ROOT-REPELLING PIPE JOINTS

Introduction

U.S. patent application Serial Number 555,113 is directed to the long term control of root growth to prevent intrusion of roots into unwanted areas. One of the embodiments disclosed therein is the prevention of intrusion into underground pipelines, particularly storm sewers, domestic sewage lines, septic tank drain fields, and so forth. This application is a more detailed embodi- ment of that portion of the above application.

It is well known that the intrusion of roots into underground lines presents a serious problem in many situa¬ tions. This is particularly true in the case of sewage lines because of the nutrient materials which are present and which encourage growth of roots within the pipes, frequently clogging them. Various varieties of willows are notoriously troublesome but many other plants likewise create problems.

Summary of the Invention This invention involves the exclusion of roots by positioning, in the joints of the pipes, an organic polymer mixed with a dinitroaniline. The dinitroaniline slowly diffuses from the polymer at a sufficient rate to keep roots away from the joints, but sufficiently slowly to cause the protection to last for many years. At the same time, the dinitroanilines, as a class, do not trans¬ locate within the plants and kill them, as do other herbi¬ cides, such as 2,4-dichlorophenoxy acetic acid (2,4-D). The preferred dinitroaniline is N,N-di-n-propyl-4-trifluoro- methyl-2,6-dinitroaniline, having the common name tri- fluralin and sold under the trademark Treflan.

In applications such as drainage pipes and septic tank drain fields where sealing is not required at the joints, a suitable polymer is polyethylene. However, in applications such as sewer lines where sealing is desired, it is preferable to use elastomeric gaskets.

The preferred elastomer is a mixture of natural rubber and synthetic polyisoprene (natural rubber is com¬ posed largely .of polyisoprene). Other suitable elastomers are styrene-butadiene rubbers (SRB), butyl rubber, chloro- prenes, nitril rubbers (NBR), ethylene-propylene, or olefin elastomers (EPM,EPDM) , chlorosulfonated polyethylene, aer late-butadienes, the thermoplastic elastomers such as those sold under the trade name "Santoprene", for instance the "dynamically vulcanized" mixture of thermo- plastic polyolefins and vulcanized mono-olefin copolymers disclosed in U.S. Patent 4,130,535.

Brief Description of Drawing

In the drawing. Figure 1, is a perspective view of an experimental setup testing the invention. Figures la and lb are perspective views of the end of the experi¬ mental setup of Figure.1. Figure 2 is a cross section of a ring containing a uniform distribution of herbicide. Figure 3 is a cross section of a gasket containing small pellets of the polyethylene-herbicide mixture. Figure 4 is a cross section of a gasket containing a core of polyethylene-herbicide. Figure 5 is a longitudinal section of a pipe joint comprising one of our gaskets.

Detailed Description

Basically this invention involves the use of annular bodies of organic polymer mixed with a dinitroaniline which are inserted in pipe joints to prevent penetration by roots.

In applications such as drainage pipes and septic tank drain fields, the polymer can be polyethylene. Since

sealing is not required in these situations, the elasticity of the material is not important. Therefore, the polyeth¬ ylene can contain from 2 to 30% dintroaniline, preferably trifluralin. A simple cross section of a ring for use in this situation is shown in Figure 2. In this case it may be a simple- mixture of the dinitroaniline with either high or low density polyethylene and, preferably, carbon black. While we have shown, in Figure 2, a circular cross section, this is simply for convenience, and the actual cross section may be whatever is most convenient for the above application. The effective life of a material consisting of polyethylene containing uniformly distributed 25% trifluralin and 25% carbon black will be from 50 to 100 years for a ring having a cross section of 1/4 sq. in. Rings of smaller cross section, those containing lower proportions of the herbicide, or dinitroanilines having a higher diffusion rate in polyethylene than tri¬ fluralin will give a lower lifetime.

When the joints are in sewer lines or other under- ground lines which require sealed joints, the ring must be of an elastic gasket material. A preferred mixture is synthetic polyisoprene or a mixture of synthetic polyi¬ soprene with natural rubber (which is primarily a natural polyisoprene). In these circumstances, the amount of trifluralin given above has been found .to adversely affect the elasticity of the gasket material and the amount is therefore limited to an upper limit of 5% by weight. We have therefore conducted experiments with this and smaller proportions in order to obtain data in this lower concentration.

Specifically we have run tests on polyisoprene containing uniformly disseminated trifluralin in the propor¬ tions of 1.0% and 5.0% (proportions of 0.5% or less were found to be ineffective) . Based on in vitro extraction experiments and correlating them with comparisons of ij

vitro and in vivo experiments carried out on polyethylene pellets, it appears that the effective lifetime for root repellency will vary from 18 years for a small gasket containing 1.0% trifluralin to 69 1/2 years for a large gasket containing 5.0% trifluralin.

In Figure 1, we have shown a "microcosm assembly" which is used to test under greenhouse conditions the effectiveness of gaskets prepared as above. Referring to Figure 1 a box tube having one side 4 made of clear plastic and the other sides of marine plywood was con¬ structed. A hinged plywood door 6 fitted over the clear panel 4 so as to shut off light, but permit opening for inspection. Within the box was a 20cm (8 inch) PVC elbow fitted with a 1.6cm (5/8 inch) diameter cap. The gasket was attached by a clear silicone adhesive to the transparent panel. The box was filled with soil. The gasket 10 was perforated at three locations (both sides and top) to permit water contained within the pipe to enter the other¬ wise dry soil. The holes in the gasket were 0.63 cm (1/4 inch) in diameter to optimize the potential for penetration of roots through the gasket into the pipe. Several radial series 12 of plugged holes are provided in the clear panel 4 to facilitate the taking of samples. The box 2 was filled with soil and planted with yellow willow (Salix alba variety Vitellina), a rather aggressively rooting variety of willows.

Twelve "microcosm assemblies" were fabricated. Each contained a polyisoprene gasket impregnated with uniformly disseminated trifluralin. There were three replicates each containing 0.0%, 0.5%, 1% and 5% triflura¬ lin. At the time of preparation of this application, they had been completed and functional for nearly three years. Figures la and lb show the approximate conditions. of roots 16 and the assemblies having untreated gaskets and those containing 5% trifluralin respectively. It

will be seen from Figure la that roots have penetrated through the drilled holes in the gasket to the interior of the elbow 8. In Figure lb, on the other hand, no roots have entered; all are on the exterior of the elbow. In Figures 2, 3, and 4, we have shown various distributions of the trifluralin in gasket material. Figure 2 shows the embodiment, which has been discussed above, wherein a body of elastomer 20 contains uniformly disseminated herbicide 22. On the basis of our experiments, it appears that for a polyisoprene gasket, 5/8 inch in diameter, and containing 3 to 4% trifluralin, roots will be effectively repelled for from 25 to 50 years. The smaller proportions (0.5% and 1%) were effective for shorter times. If it is desired to increase the longevity beyond the 25 to 50 year period, it is necessary to adopt another form of distribution. Two such forms are shown in Figures 3 and 4. In figure 3 the polyisoprene gasket 20 contains uniformly disseminated herbicide 22 in the proportions of 0.5 to 5%. Additionally, it contains particles of polyethylene 24. These may contain 10 to 30% dinitro¬ aniline, preferably about 25% trifluralin. Still another embodiment is ^■ shown in Figure 4. Again the gasket 20 contains the uniformly distributed dinitroaniline 22 in the amount of 0.5 to 5%. Furthermore, it is provided with a core 26 of polyethylene which, like the particles 24, may contain from 10% to 30% dinitroaniline preferably 25% trifluralin. In all cases it is desirable to include carbon black in very finely divided form in an amount approximately equal to the amount of dinitroaniline to improve retention. This is particularly the case in the particles or core containing large proportions of the herbicide. The carbon blacks which are used are typical "rubber grade furnace blacks" which have ultimate particle sizes of 19 to about 95 nm but which are aggregated and

agglomerated to varying degrees. They are typically supplied for use in- agglomerates of about 30 to 300 microns in size. These agglomerates are, however, broken up during the processing. In the embodiments of Figures 3 and 4, the herbicide will slowly diffuse from the polyethylene 24 or 26 and continuously replenish that in the body of the gasket material. It appears that lives up to 100 years of repellency can be obtained in-these manners.

In Figure 5, we show a root-repelling gasket as mounted in a concrete pipe joint. The gasket 30 is com¬ pressed between the bell 32 and the spigot 34 of the joint. As will be seen, the originally circular gasket is highly compressed and the release of the herbicide is over a relatively small section as indicated by the arrows 36. The temperature of the soil surrounding the gasket will most probably range between 10° and 13°C (50 to 55°F). This relatively low temperature contributes to the long life by producing a low release rate and subsequent decompo¬ sition of the dinitroanaline.