If polyethylene grass silage film (bag) is used to store freshly harvested livestock, this film bag is used to package green grass for storage. After six months, it still maintains the original nutritional content and moisture of the grass. This bagged storage method for grass utilizes anaerobic fermentation during storage to convert some of the starch components in the grass into lactic acid, which livestock prefer to consume.
In the early stage of packaging the green grass inside the bag, the cellular respiration oxidizes the sugar and consumes the oxygen inside the sealed bag, forming an anaerobic environment (at this time, the oxygen bacteria gradually stop moving, and the anaerobic bacteria continue to reproduce). Lactic acid bacteria fermentation is produced under anaerobic conditions. So it is crucial to maintain an anaerobic environment for the storage bags of green grass, which is the key to the quality of the film used in bag making.
The polyethylene green grass storage film (bag) should have the following properties.
① The strength requirement of the film is relatively high, and it should be ensured that it is not damaged during the storage of grass, has good oxygen resistance, and creates an anaerobic environment inside the packaging grass bag.
② The film bag should have good sealing performance and be able to maintain non rupture in low temperature (winter) environments Appropriate insulation should be applied, and the film should have low light transmittance to avoid heat accumulation inside the bag. The temperature inside the bag should be maintained appropriately.
(1) Raw material selection and formula
① The formula for forming single-layer polyethylene grass silage film is as follows (by mass). The main raw material for forming single-layer polyethylene grass silage film is linear low-density polyethylene, which is used in combination with other auxiliary materials.
75 parts of linear low-density polyethylene (LLDPE, MFR=12g/10min), 25 parts of low-density polyethylene (LDPE, MFR-1.2g/10min), 4 parts of white masterbatch (accounting for 40%~60% of the masterbatch), and 4 parts of anti-aging masterbatch.
② The formula for forming polyethylene grass silage composite film is polyethylene grass silage composite (two-layer) film forming material, and the outer layer of white film forming material is mainly composed of linear low-density polyethylene resin, with some auxiliary materials added. The reference formula for composition is as follows (mass fraction). 100 parts of linear low-density polyethylene (LLDPE, MFR-12g/10min), 4 parts of white masterbatch (accounting for 40%~60%), 4 parts of anti-aging masterbatch, and an appropriate amount of processing aids. The main raw materials for forming the inner layer of the composite film are a mixture of LLDPE and LDPE, and some black masterbatch is mainly added to the auxiliary materials. The composition formula is as follows (for reference only) (by weight). 60 parts of low-density polyethylene (LDPE, MFR-12g/10min), 40 parts of linear low-density polyethylene (LLDPE, MFR-1.2g/10min), and 4 parts of black masterbatch (accounting for 40%~60%).
(2) Production process sequence
① Production process sequence of single-layer polyethylene grass silage film forming a. Preparation process sequence of masterbatch
Pigments or other additives are measured after grinding, and polyethylene (LLDPE) material is measured → mixed evenly → granulated after mixing in an extruder
b. Production process sequence of single-layer polyethylene grass silage film forming
LLDPE, LDPE, and masterbatch are measured separately according to the formula → mixed evenly and extruded by a extruder for plasticization and melting → molded into tubular film blanks → blown bulging film blanks, air-cooled cooling and shaping → traction → coiling
② Production process sequence of double-layer polyethylene grass silage film forming
LLDPE and masterbatch are measured separately according to the formula → evenly mixed → extruded by plasticizing and melting
LDPELLDPE and masterbatch are measured and mixed evenly according to the formula → Extruder plasticizing and melting mold forming composite film tubular film blank → Blowing expansion film blank, air cooling and shaping → Traction → Coiling
(3) The extrusion blow molding process for polyethylene grass silage film requires the same conditions as the extrusion blow molding process for ordinary polyethylene composite film, both in terms of equipment and process temperature for extrusion plasticizing raw materials. It will not be repeated here. As shown in Figure 6-31, it is a mold structure for composite film forming, which can be used as a reference for selecting composite film forming molds.
