Monolayer Cast Polypropylene (MCPP) film is made by hot melting and plasticizing polypropylene resin particles in an extruder, followed by hot stretching using cooling rollers [1], rapid cooling with compressed air, and then being pulled and wound into a film. Cast polypropylene film has many advantages such as good transparency, high glossiness, good flatness, excellent heat resistance, easy heat sealing, and rapid production. It is widely used in the packaging of food and daily necessities, and also as the inner and outer layer materials of composite films [2,3,4].



In the industrial production of MCPP film, factors such as extrusion temperature and cold roll temperature are important process parameters that affect the performance of the film. Among them, extrusion temperature has a significant impact on the structure and properties of homopolymer polypropylene products [5,6,7,8]. This article uses the controlled variable method to explore the influence of extrusion temperature on the optical and mechanical properties of MCPP films, in order to provide data support for the optimization of extrusion temperature parameters in the production process of MCPP films.



1 Experiment

1.1 Experimental Materials

Ethylene copolymer polypropylene T28FE (Lanzhou Petrochemical Branch of China National Petroleum Corporation).



1.2 Experimental equipment

Casting film machine (ME-30/9100V3 and CR-9/320, Optical Control Systems GmbH (Germany));



Haze meter (HGM-2DP, Shimadzu Corporation, Japan);



Electronic tensile machine (Instron 1121, British Instron company);



Cutting prototype (Shanghai Zhongyi Machinery Factory);



Polarization microscope (DM 2500P, Leica Microsystem);



Differential scanning calorimeter (TGA/DSC synchronous thermal analyzer (Switzerland)).



1.3 Experimental methods

The extrusion device of the casting film machine is a single screw extruder with a length to diameter ratio of 25:1, and is equipped with 8 temperature control zones. Using ethylene copolymer polypropylene T28FE as raw material and using the controlled variable method, 7 sets of experiments were designed according to the experimental conditions in Tables 1 and 2. MCPP film samples with a thickness of 35 were prepared at different extrusion temperatures μ m) And complete the test within 48 hours. Examine the effect of extrusion temperature on the structure and properties of thin films.



Table 1: Scheme for Setting Extrusion Temperature Download the Original Table



Table 1 Scheme for Setting Extrusion Temperature

Table 2 Experimental Conditions Download Original Table



Table 2 Experimental Conditions

1.4 Structural characterization

(1) Polarization microscopy (PLM) method. Observe the degree of orientation of each MCPP film sample under a polarizing microscope.



(2) DSC characterization. By using a DSC differential scanning calorimeter to analyze the thermal properties of the samples, the crystallinity of each sample can be calculated according to equation (1).






In the formula: Xc represents crystallinity,%; Δ Hf is the enthalpy of sample melting, J/g; Δ Hf * is the melting enthalpy value of the standard sample, Δ Hf *=209J/g [9].



1.5 Performance testing

The transmittance and haze of MCPP film shall be in accordance with GB/T 24