Shogo Uematsu a , Atsushi Murakami b , Kimio Hiyoshi c, Yasuhiro
Tsukamoto d , Hisato Saida e, Masao Tsuji f, and Akira Hoshino fa

School of Pharmaceutical Sciences, University of Shizuoka, 52-1,Yad a
Shizuoka-shi 422-8526, Japan, (054) 264-5642, fax (054) 264-5641,
uematsu@ys2.u-shizuoka-ken.ac.jpbFuji-Tokoha University, 325, Oubuchi, Fuji-shi 417-0801, Japan,cFuji Industrial Research Institute of Shizuoka Prefecture, 25901-1
Oubuchi, Fuji-shi 417-8550, Japan,dNumazu Industrial Research Institute of Shizuoka Prefecture, 3981-1
Ouoka, Numazu-shi 410-0022, Japan,eSaida Ironworks Co., Ltd., 3-6-9 Sakaecho, Yaiz u-shi 425-0027, Japan,fBiodegradable Plastics Society, Grande Bldg., 26-9 Hatchobori 2
Chome, Chuo-ku Tokyo 104-0032, Japan
Introduction
Environmental disruption brought about by industrial waste is now
of a global concern. That is, pollution of soil and pollution of ocean to
be caused by damping industrial waste into the soil or at the sea can becausative of disruption of ecosystem including the human society, giving
raise to a serious social problem. Under such circumstances, degradationof organic waste to be achieved by microorganisms is the cleanest
purification system that occurs in the realm of nature. Accordingly, tosubstrate those substances which are now chemically synthesized withthose having microbial-degradability can be a useful measure for solving
or improving the problem of environmental disruption induced byindustrial waste as described above.
As an example of such substance having microbial degradability,
biodegradable plastics that are decomposed by soil or water
microorganisms are under development and are sharing some part oforganic industrial waste. The biodegradable plastics are expected: (1) tobe stable during the period of use, and (2) to be decomposed soon in thesoil by microorganisms after disposal. Although it is possible to measure
the period during which biodegradable plastics can be used stably, there isestablished no standardized familiar method of measuring the rate ofdegradation in biodegradable plastics to be caused by microorganisms, sothat evaluation results of biodegradable plastics are of inconsistency,
which is a main cause of hindering development of high -quality
biodegradable plastics. There exists so far no familiar evaluation
apparatus relating to total degradation of organic matters in the soil andin compost into CO 2 . As carbon dioxide analytical methods, following
methods are generally known: (1) quantitative determination of CO2
captured in a strong alkaline solution by means of neutralization
titration; and (2) quantitative det ermination of CO2 captured in a gas
reservoir by use of gas analyzer. However, since the volume or weightof the organic matter to be tested ranges widely from 1 cc to several
hundreds of ton, and besides organic matters are of different
compositions, there is reported no standardized test method.
Accordingly, the test method (1) or (2) is selected depending on therespectively subjects to be tested, with no established standardized meansfor evaluating biodegradability. Authentic method is stipulated under
ASTM (American Society for Testing and Materials D5209-92, D533892) 1 , in which the biodegradable plastics are allowed to be decomposedby activated sewage sludge microorganisms to measure the amount ofCO2 formed by decomposition by means of titration. Especially, JISK6953 based on ISO 14855 2 , 3 under controlled composting conditions
was established in May 2000. It is an excellent test -method with
automatically calibrating the evolved carbon dioxide by the gas
chromatography, but presents some difficulties. First, the part of reactor
is on a large scale and the apparatus is expensive. Second, it costs a great
deal to examine the specimens for developing biodegradable polymers,
compounds and manufactured goods. The present study is to carrying out
an accurate and easy evaluation of microbial-degradability of organic
matters with a simplified apparatus in a laboratory scale.
Experimental
Materials. The compost manufactured by Yahata Bussan Co.,
Ltd. (Shizuoka, Japan) was used as inoculum and was subjected toselection using a 6.5-mesh official sieve. T he resulting compost under
6-mesh was used as such. The aged farmyard compost was made fromwasted mushroom bed and poultry-manure. The chemical properties
were total dry solid (42%), volatile solid (70%), pH (7.0), total organiccarbon (12%), total nitrogen (1.7%), and C/N ratio (6.8), respectively.
The biodegradable polymer (250µm-pass) was prepared by mixing thegranular polymer and dry ice pieces by a blender. As the cellulose, a filter
paper powder (40 mesh) manufactured by K.K. Tokyo seisakusho wasused. As the sea sand (grain size: 20 to 35 mesh), 5 Kg of Wako's
reagent grade sand was rinsed three times with distilled water, and theresulting sand which was dried at 100¡C was used. The role of sea sand is
involved for the advantages of the water-holding and soil texture
between the inoculum and test material. All the components were mixed
with gently and then put into a reactor.
Apparatus. An apparatus (MODA: Microbial Oxidative
Degradation Analyzer 4 ) is designed for evaluating microbialdegradability of an organic matter, the apparatus comprising: a reaction
column maintained constantly at a fixed temperature and containing anorganic matter as an evaluation subject or a cellulose as an evalua tionreference together with a prescribed microbial source; means for forming
saturated water vapor, connected to one end of the reaction column, themeans being provided with first CO2 adsorption means and feeding CO2 free saturated water vapor into the reaction column; and an adsorption
column, connected to the other end of the reaction column, theadsorption column containing second CO2 adsorption means as shown in
Figure 1. The amount of CO 2 can be determined by measuring theweight gain in the adsorption means having adsorbed CO2 . As describedabove, it is extremely easy to determine the weight if CO2 by measuring
the weight gain in the adsorption means caused by adsorption of CO2 ,and even inexperienced operators can carry out easy measurement.
OutletDetector
CaCl2
Thermometer

CO2NH 3H 2O

Soda lime

Reaction column
CaCl2
Electric heater

SiO2

Soda lime

ACCURATE AND EASY EVALUATION OF AEROBICMICROBIAL-DEGRADABILITY OF BIODEGRADABLE
PLASTICS UNDER CONTROLLED SOIL

Air
Wate r2N H2SO4

Fi gure 1. Scheme of apparatus MODA
Cellulose biodegradation test Rinsed sea sand, compost ,cellulose and water according to the formulation shown in Table 1 weretaken to a 5-liter plastic vessel. Then the resulting mixture was starredwell, and consequently introduced to the reaction column in theapparatus shown in Figure 1 to measure the amount of CO 2 formed under
the following conditions: quantity of air flow: 40ml/min; reaction
temperature: 58¡C. Measurement of CO2 carried out for 46 days, and thesample in the reaction cylinder was subjected to turning after 7, 14, 21,28, 35 days of the reaction. The turning was carried out by transferring
the sample in the reaction column into a 5-liter plastic vessel andstirring it well therein.
At the same time, the water content of the sample was adjusted at35~40%? After completion of turning, the sample was returned into
the reaction column.
Biodegradation test of biodegradable polymers . Difference inthe biodegradability depending on the structure of biodegradable polymer
was examined. Sea sand rinsed with distilled water, compost and apolymer were taken into a 5-liter plastic vessel according to theformulation shown in Table 2, and after the resulting mixture was stirred

Polymer Preprints 2002,43(2),930

well, it was introduced to the reaction column to measure the amount of
CO2 formed under the same condition of the cellulose biodegradation
test. Each polymer was rinsed three times with distilled water, and thethus treated polymer from which the excess of water was decanted off
was used. T he water content in a reactor was adjusted at 40%.

showed the high biodegradability than cellulose. As the starch derivative
polymer mixed with PVA, the biodegradation proceeded slowly in thisexperiment. Polybutylene succinate adipate (#3030) showed the same
biodegradability as cellulose at the end of the experiment during 38 days,
but the time lag with biodegradation was observed.
cellulose (5 g)Table 1. Cellulose biodegradation test
cellulose

1, 23, 4
5, 67, 80
51015water

195
195
195
195

Table 2. Biodegradation test of polymer
Mixing ratio
NoPolymer derivative

Compost(cc)250

Sea sand (cc)3-Hydroxybutyrate

2Cellulose

10250

250

310250250

4Polybutylene
succinate adipate
Starch derivativ e

10250

250

5Control

0250

250

Sea sand, compost,
cellulose (15g)

Amount of CO2 gas formed(g)Sea sand, compost,
cellulose (10g)20
Sea sand, compost,
cellulose (5g)

10

Sea sand, compost,

50Turning0

1020

30

4020Turning01020304050250

Results and Discussion
Cellulose biodegradation test. The results of measurement ofamount of evolved CO2 and the estimated biodegradability3 are shown inFigure 2 and 3, respectively . The measurements were carried out at theend of the experiment within the prescribed time intervals dur ing 46days. The total amount of CO2 evolved from the test material for
46days was increased with the amount of cellulose. The relation wasshown as the linear equation y=1.230x+9.559 with the correlation
coefficient 0.994. The percentage of biodegradation was over the 70 %biodegradability of cellulose as a reference material established by ISO14855. It was considered that the biodegradability over 70% was basedon the advantages of the water-holding and soil texture between theinoculum and test material by the addition of sea sand. The highlinearity showed the stable and constant activity of microorganisms inreaction column to be maintained during the experimental period.

1540

Aeration period(days)

125cellulose (15 g)

60

0polymer(g)1030cellulose (10 g)

8050

Aeration period(days)

Figure 2. Biodegradation of cellulose in controlled soil at 58¡C
Biodegradation test of biodegradable polymers . Figure 4
show the biodegradability of biodegradable plastics in controlled soil at35¡C. Difference in the biodegradability depending on the structure ofbiodegradable polymer was distinctly observed. Poly 3-hydroxybutyrate

Figure 3. Biodegradability of cellulose in controlled soil at 58¡C.
25
3-Hydroxy derivative

Amount of CO2 gas formed(g)TestNo.

Ratio of components(g)compostsea sand(dryweight)
60
320
60
320
60
320
60
320

Biodegradability of cellulose(%)

100

20Cellulose15Polybutylene
succinate

10Starch derivative

50Control010203040

Aeration period(days)

Figure 4. Biodegradability of biodegradable plastics in controlled soil at35¡C.
Conclusions
Cellulose biodegradation test showed the amount of cellulose inreaction column to be determined in an error with few percent. It wasobvious from the biodegradability over 70% that the advantages of thewater-holding and soil texture between the inoculum and test material
was gained by the addition of sea sand to compost. The results of thismethod by using MODA-apparatus were approximately coincided withJIS K6953 (ISO14855). In conclusion, under the controlled composting
condition during the experiment, this method demonstrates an effective
screening test method for the compostability of plastic materials in alaboratory scale.
Acknowledgements. The authors of this paper would like tothank Dr.Ohshima (BPS) for his scientific advice. We also thank Daicel
Chemical Industries, Ltd., Showa High Polymer Co., Ltd. and Mitsui
Chemicals, Inc. for supplying the plastics.
References(1) ASTM D 5338-92, ASTM D 5209-92.
(2) Pagga, U.; Beimborn, D.B; Boelens, J.; Wilde, B.De. Chemosphere
1995, 31, 4475-4487.
(3) ISO 14855, JIS K 6953.
(4) JP 11113595, US 6143515, EP 0908513.

Polymer Preprints 2002,43(2),931