Abstract:
A method of making a non-clogging porous fibrous mass is disclosed. The fibrous mass comprises intimately blended first and second groups of staple fibers having different tack points and longitudinal stress-free shrinkages. The fibrous mass is fed into and pulled through a heat bonding and shaping die and cut to a desired length. Specific ratios of weight percent to fiber denier and differences between the longitudinal stress-free shrinkages of the groups of fibers are utilized in order to render the bonded fibrous mass non-clogging.

Description:
FIELD OF AND AN OVERVIEW OF THE INVENTION 
     The present invention is in the field of air scenting methods and devices for commercial, industrial and home applications. In particular, it is directed to a non-clogging, non-dripping and spillage and leakage-proof air-scenting method and device which are achieved by making, providing and using a resilient porous bonded fibrous foam/mass having open pores/open cells formed between bonded fibers with different stress-free thermal shrinkages and eliminating the presence of any free-to-flow air-scenting liquid mass in the device. In accordance with the present invention, the air-scenting liquid mass is contained/retained substantially entirely within the open pores/cells of the porous bonded fibrous mass. The fibrous mass has a body B and an exterior surface S. Body B has a capillary pressure BCP, a mass density MDB (gram per cubic centimeter), an average fiber denier FDB, and a fiber orientation index FOIB relative to an axis or a direction. The exterior surface S comprises surface segments SG. Surface segments SG have at least one of i) a capillary pressure SCP, where SCP is higher than said capillary pressure BCP, ii) a mass density of MDSG (gram/cubic centimeter) where MDSG is higher than said mass density MDB, iii) an average fiber denier FDSG where FDSG is lower than said FDB, iv) fiber orientation/alignment index FOISG where FOISG is higher than said FOIB as measured relative to said axis or direction, and v) a surfactant coating applied to said surface segments. 
     In accordance with the present invention, a method of making a non-clogging resilient porous bonded fibrous foam or mass comprises the steps of: 
     1) providing an intimately-blended fibrous mass, said fibrous mass comprising a first group of staple fibers and a second group of staple fibers, said first group of staple fibers and said second group of staple fibers being non-absorbent of and non-reactive with (i.e., inert to) the liquid to be wicked by and evaporated through the surface of the formed non-clogging resilient porous bonded fibrous foam/mass or to be held within the open pores/open cells of said foam/mass, said first group of staple fibers having i) a percent weight W1 (%) of weight of said fibrous mass, ii) an average fiber denier D1, iii) a ratio N1 where N1 is equal to W1/D1, iv) a staple length L1, in the range of 1.5 to 3.5 inches, v) a tack point T1 and vi) a percentage longitudinal stress-free shrinkage S1 (%) at said tack point T1, said second group of staple fibers having i) a percent weight W2 (%) of weight of said fibrous mass, ii) an average fiber denier D2, iii) a ratio N2 where N2 is equal to W2/D2, iv) a staple length L2, in the range of 1.5 to 3.5 inches, v) a tack point T2, where T2 is higher than T1 by at least 50 degrees Fahrenheit, vi) a percentage longitudinal stress-free shrinkage S2 (%) at said tack point T1,and a ratio R equal to N1/N2 and being within the range of 0.5 to 3.0, and preferably within the range of 1.0 to 2.25 and a percentage longitudinal stress-free shrinkage difference SD (%) equal to the absolute (positive), value of the difference between S1 (%) and S2 (%) and being at least equal to 5.0%,
 
2) heating said fibrous mass to a temperature of at least T1 but lower than T2 by feeding said fibrous mass into a heat bonding (cohesive bonding) die, said bonding die having a feed/inlet zone, a heating zone, a tapered compaction zone and a shaping/cross-section-forming zone for making/shaping the final cross sectional shape of the bonded fibrous mass. The heating zone of said die is fed with hot steam or hot air at a temperature of at least T1 but lower than T2. The compaction zone is preferably tapered, towards the delivery/exit end of the die, at an angle within the range of 10 degrees to 45 degrees and preferably within the range of 25 degrees to 35 degrees, per side, relative to the axis of the die in order to provide more effective contact and higher heat transfer contact time and rate from the die body to the fibrous mass surface/surface segments thus effecting a calendaring or glazing action that renders the exterior surface/surface segments, of the bonded fibrous mass, having higher capillary rise and/or a higher density than the interior of the bonded fibrous mass,
 
3) Pulling the fibrous mass through said die thus dragging the fibrous mass, through the tapered compaction zone of the die, against the interior surface of the die and causing the fibers on the exterior surface of the bonded fibrous mass to have a higher fiber orientation index, relative to the direction of the axis of the die, than the fibers contained within the interior of the bonded fibrous mass, and
 
4) Cutting the bonded fibrous mass to a desired length.
 
     In embodiments, in accordance with the present invention, the intimately blended fibrous mass may be in the form of slivers, yarns (single and/or plied yarns), braided yarns, woven fabrics, knitted fabrics (tubular or flat) or needle punched nonwoven sheets which may also be arranged in layers which may be parallel flat layers or concentric circular layers/annular rings having outer layer(s) made of finer fibers (lower denier). The heating zone of the die is fed and filled with hot steam or hot air at a temperature of approximately 10 to 20 degrees Fahrenheit above T1 thus cohesively bonding fibers of the intimately blended fibrous mass at common contact and cross-over points and causing bonded fibers to form open cells with aspect angle (a), shown in FIG.  10 - b , of at least 18 degrees. 
       FIG. 10  shows a representation of the non-clogging bonded fibrous foam/mass of the present invention. As shown therein, bonded fibrous foam/mass  101  is an intimately-blended fibrous mass comprising a first group of staple fibers  102 , shown in solid lines, and a second group of staple fibers  103 , shown in dashed lines. Fibers from the first group and from the second group are intimately blended and bonded at common contact points  104  and cross-over points  105 . Open pores/cells  106  are formed between the fibers upon heating the intimately blended fibrous mass, bonding fibers at points  104  and  105  and allowing the difference in longitudinal stress-free shrinkage to cause the fibers with the lower longitudinal stress-free shrinkage to buckle and form open pores/cells throughout the bonded porous fibrous mass. The size and dimensions of open pores/open cells  106  depend on the dry mass density of the bonded fibrous foam/mass and on the difference between the percentage longitudinal stress-free shrinkages of the first group of fibers and of the second group of fibers. 
     To illustrate how open pores/cells  106  are formed, FIG.  10 - a  shows two fibers, initially straight and of equal length, fiber  107  and fiber  108 , bonded together at points  109  and  110 . The initial distance between bonding points  109  and  110  is, as shown in FIG.  10 - a , distance  111 . For the case where, upon heating the bonded together fibers  107  and  108  to a temperature where the percentage longitudinal stress-free shrinkage of fiber  107  is higher than the percentage longitudinal stress-free shrinkage of fiber  108  by only 5%, the bonded assembly of fibers  107  and  108  will assume the shape shown in FIG.  10 - b . As shown in FIG.  10 - b , fiber  108 , having undergone lower longitudinal shrinkage than fiber  107 , forms a curved path  112  which may be approximated by straight lines  113  and  114 , forming an aspect angle (a) as shown in FIG.  10 - b . For a difference in longitudinal stress-free shrinkage of only 5%, a simple calculation yields an approximated aspect angle (a) of 18 degrees and height  115  of formed cell equal to [(tangent of 18 degrees X the shrunk length of high shrinkage fiber  107 )/2]. For the typical case of a 2 denier polyester fiber having a diameter of 0.000564 inch, an aspect angle (a) of 18 degrees and a distance between bonding points of 0.1 inch, the open cell has a theoretically calculated maximum pore size equal to (0.32×0.1×0.5)=0.016 inch which is (0.016/0.000564)=28.3 times the diameter of the fiber. Such an open pore permits flow of air-scenting liquid without any clogging that may be caused by solids left on the surface of the fibers after the solvent or water content of the air-scenting liquid evaporates. 
     In an actual embodiment of the present invention, a non-clogging porous resilient bonded fibrous foam/mass was made of an intimate blend of two groups of staple fibers. The first group of staple fibers is bicomponent polyester fibers having a sheath material made of low melting point polyester with a melting point of 110 degrees Celsius and a core made of regular polyester with a melting point of 260 degrees Celsius and has i) a percent weight W1=50(%) of the weight of said fibrous mass, ii) an average fiber denier D1=2 denier, iii) a ratio N1 where N1 is equal to W1/D1=50/2=25, iv) a staple length L1=2 inch, v) a tack point T 1 =95 degrees Celsius and vi) a percentage longitudinal stress-free shrinkage S1 (%)=24.4% at said tack point T1. The second group of staple fibers has i) a percent weight W2 (%)=50% of the weight of said fibrous mass, ii) an average fiber denier D2=4, iii) a ratio N2 where N2 is equal to W2/D2=50/4=12.5, iv) a staple length L2,of approximately 2 inches v) a tack point T2 of approximately 240 degrees Celsius, vi) a percentage longitudinal stress-free shrinkage S2 (%)=1.47% at said tack point T1,and a ratio R equal to N1/N2=25/12.5=2. For this intimately blended fibrous mass/foam, the percentage longitudinal stress-free shrinkage difference SD (%)=24.4−1.47=22.93%. The above intimately blended fibrous mass was fed, in the form of slivers weighing 4 gram per yard, into a die, as described above. The die heating zone was fed with steam at nearly atmospheric pressure and a temperature of 212 degrees Fahrenheit. The bonded slivers were formed into a tube having an outer diameter of 1.53 inch and an inner diameter of 0.5 inch and a dry density DD of 0.165 gram per cubic centimeter and used as a wick. One end of the wick (of length 4 inches) was dipped into a bath containing 4 ounces of water-base ink. After 16 days of nearly linear evaporation rate, the entire 4 ounces of water-base ink were wicked through the wick and evaporated leaving a high concentration of ink solids at the top end of the wick. This indicates that such a non-clogging nature of the bonded porous fibrous foam of the present invention is a result of the choice of fibers for making the intimately blended fibrous mass in accordance with the criteria and within the ranges described and detailed above. 
     The non-clogging resilient porous bonded fibrous foam/mass made in accordance with the teachings of the present invention is also suited for use as an ink reservoir for ink jet printer cartridges. 
     In accordance with the present invention, the fibrous mass serves the function of being a high capacity reservoir for holding the air-scenting liquid mass, by capillary action, within its pores. Segments of the exterior surface of the fibrous mass, having at least one of the above-mentioned five (5) characteristics, draw the air-scenting liquid from the reservoir (the body of the fibrous mass) to the surface of the fibrous mass and allow it to evaporate at an unexpectedly nearly linear/constant rate the magnitude of which is controlled by allowing evaporation of the air-scenting liquid from predetermined uncovered portion(s) of said segments of the exterior surface of said fibrous mass. To prevent dripping, spillage and leakage of the air-scenting liquid from the device of the present invention, the mass of the air-scenting liquid contained within the body of the fibrous mass (reservoir) is not exceeding, and preferably is less than, the Dripping Liquid Mass (DML) of the extent L of the fibrous mass. The air-scenting device of the present invention also features a long duration of air-scenting at a nearly linear/constant rate of evaporation of the air-scenting liquid. This unexpected feature (the nearly linear rate of evaporation) was found to be possible only when the fibers used for making the porous fibrous mass are non-reactive with and non-absorbent of (i.e., inert to) the air-scenting liquid held within the pores of the bonded porous fibrous mass. 
     Also, the combination of i) use of non-absorbent and non-reactive fibers for making the bonded porous fibrous mass, ii) said fibers being made of a polymeric material having a density in the range of 1.1 to 1.4 gram per cubic centimeter, iii) said fibers having a denier in the range of 0.9 to 15 denier and preferably in the range of 0.9 to 6 denier, and iv) said fibrous mass having a dry density in the range of 0.1 to 0.45 gram per cubic centimeter yielded the significant and unexpected result of the device non-clogging throughout its long duration performance (air-scenting) period. The unexpected non-clogging performance of the device of the present invention is an indication that the open pores/open cells/open capillaries, of the bonded porous fibrous mass, remain open throughout the entire long-duration performance of the device. 
     DEFINITIONS 
     In accordance with the present invention, the following terms are defined as follows: 
     1) “Free-to-flow liquid mass” is an initially motionless liquid mass or body i) having a planar top surface, said surface being perpendicular to the direction of the gravitational acceleration force, (e.g., as indicated by arrow g in  FIGS. 1 and 2 ), and ii) being contained in a container or placed on top of an impermeable surface whereby upon tilting said container or said impermeable surface the liquid mass may be poured out of the container or flow onto the impermeable surface. Accordingly, liquids  3  in  FIGS. 1 and 24  in  FIG. 2  are free-to-flow liquid masses.
 
2) “Porous mass” is a mass or a body having or containing open cells/pores/interstices and permitting the flow of gas or liquid through its pores, open cells or interstices upon the application of a pressure or a force difference between two spaced-apart points in or on the mass.
 
3) “Fibrous mass” is a mass or a body made of fibers.
 
4) “Surface Segment of a Mass” is a skin layer of the mass having a thickness within the range of 0.25 to 1.0 millimeter.
 
5) “Mass Density of a Fibrous Mass or a Surface Segment” is the mass per unit volume of the fibrous mass or the surface segment.
 
6) “Fiber Orientation Index (FOI) Relative to an Axis or a Direction” is the quotient of (the summation of the number of fibers X their respective angle of orientation, measured in degrees from a specified axis or direction) divided by the total number of fibers. For example, a mass of fibers composed of 50 fibers oriented at an angle of 5 degrees relative to an axis, 30 fibers oriented at angle of 30 degrees relative to the same axis and 20 fibers oriented at an angle of 20 degrees relative to the same axis, has a Fiber Orientation Index FOI relative to the axis=[(50×5)+(30×30)+(20×20)]/(50+30+20)=15.5 Degrees.
 
7) “Extent of an object, a body or a mass” is the longest distance between two points located on the surface of the object, body or mass. For example, the extent of a rectangular block of 3 inch thickness×4 inch width×5 inch length is the distance between the farthermost corners, which is 7.071 inch.
 
8) “Dry fibrous mass” is a fibrous mass containing no liquids, whether said liquids are i) contained within the fibers (i.e., absorbed by the fibers) and/or ii) held in the pores or spaces between the fibers.
 
9) “Average Fiber Denier of a Fibrous Mass or a Surface Segment” is the quotient of 100 divided by (the summation of the weight percent of each fiber denier contained in the fibrous mass or surface segment divided by its respective fiber denier). For example, a fibrous mass or surface segment composed of 30% (by weight) of 3 denier fiber, 20% (by weight) of 2 denier fiber and 50% (by weight) of 5 denier fiber has an average fiber denier of (100/[(30/3)+(20/2)+(50/5)])=100/[10+10+10]=100/30=3.33 denier.
 
10) “Capillary pressure or Capillary Rise” is the highest level, vertically measured from the top surface of a liquid, reached by the liquid through a porous or a fibrous body or mass as a result of dipping a portion of the porous or fibrous body or mass into the liquid and allowing wicking action to take place until the liquid rise, above the surface of the liquid and through the porous or fibrous body or mass, reaches an equilibrium point (i.e., the point at which the liquid ceases to rise).
 
11) “Bonded fibrous mass” is a mass of fibers having at least a portion of its fibers attached, to each other at their contact and/or crossover points and thereby rendering the mass to act as a coherent body which may be handled or moved as a whole even when only a portion of the fibrous mass is moved. The fibers may be attached at their contact and/or crossover points cohesively or by using an adhesive. Cohesively attached fibers are attached to each other by a melting action occurring at the fiber surfaces at said contact and/or crossover points and co-solidification of the melted fiber surfaces upon cooling the fibers. In accordance with the present invention, adhesives used for bonding fibers in a bonded fibrous mass are of a non-absorbent and non-reactive nature to the air-scenting liquid held within the bonded fibrous mass and used for air-scenting.
 
12) “Liquid Volume Ratio” is the ratio of the volume of the air-scenting liquid held within the pores/capillaries/open cells of the porous fibrous mass to the total volume of the porous fibrous mass. For example a bonded porous fibrous mass in the form of a 1 inch×1 inch×1 inch cube containing 0.60 cubic inches of air-scenting liquid within its pores, has a fluid volume ratio of 0.6 or 60%.
 
13) “Dripping Liquid Mass of an Extent of a Bonded Porous Fibrous Mass (DML)” is the maximum mass of a liquid withheld entirely within the pores/capillaries/open cells of a bonded porous fibrous mass after initially soaking completely the fibrous mass in a pool of the liquid, removing it from the liquid pool and allowing it to drip, with its extent oriented parallel to the direction of gravitational force, until dripping ceases, i.e., equilibrium is reached and no dripping occurs.
 
14) “Fibrous Foam” is a network of interconnected fibers having bonds (adhesive and/or cohesive) between fibers having common contact points and joining said fibers at said common contact points and open spaces/pores/cells separating said fibers when the network of fibers is subjected to no externally-applied loading (tensile, compressive and/or shear forces), bending action/moment or torsional/twisting moment/torque. As such, a fibrous foam not subjected to any externally-applied load, bending action and/or twisting moment has a packing factor of less than 0.91 which is the maximum possible packing factor for the case of a fibrous mass made of circular cross-section fibers. The non-clogging resilient porous bonded fibrous foam/mass of the present invention has a packing factor within the range of 0.07 to 0.32.
 
15) “Packing Factor of a Fibrous Foam/Mass” is the ratio of the volume occupied by the fibers to the total external volume enveloping the fibrous foam/mass.
 
16) “Resilient Fibrous Foam/Mass” is a fibrous foam/mass, as defined above, which recovers—from a 30% lateral compressive deformation/strain imposed on the foam/mass and maintained for a period of one (1) minute—to at least 95% of its original (pre-deformation) dimensions within a period of one (1) minute from removal of said lateral compressive strain, i.e., has an unrecovered lateral deformation/strain of 5% or less.
 
17) “Intimately Blended Fibrous Mass” is a fibrous mass comprising at least two different types of fibers dispersed uniformly and randomly throughout the mass such that the probability of finding a particular type fiber at any location, within the fibrous mass, does not vary substantially from one location to another location.
 
18) “Tack Point or Temperature of a Fiber” is the lowest temperature at which the fiber, upon being folded and pressed against itself or upon being pressed against another object, would stick to itself or to the surface of the object against which it is pressed.
 
19) “Stress-Free Linear Thermal Shrinkage” is the negative change (final length−initial length) in length per unit length a fiber experiences upon being heated while it is placed on a horizontal surface and allowed to shrink under no external constraints. Expressed as a positive percentage, it is equal to [(Initial Fiber Length Before Heating−Final Fiber Length After Stress-Free Thermal Shrinkage Occurs)/(Initial Fiber Length Before Heating)]×(100).
 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows an air-scenting device of the prior art. 
         FIG. 2  shows an air scenting device of the prior aft. 
         FIG. 3  shows an isometric view of an embodiment of the device of the present invention. 
         FIG. 4  shows a longitudinal cross-sectional view of a container-type device of the present invention. 
         FIG. 5  shows a flat configuration of the device of the present invention. 
         FIG. 6  shows a cross-sectional view of the device shown in  FIG. 5 . 
         FIG. 7  shows an elongated (air-scenting reed) type of the device of the present invention. 
         FIG. 8  shows a cross-sectional view of a circular composite embodiment of the non-clogging fibrous foam of the present invention. 
         FIG. 9  shows a cross-sectional view of a flat composite embodiment of the non-clogging fibrous foam of the present invention. 
         FIG. 10  shows a representation of the non-clogging bonded fibrous foam/mass of the present invention. 
       FIG.  10 - a  shows two fibers, initially straight and of equal length, bonded together at two points. 
       FIG.  10 - b  shows the fibers shown in FIG.  10 - a  after being heated and forming open cell/spacing between the fibers. 
     
    
    
     BACKGROUND OF THE INVENTION 
       FIG. 1  shows an air-scenting device  1  of the Prior Art. As shown therein, it comprises a container or bottle  2  made of glass, non-reactive and non-absorbent plastics or metal. Container  2  is filled, at least partially, with a free-to-flow liquid mass  3  of an air-scenting liquid which may be a water-base, oil-base and/or solvent-base liquid. A wick  4  is placed into container  2 , usually in a substantially vertical orientation, and is partially immersed into liquid mass  3 . Wick  4  is usually guided/surrounded by a guide/spacer  5  through the neck  9  of container  2 . An air pressure equalization vent or hole  6  is provided in order to maintain the same air pressure inside of and outside of container  2 . A cap  7  is used for covering the top portion of wick  4  and sealing container  2  at sealing closure  8 . Upon removing cap  7 , the air-scenting liquid, contained within the pores of wick  4 , evaporates into the ambient air and scents the ambient air accordingly. Optionally, the top portion of wick  4  may be heated in order to accelerate the rate of evaporation of the air-scenting liquid. Also, optionally, a fan-type air blower is used for the same purpose of increasing the rate of evaporation of the air-scenting liquid. 
     Because of sealing closure  8 , no leakage or spillage occurs while transporting air-scenting device  1  and prior to removing cap  7 . On the other hand, some liquid may accumulate in space  10  between cap  7  and wick  4  which might contact the hand of the user of device  1  or drip on the floor upon removing cap  7 . Since a majority of air-scenting liquids have skin and/or eye irritating effects, extra care must be exercised by the user of device  1 . Also a dripping/dripped liquid, especially on a tile floor, may present a slipping and falling hazard to persons stepping on it or walking on it. 
     The air-scenting device of the present invention overcomes the above mentioned drawbacks of prior art air-scenting devices by containing no free-to-flow air-scenting liquid mass. Another drawback of the prior art air-scenting devices, which are designed to operate similarly, is that they can perform only in a substantially vertical orientation with the free-to-flow air-scenting liquid mass at the bottom of container  4 . Also, when turned upside down, device  1  tends to drip liquid  3 , through vent  6 , when the ambient temperature rises. The air-scenting device of the present invention overcomes these drawbacks and does not drip or leak any air-scenting liquid regardless of its orientation relative to the direction of the gravitational acceleration force. 
       FIG. 2  shows another air-scenting device  20  of the prior art. As shown therein, it comprises an initially sealed container  21  having a container lid  22  and a thin pierceable (i.e., may be pierced) membrane  23 . Container  21  contains free-to-flow air-scenting liquid mass  24 . As shown in  FIG. 2 , an air gap  21   a  exists between the planar top surface of liquid mass  24  and lid  22 . Container  21  is surrounded with a wick  25 , usually in the form of a sleeve which may be made of a fibrous material such as paper or a textile material or a sintered plastics particles. As shown in  FIG. 2 , the assembly of container  21  and wick  25  are placed into external cup  26 . Cup  26  has a trough or basin  27  which is impermeable and has a height  29 , as shown in  FIG. 2 , and membrane piercing tip  26   a  and an aperture zone  28 . Upon pushing membrane  23  against tip  26   a  and thereby piercing membrane  23  liquid  24  flows out of container  21  into basin  27  and rises to level  29   a  which, by design, is lower than height  29 . As a result of liquid  24  flowing out of container  21  into basin  27  the air pressure in air bubble  21   a  becomes lower than the surrounding atmospheric pressure and flow of liquid  24  stops. As air-scenting liquid gets absorbed by wick  25 , it evaporates into the ambient air and scents the surrounding air. Also, as the level of air scenting liquid in basin  27  gets lower, due to continuous wicking and evaporation, a certain low level  29   b  is reached where, similar to what occurs in a bottle-type water bubbler, an air bubble escapes through punctured membrane  23  into the interior of container  21  in order to re-establish a new pressure equilibrium between the interior of container  21  and the surrounding atmospheric pressure. Similar to device  1 , shown in  FIG. 1 , air scenting may, optionally be accelerated by the use of a fan-type blower. 
     Some of the drawbacks of air-scenting devices of the type shown n  FIG. 2  are that spillage occurs when the device is tilted and therefore, these devices must be kept vertically oriented once membrane  23  is pierced. Also, when the ambient temperature increases, the air pressure in air space  21   a  increases and additional liquid flows from container  21  into basin  27 , overflows beyond level  29 , and drips below the entire device. 
     The above description of prior art air-scenting devices is hereby incorporated in this present invention disclosure for the purpose of incorporating portions of it in future Continuation-in-Part patent applications and/or in future amendments of claims. 
     The air-scenting device of the present invention overcomes all of the above-mentioned drawbacks while providing a long lasting duration of scenting the ambient air at a nearly linear rate of releasing air freshening liquid into the surrounding environment. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Device 
       FIG. 3  shows an embodiment of the device of the present invention. As shown therein, non-dripping, and spillage and leakage-proof air-scenting device  30 , comprises the following elements/components which are described and arranged relative to each other as follows: 
     A) An initially-dry porous bonded fibrous mass  31 , having an initial dry mass MD, a volume V and an extent L, as shown in  FIG. 3 . Fibrous mass  31  has a dry density DD=(MD)/(V). Dry density DD may be within the range of 0.08 to 0.9 gram per cubic centimeter. A preferred range of dry density DD is within the range of 0.10 to 0.45 gram per cubic centimeter. In accordance with the present invention, fibrous mass  31  is non-reactive to and non-absorbent of the air-scenting liquid that is or that will be used for scenting the surrounding atmosphere. This is assured by selecting non-absorbent and non-reactive fibers (i.e., fibers that are non-absorbent of and inert to the air-scenting liquid that is or that will be used for scenting the surrounding atmosphere) for making fibrous mass  31 . Examples of such fibers are polypropylene, polyethylene, nylon and polyester fibers. As a result, and in accordance with the present invention, the air-scenting liquid mass is retained/held substantially entirely within the capillaries/open cells/interstices/pores of body  32  of fibrous mass  31  and in a squeezable liquid-phase. A squeezable liquid-phase means that the air-scenting liquid may be extracted, from the fibrous mass, by applying a squeezing action, on the fibrous mass, which is sufficient for extracting the air-scenting liquid, at least in droplet form, without resulting in disintegration of the fibrous mass holding the air-scenting liquid. 
     As compared to non-dripping prior art air-scenting devices, (for example parchment-type paper air-scenting devices used for scenting the interior of cars and trucks), the air-scenting device of the present invention retains the air-scenting liquid, stored in fibrous mass  31 , in a squeezable liquid-phase held substantially entirely within the open cells/pores of body  32  of fibrous mass  31 . 
     In accordance with the present invention, fibrous mass  31  is impregnated with a non-reactive air-scenting liquid (not shown) having a mass MF where MF is not exceeding the Dripping Liquid Mass (DML) of the specific combination of i) extent L of body  32 , ii) dry density DD of fibrous mass  31 , iii) the specifications and types of fibers from which fibrous mass  31  is made and iv) the selected air-scenting liquid. Accordingly, membrane, coating, enclosure or container  35 , shown in  FIG. 3 , contains no free-to-flow air-scenting liquid and the air-scenting liquid held within fibrous mass  31  is retained only in a squeezable liquid-phase and is held entirely within the open cells/capillaries of body  32  of fibrous mass  31  without dripping under the action of the gravitational force and regardless of the orientation of fibrous mass  31  or device  30  relative to the direction of the gravitational force, thereby making air-scenting device  30  non-dripping and spillage and leakage-proof. 
     The fibers comprising fibrous mass  31  are bonded to each other, either cohesively or using an adhesive that is non-reactive to and non-absorbent of (i.e., inert to) the air-scenting liquid that is stored in body  32  of fibrous mass  31 . An example of a non-reactive adhesive is water-base polyurethane adhesive which is readily available from a variety of suppliers. Fibrous mass  31  may be in any solid (three-dimensional) form or shape, including flat, cylindrical, prism, spherical, cubical, hollow or any other three dimensional shape, including profile-cut, embossed and sculptured shapes. 
     In accordance with the present invention, body  32 , (as impregnated with a mass MF of air-scenting liquid, where MF, as described earlier, is not exceeding Dripping Liquid Mass (DML)), of fibrous mass  31  serves the function of being a high capacity reservoir for holding, in a squeezable liquid-phase, the air-scenting liquid. 
     In an embodiment of the present invention, fibrous mass  31  is made of polyester fibers. Generally speaking, polyester fibers are inert to most water-base, solvent-base and oil air-scenting liquids. In accordance with the present invention the denier of fibers used for making fibrous mass  31  is within the range of 0.9 to 15 and preferably in the range of 0.9 to 6 denier. 
     For the same dry density DD of fibrous mass  31 , the use of finer fibers, for making fibrous mass  31 , usually results in a higher Capillary Rise/Capillary Pressure, higher Liquid Volume Ratio, higher Dripping Liquid Mass (DML) and a greater wicking action. 
     In accordance with the present invention, a variety of fiber blends may be used for making the feedstock slivers for making cohesively-bonded fibrous mass  31 , for example i) slivers weighing 4 gram per yard and made of a blend of bicomponent (Sheath-Core type) 2 denier polyester fibers having a weight of 50% and 4 denier regular polyester fibers having a weight of 50%. The sheath of the bicomponent fibers has a lower melting point than the core and than the regular polyester fibers. The melting point of the sheath of the bicomponent fibers is around 110 degrees Celsius and the melting points of the core of the bicomponent fibers and the regular polyester fibers are much higher, around 260 degrees Celsius. Such bicomponent fibers are readily available from a variety of suppliers and in a variety of deniers and colors, ii) slivers weighing 5 gram per yard and made of a blend of bicomponent (Sheath-Core type, as described above) 2 denier polyester fibers having a weight of 50% and 1.5 denier regular polyester fibers having a weight of 50%, and iii) slivers weighing 5 gram per yard and made of a blend of bicomponent (Sheath-Core type, as described above) 2 denier polyester fibers having a weight of 75 to 80% and 1.5 denier regular polyester fibers having a weight of 20 to 25%. An advantage of using a fiber blend with a higher %, by weight, of such bicomponent fibers is that the resulting bonded fibrous mass has higher rigidity and therefore is easier to handle in subsequent processes. The slivers used as feedstock material for making bonded fibrous mass  31  may be made on cotton/synthetic fiber cards or on woolen or worsted cards. Cotton/synthetic fiber cards are preferred though their use is usually limited to a relatively shorter staple fiber length, for example around 2 inches. 
     Other non-absorbent and non-reactive fibers, including regular and bicomponent type fibers may also be used, for example similar blends of regular and bicomponent polypropylene fibers. 
     In a preferred embodiment of the present invention, polyester fibers in the form of slivers (weighing 4 gram per yard and made of a blend of bicomponent (Sheath-Core type, as described above) 2 denier polyester fibers having a weight of 50% and 4 denier regular polyester fibers having a weight of 50% were used for making a tubular porous bonded fibrous mass having an outer diameter of 1.53 inch, an inner diameter of 0.5 inch, a length of 4 inch, an Extent L of 4.283 inch a dry mass (MD) of 17.8 gram and a dry density (DD) of 0.165 gram/cc. The bonded porous fibrous mass had a water and alcohol-base air scenting Dripping Liquid Mass of 90.1 gram and a saturated non-dripping weight of 107.9 gram and a saturated non-dripping density of 1.0024 gram/cc. The saturated non-dripping mass is defined as the summation of the dry mass of the fibrous mass plus the Dripping Liquid Mass (DML). The saturated non-dripping density is defined as the saturated non-dripping mass divided by the volume of the bonded fibrous mass. An analysis of the above data yields a Liquid Volume Ratio of 83.7%. This is an unexpected and unusually high Liquid Volume Ratio, especially as compared to air-scenting devices that utilize sintered plastic particles for holding the air-scenting liquid and or for wicking. 
     In another embodiment of the present invention polyester fibers in the form of slivers (weighing 5 gram per yard and made of a blend of bicomponent (Sheath-Core type, as described above) 2 denier polyester fibers having a weight of 75% and 1.5 denier regular polyester fibers having a weight of 25% were used for making a cylindrical porous bonded fibrous mass having an outer diameter of 3.00 inch, a length of 4.75 inch, an Extent L of 5.62 inch a dry mass (MD) of 92.0 gram and a dry density (DD) of 0.167 gram/cc. The bonded porous fibrous mass had a water and alcohol-base air scenting Dripping Liquid Mass of 309.7 gram and a saturated non-dripping weight of 401.7 gram and a saturated non-dripping density of 0.730 gram/cc. The saturated non-dripping mass is defined as the summation of the dry mass of the fibrous mass plus the Dripping Liquid Mass (DML). The saturated non-dripping density is defined as the saturated non-dripping mass divided by the volume of the bonded fibrous mass. An analysis of the above data yields a Liquid Volume Ratio of 56.28%. 
     In yet another relatively high dry density embodiment of fibrous mass  31  of the present invention, polyester fibers in the form of slivers (weighing 4 gram per yard and made of a blend of bicomponent (Sheath-Core type, as described above) 4 denier polyester fibers having a weight of 50% and 4 denier regular polyester fibers having a weight of 50% were used for making a rectangular cross-section (0.307 inch×0.357 inch) porous bonded fibrous mass having a length of 7.02 inch, an Extent L of 7.036 inch, a dry mass (MD) of 6.178 gram and a dry density (DD) of 0.49 gram/cc. The bonded porous fibrous mass had a water and alcohol-base air scenting Dripping Liquid Mass of 5.202 gram and a saturated non-dripping weight of 11.4 gram and a saturated non-dripping density of 0.90 gram/cc. The saturated non-dripping mass is defined as the summation of the dry mass of the fibrous mass plus the Dripping Liquid Mass (DML). The saturated non-dripping density is defined as the saturated non-dripping mass divided by the volume of the bonded fibrous mass. An analysis of the above data yields a Liquid Volume Ratio of 41.4%. 
     Fibrous mass  31  of device  30  may be impregnated with the air-scenting liquid by injection, soaking, dipping or spraying. 
     Polyester fibers, being non-reactive to and non-absorbent of most air-scenting liquids, are particularly preferred for making fibrous mass  31  since their use offers the following advantages; i) making the device of the present invention useful for water-base, alcohol-base, solvent-base and oil air-scenting liquids without absorption of and/or reaction with the fibers of the porous fibrous mass  31  and ii) increasing/maximizing the Dripping Liquid Mass (DML), the Liquid Volume Ratio and the air-scenting liquid holding capacity of the porous fibrous mass  31 , as compared to devices having the same dry density but made of fibers having lower density, such as polypropylene. (Density of polypropylene=0.91 gram/cc and density of Polyester=1.38 gram/cc). 
     In a process for making bonded fibrous mass  31 , feedstock slivers of staple polyester fibers (for example in blends as described above) are fed into a heat bonding (cohesive bonding) die. The bonding die has a feed/inlet zone, a heating zone, a tapered compaction zone and a shaping/cross-section-forming zone for making/shaping the final cross sectional shape of the bonded fibrous mass. The compaction zone, is preferably tapered at an angle of 10 degrees to 45 degrees, per side, relative to the axis of the die in order to provide more effective contact and higher heat transfer rate from the die body to the feedstock slivers thus effecting a calendaring or glazing action that renders the exterior surface, of the bonded fibrous mass, having higher capillary rise and/or a higher density than the interior of the fibrous mass. Dragging of the feedstock fibers against the interior surface of the die causes the fibers on the exterior surface of the bonded fibrous mass to have a higher fiber orientation index. In other embodiments, the feedstock slivers or needle punched nonwoven sheets may be arranged in layers which may be parallel flat layers or concentric circles having outer layer(s) made of finer fibers (lower denier). The heating zone of the die is fed and filled with hot steam or hot air at a temperature of approximately 200 to 220 degrees Fahrenheit and the feedstock is pulled through the die. Cohesive bonding between the fibers occurs inside the die. The pulled bonded fibrous mass is subsequently cut to a desired length. 
     Alternatively, the fibrous feedstock is adhesively bonded by dipping it into an adhesive bath, feeding it through a squeezing die and subsequently into a shaping die and curing the adhesive. This process is also known in the art as Pultrusion. 
     Optionally, the surface of fibrous mass  31  is treated/coated with a surfactant. An example of a surfactant that may be used for coating the exterior surface of fibrous mass  31  is sold by Sybron Chemicals, Inc., under the Tradename of TANAWET RCN. Other surfactants are readily available from other suppliers. In some applications of the present invention, the entire fibrous mass may be soaked into a 1% concentration surfactant in order to enhance the wicking rate of the air-scenting liquid contained inside the fibrous mass. 
     Fibrous mass  31  has a body  32  and an exterior surface  33 . Body  32  has a capillary pressure BCP, a mass density MDB, an average fiber denier FDB, and a fiber orientation index FOIB relative to an axis or a direction. The exterior surface  33  comprises surface segments  34 . Surface segments  34  have at least one of i) a capillary pressure SCP, where SCP is higher than said capillary pressure BCP, ii) a mass density of MDSG (gram/cubic centimeter) where MDSG is higher than said mass density MDB, iii) an average fiber denier FDSG where FDSG is lower than said FDB, iv) fiber orientation/alignment index FOISG where FOISG is higher than said FOIB as measured relative to said axis or direction, and v) a surfactant coating applied to said surface segments. 
     B) As shown in  FIG. 3 , portion(s)  36  of surface segment(s)  34  are covered with or contained in a liquid-impermeable membrane, coating, enclosure or container  35 . Membrane, coating, enclosure or container  35  is made of a material which is non-reactive to and non-absorbent of the air-scenting liquid used for impregnating fibrous mass  31 . The mass of air-scenting liquid (MF) impregnated into fibrous mass  31  is not exceeding the Dripping Liquid Mass (MDL) of the specific combination of i) extent L of body  32 , ii) dry density DD of fibrous mass  31 , iii) the specifications and types of fibers from which fibrous mass  31  is made and iv) the selected air-scenting liquid. Additionally, and in accordance with the present invention, liquid-impermeable membrane, enclosure or container  35  contains no free-to-flow liquid mass. 
     Membrane, coating, enclosure or container  35  is adapted to cover predetermined portion(s)  36  of surface segment(s)  34  and to allow certain remaining segment(s)  37  to be uncovered or to remain uncovered, thereby i) allowing a predetermined rate of evaporation of the air-scenting liquid-upon impregnating fibrous mass  31  with said air-scenting liquid and exposing/uncovering said remaining portion(s)  37  of said surface segment(s)  34  to surrounding atmosphere- to occur through said remaining portion(s)  37  of said surface segment(s)  34  and ii) controlling the rate of release of the air-scenting liquid into the surrounding atmosphere. 
     Examples of membrane  35 , wrapped around the exterior of fibrous mass  31 , are polyethylene, polyester and polypropylene films, including heat-shrink-type wrapping films, preferably in a thickness in the range of 0.001 inch to 0.006 inch. Membrane  35  may also have surface discontinuities such as perforations, microperforations, or slits or have no surface discontinuities. Membrane  35  may be wrapped around fibrous mass  31  and heat sealed to itself and/or onto fibrous mass  31 , stapled into fibrous mass  31 , or ultrasonically sealed to itself and/or attached to fibrous mass  31 . 
     Alternatively, an example of coating  35  is a water-base polyurethane coating which is self curing and may be partially applied onto the surface of fibrous mass  31  by brushing, spraying, quick dipping or other methods. Also, alternatively, container or enclosure  35  may be made of plastics materials, non-corroding metals or glass. 
     As such, the combination of impregnated fibrous mass  31 , as described above, and membrane, coating, enclosure or container  35 , as described above, constitute the device of the present invention which features the following novel and distinguishing combination: 
     1) Absence of any free-to-flow air-scenting liquid in the entire device and therefore a non-dripping and spillage and leakage-proof air-scenting device and method, regardless of the orientation of the device. This is made possible by impregnating fibrous mass  31  with a mass (MF) of air-scenting liquid where (MF) is not exceeding the Dripping Liquid Mass (DML) of the specific combination of i) extent L of body  32 , ii) dry density DD of fibrous mass  31 , iii) the specifications and types of fibers from which fibrous mass  31  is made and iv) the selected air-scenting liquid,
 
2) A novel combination of i) low dry density of fibrous mass  31 , preferably within the range of 0.1 to 0.45 gram/cc, and ii) use of fine (low denier) fibers, preferably within the range of 0.9 to 6 denier, made from materials having density within the range of 1.1 to 1.4 gram/cc, thus resulting in body  32 , of fibrous mass  31 , having a high Liquid Volume Ratio that enables it (body  32 ) to function as a high capacity reservoir of air-scenting liquid and therefore long lasting/long duration of operation of device  30 . In a preferred embodiment of the device of the present invention the Liquid Volume Ratio is in the range of 40% to 87%.
 
3) Large open cells/pores/capillaries and therefore non-clogging performance throughout the duration of operation of the device. Such large open cells and non-clogging performance of device  31  are another result of the novel combination of i) low dry density of fibrous mass  31 , preferably within the range of 0.1 to 0.45 gram/cc, ii) use of fine (low denier) fibers, preferably within the range of 0.9 to 6 denier, made from materials having density within the range of 1.1 to 1.4 gram/cc and iii) a high Liquid Volume Ratio of body  32  of fibrous mass  31 ,
 
4) Controllable rate of release of air-scenting liquid, by allowing release and evaporation of the air-scenting liquid from pre-determined exposed or adapted to be exposed surface segments,
 
5) Nearly linear rate of release of the air-scenting liquid, and
 
6) Availability in any solid (three-dimensional) form or shape, including flat, cylindrical, prism, spherical, cubical, hollow or any other three dimensional shape, including profile-cut, embossed and sculptured shapes.
 
       FIG. 4  shows another embodiment  40  of the air-scenting device of the present invention. As shown therein, air scenting device  40  comprises an initially dry non-clogging porous bonded fibrous mass  41 , made in accordance with the teachings of the present invention, in the form of a cylinder having surface segments  41 - a . In comparison to the body (interior) of bonded fibrous mass  41 , surface segments  41 - a  have at least one of i) higher capillary pressure, ii) higher mass density, iii) lower average fiber denier, iv) higher fiber orientation index relative to the axis of the cylinder and v) a surfactant coating. As shown in  FIG. 4 , fibrous mass  41  is partially wrapped with impermeable membrane  42  which covers a portion of its exterior surface and leaves an uncovered portion  41 - b . As desired and as a means for controlling the rate of evaporation of the air scenting liquid from device  40 , the area of uncovered portion  41 - b , of the exterior surface of fibrous mass  41 , may be increased or decreased. Alternatively and/or additionally impermeable membrane  42  may be perforated as desired in order to allow evaporation of the air-scenting liquid through the perforated areas or holes. Bonded fibrous mass  41  is impregnated with an air-scenting liquid mass not exceeding the Dripping Liquid Mass (DML) of the extent of bonded porous fibrous mass  41 . Fibrous mass  41  is held by holder  44 . Holder  44  may take a variety of shapes, forms and dimensions. As shown in  FIG. 4 , holder  44  is in the form of a bottle cap having a threaded interior to engage with the threaded top of external container  49 . Holder  44  is also adapted to have projection  45  which engages with the top end of cylindrical pin  43 - a  of encapsulating member  43 , thereby encapsulating bonded fibrous mass  41 . Prior to use, cap  44  and external container  49  provide a sealed containment means for air-scenting liquid-impregnated body  41 . To use device  40  for air-scenting, container  49  is removed and cap  44 , acting as a holder of body  41  is suspended in the space to be air-scented. A variety of means are possible for suspending device  40 . As shown in  FIG. 4 , cap  44  is adapted to have a peripheral extension  46  with at least one hole  47  adapted to receive hook  48  anchored to surface, wall, or device enclosure body  48 - b . To avoid contacting the air-scenting liquid contained within body  41 , device  41 , as received, i.e., with container  49  fully engaged with cap  44 , is first suspended by engaging hook  48  into hole  47  of extension  46 . Next, the user of device  40  swings device  40  in direction of arrow R, shown in  FIG. 4 , untwists, slides and removes away container  49  and allows the device to swing back to its intended orientation. Alternatively, holding cap  44  may be adapted with two parallel non-conductive electric outlet-type prongs ( 46 - b ) which may be inserted in a standard electric outlet. Also alternatively, holder  44  may be adapted to have a hook  46 - a  which may be used for suspending device  40  from rod or pin  48 - a.    
       FIG. 5  shows a flat embodiment of the device of the present invention. As shown therein and in  FIG. 6 , device  50  comprises non-clogging bonded porous fibrous mass  51  which is impregnated with a mass of air-scenting liquid not exceeding the dripping liquid mass of its extent. As compared to the interior of body  51 , outer surface segments  51 - a  have at least one of i) higher capillary pressure, ii) higher mass density, iii) lower average fiber denier, iv) higher fiber orientation index relative to the axis of device  50  and v) a surfactant coating. Impregnated bonded fibrous mass  51  is enclosed between two layers of impermeable membranes  52  which are sealed around their perimeter in order to provide a sealed enclosure for air-scenting liquid-impregnated fibrous mass  51 . At least one side of impermeable membranes  52  has at least one opening/aperture  54  which is initially covered by removable/peelable impermeable linear  53 . Membranes  52  may be adapted to have an extension  56  and a hook  56 - a  for adapting device  50  for suspension onto pin or rod  58 . To use air-scenting device  50 , the user holds tab  57  and peels liner  54  thereby allowing the evaporation of the air-scenting liquid through aperture  53 . 
       FIG. 7  shows another embodiment of the device of the present invention in the form of an air-scenting reed  70 . As shown therein, reed  70  comprises a non-clogging porous bonded fibrous mass  71  which is partially covered by impermeable membrane  72 . As compared to interior of body of fibrous mass  71 , outer surface segments  71 - a  have at least one of i) higher capillary pressure, ii) higher mass density, iii) lower average fiber denier, iv) higher fiber orientation index relative to the axis of the reed and v) a surfactant coating. Additionally, to increase the rate of evaporation of the air-scenting liquid contained within the pores of bonded fibrous mass  71 , membrane  72  may also have perforations  73  at locations as desired or preferred. The end of reed  70  may be cut in a plane A perpendicular to its axis, as shown in  FIG. 7  where angle q is 90 degrees. Alternatively, a beveled cut may be desirable for which angle, q may be larger than or smaller than 90 degrees. 
       FIGS. 8 and 9  show cross-sectional views of alternative constructions of the non-clogging bonded porous fibrous mass.  FIG. 8  shows a cross section of a cylindrical configuration porous bonded fibrous mass  71  comprising an external bonded porous fibrous region  71 - a  and a core/interior bonded fibrous region  71 - b . In accordance with the present invention, fibrous regions  71 - a  and  71 - b  may have different capillary pressures, mass densities, average fiber deniers, fiber orientation indexes and/or surface coatings. 
     Similarly, as shown in  FIG. 9 , flat configuration porous bonded fibrous mass  51  comprising an external bonded porous fibrous regions  51 - a  and interior bonded fibrous region  51 - b . In accordance with the present invention, fibrous regions  51 - a  and  51 - b  may have different capillary pressures, mass densities, average fiber deniers, fiber orientation indexes and/or surface coatings. 
     Method 
     In accordance with the present invention, with reference to  FIG. 3  and with reference to and incorporation, by reference and in its entirety, of the above section, titled DEVICE, a non-dripping and spillage and leakage-proof air-scenting method comprises the following steps: 
     1) Providing an initially-dry porous bonded fibrous mass ( 31 ), said fibrous mass having an initial dry mass MD, an extent L and a volume V, said fibrous mass having a body B ( 32 ) and an exterior surface S ( 33 ), said body having a capillary pressure BCP, a mass density MDB, an average fiber denier FDB, a fiber orientation index FOIB relative to an axis or a direction, said exterior surface S ( 33 ) comprising surface segments SG ( 34 ), said surface segments SG ( 34 ) having at least one of i) a capillary pressure SCP, where SCP is higher than said capillary pressure BCP, ii) a mass density of MDSG (gram/cubic centimeter) where MDSG is higher than said mass density MDB, iii) an average fiber denier FDSG where FDSG is lower than said FDB, iv) fiber orientation/alignment index FOISG where FOISG is higher than said FOIB as measured relative to said axis or direction, and v) a surfactant coating applied to said surface segments SG ( 34 ),
 
2) Covering or containing a portion P ( 36 ) of said surface segments SG ( 34 ) with a liquid-impermeable membrane or enclosure or within a container E ( 35 ), said membrane, enclosure or container containing no free-to-flow liquid mass, and adapting the remaining portion RSG ( 37 ), of said surface segments SG ( 34 ), to be or to remain uncovered, thereby i) allowing a predetermined rate of evaporation of an air-scenting liquid-upon impregnating said fibrous mass with said air-scenting liquid and exposing/uncovering said remaining portion RSG ( 37 ) of said surface segments to surrounding atmosphere- to occur through said remaining portion RSG ( 37 ) of said surface segments SG ( 34 ) and ii) controlling the rate of release of said air-scenting liquid into said surrounding atmosphere, said fibrous mass and said membrane, enclosure or container E ( 35 ) being non-reactive (inert) to and non-absorbent of said air scenting liquid, and
 
3) Impregnating said fibrous mass with said air-scenting liquid of mass MF where MF is not exceeding the dripping liquid mass DML of said extent L of said body, thus retaining said air-scenting liquid in a squeezable liquid-phase and held entirely within the open cells/pores/capillaries of said body of said fibrous mass without dripping under the action of the gravitational force and regardless of the orientation of said fibrous mass relative to the direction of the gravitational force, thereby making said air-scenting method non-dripping and spillage and leakage-proof.
 
     In accordance with the present invention, a linear rate (or a constant rate) of releasing air freshening/scenting liquid/vapor, means that the rate of release and evaporation of the air-scenting liquid during the period starting after the first 10% of the recommended/design duration, of use and ending upon reaching 90% of the recommended duration of use is substantially constant. 
     For example, a nearly linear/constant rate air scenting device having a nearly linear rate of release of air-scenting liquid and a designed/recommended use period of 30 days has a nearly constant rate of release of air-scenting liquid starting from about the 4 th  day of use through the end of the 27th th  day of use. Naturally, in actual use, and due to fluctuations in ambient conditions, the rate of release and evaporation of the air-scenting fluid, though characterized as nearly linear, fluctuates within a range of about +/−15% of the average release and evaporation rate of the air-scenting liquid.