NONWOVEN FABRICS COMPRISING POLYLACTIC ACID AND SURFACE-TREATED CALCIUM CARBONATE

Abstract

A process for the production of a nonwoven fabric. In particular, it relates to the production of a nonwoven fabric having desirable tactile and haptic as well as mechanical properties, as well as to the nonwoven fabric itself. The process requires the selection of specific polylactic acid polymers and corresponding process conditions.

Claims

1. A process for producing a nonwoven fabric, the process comprising the following steps: a) providing a surface-treated calcium carbonate-containing filler material, the surface-treated calcium carbonate-containing filler material comprising a calcium carbonate-containing filler material and a surface-treatment layer on at least a part of the surface of said calcium carbonate-containing filler material, wherein the surface-treatment layer is formed by contacting the calcium carbonate-containing filler material with a surface treatment agent, wherein the surface treatment agent comprises at least one mono-substituted succinic anhydride and/or mono-substituted succinic acid and/or a salt thereof; b) providing a first polylactic acid polymer; c) providing a second polylactic acid polymer being the same or different from the first polylactic acid polymer; d) forming a masterbatch by compounding the surface-treated calcium carbonate-containing filler material of step a) in an amount of from 20 to 80 wt.-%, based on the total weight of the masterbatch, with the first polylactic acid polymer of step b); e) mixing the masterbatch of step d) with the second polylactic acid polymer of step c) to obtain a mixture; f) forming the mixture of step e) into fibers; g) forming a fibrous web from the fibers of step f); and h) forming the non-woven fabric by calendering or hydroentanglement of the fibrous web of step g).

2. The process of claim 1, wherein the calcium carbonate-containing filler material has prior to the surface treatment i) a weight median particle size (d.sub.50) value in the range from 0.1 μm to 7 μm, ii) a top cut (d.sub.98) value of 15 μm or less, iii) a specific surface area (BET) from 0.5 to 120 m.sup.2/g, as measured by the BET method, and/or iv) a residual total moisture content from 0.01 wt.-% to 1 wt.-%, based on the total dry weight of the at least one calcium carbonate-containing filler material.

3. The process of claim 1, wherein the mixture of step e) has a surface-treated calcium carbonate-containing filler material content in the range of 5 to 25 wt.-%, based on the total weight of the mixture.

4. The process of claim 1, wherein the fibers formed in step f) are filaments having an average fiber diameter in the range from 9 to 25 μm, and/or titer in the range from 1 to 6 dtex, as measured by EN ISO 2062:2009, and/or are formed from the mixture of step e) by spunbonding.

5. The process of claim 1, wherein the fibers formed in step f) are staple fibers having an average fiber diameter in the range from 9 to 25 μm, and/or a titer in the range from 1 to 6 dtex, as measured by EN ISO 2062:2009 and/or a staple fiber length in the range from 30 to 90 mm.

6. The process of claim 1, wherein the non-woven fabric is formed in step h) by hydroentanglement.

7. The process of claim 1, wherein the non-woven fabric is formed in step h) by calendering.

8. A nonwoven fabric formed from fibers composed of a mixture comprising a first polylactic acid polymer, a second polylactic acid polymer being the same or different than the first polylactic acid polymer and a surface-treated calcium carbonate-containing filler material comprising a calcium carbonate-containing filler material and a surface-treatment layer on at least a part of the surface of said calcium carbonate-containing filler material, wherein the surface-treatment layer is formed by contacting the calcium carbonate-containing filler material with a surface treatment agent, and wherein the surface treatment agent comprises at least one mono-substituted succinic anhydride and/or mono-substituted succinic acid and/or a salt thereof.

9. The nonwoven fabric of claim 8, wherein the calcium carbonate-containing filler material has prior to the surface treatment i) a weight median particle size (d.sub.50) value in the range from 0.1 μm to 7 μm, ii) a top cut (d.sub.98) value of 15 μm or less, iii) a specific surface area (BET) from 0.5 to 120 m.sup.2/g, as measured by the BET method, and/or iv) a residual total moisture content from 0.01 wt.-% to 1 wt.-%, based on the total dry weight of the at least one calcium carbonate-containing filler material.

10. The nonwoven fabric of claim 8, wherein the surface-treatment layer is formed by contacting the calcium carbonate-containing filler material with a surface treatment agent in an amount from 0.1 to 3.0 wt.-%, based on the total dry weight of the calcium carbonate-containing filler material.

11. The nonwoven fabric of claim 8, wherein the nonwoven fabric is formed by a process comprising a calendering or hydroentanglement step.

12. The nonwoven fabric of claim 8, wherein the mixture comprises from 5 to 25 wt. % of the surface-treated calcium carbonate-containing filler material.

13. The nonwoven fabric of claim 8, wherein the first polylactic acid polymer has a melt flow rate MFR (210° C./2.16 kg) in the range from 10 to 40 g/10 min, as measured according to EN ISO 1133:2011, and/or wherein the second polylactic acid polymer has a melt flow rate MFR (210° C./2.16 kg) in the range from 10 to 40 g/10 min, as measured according to EN ISO 1133:2011.

14. A surface-treated calcium carbonate-containing filler material for the manufacture of a nonwoven fabric comprising a polylactic acid polymer, wherein the surface-treated calcium carbonate-containing filler material comprises a calcium carbonate-containing filler material and a surface-treatment layer on at least a part of the surface of said calcium carbonate-containing filler material, wherein the surface-treatment layer is formed by contacting the calcium carbonate-containing filler material with a surface treatment agent, and wherein the surface treatment agent comprises at least one mono-substituted succinic anhydride and/or mono-substituted succinic acid and/or a salt thereof.

15. An article comprising the nonwoven fabric of claim 8.

Description

EXAMPLES

Measurement Methods

[0360] In the following, measurement methods and materials implemented in the examples are described.

[0361] Particle Size

[0362] The particle distribution of the calcium carbonate filler was measured using a Sedigraph 5120 from the company Micromeritics, USA. The method and the instruments are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement was carried out in an aqueous solution comprising 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and supersonics.

[0363] Filter Pressure Value (FPV)

[0364] The filter pressure test was performed on a commercially available Collin Pressure Filter Test Teach-Line FT-E20T-IS (Colin Lab & Pilot Solutions GmbH, Maitenbeth, Germany). The test method was performed in agreement with European Standard EN 13900-5 with each of the corresponding polymer compositions (16 g effective calcium carbonate per 200 g of final sample, diluent: PLA NatureWorks Ingeo™ Biopolymer 6100D) using a 14 μm type 30 filter (GKD Gebr. Kufferath AG, Düren, Germany), wherein no melt pump was used, the extruder speed was kept at 100 rpm, and wherein the melt temperature was 225 to 230° C. (temperature setting: 190° C./210° C./230° C./230° C./230° C.).

[0365] Titer or Linear Density (Continuous Filaments)

[0366] The titer or linear density [dtex] was measured according to EN ISO 2062:2009 and corresponds to the weight in grams of 10 000 m fiber. A sample of 25 or 100 metres was wound up on a standard reel under a pretension of 0.5 cN/tex and weighted on analytical scale. The grams per 10 000 m fiber length were then calculated.

[0367] Fiber Diameter (Staple Fibers and Spunlaid Fibers)

[0368] The fiber diameter [μm] was measured according to EN ISO 137:2015. A nonwoven sample, or fiber sample was placed into a microscope (MESDAN Micro Lab 250E). The analysis consists of the measurement of the distance between each side of the fiber to determine the fiber diameter using the best optical degree. Generally, between 20 to 50 measures were taken to determine the mean value.

[0369] Fabric Weight

[0370] Fabric weight or mass per unit area [g/m2] was measured according to EDANA/INDA test procedure NWSP 130.1.RO (15) or ISO 9073-1:1989.

[0371] Tensile Strength and Elongation at Break of the Nonwoven Fabrics

[0372] The tensile strength, expressed in [N/50 mm] is the strength of a material when subjected to either pulling or to a compressive stress test, i.e., represents the stress the material can bear without rupturing or tearing. The elongation at break represents the deformation in the direction of load caused by a tensile force at the point of rupture. Elongation is generally expressed as a ratio of the length of the stretched material as a percentage to the length of the unstretched material. Elongation may be determined by the degree of stretch under a specific load or the point where the stretched material breaks.

[0373] Tensile strength and elongation at break were determined according to Standard Procedure NWSP 110.4.R0 (15) published by EDANA and INDA using a 50 mm strip tensile at constant-rate-of-extension (CRE). A test specimen is clamped in a tensile testing machine and a force is applied to the specimen until it breaks. Values for the breaking force [N/50 mm] and elongation [%] of the test specimen are obtained.

[0374] Ash Content

[0375] The ash content in [%] of the fibres and the masterbatches was determined by incineration of a sample in an incineration crucible which is put into an incineration furnace at 570° C. for 2 hours. The ash content is measured as the total amount of remaining inorganic residues.

[0376] Air Permeability of Nonwoven Fabrics

[0377] The air permeability of the nonwoven fabric samples was determined by using a Textest Air Permeability Tester FX 3300 Labair IV (Textest AG, Schwerzenbach, Switzerland) equipped with the test head FX 3300-IV 20 with a surface area of 20 cm.sup.2 according to ISO 9237 (1995). The air permeability is measured in [L/(m.sup.2 s)].

Materials

[0378] PLA1: Polymer 1: PLA polylactic acid : NatureWorks Ingeo™ Biopolymer 6202D (MFR: 15 -30 g/10 min (210° C., 2.16 kg) according to technical data sheet), commercially available from NatureWorks, Minnetonka, Minn., USA. PLA1 was pre-dried in an oven at 80° C. for 6 h prior to use.

[0379] PLA2: Polymer 2: PLA polylactic acid : NatureWorks Ingeo™ Biopolymer 6100D (MFR: 24 g/10 min (210° C., 2.16 kg) according to technical data sheet), commercially available from NatureWorks, Minnetonka, Minn., USA. PLA2 was pre-dried in an oven at 80° C. for 6 h prior to use.

[0380] PBS: BioPBS, product FZ71PB, bio-based polybutylene succinate (PBS), (MFR: 22 g/10 min (210° C., 2.16 kg), moisture content less than 700 ppm according to technical data sheet), commercially available from PTT MCC Biochem Company Limited, Bangkok, Thailand.

[0381] CC1 (inventive): Natural ground calcium carbonate, commercially available from Omya International AG, Switzerland (d.sub.50: 1.7 μm; d.sub.98: 6 μm, content of particles <0.5 μm =12%), surface-treated with 1.7 wt. % alkenyl succinic anhydride (CAS [68784-12-3], concentration >93%), based on the total weight of the natural ground calcium carbonate. BET: 3.4 m.sup.2/g, residual moisture content: 0.1 wt.-%.

[0382] CC2 (inventive): Natural ground calcium carbonate, commercially available from Omya International AG, Switzerland (d.sub.50: 0.8 μm; d.sub.98: 3 μm, content of particles <0.5 μm=35%), surface-treated with 0.7 wt. % alkenyl succinic anhydride (CAS [68784-12-3], concentration >93%), based on the total weight of the natural ground calcium carbonate. BET: 8.5 m.sup.2/g, residual moisture content: 0.5 wt.-%.

Example 1—Preparation of Masterbatches

[0383] Masterbatches containing PLA1 and one of the calcium carbonate fillers CC1 and CC2 were prepared on a lab scale Twin screw extruder (ZSE27HP-40D from Leistritz, Germany). The compositions and filler contents of the prepared masterbatches are compiled in Table 1 below. The precise filler content was determined by the ash content.

TABLE-US-00001 TABLE 1 Composition and filler content of prepared masterbatches. Filler content Ash content Mineral dispersion Masterbatch Filler [wt.-%] [wt.-%] quality MB1 (inventive) CC1 50 49.6 good MB2 (inventive) CC2 50 50.0 good

[0384] The results shown in Table 1 confirm that masterbatches with good quality were produced.

Example 2—Preparation of Nonwoven Fabrics (Via Spunlaid Process A with Thermobonding)

[0385] Masterbatches according to Example 1 were mixed with polymer PLA2 and/or PBS and were directly dosed together into a single screw extruder equipped with a melt pump. Nonwoven fabrics were produced from these mixtures on a Hills spunbond pilot line, width 550 mm (Hills Inc. West Melbourne, Fla.; USA), equipped with a spin pack with 1003 holes/500 mm, 0.35 mm hole diameter. The extruder temperature was set at 220-225° C. with a throughput of 0.6 g/hole/min. The quenching temperature was 14° C. at 830 mm distance. The extruded filaments were produced with filament speed at 2900 m/min with a fiber gap of 5.33 mm and 1.5 bar air pressure and formed into a nonwoven web. The filament laying distance was 600 mm and conveyor the belt speed was adjusted to receive 15 and 50 gsm nonwoven fabric weight.

[0386] The calendering (thermobonding) process was used for the bonding of the nonwoven web with an Andritz Nexcal XT type 410.11×800 LSR, machine width 600 mm (Andritz Kuesters, Krefeld, Germany) with a smooth and an engraved roll. The temperature of the roll was set between 135-150° C. The rolls are heated (by circulating heated oil) and the temperature is measured (by temperature sensor into the rolls oil feeding pipes and the surface temperature is measured with a contact-type surface temperature meter).The engraving roll has an ovoid pattern with a bonding area of 18.1%, the points density is 43.9 points/cm.sup.2 and the engraving depth is 0.68 mm. The linear pressure was set to 30 N/mm.

[0387] The compositions and properties of the produced nonwoven materials are compiled in Table 2 below.

TABLE-US-00002 TABLE 2 Compositions and properties of the prepared nonwoven fabrics (wt.-% is based on total weight of the sample). Tensile Elongation Basis strength at break Air weight [N/50 mm] [%] permeability Sample Composition [g/m.sup.2] MD CD MD CD [L/(m.sup.2 s)] 1 PLA2 (100) 52.2 70.4 50.2 18.4 17.4 1.573 2 PLA2 (80) MB1 (20) 51.5 103.5 54.7 26.9 23.8 1.783 3 PLA2 (80) MB2 (20) 51.1 102.1 46.9 24.7 26.4 1.707 4 PLA2 (100) 15.5 17.2 7.9 14.5 14.2 6.247 5 PLA2 (80) MB1 (20) 15.3 21.1 8.0 15.7 16.3 7.373 6 PLA2 (80) MB2 (20) 15.4 22.2 9.1 18.9 20.3 7.127 7 PLA2 (75) MB1 (20) PBS (5) 15.1 22.4 12.6 19.7 25.9 7.016 8 PLA2 (75) MB2 (20) PBS (5) 15.2 27.9 11.5 24.3 23.5 5.843

[0388] As can be gathered from Table 2, the addition of the inventive fillers significantly increased the tensile strength of the calendered nonwoven fabric in machine direction (MD), whereas the tensile strength in cross direction (CD) was retained or increased. At the same time, the elongation at break in MD and CD, as well as the air permeability is increased by the addition of the inventive fillers.

Example 3—Preparation of Nonwoven Fabrics (Via Spunlaid Process B with Thermobonding)

[0389] Masterbatches according to Example 1 were mixed with polymer PLA1 or PLA2 and were directly dosed together into a single screw extruder equipped with a melt pump. Nonwoven fabrics were produced from these mixtures on a Reicofil 4 pilot line, 1 meter width (Reifenhäuser Reicofil GmbH & Co. KG, Troisdorf, Germany), equipped with a spin pack with 7377 holes, core/sheath configuration, 0.6 mm hole diameter. Extruder temperature at 220° C., die temperature at 240° C. with a throughput of 0.77 to 0.90 g/hole/min. The quenching temperatures were at 35°/25° C. and the cabin pressure was set to 9000 Pa. The extruded filaments were formed into a nonwoven web.

[0390] The calendering (thermobonding) process was used for the bonding of the nonwoven web with an Andritz Kuesters type 419.40A with HOT-S-ROLL 275 “Twin”, machine width 1300 mm (Andritz Kuesters, Krefeld, Germany) with a smooth and an engraved roll. The temperature of the roll was set between 127-147° C. The rolls are heated (by circulating heated oil) and the temperature is measured (by temperature sensor into the rolls oil feeding pipes and the surface temperature is measured with a contact-type surface temperature meter).The engraving roll has a U 2888 pattern with a bonding area of 18.1%, the points density is 49.9 points/cm.sup.2 and the engraving depth is 0.68 mm. The linear pressure was set to 50 N/mm.

[0391] The final bonded nonwoven fabrics had a target fabric weight of 30 and 50 g/m.sup.2, which was adjusted by the line speed. The compositions and properties of the produced nonwoven materials are compiled in Table 3 below.

TABLE-US-00003 TABLE 3 Compositions and properties of the prepared nonwoven fabrics (wt.-% is based on total weight of the sample). Tensile Basis strength Elongation at weight [N/50 mm] break [%] Sample Composition [g/m.sup.2] MD CD MD CD 1 PLA2 (100) 49.3 33.5 9.4 5.2 13.8 2 PLA2 (90) MB1 (10) 47.0 52.8 10.9 7.0 13.0 3 PLA2 (80) MB1 (20) 52.3 71.5 18.4 9.4 16.9 4 PLA1 (80) MB1 (20) 50.3 81.9 21.8 12.8 20.2 5 PLA1 (70) MB1 (30) 51.0 76.7 23.5 11.5 22.8 6 PLA1 (80) MB2 (20) 29.5 31.4 6.8 6.2 17.8 7 PLA1 (70) MB1 (30) 29.8 32.1 8.4 6.5 14.7

[0392] As can be gathered from Table 3, the addition of the inventive fillers significantly increased the tensile strength of the calendered nonwoven fabric in MD, whereas the tensile strength in CD was retained or increased. At the same time, the elongation at break in MD and CD is increased by the addition of the inventive fillers.

Example 4—Preparation of Nonwoven Fabrics (Via Spunlaid Process with Hydro-Entanglement)

[0393] This example was designed to obtain soft and less rigid nonwoven fabrics. As representative parameters, the elongation at break and the air permeability of the nonwoven fabrics were measured. Masterbatches according to Example 1 were mixed with polymer PLA1 or PLA2 and were directly dosed together into a single screw extruder equipped with a melt pump. Nonwoven fabrics were produced from these mixtures on a Hills spunbond pilot line, width 550 mm (Hills Inc. West Melbourne, Fla.; USA), equipped with a spin pack with 1003 holes/500 mm, 0.35 mm hole diameter. The extruder temperature was set at 220-225° C. with a throughput of 0.6 g/hole/min. The quenching temperature was 14° C. at 830 mm distance. The extruded filaments were produced with filament speed at 2900 m/min with a fiber gap of 5.33 mm and 1.5 bar air pressure and formed into a nonwoven web. The filament laying distance was 610 mm and conveyor the belt speed was adjusted to receive 40 and 70 gsm nonwoven fabric weight.

[0394] The hydroentanglement process was used for bonding of the nonwoven web with an Andritz Jetlace 3000, machine width 600 mm (Andritz Perfojet SAS, Montbonnot, France). Pre-bonding was performed at 80 bar water pressure. The bonding was performed with 2 cylinders and 4 injectors (2J12 strips at 2 rows with diameter 120 μm and 1.2 mm gap) in two bonding steps. Bonding was performed at a water pressure of 200 bar. The nonwoven fabrics were dried at 90° C. with high air flow in an omega oven. The compositions and properties of the produced nonwoven materials are compiled in Table 4 below.

TABLE-US-00004 TABLE 4 Compositions and properties of the prepared nonwoven fabrics (wt.-% is based on total weight of the sample). Basis Elongation at Air weight break [%] permeability Sample Composition [g/m.sup.2] MD CD [L/(m.sup.2 s)] 1 PLA2 (100) 41.2 46.4 80.3 4,367 2 PLA2 (80) MB1 (20) 42.1 36.7 88.5 4,450 3 PLA2 (80) MB2 (20) 41.9 29.1 69.3 4,360 4 PLA2 (100) 69.7 47.2 77.9 2,620 5 PLA2 (80) MB1 (20) 70.9 33.0 71.0 2,473 6 PLA2 (80) MB2 (20) 70.9 22.5 61.2 2,613

[0395] As can be gathered from Table 4, the hydroentangled nonwoven fabrics comprising the inventive fillers had an MD and CD elongation at break comparable to the unfilled nonwoven fabric. At the same time, also the air permeability of the inventive nonwoven fabrics was retained. Consequently, the inventive nonwoven fabrics are less rigid and softer than the unfilled nonwoven fabrics, i.e., show desirable haptic properties while maintaining acceptable mechanical properties.

Example 5—Tactile Properties Testing with Sensorics Panel

[0396] The tactile properties were evaluated with a sensorics panel. The purpose is to characterize the tactile properties of nonwoven fabric samples in a comparative way by means of human perception. The retained sensory methodology is an analytic quantitative approach permitting to describe and position the studied nonwoven fabrics on every pertinent tactile components generated by the panel (descriptors) in an adapted lexicon (monadic sensory profile: study one by one) based on the standard NF ISO 13299:2016.

[0397] The sensory expert tactile panel was composed of 9 experienced and trained persons. The descriptors, which were determined by the panel, are given in Table 5.

TABLE-US-00005 TABLE 5 Sensory descriptors Descriptor Rating Description Testing Method Softness 0-the least soft Overall feeling of the Stroke the surface of the 10-the softest touch of the material material without pressure with an individual and in both directions. perceptive character. Judge the pleasant aspect of the material. Downiness 0-the least downy Describes the Appose the hand flat on the 10-the most downy presence of fibers in surface of the sample the surface of the without pressure. Make material. microdeplacement of the digital pulp by small circular movements on the surface of the material, so as the fibers to roll under the fingers. Fluidity 0-the least fluid Describes the ease Seize the sample by a 10-the most fluid with which the corner and slide the sample glides and material in the hollow of the flows between the other hand. finders (lack of manipulation resistancy) Tearability 0-the least tearable Describes the Seize the sample with both 10-the most tearable capacity of the hands by a side like a sheet material to burst after of paper and tear the tearing material until rupture Elasticity 0-the least elastic Describes the Seize the sample in both 10-the most elastic capacity of the hands in the diagonal and material to recover slowly exercise a delicate its shape after being strength of tear on the submitted to a material (answer to the stretching of both deformation) hands

[0398] The sensory test results were verified on statistical reliability by the mean of interferential statistic tools: ANOVA and Friedman Test.

[0399] The haptics characterization of the nonwoven samples revealed a tactile profile of the samples with significant differences. These differences are statistically relevant and unique. The results are summarized in Table 6.

TABLE-US-00006 TABLE 6 Results of the tactile properties testing. Descriptor Sample Softness Downiness Fluidity Tearability Elasticity 3 of Example 3 8.2 5.6 9.7 8.7 6.3 (inventive) 1 of Example 3 7.7 4.3 8.9 6.7 3.5 (comparative)