DE69431767T2 - Method for determining the absorbency of liquids from Sphagnum-Moss material - Google Patents

Description

Scope of the invention

The invention relates to a novel sphagnum moss composition for making a fluid-absorbent medium for use in disposable absorbent articles such as sanitary napkins, tampons, diapers, adult pads, urinary pads, wound dressings and the like. The novel composition primarily comprises species of sphagnum mosses selected from the botanical sub-family PALUSTRIA, ACUTIFOLIA, RIGIDA, CUSPIDATA SUBSECUNDA and combinations thereof. The invention extends to a novel method for evaluating the capacity of sphagnum moss material to absorb fluid, a method for selectively harvesting undecomposed sphagnum moss and a novel method for making an unusually absorbent, structurally integral article containing sphagnum moss material.

Background of the invention

It is known in the art that sphagnum moss material is suitable for use as an absorbent medium in structures for absorbing body exudates. Sphagnum moss has highly desirable liquid absorption properties such as a remarkable absorbent capacity as well as the ability to desorb adjacent materials by continuing to draw or absorb liquid therefrom over a long period of time so that virtually all of the liquid is collected in the sphagnum moss core. These properties enable the material to create highly effective absorbent components which can be made relatively thin for better fit, comfort and discretion, while having sufficient absorbent properties to prevent leakage and contamination of clothing.

The following United States patents mention the use of sphagnum moss material for the production of absorbent components for disposable absorbent products:

The sphagnum moss material for use in the manufacture of absorbent components is harvested from the peat bog and transported to a processing plant where it is cleaned and processed into a structurally integral continuous layer. In sheet form, the sphagnum moss can be conveniently rolled for storage and transportation and is suitable for direct processing in high-speed automated equipment commonly used in the manufacture of multi-layer disposable absorbent products.

In the broadest sense, the process for converting the natural sphagnum moss into a structurally integral sheet begins with the preparation of an aqueous slurry which is classified while wet to remove from the particle suspension the extremely fine particles, commonly referred to as fines, and coarse material including roots, branches and the like which do not contribute significantly to the absorbency of the finished product. The cleaned slurry is cast into a sheet on a fourdrinier wire, dewatered and dried. The resulting structurally integral sheet is rolled to reduce the average pore size of the network to increase its drying capacity.

The state of the art also proposes the use of additives to improve certain properties of the structurally integral layer. In particular, the sphagnum moss can be treated with a wetting agent to improve its binding capacity for aqueous liquids. Polyester fibers can be incorporated into sphagnum moss matrix to increase its strength. These examples illustrate the variety of possible treatments that have the common goal of improving the liquid absorption and the mechanical properties of the structurally integral layer.

One area of integral layer structures that has not yet been investigated with the aim of further improving liquid absorption properties is the composition of the sphagnum moss material. A better understanding of the relationships between the absorbency and the composition of the plant absorbent medium is highly desirable to enable the manufacture of sanitary products with greatly improved absorption properties.

Objects and summary of the invention

It is an object of the present invention to provide a method for evaluating the liquid absorption properties of a material consisting primarily of substantially undecomposed sphagnum moss plants (hereinafter "plant" refers to a plant organism in its entirety or a part of that organism, such as a leaf or part of a leaf) selected from the botanical subgroups PALUSTRIA, ACUTIFOLIA, RIGIDA, CUSPIDATA, SUBSECUNDA and combinations thereof. This method is particularly useful for determining whether a naturally occurring unprocessed sphagnum moss composition is a suitable starting material for producing a highly absorbent structurally integral layer. Broadly stated, the method comprises the following steps:

A) sorting the sphagnum moss plants into predetermined classes based on the liquid absorption properties of the sphagnum moss plants, wherein one class contains sphagnum plants that are more desirable with respect to liquid absorption than sphagnum moss plants assigned to another class;

B) determining the proportions of the predetermined classes in terms of the amount of Sphagnum moss plants per class; and

C) calculating an average of the proportions determined in step B adapted to represent different liquid absorption characteristics of sphagnum moss plants belonging to different classes, the average being representative of the ability of the material is indicative of the ability to absorb liquid.

The assignment of the sphagnum moss plants into classes allows the plants to be classified with respect to the ability to absorb liquid. Consequently, sphagnum moss plants belonging to a common class exhibit similar liquid absorption properties. In a preferred embodiment, the classification of the sphagnum moss plants is established according to visually observable morphological relationships. Because the liquid absorption attributes of a sphagnum moss plant are dependent on its shape and structure, morphological similarity between the plants results in common liquid absorbing properties. This approach has the practical advantage that a simple microscopic examination of the sphagnum moss is usually sufficient to complete the classification procedure, with no need to perform complicated and time-consuming tests.

In a most preferred embodiment, the classes of sphagnum moss plants correspond to botanical units. For example, from performing a microscopic examination of the sphagnum moss composition to identify the botanical species present in the sample. A visual count is performed to approximately determine the proportions of the identified species of the sphagnum moss composition. The results for the species belonging to a common botanical section are added together to express the proportions per botanical section.

The botanical sections are ranked in terms of ability to absorb liquid using the same system used to calculate the Performance Index as discussed above. More specifically, each section is assigned a parameter whose value provides a relative measure of the liquid/absorption property of the section and a weighted average of the various parameter values is calculated to obtain a measure of the absorbency of the sphagnum moss composition.

As embodied and broadly described herein, the invention provides a liquid-absorbent material containing primarily sphagnum moss of a controlled composition, which has improved liquid absorption properties

As embodied and broadly described herein, the invention provides a method of evaluating the liquid absorption properties of sphagnum moss material, particularly the naturally occurring unprocessed Sphagnum moss aggregate to determine whether it represents a suitable starting material for producing a highly absorbent, structurally integral layer.

As embodied and previously described, the invention provides a method for selectively harvesting sphagnum moss from a peat bog to collect raw material most suitable for producing highly absorbent structures.

As yet another embodiment, which is broadly described, the invention provides a novel process for making a structurally integral product containing sphagnum moss material having improved liquid-absorbing properties.

The generic term "sphagnum moss" refers to a wide range of botanical species which occur in random proportions in peat bogs. The inventors of the present invention have made the unexpected discovery that when the sphagnum moss is obtained from a layer of the bog in which the plants are essentially undecomposed, i.e. having a Von Post value ranging between about 1 and about 3 on a ten-point scale, the composition of the sphagnum moss greatly influences the liquid absorption behavior of the absorbent product.

As embodied and broadly explained herein, the invention provides a structurally integral liquid absorbent article comprising primarily undecomposed portions of sphagnum moss plants belonging to at least two botanical subgroups selected from the group consisting of PALUSTRIA, ACUTIFOLIA, RIGIDA, SUBSECUNDA and CUSPIDATA, wherein the structurally integral liquid absorbent article has an absorption performance index in the range of about 1 to less than 4. Preferably, the performance index is in the range of about 2 to less than 4, more preferably in the range of about 3 to less than 4.

The Absorption Performance Index is established based on two factors. The first is the identity of the sphagnum moss species present in the absorbent product and the second is the ratio of the species in the composition.

A wide variety of sphagnum moss species exist in nature. According to the taxonomy rules, the individual sphagnum moss species are divided into subgroups according to common characteristics. The most important subgroups used to calculate the absorption performance index are PALUSTRIA, ACUTIFOLIA, RIGIDA, SUBSECUNDA and CUSPIDATA. These five subgroups are predominant on the North American continent and result in the following Evaluation based on a decision of the observed fluid absorption performance.

Subgroup Evaluation

PALUSTRIA 4

ACUTIFOLIA 3

RIGIDA2

SUBSECONDARY 2

CUSPIDATA 1

A species belonging to another subgroup is given a score of zero (0), i.e. this species does not contribute to the improved absorption performance index, which will be described later.

The absorption performance index is the weighted average of the evaluation of the different botanical subgroups present in a sphagnum moss body. This step is best illustrated by an example. A sphagnum moss body with the following composition:

Subgroup Percentage of one or more species that belong to a common subgroup in the Sphagnum moss body

PALUSTRIA 60,3

ACUTIFOLIA 31,7

CUSPIDATA 4.1

RIGIDA 1.7

SUBSECUNDA 1.5

SQUARE PINK 0.1

results in the following performance index

(4 · 0.603) Palustria

+(3 · 0.317) Acutifolia

+(1 · 0.041) Cuspidata

+(3 · 0.017) Rigid

+ (2 · 0.015) Subsecunda

+ (0 · 0.001) Squarrose

3,488

It should be noted that the absorption performance index calculation only takes into account the types of sphagnum moss and does not take into account other components that may be mixed with the sphagnum moss. For example, the absorption performance index of a structurally integral layer of sphagnum moss that also contains other components such as kraft pulp or polyester fibers is determined based solely on the characteristics of the sphagnum moss components, and the presence of kraft pulp fibers does not contribute to the calculated absorption performance index.

A rating of zero (0) points for certain species of sphagnum mosses does not mean that that species necessarily has little or no ability to absorb liquid. The zero rating is applied only to exclude the contribution of a particular species to the performance, either because that species is not actually absorptive or because its performance is unknown. It should be noted that the performance index is only valid and meaningful if the sphagnum moss primarily contains one or more species selected from the botanical subgroups PALUSTRIA, ACUTIFOLIA, RIGIDA, SUBSECUNDA CUSPIDATA or mixtures thereof. Small proportions of one or more species in the composition belonging to another subgroup do not significantly affect the accuracy of the performance index. However, if species of subgroups other than PALUSTRIA, ACUTIFOLIA, RIGIDA, SUBSECUNDA or CUSPIDATA predominate, the performance index is no longer a valid indicator of the liquid absorption potential of the Sphagnum moss.

As embodied and broadly described herein, the invention provides a disposable absorbent article comprising:

- an absorbent core comprising substantially non-decomposed particles of sphagnum moss plants belonging to at least two botanical subgroups selected from the group consisting of PALUSTRIA, ACUTIFOLIA, RIGIDA, SUBSECUNDA and CUSPIDATA, the absorbent core having an absorption performance index in the range of about 1 to less than 4 and

- a body-contacting, fluid-permeable layer is placed over this core.

In a preferred embodiment, the disposable absorbent product is a hygienic a napkin, a diaper, an adult incontinence pad, a urinary pad or a wound dressing and further comprises a liquid-impermeable layer beneath the absorbent core to prevent body fluid from escaping from the disposable absorbent article on its garment-facing side. Most preferably, the liquid-permeable and liquid-impermeable layers are bonded together to form an envelope in which the absorbent core is kept enclosed.

The rating system established to calculate the rating index assumes that a sphagnum moss consisting entirely of one or more species belonging to the subgroup PALUSTRIA should have excellent liquid absorption properties. However, an unprocessed sphagnum moss with such an ideal composition is rarely found in nature. Rather, aggregates of species from different subgroups predominate. Since the composition of such aggregates can vary widely and may also contain species that are not particularly desirable from the standpoint of liquid absorption, the absorption properties of sheets made from this material are likely to vary according to the particular composition of the raw material.

From this point of view, the invention can be defined in general terms as a structurally integral absorbent product which primarily comprises essentially processed particles of Sphagnum moss, the composition comprising a major fraction formed by at least one species belonging to the botanical subgroup PALUSTRIA and a minor fraction comprising one or more Sphagnum moss species selected from the group consisting of ACUTIFOLIA, RIGIDA SUBSECUNDA and CUSPIDATA.

The invention also provides a method for producing a highly absorbent, structurally integral layer. The method comprises the steps of:

- Providing a starting material containing particles of sphagnum moss plants belonging to at least two botanical subgroups selected from the group consisting of PALUSTRIA, ACUTIFOLIA, RIGIDA, SUBSECUNDA and CUSPIDATA, wherein the sphagnum moss has a Von Post value in the range of about 1 to about 3, the starting material has an absorption performance index in the range of about 1 to less than 4 and

- Forming the raw material into a structurally integral layer.

As embodied and broadly described herein, the invention further provides a method for selectively Harvesting a plant source material from a growth site of sphagnum moss for use in liquid-absorbing structures, the growth site containing an aggregate of sphagnum moss species consisting predominantly of a group of the botanical subgroups PALUSTRIA, ACUTIFOLIA, RIGIDA, CUSPIDATA, SUBSECUNDA, the composition of the aggregate varying randomly across the growth site, whereby the plant source material harvested from different locations at the growth site has non-uniform liquid-absorbing properties, the method comprising the steps of:

- identifying an area at the growth site where a sphagnum moss aggregate is present having a composition that satisfies a certain criterion, the criterion relating to the ability of the sphagnum moss aggregate to absorb liquid; and

- Harvesting a plant stock from the area having a Von-Post in the range from about 1 to about 3.

This method allows for efficient exploitation of the biomass present in a peat bog where the Sphagnum moss species are present in a random manner. By sampling the bog and evaluating the fluid absorption potential of the unprocessed Sphagnum moss at different locations, a map of the bog can be created to indicate the areas where the most desired Sphagnum moss is located.

As embodied and broadly described herein, the invention further provides a method of making a structurally integral liquid-absorbent product from plant source material harvested from a sphagnum moss growth site, the growth site containing an aggregate of sphagnum moss species predominantly belonging to a group of the botanical subgroups consisting of PALUSTRIA, ACUTIFOLIA, RIGIDA, SUBSECUNDA and CUSPIDATA, the composition of the aggregate varying randomly across the growth site, whereby plant source material harvested from different locations at the growth site exhibits non-uniform liquid-absorbent properties, the method comprising the steps of:

- identifying a region of the growth site in which a sphagnum moss aggregate is present having a composition satisfying a predetermined criterion, the criterion relating to an ability of the sphagnum moss aggregate to absorb liquid;

- Harvesting of plant starting material from the range having a From-Post in the range of about 1 to about 3; and

- Forming the plant raw material harvested from the area into a structurally integral liquid-absorbing product

As embodied and broadly described herein, the invention also provides a structurally integral liquid absorbent product primarily comprising substantially unadded particles of sphagnum moss plants belonging to at least one species selected from the group consisting of:

1) all species of the botanical subgroup ACUTIFOLIA;

2) all species from the botanical subgroup RIGIDA;

3) all species from the botanical subgroup SUBSECUNDA;

4) all species from the botanical subgroup CUSPIDATA;

5) Sphanum centrale, Spagnum Erythrocalyx, Sphagnum henryense, Sphagnum perichaetiale, Sphagnum portoricence from the botanical subgroup PALUSTRIA,

wherein the structurally integral liquid-absorbent product has an absorption performance index in the range of about 1 to about 4

Short description of the drawings

Figures 1 to 4 are color samples prepared as reference samples to determine the Von Post value of sphagnum moss material;

Fig. 5 is a partial perspective view of a structurally integral sphagnum moss layer according to the invention; and

Fig. 6 is a partial perspective view of a sanitary napkin according to the present invention.

Description of a preferred embodiment

Sphagnum moss is a plant that grows at the top, while the lower part of the plant dies off and gradually decomposes into peat. As is well known, sphagnum bogs, commonly referred to as peat bogs, typically have a striped structure in vertical section. The top layer comprises the leaves, branches and flowers of the living flora, predominantly living sphagnum moss, but also other plants growing in the moor. The top layer extends to a depth of about 2.5 centimeters to about 18 centimeters.

Beneath the top layer there is also a first intermediate layer consisting of undecayed, dead sphagnum moss including the roots of other living plants. The first intermediate layer is characterized by being fibrous and relatively lightly colored, with the plant structure generally still intact. Such a layer may extend from a depth of about 18 cm to about 1 m below the surface.

Beneath the first interlayer lies a second interlayer of partially decayed sphagnum moss, which can generally be distinguished from the first interlayer by a clear color demarcation. The second interlayer is characterized by a progressively darker color with increasing depth, and by decay of the plant structure with increasing depth to a point where the plant structure is no longer visible and the color changes from brown to black. The lower part of the second interlayer is typically the part of the sphagnum peat that is used as fuel. This layer can extend to a depth ranging from about 1 meter to about 2.5 meters from the surface.

Beneath the second intermediate layer is the soil layer, which represents the final stage of decomposition of the sphagnum moss plants. This soil layer is commonly referred to as "black soil" and is characterized by the fact that it no longer contains any recognizable plant structure and is black in color. This material can be found at a depth range of about 2.5 meters to about 4 meters below the surface. In some cases, peat bogs do not have this layer.

The Von Post method is an effective means of characterizing the degree of decay of dead sphagnum moss. The test consists in pressing samples of sphagnum moss taken from various depths and comparing the water released with the color charts of Figs. 1, 2, 3 and 4. A value of 1 is assigned to sphagnum moss from that layer of the bog which releases a clear liquid the color of which corresponds to Fig. 1. A value of 2 is assigned to sphagnum moss which is somewhat deeper and shows some degree of decay. The water released from it is slightly colored as shown in Fig. 2. Von Post values of 3 to 10 are assigned to sphagnum moss taken from increasing depths and which shows an increasing degree of decay so that the water released becomes progressively darker and contains more and more organic particles. Figures 3 and 4 show the colour of water obtained from samples with Von Post values of 3 and 4, respectively. Color charts with Von Post values beyond 4 were not prepared because they are not necessary for understanding the present invention.

The number of Sphagnum species found in North America is considerable. The following list indicates the Sphagnum species found north of Mexico:

A Subgroup PALUSTRIA

* Sphagnum centrale

Sphagnum erythrocalyx

Sphagnum henryense

* Sphagnum spp.

* Sphagnum magellanicum

* Sphagnum spp.

* Sphagnum spp.

Sphagnum perichaetiale

Sphagnum portoricence

B. Subgroup RIGIDA

Sphagnum spp.

Sphagnum strictum

C. Subgroup SQUARROSA

* Sphagnum squarrosum

* Sphagnum spp.

D. Subgroup INSULOSA

* Sphagnum aongstroemii

E. Subgroup SUBSECUNDA

* Sphagnum auriculatum

Sphagnum carolinianum

* Sphagnum contortum

Sphagnum spp.

Sphagnum cyclophyllum

* Sphagnum inundatum

Sphagnum orientale

* Sphagnum platypus

Sphagnum spp.

Sphagnum pylaesii

Spahgnum subobesum

Spahgnum subsecundum

F. Subgroup ISOCLADUS

Sphagnum macrophyllum

G. Subgroup CUSPIDATA

* Sphagnum spp.

Syn: S. parvifolium

S. recurvum var. tenue

* Sphagnum spp.

* Sphagnum annulatum var porosum

Syn: S. jensenii

* Sphagnum balticum

* Sphagnum cuspidatum

*Sphagnum fallax

Syn: S. apiculatum

S. recurvum var. mucronatum

Sphagnum fitzgeraldii

Sphagnum flexuosum

Syn: S. amblyphyllum

S. recurvum var amblyphyllum

* Sphagnum lenense

* Sphagnum lindbergii

* Sphagnum majus

Syn: S-dusenii

Sphagnum mendocium

* Sphagnum obtusum

* Sphagnum pulchrum

* Sphagnum riparium

* Sphagnum splendens

* Sphagnum tenellum

* Sphagnum torreyanum

H. Subgroup POLYCLADA

* Sphagnum vulgaris

I. Subgroup ACUTIFOLIA

* Sphagnum andersonianum

* Sphagnum spp.

Sphagnum bartlettianum

* Sphagnum spp.

* Sphagnum flavicomans

* Sphagnum fuscum

* Sphagnum girgensohnii

Sphagnum sylvatica

Sphagnum meridense

* Sphagnum spp.

Syn: S. capillaceum

S. acutifolium

S. Capillifolium

* Sphagnum quinquefarium

* Sphagnum rubellum

* Sphagnum russowii

Syn: S. Robustum

* Sphagnum subfulvum

Sphagnum subnitens

Syn: S. plumulosum

Sphagnum subtle

Sphagnum tenerum

* Sphagnum warnstorfii

Syn: S. warnstorfianum

An evaluation of the absorption properties of individual Sphagnum species of different subgroups has led to the unexpected finding that the absorption properties differ significantly from subgroup to subgroup. This finding was made when studying the following living species of Sphagnum mosses:

Type Subgroup

Fuscum ACUTIFOLIA

Rubellum sylvestris

Magellanicum PALUSTRIA

Papillosum PALUSTRIA

Recurvum CUSPIDATA

Cuspidatum CUSPIDATA

Subsecundum SUBSECUNDA

Compactum RIGIDA

The evaluation of the liquid absorption capacity of these species was carried out by forming the pure sphagnum species into structurally integral sheets on which the tests were carried out. A structurally integral sheet is formed by first turning the raw sphagnum moss of a given species into a slurry. This was done by treating the sphagnum moss in a 0.45 kg Standard valley beater with a load of 1 kg for a period of 5 minutes. At the end of the treatment, a solution of di-octyl sulfosuccinate (0.1% by mass of the total suspension) is added to the slurry. The di-octyl sulfosuccinate solution is a rewetting agent sold under the brand "Alcopol 60" by the Allied Colloid Company.

The slurry is then placed on a 12" by 12" square punctured plate and dried at 150ºC to a bone dry state. The sheet is then re-moistened in a standard Tenney cabinet at 65% relative humidity. The sheet is kept in the Tenney cabinet until it has re-absorbed 20% water vapor by mass.

For some of the liquid absorbency tests, the sheet is rolled between a pair of rollers with a diameter of 20.3 cm and at a pressure of about 550 kg per cm of length.

The sample layers of each sphagnum moss species are subjected to tests B to G described below. Test A is an exception because it uses a slurry of sphagnum moss and not, as in the other tests, a structurally integral layer.

A. Retention profile of the undried paste under various loads of 0 grams per square centimeter (g/cm²); 17.6 g/cm²; 105.5 g/cm²

A slurry of sphagnum moss is completely saturated with water and placed in a cylindrical container having a perforated bottom. A uniform pressure is applied to the sphagnum moss and the amount of water expressed at the pressures of 0 g/cm², 17.6 g/cm² and 105.5 g/cm² is recorded to calculate the amount of water retained at these pressures per gram of dry sphagnum moss. The results are given in the table below.

B. Saturation capacity (Gravimetric Absorption Test System) under a ballast of 7.04 g/cm² on the uncalendered layer

The Gravimetric Absorption Test System (hereinafter referred to as "GATS") is used to measure the ultimate absorption capacity of a porous network. The GATS instrument comprises a horizontal porous sintered glass plate connected to a vertical burette filled with an aqueous solution. The test procedure consists of bringing an uncalendered sample layer into contact with the sintered glass plate under a pressure of 7.04 g/cm2 and allowing the sample layer to absorb the aqueous solution under the action of capillary force. The aqueous solution is supplied to the interface between the sintered glass plate and the sample material under a negative pressure head of one centimeter, which is achieved by maintaining the level of the aqueous solution in the burette one centimeter below the top of the sintered glass plate. To prevent the pressure head from increasing excessively as a result of the absorption of the aqueous solution by the sintered glass plate, an electromechanical control system refills the burette at the same rate as the aqueous solution is sucked out in order to keep the level of the aqueous solution constant.

The absorption of the aqueous solution stops when the residual capillary force of the sample material is in equilibrium with the negative pressure head. The amount of aqueous solution aspirated from the burette is then determined and divided by the weight of the sample to obtain the maximum absorption capacity of the sample material per unit mass. The results of this test are given in the table below.

Type GATS results in cm³/g

Fuscum 24.5

Rubellum 22.0

Magellanicum 18.0

Papilloma 20.0

Recurvum 23.5

Cuspidatum 21.5

Subsecundum 26.0

Compactum 23.0

C. Saturation capacity (Gravimetric Absorption Test System) under a load of 7.04 g/cm² on the calendered layer in the context of a cycle of 7.04 g/cm² then 35.19 g/cm² and finally again 7.04 g/cm²

The same procedure as in B is followed, with the following exception. When the absorption of the aqueous solution is complete under a pressure of 7.04 g/cm², the pressure is increased to 35.19 g/cm² and the amount of aqueous solution remaining in the sample is noted. The pressure is then reduced to 7.04 g/cm² and the amount of liquid in the sample is again noted. The results of this test are given in the table below.

D. Suction effect of the calendered layer at an angle of 45º (capacity and height)

The sample is tilted at an angle of 45º and its lower edge is immersed in a container containing the aqueous solution. Due to capillary action, liquid is absorbed by the sample and migrates longitudinally against gravity. The distance travelled by the liquid from the lower edge of the sample in centimetres is measured and recorded after 15 min, 30 min, 60 min and 120 min. The amount of liquid in the sample is also recorded at these intervals. This measurement is made by weighing the sample and subtracting the mass of the dry sample from this measured value. The amount of liquid absorbed by the sample is standardised on the basis of a rather dry sample with an initial mass of 100 g/m² and a width of 1 cm. The results of these tests are given in the tables below.

E. Absorption capacity of the calendered position at 45º inclination in the event of sudden fluid intake

Absorbency is measured by weighing the amount of liquid retained in a 10.16 cm by 17.76 cm sample inclined at 45º while an amount of aqueous solution equal to ten times the mass of the sample is released from a burette placed above it. The burette touches the sample at a point 1.2 cm from its upper end. The amount of liquid retained by the sample is given as a percentage of the total amount of liquid released in the table below.

Type Absorbency below 45º in case of sudden fluid intake [%]

Fuscum 100

Rubellum 88

Magellanicum 93

Papilloma 99

Recurvum 43

Cuspidatum 76

Subsecundum 10

Compactum 99

F. Drying capacity of the calendered layer

A sample of a sphagnum material sheet measuring 5.08 cm by 25.4 cm is prepared. A test pad of a fluffy slurry material having an initial weight of 200 g/m2 moistened with an amount of the aqueous solution equivalent to 5 cubic centimeters per gram is then placed on the sphagnum material sample. The amount of liquid absorbed by the sample is measured at 30 minutes, 120 minutes and 180 minutes. The measurement is made by weighing the test pad and subtracting the mass of the dry pad. The results are expressed by dividing the mass of liquid remaining in the test pad by the mass of the dry test pad. The results of this test are given in the following table.

G. Retention on a porous plate at a hydrostatic pressure of -40 cm water column

The sample of sphagnum material is completely saturated with water and then placed on a perforated plate resting on one leg of a U-shaped tube. The level of water in the tube is kept at a level 40 cm below the sample, creating a negative hydrostatic pressure with respect to the sample. pressure of 40 cm water column is maintained. The amount of water retained in the sample is determined and expressed in units of mass of the dry sample. The results of this test are shown in the table below.

Type of retention at a hydrostatic pressure of 40 cm water column

Fuscum -

Rubella -

Magellanicum 8.0

Papilloma 6.5

Recurvum 4, 5

Cuspidatum 5.0

Subsecundum 4.5

Compactum 5.5

The test results are summarized and the sphagnum moss species are ranked according to the top three species in each test category. The results are shown in the table below.

The species are then ordered according to their frequency of occurrence as follows.

The absorption properties of sphagnum moss are determined, among other things, by the plant structure, such as the relative size of the leaves and their number. Accordingly, it is theoretically assumed that the morphological similarity of all species of a given subgroup necessarily makes an equal contribution to the common liquid absorption properties. Based on this principle, the observed variance in liquid absorption properties between different sphagnum moss species can be reduced to the variance between subgroups. Consequently, the results of tests A to F can now be expressed in terms of the frequency of occurrence of each subgroup in the first three ranks of each test. This is done for each subgroup by summing the frequency of occurrence of its species. The results are shown below:

Subgroup Frequency of occurrence

PALUSTRIA 14

ACUTIFOLIA 4

CUSPIDATA 3

RIGIDA2

SUBSECONDARY 1

Finally, the following ranking was assigned to the subgroups based on the frequency of occurrence:

Subgroup ranking

PALUSTRIA 4

ACUTIFOLIA 3

CUSPIDATA 2

RIGIDA2

SUBSECONDARY 1

It is important to note that the observed relationship between the plant origin and the liquid absorption properties was only verified in the case that the sphagnum moss is dead and substantially non-decayed, i.e., has a Von Post value in the range of about 1 to about 3, more preferably in the range of about 1 to about 2. A Von Post value that is significantly higher than 3 indicates that the decayed plant has lost its morphological identity. Consequently, the liquid absorption properties of the decayed plant no longer correlate with its structure.

In situations where the sphagnum moss is a mixture comprising species of different subgroups, the quality of the composition as a liquid absorbing medium can be assessed by calculating the performance index, which is a weighted average of the ranking of the absorption capacity. This is achieved by adding the respective performance ratings assigned to the different subgroups present in the sphagnum moss composition, multiplied by the proportion of the respective subgroup. For example, the weighted average of the absorption capacity rating of a sphagnum moss composition containing 65 mass% of sphagnum moss species of the subgroup PALUSTRIA and 35 mass% Sphagnum moss species of the subgroup ACUTIFOLIA (4 · 0.65) + (3 · 0.35) = 3.65.

The calculation of the performance index takes into account only the sphagnum moss components of the composition and does not take into account other components. For example, it is common to incorporate polyester fibers into the sphagnum moss absorbent core to improve the structural integrity of the absorbent networks. In such a sphagnum moss composition, the polyester content is not taken into account in the calculation of the performance index. Secondly, the performance index is only a valid indicator of the suitability of a particular composition for absorbing liquid if the composition contains a significant proportion of sphagnum moss selected from the subgroups PALUSTRIA, ACUTIFOLIA, RIGIDA, SUBSECUNDA, CUSPIDATA or mixtures thereof. If species from another subgroup are present in reduced quantities, this is taken into account in the performance index by assigning a "zero" rating, which neutralizes the contribution of these species in the formation of the performance index. In fact, the presence of species with no contribution to the performance index weakens it by reducing the concentration of efficient sphagnum moss species in the total share of the index.

There are two reasons for assigning a zero rating to a particular subgroup. Firstly, the subgroup may have little or no ability to absorb liquids. Secondly, the subgroup may not have been tested and its liquid absorption properties are therefore unknown. In this case, the zero rating allows the performance index to be calculated, with a margin of error that in most cases it is likely that the untested species will absorb liquids to at least some extent, and therefore the sphagnum moss composition will absorb slightly better than the performance index indicates.

The ability to evaluate the liquid absorption potential of a sphagnum moss composition can be advantageously used to test whether a naturally occurring sphagnum moss composition is a suitable starting material for producing absorbent cores for disposable absorbent products which meet or exceed predetermined liquid absorption specifications. Typically, the raw sphagnum moss is obtained from a peat bog where different sphagnum moss species occur in an irregular distribution. As a result, the composition of the sphagnum moss varies from one area of the bog to another. To reduce the possibility of raw material being obtained from areas of the bog where the composition of the sphagnum moss does not result in a sufficiently absorbent finished product, the peat bog is explored by producing a map of the bog which distinguishes those areas which yield an acceptable Sphagnum moss composition from those areas which yield a poorly absorbent raw material. This procedure enables efficient exploration of the biomass to carry out selective extraction of a raw material with the correct liquid absorption properties.

The peatland survey is carried out by taking samples from different locations and recording the coordinates of each location. The sampling density is chosen according to the desired resolution of the map. Each sample is then subjected to microscopic examination to identify the species of sphagnum mosses present and also to determine the relative abundance of each species. The visually observed frequency of occurrence of each species in the sample is used to determine the proportions of species in the sphagnum moss composition. The proportions of species belonging to a common subgroup are added to express the sphagnum moss composition by subgroup accordingly.

The next step is to calculate the performance index for each sample by assigning the exact performance score to each subgroup present in the sample and calculating the weighted mean of the compositional performance score. The resulting data are correlated with the sample coordinates to draw the map of the peatland, which distinguishes the areas with sphagnum moss of acceptable composition from the areas with unacceptable material. The map is then used as a guide to selectively extract sphagnum moss to obtain a raw material of appropriate quality.

If the whole peatland or large parts of it are not to be mapped, a limited survey of a given area may be carried out immediately before extraction takes place there. If the tests indicate the presence of raw material of acceptable quality, extraction is started. However, if the raw material begins to become unacceptable, extraction is moved to another location.

The sphagnum moss obtained from a location on the bog which provides a raw material of acceptable quality is transported to the processing site for conversion into a structurally integral layer. The raw sphagnum moss is wet classified to remove extremely fine material, commonly referred to as fines, and coarse material such as roots, twigs and the like which do not contribute significantly to the absorptive capacity of the sphagnum moss material. The classification is such that all that remains in a 10 mesh sieve (2000 µm) and all that passes a 60 mesh sieve (250 µm) is discarded. Preferably, everything that remains in a 14 mesh sieve (1410 um) and everything that passes a 100 mesh sieve (149 um) is discarded.

Classification is accomplished by a wet screening process which consists of preparing an aqueous slurry of the raw sphagnum moss material and flowing the slurry through successive screening stages to separate the slurry from fines and oversized particles.

The screened sphagnum moss fraction is diluted with water to a workable slurry. If desired, a fiber component can be added to the slurry. The fiber component can contain such materials as kraft pulp fiber or mechanically processed pulp fiber. The term mechanically processed pulp fiber as used herein includes groundwood, thermo-mechanically processed pulp fiber and refiner pulp. Groundwood consists essentially of trees and branches which have been debarked, cleaned and then ground into a particulate material. Refiner pulp fiber differs from groundwood only in that the grinding process takes place in a refiner, i.e. in a disk-shaped device well known in the art, the metal ribs attached to the circumference of which contact the wood particles and separate them without significant damage. Thermo-mechanically prepared pulp fiber is similar to refiner pulp fiber except that the wood particles are usually heated by steam in the refiner and this heating assists in further separation of the wood fibers. The common characteristics of these pulp fibers are that they have been mechanically prepared and no attempts have been made to separate the fibers by chemical means, although they may later be subjected to a desired chemical treatment after they have been converted to a finely divided material.

When such mechanically prepared pulp is used in the structurally integral layers of this invention, it preferably meets a Canadian Standard Freeness (TAPPI Test Method T-227) of from about 60 to about 750, and preferably from about 400 to about 600.

The kraft pulp fiber can also be used in combination with peat moss, mainly chemically treated, as well as with long-fiber pulp, such as sulfite and sulfate pulp.

The fiber component may also include a natural or synthetic textile fiber, such as cotton linters, rayon, polyester, acrylic fiber, and the like, having a length of about 0.64 cm to about 1.91 cm, preferably about 1.27 cm and 1/9 tex to 5/9 tex (1.0 denier to 5.0 denier) and in a proportion of about 2% to about 20% by weight, most preferably about 2 mass% to about 6 mass%.

The slurry is applied as a layer to a wire and dewatered to form an initial layer. The slurry may have a solids content of about 0.1% to about 1% by weight and may have other materials added to it such as dyes, wetting agents, adhesives and the like. After the slurry is applied to the wire, initial dewatering may be carried out by applying a vacuum to bring the water content to about 5 parts water to 1 part solids by weight.

The density of the layer can be controlled by varying such factors as the pressure differential during vacuum dewatering or the speed of the wire. Generally, a reduced vacuum and an increased speed will result in a less dense product. A sufficiently low density sphagnum moss board can be made with a deposited layer of about 160 grams to about 375 grams of solids per square meter of layer and a vacuum of 2533.12 Pa to 3733.02 Pa (19 millimeters of mercury (mm Hg) to 28 mm Hg). The speed of the wire and the width of the vacuum slot under which the layer is subjected to the pressure differential of the vacuum must be varied to provide a residence time of the layer over the vacuum slots of about 1 second to about 5 seconds. For example, two slots, each 2.5 cm wide, and a wire speed of about 0.76 meters per minute will give a residence time of about 1.5 seconds and produce a low density sheet with a deposit of 215 grams per square meter. Similarly, four slots, each 2.5 cm wide, and a wire speed of 0.52 meters per minute will give a residence time of 4.4 seconds and produce a low density sphagnum moss sheet. In both of the above examples, the vacuum was about 2999.74 Pa (22.5 mm Hg).

Regardless of the parameters chosen, the resulting layer before calendering has a low density of generally about 0.04 g/cm² to about 0.12 g/cm².

In a specific embodiment of this invention, a laminate is made from the sheet and a reinforcing layer of kraft pulp. Preferably, the pulp fiber is first deposited on the wire from a slurry of about 0.1% solids by weight. The kraft slurry is dewatered and then passes through a second station where the sphagnum moss and additives are deposited directly on the surface of the kraft layer. This composite layer can be dewatered to produce a laminate of the low density sphagnum moss layer described herein and a layer of kraft pulp which are adhered to one another at their surfaces. The strength properties of such a laminate are better than when only a sphagnum moss sheet is used alone. Preferably, the kraft pulp fiber used is bleached and has a relatively high Canadian Standard freeness, for example, from about 450 to about 750. While the ratio of the kraft layer to that of sphagnum moss is not critical, a useful product is obtained when a layer of kraft pulp fiber of about 5.5 grams to about 54 grams per square meter is used.

If desired, a kraft pulp layer can also be placed on top of the sphagnum moss layer to create a sandwich-like structure of a central sphagnum moss core covered on both sides with layers of kraft pulp fiber. This type of construction further improves the strength properties of the finished layer.

The resulting laminate is dried and then rolled to further improve its drying ability. Fig. 5 shows the structure of such a laminate, which is collectively provided with the reference number 10. The reference number 12 designates the sphagnum moss layer, while the reference numbers 14 and 16 indicate the kraft pulp reinforcement layers.

In order to improve the comfort potential of the integral layer structures, the rolling process is followed by a mechanical treatment such as hole punching or microwave embossing. These treatments are well known in the professional world and have the effect of softening the layer in order to reduce its rigidity.

This tenderized layer forms an absorbent core suitable for use in disposable absorbent products such as sanitary napkins, diapers, urinary pads, adult pads, wound dressings and the like. An exemplary representation of a sanitary napkin containing an absorbent layer according to the invention is shown in Fig. 6. The sanitary napkin, collectively designated by the reference numeral 18, contains an absorbent core made of a structurally integral absorbent layer 10 according to the invention. The absorbent core is located in a pocket consisting of a body-contacting, liquid-permeable layer 20 and a liquid-impermeable layer 22 which reduces the leakage of body fluid from the garment-facing side of the sanitary napkin 18.

Claims (3)

1. A method for evaluating a liquid-absorbing property of a material predominantly comprising substantially undecomposed sphagnum moss plants, selected from the group of botanical divisions consisting of Palustria, Akutifolia, Rigida, Subsekunda and Cuspidata, the method comprising the steps of: A) sorting the sphagnum moss plants into predetermined classes based on the liquid absorption properties of the sphagnum moss plants, wherein one class contains sphagnum plants that are more desirable with respect to liquid absorption than sphagnum moss plants assigned to another class; B) determining the proportions of the predetermined classes in terms of the amount of Sphagnum moss plants per class; C) calculating an average of the proportions determined in step B, adjusted to represent different liquid absorption characteristics of sphagnum moss plants belonging to different classes, the average being indicative of the ability of the material to absorb liquid; D) Assigning to each predetermined class a value indicating an ability of sphagnum moss plants assigned to the predetermined class to absorb liquid. 2. A method as defined in claim 1, wherein the predetermined classes are botanical divisions. 3. A method as defined in claim 1, wherein the mean is a weighted average of the respective values assigned to the predetermined classes.