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Hot melt adhesives and the composting process: a study.

Adhesives are still the most widely used products in the nonwovens industry for bonding together a wide range of substrates for production of a host of end products. They have become the everyday products used by manufacturers throughout the world.

Hot melt adhesives are mixtures/blends of polymers, resins, waxes/oils and antioxidants. This produces a thermoplastic product that is a liquid when hot, a solid when cold. The adhesive is applied to substrates while hot, at temperatures from 110-180 [degrees] C, and the highly cohesive bond is formed as the adhesives cools. An almost infinite number of formulations are possible to bond the variety of substrates that are used in today's nonwovens industry.

As we have all become increasingly aware of the environmental consequences of the products we use or manufacture, National Starch has decided to examine the effect of hot melt adhesives on current waste management processes.

Composting remains - so far - one of the under-used waste management processes in Europe, compared to landfilling and other options. However, it is generally accepted that composting will become more widely used in the future.

A study, commissioned by National Starch and Chemical, was conducted at Stuttgart University under Dr. W. Bidlingmaier, a professor at the Institute for Water Quality, Waste Economics and Water System Construction of the European Commission. He works closely with the State department for environmental health. His work concerns the composting of biowaste from the European community countries.

Six different samples were given by National Starch to the university and they included:

1. Silicone paper

2A. Nonwoven without hot melt

3A. Hot melt (Type A)

4A. Hot melt (Type B)

5A. Hot melt (Type C) with nonwoven

6A. Hot melt (Type C) with silicone paper

The study covered two principal areas:

a) The effect of the hot melt adhesives on the actual composting process.

b) The changes in the structure or physical appearance of these hot melts during the composting process.

We should note that the waste used for producing the compost was not a selected compost material; ordinary household waste was used for the study

The study was carried out in two principal areas:

1. In laboratory flasks

- where the samples were added to the compost and measurements recorded every two hows.

2. In a compost heap of biowaste

- this was turned regularly and measurements taken.

The Study And Its Scope

The effect on the composting process was measured by the following parameters:

Temperature graph of the process

[CO.sub.2] emission

[O.sub.2] consumption

Exothermic reaction

Carbon content

Salt content

Structure changes on the surface of the coating.

The results during the study showed that the exothermic reaction showed a typical curve and the consumption of [O.sub.2] and emission of [CO.sub.2] were also typical of a normal process.

ln this case, the temperature of the heap of compost was measured in three places. The maximum temperature reached in the heap was 70 [degrees] C. The two temperature drops occurred when the compost was turned and this is quite normal. All the above recorded behavior was characteristic of the normal composting process.

The study also examines the changes in the physical appearance of the hot melts. This test was carried out over a period of nine weeks using a nine cubic meter heap of one week old biowaste material.

The samples were placed in perforated plastic bags within the heap, approximately 70 cm from the bottom of the heap, which was 1.5 meters high, totally surrounding the samples with composting material. During the nine week period, the heap was turned over several times.

The characteristics of the heap were as follows:
 Water content 46.6%
 pH - volume 8.6
 Density 650.7 g/l
 Carbon content 30%


At intervals of three, six and nine weeks samples were removed and photographed. The photographs above and below show these sampled hot melts.

The study states the following:

* After three weeks the samples began to dissolve or break down.

* The tack and elasticity of the adhesive coatings degraded after three weeks and gradually reduced more and more during the process.

* After nine weeks no tack could be detected and, from an initially flexible layer, only a hardened layer remained.

* After nine weeks only fragments of the hot melt could be found.

* No trace of hot melt could be found on the compost particles.

* It was not possible, even with these close observations, to determine if the hot melt was degraded or in a soluble form in the compost. One way to determine if degradation had taken place was to determine the carbon content of the samples before and after the composting process. Unfortunately, the remaining fragments could not be completely cleaned and therefore it was not possible to redetermine the carbon content after the process.

Results And Conclusions

The study concludes that 1, the rotting process will not be negatively affected if hot melt coated material is added to compost; 2, the silicone paper was biodegraded; 3, the polypropylene nonwoven remained unaffected; 4, the hot melt coating was changed during the process and lost its tacky appearance; and 5, the concentration of heavy metals and toxic compounds are so low that there is no measurable influence on composting.

The University of Stuttgart stated that "hot melt in the sampled form can be added to a composting process without any influence on that process. Regarding the quality of the final compost, there is no influence and the final compost is totally biologically active."

This compost conforms to the German criteria for compost as described in the "Bundesguetegemeinschaft fur Kompost."

The environmental consequences of the products we buy, use and produce will continue to be closely examined during the next decade. One of the aspects of this will be the examinations of different methods of handling our waste management programs. Inevitably, composting will be more widely used in the future.

This study provides an insight into the behavior of hot melt adhesives commonly used in the manufacture of nonwoven and disposable products as well as in the packaging when placed within a composting waste management system.

The positive results obtained in this study should encourage us to continue to search for products and processes that will address the problems of our environmental future.
COPYRIGHT 1992 Rodman Publications, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1992 Gale, Cengage Learning. All rights reserved.

Article Details
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Title Annotation:National Starch and Chemical study
Author:Leftwich, William; Riswick, Martin; Lochel, Inge
Publication:Nonwovens Industry
Date:Nov 1, 1992
Words:1047
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