acid present; and wherein the fiber has a heat shrinkage value of less than about 15%. 15. The fiber according to claim 14, characterized in that the aliphatic polyester polymer comprises one of polylactic acid, poly(butylene succinate), poly(butylene succinate-co-adipate), poly(hydroxybutyrate-co-valerate), polycaprolactone, sulfonated poly(ethylene terephthalate), or mixtures or copolymers of these polymers. 16. The fiber according to claim 15, characterized in that it contains polylactic acid as the aliphatic polyester polymer. 17. The fiber of claim 14, wherein the aliphatic polyester polymer is present in an amount of from about 60 to about 90 percent by weight of the thermoplastic composition. 18. The fiber according to claim 14, characterized in that it contains as multicarboxylic acid one of malonic acid, citric acid, succinic acid, glutanic acid, adipic acid, pimelic acid, parafic acid, azelaic acid, sebacic acid or mixtures thereof. 19. The fiber according to claim 18, characterized in that it contains adipic acid as the multicarboxylic acid. 20. The fiber of claim 14, wherein the multicarboxylic acid is present in an amount of from about 10 to about 40% by weight of the thermoplastic composition. -branch- ii. The fiber of Claim 14, characterized in that the multicarboxylic acid comprises a multicarboxylic acid having a total carbon number of between about 3 and about 30. 22. The fiber of claim 14, wherein the thermoplastic composition has a glass transition temperature of less than about 55°. 23. The fiber of claim 22, wherein the thermoplastic composition has a glass transition temperature of less than about 50°C. 24. The serine fiber of claim 14, wherein the aliphatic polyester polymer is selected from the group consisting of polylactic acid, poly(butylene succinate), poly(butylene succinate-co-adipate), poly(hydroxybutyrate-co-valerate), polycaprolactone, sulfonated poly(ethylene terephthalate), or mixtures or copolymers of these polymers; and the multicarboxylic acid is selected from the group consisting of malonic acid, citric acid, succinic acid, glutanic acid, adipic acid, pimelic acid, parafic acid, azelaic acid, sebacic acid, or mixtures thereof; and the thermoplastic composition has a glass transition temperature of less than about 55°C. 25. The fiber according to claim 24, characterized in that it contains polylactic acid as the aliphatic polyester polymer and adipic acid as the multicarboxylic acid. 26. The fiber of claim 25, characterized in that the - 40 thermoplastic compositions contain the polylactic acid polymer in an amount of between about 60 and about 90% by weight and the adipic acid in an amount of between about 10 and about 40% by weight. 27. The fiber of claim 25, characterized in that it has a heat shrinkage value of less than about 10%. Phone: 316-0634 1 ax 316-0635 í