Preparation And Application Of Oxygen Barrier Packaging Materials And Novel Oxygen Scavenger Compounds

The preservation of fish meat show great significance in improving people’s overall living standards.The materials used for fish preservation are mainly divided into oxygen barrier packaging materials and built-in oxygen scavenger compounds.As typical oxygen barrier packaging materials,common petroleum-based packaging materials with high oxygen permeation resistance,such as nylon 6（polyamide 6,PA6）,nylon 6,6（polyamide 66,PA66）,polyester（polyethylene terephthalate,PET）and polypropylene（PP）,are widely used in fish preservation.However,these materials are difficult to be regenerated and degraded by microorganisms.More and more scientific works have been committed to search for renewable or biodegradable packaging materials due to the sever stress from global environmental pollution and energy crisis.Recently,polylactic acid（PLA）,poly（butylene succinate）（PBS）,poly（butyleneadipate-co-terephthalate）（PBAT）and polycaprolactone（PCL）have been successfully used as biodegradable packaging materials.Howerver,their high cost and poor oxygen barrier properties severely limit their practical application in packaging materials for fish preservation.Bio-based polyamide 11（polyamide 11,PA11）is synthesized from renewable sebacic acid monomers,and thermoplastic starch（TPS）has good melt processability,and its raw materials is derived from pure natural.Notably,these two polymers possess high oxygen permeation resistance,thus they can be used as packaging materials.In this thesis,the bio-based PA11 and TPS were melt-blended with poly（vinyl alcohol）（PVA）to prepare PA11/PVA,TPS/PVA and sc CO₂TPS/PVA blend films,respectively.When they were reached the optimal ratio,the oxygen barrier properties（oxygen permeation rate,OTR）of the PA11_72.5PVA³⁰⁰_27.5,TPS₇₅PVA₂₅³⁰⁰and sc CO₂TPS₇₅PVA₂₅³⁰⁰ films reached a minimum value,respectively.The optimized PA11_72.5PVA³⁰⁰_27.5 film exhibits lowest OTR of1.07 cm³/m²?day?atm,which is almost same to that of ethylene-vinyl alcohol copolymer（EVOH）films.Therefore,the PA11_72.5PVA³⁰⁰_27.5 film with MFe/AC/Cu₂SO₄oxygen scavenger compound prepared in this thesis can increase fish preservation time.The built-in oxygen scavenger compounds can be divided into two types materials,as inorganic oxygen scavenger compounds and organic oxygen scavenger compounds.The inorganic oxygen scavenger compounds include active iron powder,sodium dithionite（Na₂S₂O₄）,platinum and palladium,and the organic oxygen scavenger compounds include enzymes,ascorbic acid,linoleic acid and so on.The main obtained in this dissertation are as follows:（1）By employing bio-based polyamide 11 with PVA（degree of polymerization,DP,DP=300）,PA11_xPVA_z³⁰⁰ can be fabricated through melt-blending.As a result,the optimized PA11_xPVA_z³⁰⁰ film with 27.5wt%PVA exhibits best OTR of 1.07 cm³/m²?day?atm,which is comparable to that of the EVOH.The DMA and DSC of PA11_xPVA_z³⁰⁰ films show that,PA11_xPVA_z³⁰⁰ film has a T_g and T_mif the PVA content was not higher than 27.5wt%.These results indicated that the PA11_xPVA_z³⁰⁰ films have achieved uniform dispersion at the molecular level or segment level.Besides,the Fourier transform infrared（FTIR）showed that the C=O stretching vibration peaks in the blends shifted to lower wavenumbers if the PVA content was not higher than 27.5wt%.And this result proves the intermolecular hydrogen bonding force gradually increased.（2）Supercritical carbon dioxide-assisted thermoplastic starch（sc CO₂TPS）and supercritical carbon dioxide-assisted thermoplastic starch/PVA（sc CO₂TPS_xPVA_z^y）are biodegradable films.The OTR are significantly improved by varying DP or sc CO₂-assisted processing.The PVA and TPS blends with different water contents can be prepared by adjusting the polymerization degree of PVA at normal pressures.The OTRs of TPS₇₅PVA₂₅³⁰⁰,TPS_77.5PVA_22.5¹⁴⁰⁰ and TPS₈₀PVA₂₀²⁴⁰⁰ films with 4wt%water exhibit 5.8,9.2 and 10.7cm³/m²?day?atm,respectively.Moreover,the OTRs of sc CO₂TPS₇₅PVA₂₅³⁰⁰,sc CO₂TPS_77.5PVA_22.5¹⁴⁰⁰ and sc CO₂TPS₈₀PVA₂₀²⁴⁰⁰ films are lowest as 4.6,5.1 and 8.4cm³/m²?day?atm,respectively.The above results show that the OTR of the blends assisted by sc CO₂ are better than that of the blends prepared at atmospheric pressure.Furthermore,the OTR of sc CO₂TPS₇₅PVA₂₅³⁰⁰ is comparable with polyvinylidene chloride.The DMA analysis of sc CO₂TPS_xPVA_z^y films show that,sc CO₂TPS_xPVA_z^y films has a T_g if the PVA contents are not higher than their critical value.These results indicated that the sc CO₂TPS_xPVA_z^y films have achieved uniform dispersion at the molecular level or segment level.Besides,the FTIR of the optimized sc CO₂TPS_xPVA_z^y films showed that O-H stretching vibration peaks shift to low wavenumbers,proving that the intermolecular hydroxyl interaction were enhanced if the PVA content were not higher than their critical value.（3）The oxygen scavenger compounds were prepared by using modified iron powder（MFe）/activated carbon（AC）/cuprous sulfate（Cu₂SO₄）in different proportions.The oxygen depletion properties,peroxide value（POV）,p H value,scanning electron microscope（SEM）and electrochemistry were characterized by using fresh grass carp as a model.The results show that the optimal proportion of(MFe_2μm^90.9AC^9.1_100nm)^52.4（Cu₂SO₄）^47.6 oxygen scavenger compounds can effectively prolong the effective shelf life of food.The oxygen depletion rates of MFe/AC or MFe/AC/Cu₂SO₄oxygen scavengers increased considerably with decreasing particle sizes of iron or activated carbon particles.After 24 hours of oxygen depletion experiments,residual oxygen concentration remained in airtight flasks containing the optimum(MFe_2μm^90.9AC^9.1_100nm)^52.4（Cu₂SO₄）^47.6 oxygen scavenger compound reduced rapidly to 0.01%.Considerably smaller peroxide or surface p H values were acquired for fresh grass carp modelled foods in(MFe_2μm^90.9AC^9.1_100nm)^52.4（Cu₂SO₄）^47.6contained bags than those of without(MFe_2μm^90.9AC^9.1_100nm)^52.4（Cu₂SO₄）^47.6 oxygen scavenger compounds.Very low peroxide or surface p H values（1.2 meq/kg and 6.72）were acquired for 15-day fresh grass carp modelled foods in nitrogen-purged PA11_72.5PVA_27.5bag containing optimum(MFe_2μm^90.9AC^9.1_100nm)^52.4（Cu₂SO₄）^47.6 oxygen scavenger compounds.It is worth emphasizing that the electrochemical active surface areas（ECSAs）and the number of contact sites of all iron/activated carbon pairing series increased substantially,as iron or activated carbon particle sizes reduced.Presumably,the beneficial effect of the optimum(MFe_2μm^90.9AC^9.1_100nm)^52.4（Cu₂SO₄）^47.6 on reducing residual oxygen concentration,peroxide and surface p H values of fresh grass carp modelled foods in optimum(MFe_2μm^90.9AC^9.1_100nm)^52.4（Cu₂SO₄）^47.6contained bags are partly due to the considerably enhanced ECSAs of Fe/AC pairings with the decrease in Fe or AC particle sizes.Therefore,the PA11_72.5PVA_27.5/(MFe_2μm^90.9AC^9.1_100nm)^52.4（Cu₂SO₄）^47.6 packaging material in nitrogen-purged was a very efficient bio-based oxygen barrier packaging material.