TABLE 5                                                          ______________________________________                                         ESCA Analysis of Nonwoven Webs                                                 Concentration in Atom-%                                                        Found              Calculated                                                  Web     Si     C         N   Si      C    N                                    ______________________________________                                         B       10.0   68.2      1.8 12.6    55.1 2.1                                  D       10.4   67.8      1.9 12.6    55.1 2.1                                  E       11.0   68.0      1.9 12.7    55.3 2.1                                  F       12.0   67.0      2.2 12.7    55.3 2.1                                  G       12.0   66.8      1.9 12.7    55.3 2.1                                  H       10.0   68.0      1.5 11.2    57.9 1.8                                  J       10.5   67.8      1.6 11.2    57.9 1.8                                  K       10.0   62.4      1.5 10.2    59.8 1.7                                  M       10.0   62.6      1.6 10.2    59.8 1.7                                  N       10.0   62.4      1.6 10.2    59.8 1.7                                  O       11.5   64.4      1.8 12.1    61.2 2.0                                  Q       11.8   65.2      1.9 12.1    61.2 2.0                                  R       12.0   64.6      1.9 12.1    61.2 2.0                                  S       14.0   65.0      2.3 --      --   --                                   ______________________________________

It is evident from Table 5 that a substantial portion of the surfaces of the fibers of the nonwoven webs studied consists of the antimicrobial compound present in the thermoplastic composition from which the webs were prepared. That is, the compounds of the present invention appear to have surface segregated to a remarkable and unexpected degree.
In an effort to aid in the visualization of the effectiveness or completeness of such surface segregation, the ratios of silicon found to theoretical silicon and nitrogen found to theoretical nitrogen were calculated from the data in Table 5 as follows:

Si=100×(silicon conc'n. found/theoretical silicon conc'n.)

N=100×(nitrogen conc'n. found/theoretical nitrogen conc'n.)

Thus, the calculations give the ESCA value of either silicon or nitrogen as a percentage of the theoretical value for that element. These calculations are summarized in Table 6, which also includes the data from Table 4 for convenience.
 TABLE 6                                                          ______________________________________                                         Silicon and Nitrogen Ratios from ESCA Data                                     Compound and Level Found:Calc'd. Ratios                                        Web    Compound  Weight-%   Silicon                                                                               Nitrogen                                    ______________________________________                                         B      II        0.5        79     86                                          D      II        1.0        83     90                                          E      III       0.5        87     90                                          F      III       0.7        94     100                                         G      III       1.0        94     90                                          H      IV        0.5        89     83                                          J      IV        1.0        94     89                                          K      IX        0.5        98     88                                          M      IX        1.0        98     94                                          N      IX        1.5        98     94                                          O      X         0.5        95     90                                          Q      X         1.0        98     95                                          R      X         1.5        99     95                                          ______________________________________

The data in Table 6 were plotted as bar graphs, grouped by compound number, and are presented as FIGS. 11-15, inclusive. Thus, FIG. 11 is a bar graph of the silicon and nitrogen ESCA values for Compound II at levels of 0.5% and 1.0% by weight, expressed as a percentage of the theoretical values, i.e., the data for webs B and D. FIG. 12 is a bar graph of the data for webs E, F, and G; FIG. 13 is a bar graph of the data for webs H and J; FIG. 14 is a bar graph of the data for webs K, M, and N; and FIG. 15 is a bar graph of the data for webs O, Q, and R.
 The basis for the statement above that the compounds of the present invention surface segregate to a remarkable and unexpected degree is clear from Table 6 and FIGS. 11-15. If the surfaces of the fibers of the nonwoven webs were completely covered by or with an antimicrobial compound of the present invention, the ESCA values for silicon and nitrogen would be equal to the theoretical values. Stated differently, the ESCA values would be equal to the theoretical values if the antimicrobial compound were present on the surfaces of the fibers to an approximate depth of 100 Å. Even with the experimental error inherent in ESCA analyses, the 100-Å portion of the fiber surfaces measured by ESCA consist essentially of antimicrobial compound. Equally significant is the fact that essentially complete coverage of the fiber surfaces was obtained with several compounds even at levels of 0.5 percent by weight. For those compounds, it is evident that lower levels can be used without sacrificing the antimicrobial activity of the nonwoven webs.
The fact that the antimicrobial compounds are found in such high concentrations to a depth of 100 Å (and possibly deeper) strongly suggests that the antimicrobial properties demonstrated to be present at the surfaces of the fibers are likely to be durable. That is, such compounds form an extended antimicrobial surface, i.e., an antimicrobial surface which extends below the air/fiber interfacial surface. Because of the high concentrations of antimicrobial compounds near (i.e., within 100 Å of) the fiber interfacial surfaces, compound which may be removed from the interfacial surface by dissolution in a solvent or other process can be replenished from the extended surface reservoir of antimicrobial compound.
 EXAMPLE 14 Antimicrobial Activities of the Nonwoven Webs of Example 13

The bacterial strains Escherichia coli (ATCC No. 13706) and Staphylococcus epidermidis (ATCC No. 1859) were used to evaluate the antibacterial activity of the nonwoven webs prepared in Example 13. Bacterial suspensions containing about 10⁸ colony forming units (CFU's) per ml were obtained by collecting overnight growth from tryptic soy agar (Difco, USA) in saline.
 Each web was cut into 1"×1" (about 2.5 cm×2.5 cm) samples. Each sample was placed in a 50-ml centrifuge tube, to which was added 100 μl of a bacterial stock suspension containing 2.8×10⁸ CFU's/ml. Samples were left at ambient temperature for four hours. At the end of the four-hour period, 30 ml of Letheen broth (Difco, USA) was added to each centrifuge tube. The tubes were vortexed at a setting of 4 G for one minute. The survival of bacteria in the presence of the nonwoven web was determined as described in Example 11. The antibacterial activities of the webs of Example 13 are summarized in Table

                  TABLE 7                                                          ______________________________________                                         Antibacterial Activities of the Nonwoven Webs of                               Example 13 Reported as Log Drop Values                                                Log Drop Values for Bacterial Strain                                    Web      Escherichia Coli                                                                           Staphylococcus Epidermidis                                ______________________________________                                         A        No Change   No Change                                                 B        1.2         1.9                                                       C        1.2         1.9                                                       D        1.8         2.2                                                       E        1.6         2.2                                                       F        1.6         2.2                                                       G        1.8         2.3                                                       H        3.1         3.8                                                       I        3.1         3.8                                                       J        3.5         4.0                                                       K        3.8         4.4                                                       L        3.8         4.4                                                       M        4.0         4.5                                                       N        4.1         4.5                                                       O        3.8         4.4                                                       P        3.8         4.4                                                       Q        4.1         4.5                                                       R        4.1         4.5                                                       S        0.9         1.6                                                       ______________________________________

A careful study of the data in Table 7 makes it clear that the compounds previously demonstrated to be at the surfaces of the fibers making up the nonwoven webs are effective as antimicrobial agents. In order to assist in the visualization and appreciation of the data, however, two bar graphs were prepared and are included as FIGS. 16 and 17. FIG. 16 is a three-dimensional bar graph of the log drop data for Escherichia coli, with the data being grouped by compound level; the figure also includes the log drop data for the compounds in solution and the topically applied compound. FIG. 17 is similar to FIG. 16, except that the log drop data are for Staphylococcus epidermidis.
 FIGS. 16 and 17, in conjunction with Table 7, clearly support at least the following conclusions:

(1) all of the internally incorporated compounds resulted in fibers having antimicrobial activity as good as or better than the topically applied compound;

(2) of the five compounds investigated as internal additives, Compounds IV, IX, and X were more effective in imparting antimicrobial properties to the surfaces of the fibers;

(3) Compound IV was almost as effective as an internal additive as when used in solution;

(4) Compounds IX and X were as effective or more effective as internal additives as when used in solution; and

(5) the effectiveness of Compounds IX and X as internal additives does not appear to be concentration dependent at the levels studied.
Two particularly interesting aspects of FIGS. 16 and 17 are worthy of further comment. First, FIGS. 16 and 17 dramatically illustrate the relatively constant high effectiveness of Compounds IX and X. Consequently, levels of these compounds below 0.5 percent by weight clearly can be used. Based on the increases in effectiveness with increasing concentration of all five compounds, levels as low as 0.1 percent by weight should be feasible. Depending on the level of antimicrobial activity desired, even lower levels probably can be used. Although levels above 1.5 percent by weight also can be used, significant increases in antimicrobial activity would not be expected. However, such higher levels may be useful in instances where it is desired to provide a reservoir of antimicrobial compound at the surfaces of the fibers of the nonwoven webs. Thus, levels of from about 0.1 to about 3 percent by weight represent a practical range.
 Second, the increases in log drop for Compounds II, III, and IV are generally similar. Moreover, the antimicrobial effectiveness of each of these compounds when incorporated into a nonwoven web appears to be directly proportional to the thermal stability of the compound. That is, the compounds having higher thermal decomposition also resulted in lower antimicrobial activity, even though such activity still is equal to or greater than the activity of the topically applied compound.
The antimicrobial activity of the compounds, when incorporated into nonwoven webs, is less than what have been expected, based only on the ESCA analyses; compare FIGS. 11-13 with FIGS. 16 and 17 (or compare Tables 5 and 6 with Table 7). This is particularly true for compounds II and III. While the ESCA analyses gave values for silicon and nitrogen which were at least 80 percent of the theoretical values, the differences in log drop values were much greater. For example, the log drop values for Compound II with E. coli and S. epidermidis were 3.5 and 4.0 respectively (see Table 1). The corresponding log drop values obtained upon incorporating Compound II into the fibers of a nonwoven web, however, were lower by approximately 2 (1.7-2.3 and 1.8-2.1, respectively). The log drop values for Compound III with E. coli and S. epidermidis were 3.5 and 4.1 respectively (see Table 1). The corresponding log drop values obtained upon incorporating Compound III into the fibers of a nonwoven web also were lower by approximately 2 (1.7-1.9 and 1.8-1.9, respectively). Since each log drop unit represents a ten-fold difference, the lower log drop values just described represent an approximately 100-fold difference.
 The explanation for the apparent anomaly between the antimicrobial effectiveness observed upon incorporating Compounds II and III into nonwoven webs and the ESCA data is believed to be based on the nature of the products which result upon the thermal degradation of these compounds. Based on thermogravimetric analyses or TGA (not reported), it was determined that the compounds of the present invention in general did not undergo significant weight loss upon being heated to approximately 230° C. From the results described in Example 12 , it is clear that Compounds II and III do, in fact, experience some thermal degradation. Because of the TGA results, however, it appears that the thermal degradation products are not significantly volatile under the conditions encountered in the melt-extrusion process, even though no attempt was made to characterize or identify such products. It is assumed, therefore, that such products are at least in part carried to the surfaces of the fibers, or that degradation occurs at the surfaces of the fibers, and such products lack antimicrobial properties sufficient to have an effect upon the antimicrobial effectiveness of the nonwoven webs. However, the presence of degradation products at the surfaces of the fibers still would contribute to the silicon and nitrogen values observed by ESCA analyses. FIGS. 16 and 17 make it clear that the effect of thermal degradation, whenever it occurs, can be partially offset by increasing the level of the compound in the thermoplastic composition from which the nonwoven web is prepared. Whenever permitted by process requirements, reducing melt extrusion temperatures and/or residence times in the melt will contribute to reducing the extent of thermal degradation.
 While the specification has been described in detail with respect to specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. Accordingly, the scope of the present invention should be assessed as that of the appended claims and any equivalents thereto.
 What is claimed is:
 1.  2. The method of claim 1, in which said molten composition is extruded at a shear rate of from about 50 to about 30,000 sec⁻¹ and a throughput of no more than about 5.4 kg/cm/hour.
3. The method of claim 1, in which Z is a monovalent group having the general formula, ##STR22## in which each of R₁₂ -R₁₄ is an independently selected monovalent alkyl group wherein the total number of carbon atoms in all of R₁₂ -R₁₄ is from about 6 to about 28 and at least one of R₁₂ -R₁₄ contains at least about 6 carbon atoms in a single continuous chain.
4. The method of claim 1, in which Z is a monovalent group having the general formula, ##STR23## in which each of R₁₅ -R₁₉ is a monovalent group independently selected from the group consisting of hydrogen and alkyl, and wherein the total number of carbon atoms in all of R₁₅ -R₁₉ is from about 8 to about 23, with at least one of R₁₅ -R₁₉ having at least about 6 carbon atoms in a single continuous chain.
5. The method of claim 4, in which each of R₁₅, R₁₆, R₁₈, and R₁₉ is hydrogen and R₁₇ is hexadecyl.
6. The method of claim 1, in which each of Y₁ and Y₂ independently is selected from the group consisting of a weak base.
 7. The method of claim 1, in which said additive has the formula, ##STR24##
 8. The method of claim 1, in which said additive has the formula, ##STR25##
 9. The method of claim 1, in which said additive has the formula, ##STR26##
 10. The method of claim 1, in which said additive is present in said melt-extrudable composition at a level of from about 0.1 to about 3 percent by weight, based on the weight of the thermoplastic polyolefin.
11. The method of claim 1, in which said thermoplastic polyolefin is polyethylene or polypropylene..
