Patent Application
20140315461
The present invention concerns cellulosic fibers with hydrophobic properties showing more softness and bulk and a process for production thereof.
Cellulosic Man Made Fibers are known for their hydrophilic, water absorbing attributes. In contrast synthetic fibers such as polyester, polyethylene and polypropylene are inherently hydrophobic which means that they do not absorb water into their interior structure. Some natural grown fibers like cotton possess natural waxes which protect the plants in nature and make the raw fiber hydrophobic. Usually these waxes are removed to achieve an absorbent, soft cotton fiber for textile and nonwoven processing.
Cellulosic fibers of the viscose type and modal type are produced according to the viscose process. Such fibers have been given the generic names, Viscose and Modal by BISFA (The International Bureau for the Standardization of man-made Fibers)
In recent years the “amine-oxide-process” or “Lyocell process” has been established as an alternative to the viscose process, wherein cellulose, without forming a derivative, is dissolved in an organic solvent of an amine-oxide, in particular N-Methylmorpholine-N-oxide (NMMO). Cellulosic fibers produced from such solutions are called “solvent-spun” fibers and have been given the generic name Lyocell by BISFA (The International Bureau for the Standardization of man-made Fibers).
Other man-made cellulose fibers can be made using chemical processes (e.g. the cuproammonium process) or using other direct solvents such as ionic liquids.
For hygiene applications, synthetic fibers such as polyester are widely used as they enhance bulk, opacity and softness in nonwoven and textile applications.
For ecological reasons, cellulosic fibers and especially man-made cellulosic fibers continue to gain importance as they are made from a renewable raw material and are biodegradable. As a result, there is a growing demand for cellulosic fibers which are soft, hydrophobic, give higher bulkiness and are biodegradable.
The object of the invention is to provide hydrophobic cellulose fibers which are biodegradable and water repellent. Said fibers are extra soft and show higher bulk in nonwoven fabrics.
Said object is achieved by means of a cellulosic fiber comprising a hydrophobic surface agent and the fiber is characterized in that the softness of the fiber according to the sledge test is at least 1.3 times higher than the softness of a cellulosic man-made fiber of an untreated fiber of the same type.
The cellulosic fibers can be natural grown like cotton, or be a man-made cellulosic fiber, such as viscose, modal or lyocell.
The cellulosic man-made fibers can also
a) be physically modified for example, in shape (trilobal, multilobal) or length (flock, short cut to continuous filament)
b) have incorporated materials, such as color pigments, flame retardants, ion exchange resins, carbon blacks.
c) be chemically modified, for example as is the case with Modal or cross linked fibers.
In the context of the invention, the term “untreated fiber” refers to a fiber where the surface of the fiber is non-modified. In case of a freshly spun fiber, i.e. a never-dried fiber, the surface is non-modified initially. Commercially available fibers usually contain a soft finish which has to be completely removed to get a non-modified surface before the hydrophobic treatment.
The term “same type” means a fiber of the same nature, titer and length.
As hydrophobizing agents Alkyl or Alkenyl Ketene Dimer (AKD) is used, which is shown in formula (1), where R1 and R2 are hydrocarbon groups with between 8 and 40 carbon atoms and which can be both, saturated or unsaturated, straight-chained or branched.
Formulations which have similar effects are substituted cyclic dicarboxylic acid anhydrides like substituted succinic or glutaric acid anhydrides and similar.
The preferred Alkyl Ketene Dimers are prepared from acid chlorides by e.g. the method described by R. Adams, Org. Reactions Vol. III, p 129 John Wiley & Sons Inc. NY 1946 or J. C. Saner; Journal of the American Chemical Society, Vol. 69, p. 2444 (1947).
Alkyl Ketene Dimer (AKD) is well known in the paper industry to enhance the water repellence of surfaces e.g. used in food packaging. The use of AKD is known for sizing papers as known from GB 2 252 984 A and EP 0 228 576 B1. The joint use of AKD and ASA (alkyl succinic acid) is described in WO99/37859. AKD is usually used at the wet end of the paper machine.
In a process for producing a cellulosic fiber with hydrophobic properties the process is characterized by the steps
a) providing a cellulosic fiber with a non-modified surface
b) treating the cellulosic fiber with a hydrophobic agent
The hydrophobic agent can be applied during man-made fiber production—this means after the fiber is already formed and washed but before drying, i.e. never-dried fibers. In this case the surface is non-modified.
If commercial available cellulosic fibers, comprising a finish, are used, this finish has to be removed.
The hydrophobic agents, such as AKD formulations are commercially available (for example Hydrores© compounds sold by Kemira). The most common are formulations with around 5-25% of active compound. In the case of the examples, Formulation A is an acidic solution with around 10-12% of active material while Formulation B is an acidic emulsion with an active compound of around 20-22%.
The cellulosic fibers are preferably treated with the AKD formulation in a concentration range of 0.0001% to 10%, preferably of 0.001% to 5%, and most preferred of 0.001% to 3% on cellulosic fiber.
The invention is shown by the following examples
Trials were made using Lenzing Viscose, Lenzing Tencel or Cotton. Table 1 shows the main fiber types which have been used. As hydrophobic agents, an AKD-formulation such as Hydrores© from Kemira was used. The commercial available formulations where diluted with water to get the concentrations shown in the examples: AKD 1 means the AKD solution used for the treatment has been prepared from Formulation A, AKD 2 means the AKD solution used for the treatment has been prepared from Formulation B.
7 g of bone dry viscose fibers, where the soft finish has been removed with alcohol, are soaked in 100 ml of an aqueous Hydrores© solution containing 0.07 g of AKD (1% AKD on cellulose) at room temperature (liquor ratio 1:15). After 30 min stirring, fibers were centrifuged until they had a moisture content of 50%, dried at 70° C. in a desiccator's cabinet to a moisture content of 6%. The resulting fibers are bulky, soft and show hydrophobic characteristics.
14 g of viscose fibers from the viscose process before aftertreatment, were pressed to a moisture content of 50% (never dried Viscose) and put into a basin containing an aqueous solution of 100 ml Hydrores© containing 0.035 g of AKD (0.5% AKD on cellulose) at room temperature (approximate liquor ratio of 1.15) After 30 min stirring, fibers were centrifuged to a moisture content of 50% and dried at 70° C. in a desiccator's cabinet to a moisture content of 6%. The resulting fibers are bulky, soft and show hydrophobic characteristics.
7 g of bone dry Tencel fibers, where the soft finish has been removed with alcohol, were soaked in 100 ml of an aqueous solution of Hydrores© containing 0.07 g of AKD (1% AKD on cellulose) at room temperature (liquor ratio 1:15). After 30 min stirring, the fibers were centrifuged to a moisture content of 50% and dried at 70° C. in a desiccator's cabinet to a moisture content of 6%. The resulting fibers are bulky, soft and show hydrophobic characteristics.
14 g of never dried Tencel fibers, taken wet from the lyocell production before aftertreatment were pressed to a moisture content of 50% and soaked in an aqueous solution of Hydrores© containing 0.035 g of AKD (0.5% of AKD on cellulose) at room temperature (approximate liquor ratio of 1:15)). After 30 min stirring, the fibers were centrifuged to a moisture content of 50% and dried at 70° C. in a desiccator's cabinet to a moisture content of 6%. The resulting fibers are bulky, soft and show hydrophobic attributes.
7 g of bone dry bleached cotton fibers, where any soft finish has been previously removed with alcohol, were soaked in an aqueous solution containing 0.035 g of AKD (0.5% of AKD on cellulose) at room temperature (liquor ratio 1:15). After 30 min stirring, the fibers were centrifuged to a moisture content of 50% and dried at 70° C. in a dessicator overnight. The resulting cotton fibers are water repellent and very soft.
Table 1 shows an overview of the fiber samples according to examples A to E
The softness of the fiber was determined by the Sledge test which is described in EN 1202 PPS. The key elements of this test are:
5 g Fiber samples are collected and carded twice using e.g. MTDA-3 Rotorring equipment. Fibers are conditioned according to ED ANA instructions (ERT 60.2-99) for at least 24 hours and cut into pieces using a master plate. The material is put into the test machine and a sledge (carrying a weight of 2000 g) is mounted and laid on the sample. The test is started and a measurement of the power required to drag the sledge is taken after 10 seconds.
The softer the fiber surface, the less power is needed to pull the sledge forward. To compare the softness of the various samples, a ratio of the power to drag a treated fiber sample compared to the power to drag either a similar commercial sample or a similar commercial sample with soft finish removed has been calculated. For example, in table 2 it can be seen that the softness of the viscose fiber treated with the hydrophobic agent is 2.23 times higher than the equivalent commercially available product.
In a second test series, never dried cellulosic fibers have been treated with lower concentrations of AKD (table 3):
The test results show that cellulosic fibers treated even with low levels of the hydrophobic agents have a softness which is around 2 to 2.5 times greater than an untreated, unfinished man made cellulosic fiber and around 1.7 to 2 times greater than the equivalent commercial man made cellulosic fibers.
The results in table 4 show that treatment with the hydrophobic agent is equally effective on bright or dull fibers, on fibers with different linear densities and on fibers with multilobal cross sections.
In a third test series, the effects of the hydrophobic agents on cotton were evaluated (table 5):
Although commercial bleached cotton with an added soft finish is softer than the natural, unbleached equivalent, this is achieved at the expense of losing its hydrophobic character. The use of the hydrophobic agents, allow this hydrophobic attribute to be maintained while also producing a fiber which is 1.4 times softer than the naturally occurring product and similar to the bleached and finished commercial product.
The material can be processed with all state of the art nonwoven techniques, including for example, needle punching, spunlacing and air laying. Conventional textile processing routes are also possible.
The inventive fiber can be used in different applications, especially in nonwovens, for example
A further object of the invention is to provide nonwoven fabrics which show lower bulk density and higher softness which are desirable in many applications. The treated fibers can be processed using most state of the art nonwoven techniques, e.g. Needle punch, spun lace and air laid. In particular, because the chemical bonding between AKD and regenerated cellulosic fibers is so strong, treated fibers can withstand the relatively severe spunlacing process conditions.
Nonwoven webs and fabrics according to the invention are characterized in that they contain hydrophobic cellulosic fibers according to the invention. The fabric can be made from hydrophobic cellulosic fibers alone or also in blends with rayon, Tencel, polyester or any other fiber used in nonwoven production.
To demonstrate the benefits of the invention in terms of fabric properties, a range of samples were produced using both needlepunched and spunlaced technologies and these were tested for softness and flexibility using flexural rigidity and Handle-o-meter tests and for bulk density. Needlepunched fabrics were produced on a pilot line built by Tec Tex (Italy) and made to 60 gsm (grams per square meter) or 120 gsm fabrics, needled from both sides in a range from 100 to 200 needle punches per unit and with the needle depth between 16 and 18 mm. Spunlaced fabrics were produced on a pilot plant at NIRI to a basis weight of 55 gsm.
Flexural rigidity was tested according to ED ANA WSP 90.5 (05) for bending length. In this test, a strip of fabric is fixed at one end, free at the other end and supported on a horizontal platform. The strip of fabric is advanced over the edge of the platform until the leading edge of the test specimen has reached a plane passing through the edge of the platform and inclined at an angle of 41.5° below the horizontal At this point, the overhanging length equals twice the bending length of the test specimen, and thus the bending length can be calculated. Flexural rigidity was measured according to the WSP method in four ways—MD (machine direction) and CD (cross direction), for both the front and back sides of the fabric. The values were averaged and compared to fabrics of comparable weight which were made from untreated fibers.
Handle-O-Meter testing was carried out according to WSP 90.3.0 (05). In this test, the nonwoven to be tested is deformed through a restricted opening by a plunger and the required force is recorded. A lower required force equates to a softer, more flexible fabric. Bulk density was calculated from area weight [WSP 130.1(05)] and thickness [WSP 120.6(05)], according to EDANA methods.
For all tests, results were normalized to the relevant control for fabrics made from untreated fibers and then expressed as a percentage. For all tests, a percentage result lower than 100 shows an improvement in that property, like lower bending length, lower flexural rigidity, lower force required in the Handle-O-Meter test or lower bulk density, and hence thicker fabrics for the same basis weight. Results can be found in tables 6, 7 and 8.
Examples of needle punched fabrics:
Never dried Viscose fibers 1.7 dtex/40 mm were treated with 0.5% AKD solution according to Example B. The dried fiber was processed to form fabrics with basis weights of nominally 60 gsm and 120 gsm.
Never dried Tencel fibers 1.7 dtex/38 mm were treated with 0.5% AKD solution according to Example D. The dried fiber was processed in a needle punch pilot plant to form fabrics with basis weights of nominally 60 gsm and 120 gsm.
Table 6 shows the softness/flexibility results for needlepunch fabrics according examples F and G.
In all cases, the use of treated fibers results in fabrics which are softer/more flexible and by between 17 and 61% compared to fabrics made from standard, untreated fibers. There is good correlation between the flexural rigidity and Handle-O-Meter tests.
Fibers made according to sample B and D were converted on a spunlace pilot plant and processed to form fabrics with a basis weight of nominally 55 gsm. Fabrics in both 100% and blends with commercially available Viscose and Tencel were made. Tables 7 and 8 show the effects on fabric softness as measured by the Handle-O-Meter. The use of treated fiber has a very significant effect on fabric softness and flexibility as measured by the Handle-O-Meter with 100% treated fiber giving over a 50% improvement in softness.
The addition of even small blend percentages of treated fiber also have a very significant effect on fabric softness as measured by the Handle-O-Meter with softness increasing as the blend percentage is increased (table 8):
Fabrics made from treated fibers show lower bulk densities than fabrics made from the same untreated fibers and would typically allow a 10% reduction in basis weight to give the same thickness in a needle punched fabric (table 9).
When treated fibers are used as a 100% substitute for the same untreated fibers, bulk density is reduced by over 25% (table 10):
Low blends of treated fiber down to 5% reduce the bulk density of the fabrics (table 11):
Overall, Nonwoven fabrics according to the invention show increased softness and are characterized in that the flexural rigidity (stiffness) of the nonwoven is at least 15% but up to 49% lower than the stiffness of a nonwoven consisting of comparable untreated fibers.
It was also found that nonwovens according to the invention show lower bulk density compared with untreated fibers under the same conditions with up to a 25% reduction in bulk density for fabrics made from 100% treated fibers.
Cellulosic Webs or Fabrics Treated with the Hydrophobic Agents
It is also possible to treat cellulosic fabrics made from standard man made cellulose fiber or bleached cotton with the hydrophobic agent provided that any soft finish on the fabric is first removed. In the case of a spunlaced fabric, soft finish removal may be achieved by the spunlacing process itself or subsequently in a separate removal step. This process is useful if a totally hydrophobic fabric is required.
Spun laced fabric samples produced from standard commercial Tencel or from standard commercial viscose samples were put into 0.1% AKD 2 solution and stirred. After 5 min the samples were taken out, squeezed and put into a desiccators' cabinet at 70° C. to dry. The resulting fabrics were completely water repellent and soft. Softness was measured relative to untreated fabrics using the Handle-O-Meter method described previously and the results are shown in tables 12 and 13. The softness of fabrics treated with the hydrophobic agent is around 50% of that for standard untreated spunlaced fabrics.
Needle punched fabrics (chosen from those used to assess softness and bulk density—see tables 6 and 9) made from fibers treated with the hydrophobic agent were cut into pieces of around 3×4 cm, weighed and then buried in soil. Samples were taken after 2 weeks, 1 month and 2 months and weighed to check the level of biodegradation. All samples had completely degraded after two months. Results are given in table 14.
Tests according to ASTM D 6400 (or DIN EN ISO 14855 or DIN EN 14046) say that a material is biodegradable if all organic compounds are decomposed in different chemical structures which are also naturally metabolites. This must happen during organic composting. Nonwoven consisting of Viscose and Lyocell fibers (commercially available and treated with AKD 2) are fulfilling these parameters.
| Number | Date | Country | Kind |
|---|---|---|---|
| A 1651/2011 | Nov 2011 | AT | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/AT2012/000258 | 10/11/2012 | WO | 00 | 5/6/2014 |
