Optimized Polymer Rheology for High Extensibility Spunbond Filaments

Abstract

A method for producing spunbond fibers including providing a base polypropylene having initial rheologic properties with high molecular weight average (Mw) and melt flow rate (MFR) following the correlation Mw>270-2*MFR, where Mw is measured in kilodaltons (kDa) and MFR is measured in accordance with ASMT1238, 230C/2.16 kg, mixing the base polypropylene with an additive at a concentration to produce an adjusted base polypropylene with adjusted rheologic properties following the correlation Mw>260-MFR, with MFR in a range of 100 g/10 min (230C/2.16 kg) to 250 g/10 min (230C/2.16 kg), and melt-extruding the adjusted base polypropylene at cabin pressures above 7000 Pa to produce highly extensible filaments.

Claims

1. A method for producing spunbond fibers comprising: a. providing a base polypropylene having initial rheologic properties with high molecular weight average (Mw) and melt flow rate (MFR) following the correlation Mw>270-2*MFR, where Mw is measured in kilodaltons (kDa) and MFR is measured in accordance with ASMT1238, 230C/2.16 kg; b. mixing the base polypropylene with an additive at a concentration to produce an adjusted base polypropylene with adjusted rheologic properties following the correlation Mw>260-MFR, with MFR in a range of 100g/10 min (230C/2.16 kg) to 250 g/10 min (230C/2.16 kg); and c. melt-extruding the adjusted base polypropylene at cabin pressures above 7000 Pa to produce highly extensible filaments; d, wherein the produced filaments have an average denier below 1.5.

2. The process of claim 1, wherein the additive comprises at least one of a stearate metallic salt oxidation catalyst or a visbreaking additive.

3. The process of claim 1, wherein the initial rheologic properties of the base polypropylene comprises a Mw above 200 kDa at an MFR of 35 g/10 min (230C/2.16 kg).

4. The process of claim 1, wherein the initial rheologic properties of the base polypropylene comprises a Mw above 230 kDa at an MFR of 20 g/10 min (230C/2.16 kg).

5. The process of claim 1, wherein adjusted rheologic properties of the adjusted base propylene comprises a Mw above 140 kDa at an MFR of 120 g/10 min (230C/2.16 kg).

6. The process of claim 1, wherein the adjusted rheologic properties of the adjusted base propylene comprises and a Mw above 160 kDa at an MFR of 100 g/10 min (230C/2.16 kg).

7. The process of claim 1, further comprising mixing the base polypropylene with other additives comprising pigments, slip additives, surfactants, or polymer modifiers before or after the step of melt extruding to adjust filament and nonwoven material properties.

8. The process of claim 1, wherein the filaments have a monofilament configuration or alternatives to monofilament configurations comprising alternative types selected from the group consisting of bicomponent core/sheath, bicomponent side by side, trilobal and islands-in-the-sea.

9. The process of claim 1, wherein the initial rheologic properties of the base polypropylene comprises an MFR within a range of 10 to 60 g/10 min (230C/2.16 kg).

10. The process of claim 1, wherein the initial rheologic properties of the base polypropylene comprises an MFR within a range of 1 to 100 g/10 min (230C/2.16 kg).

11. The process of claim 1, wherein the additive is a visbreaking additive mixed with the base polypropylene at an active compound concentration within a range of 50 and 500 ppm.

12. The process of claim 1, wherein the additive is a visbreaking additive mixed with the base polypropylene at an active compound concentration within a range of 25 and 750 ppm.

13. The process of claim 1, wherein the additive is a visbreaking additive mixed with the base polypropylene at an active compound concentration within a range of 10 and 2500 ppm.

14. The process of claim 1, wherein the adjusted rheologic properties of the adjusted base polypropylene comprises an MFR within a range of 75 to 300 g/10 min (230C/2.16 kg).

15. The process of claim 1, wherein the adjusted rheologic properties of the adjusted base polypropylene comprises an MFR within a range of 50 to 400 g/10 min range (230C/2.16 kg).

16. The process of claim 1, wherein the adjusted base polypropylene is melt-extruded at a throughput between 180 and 280 kg/h/m.

17. The process of claim 1, wherein the adjusted base polypropylene is melt-extruded at throughputs between 150 kg/h/m and 300 kg/h/m.

18. The process of claim 1, wherein the adjusted base polypropylene is melt-extruded at a throughput above 300 kg/h/m and below 150 kg/h/m.

19. The process of claim 1, wherein the adjusted base polypropylene is melt-extruded at cabin pressures between 8000 and 13000 Pa.

20. The process of claim 1, wherein the adjusted base polypropylene is melt-extruded at cabin pressures between 7000 and 15000 Pa.

21. The process of claim 1 wherein the adjusted base polypropylene is melt-extruded at cabin pressures above 15000 Pa.

22. The process of claim 1, wherein the average denier is between 1.2 and 0.8.

23. The process of claim 1, wherein the average denier is between 1.5 and 0.6.

24. The process of claim 1, wherein the average denier is below 0.6.

25. A method for producing spunbond fibers comprising: a. mixing a base polypropylene with an additive to obtain an adjusted base polypropylene with reduced viscosity and increased melt flow rate (MFR); and b. melt extruding the adjusted base polypropylene to produce highly extensible filaments.

26. The process of claim 25, further comprising mixing the base polypropylene with other additives comprising pigments, slip additives, surfactants, or polymer modifiers before or after the step of melt extruding to adjust filament and nonwoven material properties at an amount above 3 wt % based on the weight of polypropylene so that the produced filaments have a denier below 1.8.

27. The process in claim 26, wherein the denier is below 1.6.

28. The process in claim 26, wherein the denier is below 1.4.

29. The process of claim 25, wherein the filaments have a monofilament configuration or alternatives to monofilament configurations comprising alternative types selected from the group consisting of bicomponent core/sheath, bicomponent side by side, trilobal and islands-in-the-sea, and the alternatives to monofilament configurations are used so that the produced filaments have a denier below 1.8.

30. The process in claim 29, wherein the denier is below 1.6.

31. The process in claim 29, wherein the denier is below 1.4.

32. The process in claim 29, further comprising mixing the base polypropylene with other additives comprising pigments, slip additives, surfactants, or polymer modifiers before or after the step of melt extruding to adjust filament and nonwoven material properties.

33. The process of claim 25, wherein the filaments have a polypropylene/polyethylene bicomponent configuration and the filaments produced are under 1.8 denier.

34. The process in claim 33, wherein the filaments produced are under 1.6 denier.

35. The process in claim 33, wherein the filaments produced are under 1.4 denier.

36. A polypropylene spunbond nonwoven comprising the following properties: a. a basis weight within a range of 5 and 100 gsm; b. reduced air permeability of at least 15% lower than a control web with same basis weight and processed at the same conditions except cabin pressure is ran at highest possible before triggering instabilities; c. enhanced machine direction tensile strength (MDT) of at least 15% higher than a control web with same basis weight and processed at the same conditions except cabin pressure is ran at highest possible before triggering instabilities; and d. enhanced cross direction tensile strength (CDT) of at least 10% higher than a control web with same basis weight and processed at the same conditions except cabin pressure is ran at highest possible before triggering instabilities.

37. A polypropylene spunbond nonwoven with basis weight within a range of 13 to 15 gsm and air permeability within a range of 240 to 200 m3/m2/min.

38. A polypropylene spunbond nonwoven with basis weight within a range of 13 to 15 gsm and a machine direction tensile strength (MDT) within a range of 6 to 10 N/cm.

39. A polypropylene spunbond nonwoven with basis weight within a range of 26 to 31 gsm and air permeability within a range of 110 to 40 m3/m2/min.

40. A polypropylene spunbond nonwoven with basis weight within a range of 26 to 31 gsm and a machine direction tensile strength (MDT) within a range of 14.5 to 18N/cm and a CDT between 6 and 10 N/cm.

41. A polypropylene spunbond nonwoven comprising the following properties: a. a basis weight within a range of 20 and to 100 gsm; b. reduced air permeability of at least 20% lower than a control web with same basis weight and processed at the same conditions except cabin pressure is ran at highest possible before triggering instabilities; c. enhanced machine direction tensile strength (MDT) of at least 20% higher than a control web with same basis weight and processed at the same conditions except cabin pressure is ran at highest possible before triggering instabilities; d. enhanced cross direction tensile strength (CDT) of at least 15% higher than a control web with same basis weight and processed at the same conditions except cabin pressure is ran at highest possible before triggering instabilities.

42. A method for producing spunbond or SMS fabric in a high-speed continuous filament spinning line comprising: mixing a base recycled polypropylene with an additive to reduce viscosity and increase melt flow rate (MFR) of the base recycled polypropylene, the base recycled polypropylene having an MFR below 10 g/10 min (230C/2.16 kg).

43. A method for producing spunbond or SMS fabric in a high-speed continuous filament spinning line comprising: mixing a base recycled polypropylene with an additive to reduce viscosity and increase melt flow rate (MFR) of the base recycled polypropylene, the base recycled polypropylene having an MFR below 5 g/10 min (230C/2.16 kg).

44. A process of making an SMS composite fabric by producing fine fiber spunbond layers in accordance with the process of claim 1 and a meltblown layer, wherein: a. the SMS composite fabric has enhanced hydrohead of at least 15% higher than a control web with same basis weight and processed at the same conditions except cabin pressure is ran at highest possible before triggering instabilities; b. the SMS composite fabric has reduced air permeability of at least 15% lower than a control web with same basis weight and processed at the same conditions except cabin pressure is ran at highest possible before triggering instabilities.

45. A process of making an SMS composite fabric by producing fine fiber spunbond layers in accordance with the process of claim 1 and a meltblown layer, wherein: a. the SMS composite fabric has enhanced hydrohead of at least 30% higher than a control web with same basis weight and processed at the same conditions except cabin pressure is ran at highest possible before triggering instabilities; b. the SMS composite fabric has reduced air permeability of at least 30% lower than a control web with same basis weight and processed at the same conditions except cabin pressure is ran at highest possible before triggering instabilities.

46. A process of making an SMS composite fabric with improved properties by producing fine fiber spunbond layers in accordance with the process of claim 1 and a meltblown layer, wherein: a. the SMS composite fabric has enhanced hydrohead of at least 50% higher than a control web with same basis weight and processed at the same conditions except cabin pressure is ran at highest possible before triggering instabilities; b. the SMS composite fabric has reduced air permeability of at least 50% lower than a control web with same basis weight and processed at the same conditions except cabin pressure is ran at highest possible before triggering instabilities.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The above and related objects, features and advantages of the present invention will be more fully understood by reference to the following, detailed description of the preferred, albeit illustrative, embodiments of the present invention when taken in conjunction with the accompanying figures, wherein:

[0010] FIG. 1 shows MWD of a control 35MFR Zn-PP and a peroxide-based visbreaking adjusted-rheology sample;

[0011] FIGS. 2A and 2B show a top-view and cross section of a ziegler-natta polypropylene homopolymer control sample;

[0012] FIGS. 3A and 3B show top-view and cross section of ziegler-natta polypropylene homopolymer with a low dosage between 100 and 300 ppm of a peroxide-based visbreaking additive with MFR in the 100 to 200 range in accordance with exemplary embodiment of the present invention;

[0013] FIG. 4 shows a comparison of both the mechanical strength in the machine (MD) and cross directions (CD) of the web of visbroken samples in accordance with exemplary embodiments of the present invention;

[0014] FIG. 5 shows a comparison of both the mechanical strength in the machine (MD) and cross directions (CD) of a nonwoven produced with organo-metallic salt additive in accordance with exemplary embodiments of the present invention against a control sample;

[0015] FIG. 6 shows a comparison of the air permeability (AP) of several peroxide-based visbroken samples ran between 7000 to 9000 Pa cabin pressure in one exemplary embodiment, between 9000 and 11000 Pa in another exemplary embodiment and between 11000 and 15000 Pa in yet another exemplary embodiment as well as the control, ran at its maximum stable cabin pressure, at different basis weights ranging from 14 to 31 gsm;

[0016] FIG. 7 shows a comparison of the air permeability of a 30 gsm peroxide-based visbroken spunbond fine fiber sample in accordance with an exemplary embodiments of the present invention with Exxon's Vistamaxx 7020BF between 2 and 25 wt %, ran between 7000 to 9000 Pa cabin pressure, compared to a 30 gsm control, ran at a typical 3000 Pa cabin pressure; and

[0017] FIG. 8 shows a 25% increase in both MD and CD mechanical strength on the fine fiber plus Vistamaxx sample in accordance with an exemplary embodiment of the present invention compared to the control sample;

[0018] FIG. 9 shows a 25% improvement on the drapeability of the fine fiber sample in accordance with an exemplary embodiment of the present invention with Vistamaxx 7020BF in both MD and CD directions as measured via handle-o-meter (HOM) compared to the control sample;

[0019] FIG. 10 shows a comparison of the air permeability of two 30 gsm peroxide-based visbroken spunbond bicomponent core/sheath PP/PE fine fiber samples in accordance with exemplary embodiments of the present invention with 70/30 and 80/20 PP/PE ratios; and

[0020] FIG. 11 shows a 150% and 80% increase in MD and CD mechanical strength, respectively, on the 70/30 PP/PE ratio fine fiber sample in accordance with an exemplary embodiment of the present invention and a 140% and 60% increase in MD and CD mechanical strength, respectively, on the 80/20 PP/PE ratio fine fiber sample in accordance with an exemplary embodiment of the present invention compared to the control sample.

DETAILED DESCRIPTION

[0021] The present invention relates to the field of nonwovens. More particularly, this disclosure relates to the modification of nonwoven material by the inclusion of additives. Specifically, additives that trigger polymer backbone cleavages, including oxidative catalysts or visbreaking additives, are used as melt-in aids during the nonwoven production process. In the case of visbreaking additives, low dosing enables the fine tuning of the resin rheology enhancing the material cohesion and opening the processability window. This makes possible the generation of ultra-fine fibers during the spinning process. Further, the optimization of the polymer rheology stabilizes the spinning process, mitigating typical process problems such as dripping or generation of married fibers. Base polymer, for example polypropylene, is introduced in the extruder with a low dosage of visbreaking additive, or any other chemistry capable of breaking backbone chains, and is subjected to high extensibility conditions, e.g., cabin pressures and processing temperatures. This process forms fine fibers well under 1.5 denier in the case of polypropylene. Fine fibers boost many desirable nonwovens properties including, for example, material strength, air permeability and softness, to name a few. This engineered material can be used in articles for different fields such as hygiene, medical or automotive.

[0022] In terms of nonwoven material, it is desirable to achieve material weight reduction while maintaining critical properties of the material. It is further desirable to enhance material properties. Additionally, it is desirable to adjust the rheology of polymers used to form nonwoven material to adapt the polymers to high-speed continuous filament production lines for both spunbond and SMS configurations. Oxidative aids can be used to adjust the molecular weight distribution of polymers.

[0023] The term polymer as used herein refers to any plastic material, including polyolefins, that is processed into a spunbond nonwoven material. Within this chemistry family, visbreaking additives are commonly used to reduce the molecular weight of primary resins. For example, during the development of meltblown technology, visbreaking additives are conventionally used to reduce the viscosity (by reducing the molecular weight) of spunbond grade polyolefins and condition them for the meltblown low viscosity requirements. Visbreaking technologies, including peroxide chemistries, have been profusely used with polypropylene. This technology is based on reactive chemistries. Reactive chemistries promote scission of the polyolefin backbone, thereby generating lower molecular weight material.

[0024] It is well known that resin rheology has an important role in the nonwoven material processability as well as on the final nonwoven properties. Fiber grade polypropylene with a more or less controlled rheology is mandatory to produce spunbond or meltblown nonwoven material. Resin rheology is related to a series of material properties including raw material melt flow index/rate (MFI/MFR), molecular weight (MW), branching, crystallinity, and molecular weight distribution (MWD). For example, it is known that metallocene polypropylene, having a narrower MWD than Ziegler-Natta based polypropylene, improves molecular orientation during fiber attenuation (fiber draw), thereby producing stronger nonwoven material. Further, it is believed (as pointed out in PCT Patent Application Publication No. WO1997040225A1) that the melted polymer swells when it experiences the lower pressure as it exits the high-pressure die. It is described in WO1997040225A1 that the initial swell can be reduced by eliminating high molecular weight molecules, resulting in the production of finer fibers. Further, lower molecular weight molecules (xylene solubles), with lubricant properties, are also believed to assist in the drawing process of the fiber.

[0025] Here, we show a methodology that benefits from the oxidative chemistries, including visbreaking additives and oxidative catalysis, to adjust resin rheology and enhance material properties. Visbreaking additives or oxidative catalysis, not excluding other additives capable of chain scission, e.g., reducing the molecular weight of the polymer, can be used to fine tune and optimize the raw material rheology for spunbond and meltblown material. It is important to reduce the high molecular weight species, correlated with Mz, in order to increase the resin MFR and reduce the shear stresses during fiber draw as well as to narrow the molecular weight distribution. This molecular monodispersity, narrow molecular weight distribution, favors crystallinity induced during fiber draw, which is known to improve fiber strength. Further, maintaining high molecular weight average (Mw) enhances intermolecular forces and therefore further enhances fiber strength. Without being bound by theory, we believe that this fine-tuned rheology, high strength fiber (high crystallinity and Mw) together with the resulting lower shear stresses at high MFR during fiber draw, widens the material stability window and enables the generation of highly extensible filaments enabling finer fibers production and subsequent nonwovens with enhanced properties. Further, we show this technology can achieve fabric basis weight reduction by 10% or greater and production of 5-6 gsm spunbond/SMS fabrics on existing commercial continuous filament spinning lines without significant capital upgrades. Additionally, some polypropylene grades, specifically typical recycled polypropylene grades, are not suitable for high-speed fiber/filament spinning due to their low MFR (less than 10). The exact MFR of the recycled polypropylene grade is dependent on the source raw material and in most cases the MFR is around 5 due to the wide use of injection molding polypropylene and/or packaging waste for recycling. Visbreaking technology described here enables the adjustment of low MFR recycled polypropylene to adapt it for its use in both spunbond and meltblown technologies.

[0026] Melted polymers have complex viscoelastic qualities highly dependent on their rheology. The Deborah number (De=t.sub.c/t.sub.p, where t.sub.c is the material relaxation time and t.sub.p is the experimental time) characterizes the fluidity of a material. For high De, the material exhibits a more elastic solid-like behavior, whereas for low De, the material shows a more viscous liquid-like nature. White & Ide (Journal of applied polymer science, 22, 11, 3057 (1978)) described a series of melt spinning experiments with polymers spanning a wide range of viscosities. They observed that highly elastic material was difficult to spin due to ductile failures (high De, solid-like behavior). High viscosity polymers showed dripping instabilities, attributed most likely to be capillarity driven (low De, liquid-like behavior). Intermediate viscosity polymers showed both indefinite (on the lower viscosity end) and almost indefinite elongations at low extensions rate but exhibiting cohesion failure (solid-like behavior) at higher extension rates (on the higher viscosity end). Analogously to White & Ide's work, we observe: A. For the high end of intermediate viscosities. Solid-like elastic failures when spinning pristine polypropylene only at high extension rates (high cabin pressures) resulting in A.1. Spring-like behavior upon downstream fracture of partially solidified filaments at higher working temperatures. This condition generates coils of filament material millimeter scale with characteristic lengths orders of magnitude above the filament diameter (<500 microns), indicating that the fracture is not liquid-like capillarity-driven and A.2. More upstream fractures (fully melted fibers) at lower working temperatures. This condition generates centimeter scale drips/blobs 2 orders of magnitude larger than the diameter of the filament (indicating again a non-capillarity driven phenomenon) B. For the low end of intermediate viscosities, an extremely stable processing region at both low and high extensibility rates (low and high cabin pressures) that enables extended fiber elongations well below 1 denier with no observed instabilities. This is enabled by fine tuning the polymer rheology (optimized oxidative chemistries levels) as demonstrated in FIGS. 2 through 6. C. For the even lower end of intermediate viscosities (high oxidative chemistries levels) but still high enough, material still does not exhibit liquid-like behaviors (this is not described in White & Ide). However, the process is unstable even at low extensibility rates (low cabin pressures), resulting on millimeter scale non-spherical drips/blobs, inconsistent with the mostly spherical particles generated upon capillarity driven liquid-like instabilities. Without being bound by theory, it is believed that these defects are possibly due to melted fibers coalescence, most likely triggered by some degree of air turbulence always present in the cabin chamber coupled with the small inertia of the very fine fibers produced at this lower viscosity condition.

[0027] In accordance with a method of forming a nonwoven material in accordance with an exemplary embodiment of the present invention, a polymer is fed into a spunbond extruder. A certain percentage of an oxidative enhancing additive, between 10 and 1000 ppm in one embodiment, between 50 and 500 ppm in another embodiment, between 100 and 300 ppm in yet another embodiment is added to the polymer to adjust its rheology. MFR of the rheology-adjusted polymer is between 100 and 140MFR combined with Mw above 150 kDa and 110 kDa respectively in one embodiment, above 140 MFR combined with Mw above 110 kDa in another embodiment and MFR between 70 and 100 combined with Mw above 180 kDa and 150 kDa respectively.

[0028] MFR of the rheology-adjusted polymer was measured using the following method: [0029] 1. Rheology adjusted nonwoven fabric was melted in an oven at 250C for 30 min. [0030] 2. Melted polymer was pressed into a film. [0031] 3. Film was cut into small, pellet-like, pieces. [0032] 4. Pellet-like pieces MFR was measured using standard method, (ASMT1238, 230C/2.16 kg).

[0033] In accordance with a method of forming a nonwoven material in accordance with another exemplary embodiment of the present invention, a spunbond grade polymer is fed into the meltblown extruder with initial MFR between 5 and 20MFR in one embodiment, above 20MFR in another embodiment and below 5 MFR in yet another embodiment. A certain percentage of an oxidative enhancing additive, between 100 and 5000 ppm in one embodiment, between 500 and 3000 ppm in another embodiment, between 1000 and 2000 ppm in yet another embodiment is added to the polymer to adjust its rheology. MFR of the rheology-adjusted polymer is between 1000 and 2500MFR in one embodiment, above 2500 MFR in another embodiment and MFR between 500 and 1000 in yet another embodiment.

[0034] An oxidative-enhancing additive as used herein refers to any component that helps cleave the backbone of the polymer into smaller molecular weight parts of the whole molecule. Exemplary oxidative-enhancing additives include but are not limited to visbreaking additives (peroxide and peroxide-free), organo-metallic salts, and metal oxides. The polymer/additive blend melts in the temperature-controlled extruder. The temperature in the extruder has an important effect on the final molecular weight distribution of the polymer. During this extruding process, the rpm of the extruder usually experiences a boost due to the reduction in viscosity of the blend and the need to maintain the working pressure constant. The throughput is not negatively affected for either spunbond or meltblown by this process and can be maintained high, from 0.3 to 0.8 gr/hole/min in one embodiment, from 0.4 to 0.7 gr/hole/min in another embodiment and from 0.5 to 0.6 gr/hole/min in yet another embodiment in the case of spunbond spinning and between 15 and 50 kg/h/m in one embodiment and above 50 kg/h/m in another embodiment. The filaments are drawn into fine fibers as they exit the die into the cabin chamber. In the spunbond case, the adjusted rheology of the optimized polymer enables the use of high drawn speeds, e.g., high cabin pressures, between 7000 and 9000 Pa in one embodiment, between 9000 and 11000 Pa in another embodiment and between 11000 and 15000 Pa in yet another embodiment, or even higher cabin pressures in spunbond spinning. Common spinning additives such as pigments, slip additives and polymer modifiers including but not limited to Exxon's Vistamaxx series are compatible with the herein described technology. Furthermore, different fiber configurations including but not limited to bicomponent core/sheet also show compatibility with the herein described technology.

[0035] Process stability is extremely high, common defects, such as drops and married fibers in spunbond, and shots in meltblown, have not been observed. The fibers are laid onto a moving belt. The unbonded fibers may be bonded using any type of bonding technology, including calendaring and hydroentanglement, to produce the final nonwoven material, which exhibits enhanced properties such as mechanical strength, air permeability and liquid barrier.

EXAMPLES

[0036] Example 1. FIG. 1 shows MWD of a control 35MFR Zn-PP and a peroxide-based visbreaking adjusted-rheology sample. The addition of a small amount of visbreaking additive, below 500 ppm, shifted the MWD slightly toward the low MW, reducing the material viscosity by depleting entanglement-prone high MW populations, and boosting lubricant properties with lower MW populations. MFR increased from 35 to between 100 and 200g/10 min (230C/2.16).

[0037] Example 2. FIGS. 2A and 2B show a top-view and cross section of a ziegler-natta polypropylene homopolymer control sample. Cabin pressure was maximized to just below triggering instabilities. Average fiber diameter was 16.5 m (1.75 denier). FIGS. 3A and 3B show top-view and cross section of ziegler-natta polypropylene homopolymer with a low dosage between 100 and 300 ppm of a peroxide-based visbreaking additive with MFR in the 100 to 200 range. This opened the process stability window enabling very high cabin pressures and intense fiber draw. The spunbond process ranged between 7000 to 15000 Pa cabin pressure, achieving average fiber diameter down to 11.4 m (0.83 denier).

[0038] Example 3. FIG. 4 shows a comparison of both the mechanical strength in the machine (MD) and cross directions (CD) of the web of visbroken samples. For this example, the spundbond process ran between 9000 Pa and 11000 Pa cabin pressure with a low dosage of a peroxide-based visbreaking additive between 100 and 300 ppm. Results are compared with the control run at its maximum stable cabin pressure. Results are shown at several web basis weights ranging from 26 to just above 31 gsm. A material strength gain of around 50% was observed in the machine direction compared to the control samples, whereas a close to 20% increase was observed in the cross direction.

[0039] Example 4. This is an example of how MWD affects material strength. FIG. 5 shows a comparison of both the mechanical strength in the machine (MD) and cross directions (CD) of a nonwoven produced with organo-metallic salt additive against a control sample. In this example, the spundbond process ran between 2500 Pa and 3500 Pa cabin pressure with a low dosage of an organo-metallic salt additive between 20 and 500 ppm. Results are compared with the control run at the same cabin pressure. Even though fiber diameter observed is similar, lower Mz (see table below) enabled higher crystallinity and fiber strength. Results are shown at several web basis weights ranging from 10 to 40 gsm. Material strength gains between 20 and 40% were observed in the machine direction compared to the control samples, and from 35 to 50% increase was observed in the cross direction. In both cases the difference increased with material basis weight.

TABLE-US-00001 TABLE 1 Average Molecular Weight Relative to Polystyrene Standards Sample M.sub.n Avg. M.sub.w Avg. M.sub.z Avg. ID Run (Da) (Da) (Da) (Da) (Da) (Da) M.sub.w/M.sub.n Avg. Control 1 45,900 44,951 273,860 274,526 618,310 625,114 5.966 6.110 2 44,001 275,192 631,917 6.254 0 h 1 37,571 36,699 250,487 247,243 576,606 559,394 6.667 6.739 2 35,827 243,998 542,181 6.810

[0040] Example 5. FIG. 6 shows a comparison of the air permeability (AP) of several peroxide-based visbroken samples ran between 7000 to 9000 Pa cabin pressure in one embodiment, between 9000 and 11000 Pa in another embodiment and between 11000 and 15000 Pa in yet another embodiment as well as the control, ran at its maximum stable cabin pressure, at different basis weights ranging from 14 to 31 gsm. A favorable decrease of AP was observed with increasing cabin pressure attributable to the finer fibers produced, with reductions of 20% between 7000 to 9000 Pa cabin pressure, 25% between 9000 and 11000 Pa cabin pressure and 30% between 11000 and 15000 Pa cabin pressure.

[0041] Example 6. Table 2 shows fiber diameter and denier for both control and visbroken samples processed at different cabin pressures. As expected, a reduction in fiber diameter/denier was observed with increasing cabin pressure. Also, visbroken fibers showed a reduction of fiber diameter/denier compared to the control processed at the same pressure, most likely due to its lower viscosity and higher tendency to be drawn (without being bound by theory).

TABLE-US-00002 TABLE 2 Fiber diameter & Denier vs cabin pressure. Control and visbroken samples. Cabin pressure range Fiber (Pa) Denier diameter (m) 3000-4000 control 1.57 15.6 3000-4000 visbroken 1.42 14.8 7000-9000 visbroken 1.0-1.1 12.5-13 9000-11000 visbroken 0.9 11.8 11000-15000 visbroken 0.83 11.4

[0042] Example 7. FIG. 7 shows a comparison of the air permeability of a 30 gsm peroxide-based visbroken spunbond fine fiber sample with Exxon's Vistamaxx 7020BF between 2 and 25 wt %, ran between 7000 to 9000 Pa cabin pressure, compared to a 30 gsm control, ran at a typical 3000 Pa cabin pressure. Average 1.0 denier was achieved with this configuration. A favorable decrease of AP was observed with increasing cabin pressure attributable to the finer fibers produced, with reductions of 30% for the fine fiber plus Vistamaxx sample compared to the control sample. FIG. 8 shows a 25% increase in both MD and CD mechanical strength on the fine fiber plus Vistamaxx sample compared to the control sample. FIG. 9 shows a 25% improvement on the drapeability of the fine fiber sample with Vistamaxx 7020BF in both MD and CD directions as measured via handle-o-meter (HOM) compared to the control sample.

[0043] Example 8. FIG. 10 shows a comparison of the air permeability of two 30 gsm peroxide-based visbroken spunbond bicomponent core/sheath PP/PE fine fiber samples with 70/30 and 80/20 PP/PE ratios. Visbreaking agent was added just on the PP core and the material was ran between 7000 to 9000 Pa cabin pressure. These samples are compared to a 30 gsm bicomponent core/sheath PP/PE 70/30 control, ran at a typical 3000 Pa cabin pressure. Average 1.1 denier with minimum of 0.65 denier was achieved with this configuration. A favorable decrease of AP was observed with increasing cabin pressure attributable to the finer fibers produced, with reductions of 35% and of 40% for the 70/30 and the 80/20 PP/PE ratio fine fiber samples, respectively, compared to the control sample. FIG. 11 shows a 150% and 80% increase in MD and CD mechanical strength, respectively, on the 70/30 PP/PE ratio fine fiber sample and a 140% and 60% increase in MD and CD mechanical strength, respectively, on the 80/20 PP/PE ratio fine fiber sample compared to the control sample.

[0044] While in the foregoing specification a detailed description of specific embodiments of the invention was set forth, it will be understood that many of the details herein given may be varied considerably by those skilled in the art without departing from the spirit and scope of the invention.