US20120156461A1

US20120156461A1 - Bicomponent spunbond nonwoven web

Info

Publication number: US20120156461A1
Application number: US12/971,415
Authority: US
Inventors: Lakshmi Krishnamurthy
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 2010-12-17
Filing date: 2010-12-17
Publication date: 2012-06-21
Also published as: WO2012082694A2; WO2012082694A3

Abstract

Disclosed are nonwoven webs comprising a plurality of continuous spunbonded bicomponent fibers, wherein each of the plurality of bicomponent fibers comprises 75% by weight of poly(ethylene terephthalate) in a core and 25% by weight of poly(trimethylene terephthalate) in a sheath surrounding the core, wherein the amounts in % by weight are based on the total weight of the bicomponent fiber.

Description

FIELD OF THE INVENTION

The present invention relates to bicomponent spunbond nonwoven webs having improved strength.

TECHNICAL BACKGROUND

Nonwoven webs are well known in the art and can be formed using any suitable technique, such as, flash spinning, spunbonding, meltblowing, and hydro-entanglement. Each of these techniques produces nonwoven webs with certain characteristics useful for a particular application. For example, nonwoven webs formed by meltblowing are more breathable, but are not as strong as those formed by spunbonding. Nonwoven webs formed using bicomponent fibers can further provide additional benefits.
US 20020127939 to Hwo et al. disclose a bicomponent meltblown microfiber nonwoven material wherein at least two different polymers including polytrimethylene terephthalate have been extruded, spun together, and then meltblown.
US 20030124941 to Hwo et al. disclose spunbonded nonwoven materials made from polytrimethylene terephthalate having a hydrostatic head of less than 10 cm.
There is an ongoing search for new compositions and techniques that can result in low cost, environmentally sustainable, nonwoven webs having superior mechanical properties.

SUMMARY

In an aspect of the invention, there is a nonwoven web comprising a plurality of continuous spunbond fibers, wherein each of the plurality of continuous spunbond fibers comprises:

- a) 75%, by weight of poly(ethylene terephthalate) in a core; and
- b) 25%, by weight of poly(trimethylene terephthalate) in a sheath surrounding the core,
- wherein the amounts in % by weight are based on the total weight of the continuous spunbonded fiber.

In another aspect, there is a nonwoven web comprising a plurality of continuous spunbond fibers, wherein each of the plurality of continuous spunbond fibers comprises:

- a) 50%, by weight of poly(ethylene terephthalate) in a core; and
- b) 50%, by weight of poly(trimethylene terephthalate) in a sheath surrounding the core,
- wherein the amounts in % by weight are based on the total weight of the continuous spunbonded fiber.

DETAILED DESCRIPTION

Disclosed is a nonwoven web comprising a plurality of continuous spunbonded fibers, wherein each of the plurality of continuous spunbond fibers comprises poly(ethylene terephthalate) (PET) in a core and poly(trimethylene terephthalate) (PTT) in a sheath surrounding the core.
As used herein, the term “nonwoven web” is used interchangeably with “nonwoven sheet”, “nonwoven layer” and “nonwoven fabric”. As used herein, the term “nonwoven” means a manufactured sheet, web or batt of randomly orientated fibers, filaments, or threads positioned to form a planar material without an identifiable pattern. Examples of nonwoven webs include meltblown webs, spunbond webs, carded webs, air-laid webs, wet-laid webs, and spunlaced webs and composite webs comprising more than one nonwoven layer. Nonwoven webs for the processes and articles disclosed herein are desirably prepared using a “direct laydown” process. “Direct laydown” means spinning and collecting individual fibers or plexifilaments directly into a web or sheet without winding filaments on a package or collecting a tow.
The term “spunbond fibers” as used herein means fibers that are formed by extruding molten thermoplastic polymer material as fibers from a plurality of fine, usually circular, capillaries of a spinneret with the diameter of the extruded fibers then being rapidly reduced by drawing and then quenching the fibers. Other fiber cross-sectional shapes such as oval, multi-lobal, etc. can also be used. Spunbond fibers are generally continuous and usually have an average diameter of greater than about 5 micrometers. Spunbond nonwoven webs are formed by laying fibers randomly on a collecting surface such as a foraminous screen or belt and spunbonding the fibers by methods known in the art such as by hot-roll calendering or by passing the web through a saturated-steam chamber at an elevated pressure. For example, the nonwoven web can be thermally point bonded at a plurality of thermal bond points located across the nonwoven web.
As used herein, the term “bicomponent fiber” refers to a fiber comprising a pair of polymer compositions intimately adhered to each other along the length of the fiber, so that the fiber cross-section is, for example, a side-by-side, sheath-core or other suitable cross-section. The bicomponent sheath/core polymeric fibers can be round, trilobal, pentalobal, octalobal, like a Christmas tree, dumbbell-shaped, island-in-the-sea or otherwise star shaped in cross section. The fibers may also be in a side by side arrangement.
As used herein, the term “continuous fiber” refers to a fiber of indefinite or extreme length. In practice, there could be one or more breaks in the “continuous fiber” due to manufacturing process, but a “continuous fiber” is distinguishable from a staple fiber which is cut to a predetermined length.
The nonwoven web disclosed herein comprises a plurality of continuous spunbonded bicomponent fibers in a sheath-core configuration. The weight ratio between the sheath component and the core component of the disclosed spunbonded bicomponent fibers is preferably 25:75. The bicomponent fibers have an average fiber diameter in the range of 2 microns to 20 microns. In an embodiment, each bicomponent fiber comprises 75%, by weight of PET in the core and 25%, by weight of PTT in the sheath surrounding the core. Yet, in another embodiment, each bicomponent fiber comprises 50%, by weight of PET in the core and 50%, by weight of PTT in the sheath surrounding the core.
The PTT used in the sheath component of the spunbond fibers of the disclosed nonwoven web has an intrinsic viscosity in the range of 0.9 dl/g to 1.3 dl/g or 0.95 dl/g to 1.05 dl/g.
In an embodiment, “poly(trimethylene terephthalate)” (PTT) is a homopolymer or a copolymer comprising at least 70 mole percent trimethylene terephthalate repeating units. The preferred poly(trimethylene terephthalate)s contain at least 85 mole percent, more preferably at least 90 mole percent, even more preferably at least 95 or at least 98 mole percent, and most preferably about 100 mole percent, trimethylene terephthalate repeating units.
Examples of copolymers include copolyesters made using 3 or more reactants, each having two ester forming groups. For example, a copoly(trimethylene terephthalate) can be made using a comonomer selected from the group consisting of linear, cyclic, and branched aliphatic dicarboxylic acids having 4-12 carbon atoms (for example butanedioic acid, pentanedioic acid, hexanedioic acid, dodecanedioic acid, and 1,4-cyclo-hexanedicarboxylic acid); aromatic dicarboxylic acids other than terephthalic acid and having 8-12 carbon atoms (for example isophthalic acid and 2,6-naphthalenedicarboxylic acid); linear, cyclic, and branched aliphatic diols having 2-8 carbon atoms (other than 1,3-propanediol, for example, ethanediol, 1,2-propanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-1,3-propanediol, and 1,4-cyclohexanediol). The comonomer typically is present in the copolyester at a level in the range of about 0.5 to about 15 mole percent, and can be present in amounts up to 30 mole percent.
In a preferred embodiment, PTT is made by polycondensation of 1,3-propanediol derived from a renewable source and terephthalic acid or acid equivalent. In an embodiment, the PTT contains at least 20% renewably sourced ingredient by weight and in some cases at least 30%. An exemplary PTT suitable for the disclosed nonwoven web is available from DuPont Company (Wilmington, Del.) under the trademark Sorona®. In an embodiment, the disclosed nonwoven webs have renewably sourced content of at least 5% by total weight of the web.
The renewably sourced 1,3-propanediol contains carbon from the atmospheric carbon dioxide incorporated by plants, which compose the feedstock for the production of the 1,3-propanediol. In other words, the renewably sourced 1,3-propanediol contains only renewable carbon, and not fossil fuel-based or petroleum-based carbon.
A particularly preferred renewable source of 1,3-propanediol is via a fermentation process using a renewable biological source such as corn feed stock. For example, bacterial strains able to convert glycerol into 1,3-propanediol are found in the species Klebsiella, Citrobacter, Clostridium, and Lactobacillus. The technique is disclosed in several publications, including U.S. Pat. Nos. 5,633,362, 5,686,276 and 5,821,092. U.S. Pat. No. 5,821,092 discloses, inter alia, a process for the biological production of 1,3-propanediol from glycerol using recombinant organisms. The process incorporates E. coli bacteria, transformed with a heterologous pdu diol dehydratase gene, having specificity for 1,2-propanediol. The transformed E. coli is grown in the presence of glycerol as a carbon source and 1,3-propanediol is isolated from the growth media. Since both bacteria and yeasts can convert glucose (e.g., corn sugar) or other carbohydrates to glycerol, the processes disclosed in these publications provide a renewable source of 1,3 propanediol monomer.
Therefore, PTT derived from the renewably sourced 1,3-propanediol has less impact on the environment as the 1,3 propanediol used in the compositions does not deplete diminishing fossil fuels and, upon degradation, releases carbon back to the atmosphere for use by plants once again. Thus, the compositions of the present invention can be characterized as more natural and having less environmental impact than similar compositions comprising petroleum based 1,3 propanediol.
Poly(ethylene terephthalate) (PET) can include a variety of comonomers, including diethylene glycol, cyclohexanedimethanol, poly(ethylene glycol), glutaric acid, azelaic acid, sebacic acid, isophthalic acid, and the like. In addition to these comonomers, branching agents like trimesic acid, pyromellitic acid, trimethylolpropane and trimethyloloethane, and pentaerythritol may be used. The poly(ethylene terephthalate) can be obtained by known polymerization techniques from either terephthalic acid or its lower alkyl esters (e.g. dimethyl terephthalate) and ethylene glycol or blends or mixtures of these. The PET used in the core component of the spunbond fibers of the disclosed nonwoven web has an intrinsic viscosity in the range of 0.58 dl/g to 0.75 dl/g or 0.62 dl/g to 0.69 dl/g.
The sheath and/or core component of the sheath-core spunbond fibers can include other conventional additives such as dyes, pigments, antioxidants, ultraviolet stabilizers, spin finishes, and the like. In an embodiment, the sheath comprises 0.1% to 0.33%, by weight of titanium dioxide dispersed in the PTT. The titanium dioxide having an average particle size of about 300 nm.
The nonwoven web disclosed hereinabove can be prepared using spunbonding methods known in the art, for example as described in Rudisill, et al. U.S. Patent application Ser. No. 60/146,896 filed on Aug. 2, 1999, which is hereby incorporated by reference (published as PCT Application WO 01/09425). The spunbonding process can be performed using either pre-coalescent dies, wherein the distinct polymeric components are contacted prior to extrusion from the extrusion orifice, or post-coalescent dies, in which the distinct polymeric components are extruded through separate extrusion orifices and are contacted after exiting the capillaries to form the bicomponent fibers.
The disclosed nonwoven web can be made using any suitable bicomponent spinning system, for example Model # NF5, manufactured by Nordson Fiber Systems Inc. (Duluth, Ga.) and Hills Inc. (W. Melbourne, Fla.). First, the two polymers PET and PTT are dried at a temperature in the range of 90° C. to 120° C. to a moisture content of less than 50 ppm. After drying, the two polymers are separately extruded at a temperature above their melting point and below the lowest decomposition temperature. PTT can be extruded at 245° C. to 265° C. and PET at 280° C. to 295° C. After extrusion, the two polymer are metered to a spin-pack assembly, where the two melt streams are separately filtered and then combined through a stack of distribution plates to provide multiple rows of sheath-core fiber cross-sections. The spin-pack assembly is kept at 285° C. to 295° C. The PTT and PET polymers can be spun through the each capillary at a polymer throughput rate of 0.5 g/hole/min to 3 g/hole/min. An attenuating force using rectangular slot jet can be applied to the bundle of fibers. The bicomponent fibers exiting the jet are collected on a forming belt to form a nonwoven web of bicomponent fibers. Vacuum can be applied underneath the belt to help pin the nonwoven web to the belt. The speed of the belt can be varied to obtain nonwoven webs of various basis weights.
The nonwoven web can be thermally bonded using methods known in the art. In one embodiment, the nonwoven web is thermally bonded with a discontinuous pattern of points, lines, or other pattern of intermittent bonds using methods known in the art. Intermittent thermal bonds can be formed by applying heat and pressure at discrete spots on the surface of the spunbond web, for example by passing the layered structure through a nip formed by a patterned calender roll and a smooth roll, or between two patterned rolls. One or both of the rolls are heated to thermally bond the web. When web breathability is important, such as in garment end uses, the webs are preferably bonded intermittently to provide a more breathable web.
In one method, the nonwoven web is thermally bonded in a nip formed between two smooth metal rolls at bonding temperature in the range of 110° C. to 130° C. and a bonding nip pressure in the range of 500 N/cm to 1500 N/cm. The optimum bonding temperature and pressure are functions of the line speed during bonding, with faster line speeds generally requiring higher bonding temperatures. The thermally bonded sheet was then wound onto a roll.
During thermal pattern bonding, the PTT in the sheath component of the spunbond fibers is partially melted in the discrete areas corresponding to raised protuberances on the patterned roll to form fusion bonds that bond the spunbond fibers together to form a cohesively bonded spunbond sheet. Depending on the bonding conditions and polymers used in the sheath component, the polyethylene in the sheath component may also be partially melted during thermal pattern bonding. The PET core component is not melted during thermal bonding and contributes to the strength of the web. The bonding roll pattern may be any of those known in the art, and preferably is a pattern of discrete point or line bonds. The nonwoven web can also be thermally bonded using ultrasonic energy, for example by passing the web between a horn and a rotating anvil roll, for example an anvil roll having a pattern of protrusions on the surface thereof.
Alternately, the nonwoven web can be bonded using through-air bonding methods known in the art, wherein heated gas such as air is passed through the web at a temperature sufficient to bond the fibers together where they contact each other at their cross-over points while the web is supported on a porous surface.
The disclosed spunbonded nonwoven web comprising PTT-PET as sheath-core fibers have surprisingly higher strength (tensile strength, grab tear strength, and Mullen burst) than a comparable spunbonded nonwoven web of PET-PTT as sheath-core fibers or 100% PTT fibers or 100% PET fibers. The disclosed nonwoven webs have a basis weight in the range of 25 gsm to 500 gsm or 40 gsm to 200 gsm or 50 gsm to 150 gsm. As used herein, the term “machine direction” (MD) refers to the direction in which a nonwoven web is produced (e.g. the direction of travel of the supporting surface upon which the fibers are laid down during formation of the nonwoven web). The term “cross direction” (XD) refers to the direction generally perpendicular to the machine direction in the plane of the web.
The disclosed nonwoven webs have a tensile strength per unit basis weight in the range of 0.7 N/gsm to 5 N/gsm or 0.75 N/gsm to 2 N/gsm, measured in both the machine direction and the cross-direction of the web (according to ASTM D1117-01 and D5035-95).
In another embodiment, the disclosed nonwoven webs have a grab tear strength per unit basis weight in the range of 1.5 N/gsm to 10 N/gsm or 1.5 N/gsm to 5 N/gsm, measured in both the machine direction and the cross-direction of the web (according to ASTM D1117-01
In another embodiment, the disclosed nonwoven webs have a Mullen burst per unit basis weight in the range of 3.5 KPa/gsm to 10 KPa/gsm or 3.5 KPa/gsm to 5 KPa/gsm, measured in both the machine direction and the cross-direction of the web.
In an embodiment, the disclosed nonwoven webs have a trapezoidal tear strength per unit basis weight in the range of 0.4 N/gsm to 5 N/gsm or 0.4 N/gsm to 0.75 N/gsm, measured in both the machine direction and the cross-direction of the web (according to ASTM 5733).
The disclosed spunbonded nonwoven webs can be used in a broad range of applications such as, protective apparel, hot gas filtration, and laser printable substrate.
In an embodiment, there is an article comprising the disclosed nonwoven webs. In some embodiment, the article is a protective apparel. In other embodiment, the article is a filter for hot gas filtration. In another embodiment, the article is a laser printable media comprising the disclosed nonwoven webs as a substrate.
As used herein, the phrase “one or more” is intended to cover a non-exclusive inclusion. For example, one or more of A, B, and C implies any one of the following: A alone, B alone, C alone, a combination of A and B, a combination of B and C, a combination of A and C, or a combination of A, B, and C.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the disclosed compositions, suitable methods and materials are described below.
In the foregoing specification, the concepts have been disclosed with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below.
Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all embodiments.
It is to be appreciated that certain features are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. Further, reference to values stated in ranges includes each and every value within that range.
The concepts disclosed herein will be further described in the following examples, which do not limit the scope of the invention described in the claims.
The examples cited here relate to spunbonded nonwoven web. The discussion below describes how a spunbonded nonwoven web comprising a plurality of bicomponent fibers can be formed, and tested for strength properties.
Unless specified otherwise, compositions are given as weight percents.

EXAMPLES

Preparation of Bicomponent Spunbond Nonwoven Webs

Nonwoven web comprising bicomponent fibers was made from a poly(ethylene terephthalate) (PET) component and a poly(trimethylene terephthalate) (PTT) component. The PET component was obtained from Dupont Company (Old Hickory, Tenn.) as PET resin grade 4434 and had an intrinsic viscosity (IV) of 0.67 dl/g. The PTT component, D13454709 Sorona® J2241 semi-dull is also available from Dupont Company (Wilmington, Del.). The PTT used had an IV of 1.02 dl/g; Mn˜28000; and about 37% renewably sourced ingredients by weight
Both the PET resin and the PTT resin were dried in a through air dryer at a temperature of 100° C. to a moisture content of less than 50 ppm.
A bicomponent spinning system, Model # NF5, manufactured by Nordson Fiber Systems Inc. (Duluth, Ga.) and Hills Inc. (W. Melbourne, Fla.) was used for creating the spunbond structures. The two components were separately extruded and metered to a spin-pack assembly, where the two melt streams were separately filtered and then combined through a stack of distribution plates to provide multiple rows of sheath-core fiber cross-sections. The spin-pack assembly consisted of a total of 1162 round capillary openings. The width of the forming zone was 56 cm. The spin-pack assembly was heated to 295° C. The PTT and PET polymers were spun through the each capillary at a polymer throughput rate of 1.0 g/hole/min.
The bundle of fibers were cooled in a cross-flow quench extending over a length of 75 cm. An attenuating force was provided to the bundle of fibers by a rectangular slot jet. The distance between the spin-pack to the entrance to the jet was 63 cm.
The fibers exiting the jet were collected on a forming belt. Vacuum was applied underneath the belt to help pin the fibers to the belt. The fibers were then thermally bonded in a nip formed between two smooth metal rolls, both rolls being heated to 155° C., with a nip pressure of 714 N/cm. The thermally bonded sheet was then wound onto a roll.
The speed of the belt was varied to obtain spunbonds of various basis weights. The belt speed was set at 42 m/min to obtain 50 gsm spunbond. It was slowed down to 21 m/min to obtain 100 gsm sheet and was further slowed to 14 m/min to obtain 150 gsm sheet.
Basis Weight is a measure of the mass per unit area of a web or sheet and was determined by ASTM C-3776, which is hereby incorporated by reference, and is reported in g/m², abbreviated as gsm.
Table 1 summarizes the exemplary bicomponent spunbonds composition and basis weight. The sheath and the core comprise one polymeric component each, either PTT or PET. Hence, in Example 2, 25 weight % PTT in the sheath and 75 weight % PET in the core means that the sheath comprises pure PTT and the core comprises pure PET, such that the weight ratio of sheath to core is 25:75.
In Examples 1 and 2, the core of the bicomponent spunbonds comprised PET component and the sheath comprised PTT component. Whereas, in the Comparative Examples B and C, summarized in Table 2, the core comprised PTT component and the sheath comprised PET component. The Comparative Example A was 100% PET spunbond with both the sheath and the core comprising PET. The Comparative Example D was 100% PTT spunbond with both the sheath and core comprising PTT.

TABLE 1

Composition of Exemplary Bicomponent Spunbond Web

	Composition (weight %
	based on the total	Basis
	weight of the fiber)	weight

	Example #		Sheath	Core	(gsm)

1	1-1	50% PTT	50% PET	50
	1-2	50% PTT	50% PET	100
	1-3	50% PTT	50% PET	150
2	2-1	25% PTT	75% PET	50
	2-2	25% PTT	75% PET	100
	2-3	25% PTT	75% PET	150

TABLE 2

Comparative Bicomponent spunbonds

	Composition (weight %
	based on the total	Basis

Comparative

weight of the fiber)

weight

	Example #		Sheath	Core	(gsm)

A	A-1	100% PET	100% PET	50
	A-2	100% PET	100% PET	100
	A-3	100% PET	100% PET	150
B	B-1	50% PET	50% PTT	50
	B-2	50% PET	50% PTT	100
	B-3	50% PET	50% PTT	150
C	C-1	25% PET	75% PTT	50
	C-2	25% PET	75% PTT	100
	C-3	25% PET	75% PTT	150
D	D-1	100% PTT	100% PTT	50
	D-2	100% PTT	100% PTT	100
	D-3	100% PTT	100% PTT	150

Measurement of Nonwoven Web Strength and Wear

The spunbond nonwoven webs (1, 2, A, B, C, and D), prepared supra, were tested for strength (Grab tear, Trapezoidal tear, Strip tensile and Mullen burst) using the following standard ASTM (American Society for Testing and Materials) methods for nonwovens as follows:
Strip Tensile strength is a measure of the breaking strength of a sheet and was conducted on a 2.54-cm (1-inch) wide strip according to ASTM D1117-01, D5035-95, and is reported in Table 5.

TABLE 3

Strip Tensile Strength of Exemplary and
Comparative Bicomponent Spunbond Webs

Strip Tensile, MD

Strip Tensile, XD

				Load/			Load/
Basis				basis			basis
weight	Sample	Load	Strain	weight	Load	Strain	weight
(gsm)	#	(N)	(%)	(N/gsm)	(N)	(%)	(N/gsm)

50	A-1	24.72	11.12	0.4944	11.6	22.73	0.2320
	B-1	29.59	11.61	0.5918	17.44	30.61	0.3488
	C-1	29.91	7.03	0.5982	18.26	32.45	0.3652
	D-1	26.02	7.27	0.5204	17.68	21.94	0.3536
	1-1	54.47	50.23	1.0894	51.21	57.95	1.0242
	1-2	64.17	58.24	1.2834	43.69	52.62	0.8738
100	A-2	40.59	8.98	0.4059	25.95	10.21	0.2595
	B-2	43.86	5.2	0.4386	38.16	14.36	0.3816
	C-2	41.87	5.08	0.4187	44.52	15.64	0.4452
	D-2	37.22	5.74	0.3722	41.93	17.36	0.4193
	2-1	90.94	36.6	0.9094	81.7	54.77	0.8170
	2-2	133.99	59.89	1.3399	125.05	77	1.2505
150	A-3	66.45	8.49	0.4430	40.99	5.44	0.2733
	B-3	51.81	6.66	0.3454	45.17	10.08	0.3011
	C-3	58.18	60.32	0.3879	63.71	13.69	0.4247
	D-3	44.95	5.62	0.2997	57.42	10.7	0.3828
	3-1	174.94	52.44	1.1663	168.89	73.52	1.1259
	3-1	257.75	85.31	1.7183	205.88	82.68	1.3725

Table 3 suggests that at a given basis weight, the spunbond webs with PTT in the sheath (Examples 1 and 2) exhibit substantially higher tensile strength both in the machine direction and the cross direction as compared to the spunbond webs with PTT in the core (Comparative Examples B and C); 100% pure PTT spunbond web (Comparative Example D); and 100% pure PET spunbond web (Comparative Example A). Furthermore, at 100 gsm and 150 gsm, the spunbond webs containing 25 weight % PTT in the sheath (Examples 2-2 and 2-3) are stronger than those containing 50 weight % PTT in the sheath (Examples 1-2 and 1-3).
Mullen burst test measures the pressure required to burst a web and was conducted according to ASTM D1117-01, D5035-95 and is reported in units of force per unit area KPa.

TABLE 4

Mullen burst test results of Exemplary and
Comparative Bicomponent Spunbond Webs

			Mullen
			burst/basis
[Basis weight	Sample	Mullen burst	weight
(gsm)	#	(KPa)	(KPa/gsm)

50	A-1	148.93	2.9786
	B-1	99.29	1.9858
	C-1	100.67	2.0134
	D-1	91.01	1.8202
	1-1	267.53	5.3506
	2-1	260.63	5.2126
100	A-2	319.93	3.1993
	B-2	157.21	1.5721
	C-2	153.07	1.5307
	D-2	154.45	1.5445
	1-2	479.89	4.7989
	2-2	619.17	6.1917
150	A-3	>827.4	—
	B-3	315.791	2.1053
	C-3	199.955	1.3330
	D-3	244.083	1.6272
	1-3	714.322	4.7621
	2-3	>827.4	—

Table 4 shows that at 100 and 150 gsm, the spunbond webs with PTT in the sheath (Examples 1 and 2) have higher Mullen burst pressures than the comparative examples with PTT in the core (Comparative Examples B and C). At 150 gsm, the Mullen burst of Example 2-3 (PTT in the sheath) and comparative Example A-3 (100% PET) could not be measured as they were beyond the instrument limit. However, it is clear that Example 1-3 is stronger than Comparative Examples B-3 (50% PET in the sheath), C-3 (25% PET in the sheath) and D-3 (100% PTT).
Grab tear strength, is a measure of force required to tear a piece of web into two pieces. Grab tear strength is based on the breaking strength of the individual threads of the web working in conjunction with each other. Grab tear was conducted according to ASTM D1117-01, D5035-95 in two directions: machine direction (MD) and perpendicular to the machine direction (XD) and is reported in Newton. Results are summarized in table 3

TABLE 5

Grab tear test of Exemplary and Comparative
Bicomponent Spunbond Webs

Grab Tear Strength, MD

Grab Tear Strength, XD

50	A-1	42.84	10.94	0.8568	34.44	46.99	0.6888
	B-1	59.6	11.59	1.1920	43.74	25.47	0.8748
	C-1	46.84	5.33	0.9368	51.63	28.44	1.0326
	D-1	40.94	8.61	0.8188	33.7	15.04	0.6740
	1-1	141.4	28.73	2.8280	141.4	46.51	2.8280
	1-2	141.95	30.6	2.8390	126.78	44.93	2.5356
100	A-2	84.85	13.92	0.8485	82.14	42.29	0.8214
	B-2	80.92	4.03	0.8092	87.17	16.2	0.8717
	C-2	105.63	26.49	1.0563	99.36	17.14	0.9936
	D-2	70.61	13.1	0.7061	95.24	16.55	0.9524
	2-1	298.89	35.28	2.9889	297.2	55.01	2.9720
	2-2	413.42	52.06	4.1342	337.51	53.22	3.3751
150	A-3	170.78	19.88	1.1385	146.16	51.13	0.9744
	B-3	95.96	5.33	0.6397	95.61	13.25	0.6374
	C-3	133.93	13.75	0.8929	143.53	12.67	0.9569
	D-3	126.21	25.43	0.8414	110.48	24.31	0.7365
	3-1	534.25	39.82	3.5617	495.36	52.85	3.3024
	3-1	693.58	58.03	4.6239	618.28	68.47	4.1219

Table 5 suggests that at a given basis weight, the spunbond webs with PTT in the sheath (Examples 1 and 2) exhibit substantially higher grab strength both in the machine direction and the cross direction as compared to the spunbond webs with PTT in the core (Comparative Examples B and C) and to 100% pure PTT (Comparative Example D) and 100% pure PET (Comparative Example A). Furthermore, at 100 gsm and 150 gsm, the spunbond webs containing 25 weight % PTT in the sheath (Examples 2-2 and 2-3) are stronger than those containing 50 weight % PTT in the sheath (Examples 1-2 and 1-3).
Trapezoidal tear strength, is a measure of ability to resist a continued tear. The test specimen is trapezoid in shape. A slit is made in the sample for the tear and effort required to continue the tear across the web is measured. Trapezoidal tear was conducted according to ASTM 5733, and is reported in newton.

TABLE 6

Trapezoidal tear of Exemplary and Comparative
Bicomponent Spunbond Webs

			Trapezoidal tear/
		Trapezoidal tear,	basis weight,
[Basis weight	Sample	MD	MD
(gsm)	#	(KPa)	(KPa/gsm)

Table 6 shows that at a given basis weight, the spunbond webs containing 25 weight % PTT in the sheath (Examples 2-1, 2-2, and 2-3) are more resistant to tear as compared to spunbond webs containing 50 weight % PTT in the sheath (Examples 1-1, 1-2, and 1-3).

Claims

1. A nonwoven web comprising a plurality of continuous spunbonded bicomponent fibers, wherein each of the plurality of bicomponent fibers comprises:

a) 75% by weight of poly(ethylene terephthalate) in a core; and

b) 25% by weight of poly(trimethylene terephthalate) in a sheath surrounding the core.

wherein the amounts in % by weight are based on the total weight of the each of the plurality of bicomponent fibers.

2. The nonwoven web of claim 1, wherein the bicomponent fibers have an average fiber diameter in the range of 2 microns to 20 microns.

3. The nonwoven web of claim 1, wherein the nonwoven web has a basis weight in the range of 25 gsm to 500 gsm.

4. The nonwoven web of claim 3, wherein the nonwoven web has a machine direction and a cross direction and a basis weight in the range of 50 gsm to 150 gsm.

5. The nonwoven web of claim 4, wherein the nonwoven web has a tensile strength per unit basis weight in both the machine direction and the cross direction, measured according to ASTM D1117-01, D5035-95, in the range of 0.75 N/gsm to 5 N/gsm.

6. The nonwoven web of claim 4, wherein the nonwoven web has a grab tear strength per unit basis weight in both the machine direction and the cross direction, measured according to ASTM D1117-01, D5035-95, in the range of 1.5 N/gsm to 10 N/gsm.

7. The nonwoven web of claim 4, wherein the nonwoven web has a Mullen burst per unit basis weight in both the machine direction and the cross direction, measured according to ASTM D1117-01, D5035-95, in the range of 3.5 KPa/gsm to 10 KPa/gsm.

8. The nonwoven web of claim 4, wherein the nonwoven web has a trapezoidal tear strength per unit basis weight in both the machine direction and the cross direction, measured according to ASTM 5733, in the range of 0.4 N/gsm to 5 N/gsm.

10. The nonwoven web of claim 1, wherein the poly(trimethylene terephthalate) is made by polycondensation of 1,3-propanediol derived from a renewable source and terephthalic acid or acid equivalent.

11. The nonwoven web of claim 1, wherein the poly(trimethylene terephthalate) contains at least 20% renewably sourced ingredient by weight.

12. The nonwoven web of claim 1, wherein the nonwoven web has a renewably sourced content of at least 5% by total weight of the web.

13. The nonwoven web of claim 1, wherein the poly(trimethylene terephthalate) comprises titanium dioxide.

14. An article comprising the nonwoven web of claim 1.

15. A nonwoven web comprising a plurality of continuous spunbonded bicomponent fibers, wherein each of the plurality of bicomponent fibers comprises:

a) 50% by weight of poly(ethylene terephthalate) in a core; and

b) 50% by weight of poly(trimethylene terephthalate) in a sheath surrounding the core, wherein the amounts in % by weight are based on the total weight of the bicomponent fiber.