*4.1. Test Method and Design*

The 1JRM-2000 curl-up film collector and the 11SM-1.2 curl-up film collector were used for a contrast test in the field research and development base of the Key Laboratory of Northwest Oasis Agricultural Environment of Ministry of Agriculture, in Tuobuliqi Town, Korla City, Bayingolin Mongolian Autonomous Prefecture of Xinjiang Uygur Autonomous Region, China, during March of 2022. According to the standard GB/T25412-2021, the film recycling rate of the device on the film laid in the same year and the working performance of the device were used as test indexes. The structures of the two types of collectors are shown in Figure 9.

According to Figure 9, when the 11SM-1.2 curl-up film collector was working, the eight groups of film pick-up mechanisms at the front and the two groups of side-film shovels separated the film and soil; the film-guiding and impurity separation mechanisms separated impurities from the film and sent the film to the film-curling mechanism. The film-curling mechanism rotated and winded the film on it. While unloading the film, the hydrocylinder was manually controlled, and the film unloading mechanism unloaded the film package. During the working process, the film pick-up angle remained unchanged and was determined by the angle of the film pick-up mechanism. If the film pick-up angle is too large, the soil penetration angle of the film pick-up mechanism is too large, and the soil produces high resistance against the film pick-up mechanism. If the film pick-up angle is too small, it produces high film tensile stress and tears off the film. Thus, the film pick-up angle was determined to be 45◦. During operation of the 1JRM-2000 curl-up film collector, the soil-loosening shovel on the deep limiter in the front of the film collector first loosens the soil around the side film. The film-cutting mechanism cuts the soil from the center along the film-laying direction, and then the film pick-up mechanism in the middle of the machine separates the cut film from the soil. With the forward movement of the machine, by manually controlling the hydrocylinder, the film-unloading mechanism opens, and, during the working process of the machine, the film pick-up angle increases with the increase in the diameter of the film package.

**Figure 9.** Schematic diagram of structure of two types of curl-up film collectors. (**a**) 11SM-1.2 curlup film collector: 1—film-unloading mechanism, 2—film-curling mechanism, 3—film-guiding and impurity separation mechanism, 4—body frame, 5—drive system, 6—film-pulling mechanism, 7 depth wheel components, 8—traction mechanism, 9—film pick-up mechanism, 10—side-film shovel; (**b**) 1JRM-2000 curl-up film collector: 1—operation platform, 2—depth limiter, 3—film-unloading mechanism, 3—film-curling mechanism, 4—film-cutting mechanism, 5—traction mechanism, 6—film pick-up mechanism, 8—body frame.

According to the requirements of "five-point random sampling" [23], a measurement area of 200 m × 3.8 m was selected, and test points were chosen within this area. From the four corners of the measurement area along the diagonal lines, four measurement points were randomly determined within the range of one-quarter to one-eighth of the diagonal length, in addition to the intersection of the diagonal lines as the five pre-operation measuring points. Then, five points were selected as post-operation measuring points in the same area near to, but not overlapping, the five pre-operation measuring points. The measuring points cover a length of 5 m and the width of the film, which is 1.25 m. After controlling the stubble height of the cotton plants within 120 mm, the two film collectors started working simultaneously from the start of each row on the same type of film for an operation length of 200 m. The test was repeated three times, and the test results were averaged. Before the machine reached the operation position, a length of 50 was set as the accelerating region to let the machine adjust to a suitable speed. Timing started when the machine entered the operation position, and timing stopped after the machine completed an operation length of 200 m. After operation, residue film pieces were taken from the five pre-operation and post-operation measurement points in the two measurement areas. The residual film taken from each measuring point was washed, dried, and weighed, and the average value was calculated. The film recycling rate on the film laid in the same year can be calculated according to Equation (8):

$$J = (1 - \frac{W}{W\_0}) \times 100\% \tag{8}$$

where *J* is the film recycling rate of the film laid in the same year by the machine, %; *W* is the mass of residue film laid in the same year in the field after machine operation, g; and *W*<sup>0</sup> is the mass of residue film laid in the same year before machine operation, g.

#### *4.2. Test Results and Analysis*

Test results are listed in Table 6. The results of the test come from "five-point sampling", which is suitable for the survey objects with relatively uniform population distribution and good representativeness. In order to exclude errors caused by accidental factors, three replicate groups were arranged for each sampling, and the final results were averaged.


**Table 6.** Results of field test on curl-up collecting of film.

Table 6 shows that, during the curl-up film collecting of the 1JRM-2000 curl-up film collector on film with different thicknesses, the film recycling rate of the film laid in the same year and the working performance were lower than that of the 11SM-1.2 curl-up film collector. During the working process of the 1JRM-2000 curl-up film collector, with the increase in the film pick-up angle, the curl-up force changes, and the film is easily broken down during film pick-up. In order to collect the film more easily, the 1JRM-2000 film collector used soil-loosening shovels to loosen the soil around the side film to reduce the force on film. After the soil was loosened, some side film still adhered to the soil and could not be collected, making the film recycling rate of this device lower than that of the 11SM-1.2 curl-up film collector. When the type of film to be collected was high-performance film, since the mechanical properties of the high-performance film were higher than those of the ordinary polyethylene film, the film-cutting mechanism could not effectively cut off the high-performance film, thereby preventing the machine from improving the working performance. When the type of film to be collected was high-performance film, since the mechanical properties of the high-performance film were higher than those of the ordinary polyethylene film, the film-cutting mechanism could not effectively cut it off, which shows the low working performance of the machine. When the type of film to be collected was ordinary polyethylene film, whose minimum tensile yield stress should be lower than the required film tensile stress for the normal operation of the curl-up film collector, the force direction on the film kept changing during operation, and the film was easily broken. In this case, it was necessary to pull the broken film manually to the film-curling mechanism, and thus the working performance of the machine was greatly affected. Since the film pick-up angle of the 11SM-1.2 curl-up film collector is a fixed value, during collecting of the film, the curl-up force is only determined by factors such as the soil quantity on the film. When there is little change in the curl-up force, the film is not broken, and, moreover, with the assistance of the film-guiding mechanism, in the case of film breakage during curl-up collecting, the film-guiding mechanism can transmit the newly separated film from the soil to the film-curling mechanism without manual operation. It can be obtained from the results of the field test on the curl-up collecting of the film that the 11SM-1.2 curl-up film collector achieved film recycling rates of 85.45% and 96.11% on the high-performance film with thicknesses of 0.008~0.01 mm laid in the same year; the 1JRM-2000 curl-up film collector achieved the film recycling rate of 81.16% on the high-performance film

with a thickness of 0.01 mm laid in the same year, which could satisfy the requirements of GB/T25412-2021 and achieved working performances of 8.24 km/h, 9.37 km/h, and 6.15 km/h and satisfied the requirements for agricultural production.

Due to the long-term use of ultra-thin and low-strength plastic films in China, the residual film collectors developed in China are mainly aimed at collecting low-tensile strength plastic films. The current related researches includes: The Agricultural Mechanization Research Institute of Xinjiang Academy of Agricultural Sciences [24] has developed a 4JSM-2.1A arc-reciprocating residual film collector; Jiangsu University [25] has developed a combined residual film reclaimer with upper conveyor chain; and China Agricultural University [26] has developed a collecting and separating device for strip plastic film baler. The residual film collected by this device is fragmented, and the film collection mechanism also collects some impurities into the film collecting box during the recycling process, so the collected film can only be reused through granulation, and it is difficult to completely remove impurities, such as the straw, soil and other impurities mixed in the residual film fragments. The cost of using residual film for granulation remains high, and many downstream enterprises of residual film recycling should only rely on government subsidies to support them. It can be concluded in this study that the tensile strength and weather resistance of the high-performance film for full recycling are better than those of the ordinary polyethylene film, and the residual film can be recycled by means of pickup recycling. The collection of low-tensile strength plastic film and the collected plastic film with high integrity have relatively few impurities, which greatly reduces the cost of collecting residual film for downstream enterprises.
