Study On The Preparation And Properties Of New Modified Atmosphere Packaging Polyethylene Film

In this paper,in order to control the permeability and selective permeability of traditional polyethylene films to expand the application range of polyethylene films in the preservation of fruits and vegetables,Linear Ultra-density polyethylene（ULDPE）was added into Linear Low-density polyethylene（LLDPE）.The purpose was to improve the toughness,strength,processing performance,oxygen permeability and CO₂/O₂ selective permeability of PE through blending modification,so as to meet the performance requirements of spontaneous MAP packaging of fruits and vegetables.In this experiment,blending polyethylene was prepared into film samples by blow molding method.The crystallinity and permeability of polyethylene films can be effectively controlled by changing the process formula of blending PE films.（1）In order to regulate the permeability of LLDPE 2047G,ULDPE 4404G was added to LLDPE 2047G at different ratios of 33%,50%and 67%for blending modification.Three kinds of blend films,pure LLDPE films and ULDPE films with thickness of 25μm were prepared by a small film blowing machine.The blowing process parameters of LLDPE films were studied in this process.The results show that LLDPE films are suitable for blowing processing under the conditions of blowing ratio1.8,traction ratio 4.0 and processing temperature 175°C.The effects of ULDPE content on mechanical properties,crystallization parameters and permeability of modified polyethylene films were studied.The mechanical properties test results show that the addition of ULDPE improves the strength and toughness of LLDPE.When the ULDPE content is 50%,the longitudinal tensile strength of the blend film increases by 6.9%,the longitudinal elongation at break increases by 22.1%,the transverse tensile strength increases by 18.4%,and the transverse elongation at break increases by 31.9%.Longitudinal tear strength increased by 29.0%,transverse tear strength increased by22.4%,impact quality increased by 65.5%.DSC and XRD results showed that with the increase of ULDPE content,the crystallinity of the blend films decreased gradually,and the permeability increased.When the ULDPE content increases by 17%,the crystallinity of the film decreases by 3.5%,the OTR increases by 1300cm~3?m~2·d?0.1MPa,and the selective permeability coefficient increases by about 0.2.Although this quantitative description is not universal,it still has guiding significance for the blending modification of polyethylene film.（2）Three 35μm blend films（LLDPE 2607G/ULDPE 4404G）with 33%,50%and67%ULDPE 4404G content and 25μm pure LLDPE films were prepared on a three-layer blowing machine equipped with a corona machine.The effect of ULDPE content on the properties of the blend films in industrial production was further explored.The results showed that the performance change trend of the mass-produced modified polyethylene film was the same as that of the film prepared in the laboratory.The addition of ULDPE also improved the strength and toughness of LLDPE.However,due to the high requirement of raw material stability of the three-layer coextrusion film blowing machine,the film forming ability of ULDPE is poor,which will increase the processing defects of the film.At the same time,the addition of corona discharge machine also increased the surface defects of the film and partially reduced the thickness,which jointly weakened the improvement effect of ULDPE on the mechanical properties of the film.When the ULDPE content increased from 33%to67%,the longitudinal tensile strength of the blend film increased by 9.6%,the longitudinal elongation at break increased by 7.2%,the transverse tensile strength increased by 29.4%,the transverse elongation at break increased by 14.6%,the longitudinal tear strength increased by 24.1%,the transverse tear strength increased by16.7%,and the impact mass increased by 50.7%.DSC results showed that the crystallization and permeability of the industrialized mass-produced blend films were slightly improved,but the change trend did not change.When the ULDPE content increased by 17%,the crystallinity of the films decreased by 2.5～3.5%,the OTR increased by 2000～2500cm~3?m~2·d?0.1MPa,and the selective permeability increased by about 0.2.（3）All blend modified polyethylene films prepared in this experiment were made into modified atmosphere packaging bags for packaging Xinjiang apricot,apricot,peach,mango and other fruits with different respiratory rates,and their preservation effects were compared.The mathematical model of dynamic equilibrium theory was used for derivation,and the results showed that the modified atmosphere packaging with the permeability coefficient of about 4.4 could prolong the shelf life of apricot,namely,the blend modified polyethylene films（PE-c,PE-3）with ULDPE content of50%in this experiment.The changes of sensory evaluation scores,weight loss rate and corruption index of fruits with storage time were recorded.The results showed that PE-3 and PE-c films were suitable for storage of Xinjiang apricot.Under room temperature,the preservation time of apricot could be extended from 2 days to 7 days,and the shelf life of apricot could be extended by more than three times,and the commodity rate could be increased by more than 30%.Under cold storage conditions,after 11 days of storage,the apricot showed no signs of corruption.PE-c film is suitable for storing ordinary apricots and peaches,and can increase their shelf life by more than two times.Film PE-d can extend the shelf life of mango from 3 days to 5 days.