## 3 Results and Discussion
### Biodegradability
#### 3.6.2 Soil Burial Test  
The weight loss of the samples in the soil burial test is shown in Table 2; the results indicated that the degradation degree of the three fiber/polymer films decreased in the following order: fiber/ST film > fiber/PVA film > fiber/PA film. Figure 4: Thermal gravimetric analysis (TGA) curves for the four tested films. Figure 5: The amount of microorganisms in soil covered by different films between November 1, 2014 and December 19, 2014. In the soil burial test, the three films were degraded for four weeks. The samples were characterized by FT-IR before and after degradation to identify the changes in spectra intensities in the films' functional groups [23]. The results are shown in Figure 6. Before degradation, the fiber/PVA film showed characteristic absorption bands at 3331 cm\({}^{-1}\) (O-H stretching), 2902 cm\({}^{-1}\) (C-H stretching), 1628 cm\({}^{-1}\) (C-O stretching), and 1316 cm\({}^{-1}\) (-CH\({}_{2}\) bending). In addition, the absorption bands at 1159 cm\({}^{-1}\) (anti-symmetric stretching of the C-O-C bridge) and 1028 cm\({}^{-1}\) (skeletal vibrations involving C-O stretching) were characteristic of a saccharide structure. The IR spectra for the fiber/ST film and the fiber/PA film were similar to that of the fiber/PVA film, although the fiber/PA film had a characteristic absorption band at 1727 cm\({}^{-1}\) (C=O stretching). Figure 6 shows major differences of absorption intensity in spectra for both the fiber/PVA and fiber/starch films before and after degradation, whereas the fiber/PA film spectra show little variance before and after degradation. The IR spectra indicates that the contents of the samples changed with the absorption intensity, also changing some characteristic peaks. These findings also indicate that the fiber/PVA and fiber/starch films degraded rapidly during this period, while the fiber/PA film degraded more slowly by contrast. SEM micrographs of films taken before and after the soil burial test are presented in Figure 7. The samples had many ripples and holes after 1 month of degradation, indicating the partial biodegradation of the polymer and fiber; however, degradation of the fiber requires more time. The SEM micrographs showed that the degradation degree of the fiber/PVA and fiber/ST films was greater than that of the fiber/PA film. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type of Film** & \begin{tabular}{c} **Start Time/Initial** \\ **Weight (g)** \\ \end{tabular}  & \begin{tabular}{c} **End Time/Weight** \\ **(g)** \\ \end{tabular}  & \ \begin{tabular}{c} **Weight Loss (\%)** \\ \end{tabular}  & \begin{tabular}{c} **Time, Months** \\ \end{tabular}  \\ \hline Fiber/PVA & Nov. 4/0.2578 & Nov. 18/0.2065 & 19.9\% & 0.5 month \\  & Nov. 4/0.2893 & Dec. 4/0.1896 & 34.5\% & 1 month \\  & Nov. 4/0.2697 & Dec. 18/0.056 & 79.2\% & 1.5 month \\ \hline Fiber/PA & Nov. 4/0.3448 & Dec. 4/0.2895 & 16.0\% & 1 month \\ \hline Fiber/ST & Nov. 4/0.3527 & Dec. 4/Figure 7: Scanning electron microscopy (SEM) images of film samples before and after degradation. **(A-1)** original fiber/starch film; **(A-2)** fiber/starch film after 4 weeks of degradation. **(B-1)** original fiber/PVA film; **(B-2)** fiber/PVA film after 4 weeks of degradation. **(C-1)** original fiber/polyacrylamide film; **(C-2)** fiber/polyacrylate film after 4 weeks of degradation. Both the field and laboratory tests indicate the potential usefulness of the fiber/starch film; however, because of its rapid degradation in soil (approximately 1-2 months in different seasons), it can only be used as a munching film for crops with short growth periods. The fiber/PVA and fiber/PA films can be completely degraded in 2-3 months and 3-4 months, respectively, during different seasons according to the findings of our field test. PVA and starch were reported as biodegradable polymers; however, it reported that polyacrylate was not a biodegradable polymer [24; 25; 26; 27]. Therefore, the fiber/PA film will not be suitable for large-scale applications.