10 days after the test was started in each of phosphoric acid buffer solutions of phs of 6 0 7 0 and 8 0 the obtained results are shown in fig2 fig3 fig4 and fig5 respectively from these results each retention of weight is 48 35 and 12 three weeks after showing that the sample is considerably degraded the retention of tensile strength of every one of the samples is around 23 10 days after showing that the strength is extremely reduced the retention of elastic modulus of every one of the samples is around 63 10 days after showing that the elastic modulus is remarkably reduced moreover each retention of elongation at break is 16 36 and 38 10 days after showing that it is considerably decreased in every case and the sample was made brittle it is found from these results that the degradability of the complex fiber is good the complex fiber with the following ratio by volume pbsl pga 44 56 which was obtained in example 6 was measured for the retention of weight 1 week 2 weeks and 3 weeks after the test was started the retention of tensile strength 1 week and two weeks after the test was started the retention of elastic modulus 1 week and 2 weeks after the test was started and the retention of elongation at break 1 week and two weeks after the test was started in each of phosphoric acid buffer solutions of phs of.