Efficient long-carbon-chain polyamide elastomer modified atmosphere preservative film as well as preparation method and application thereof

Abstract

The invention belongs to the field of food packaging, and particularly relates to an efficient long-carbon-chain polyamide elastomer modified atmosphere preservative film as well as a preparation method and application thereof. The high-efficiency long-carbon-chain polyamide elastomer modified atmosphere preservative film is prepared from a raw material comprising a long-carbon-chain polyamide elastomer material, and the long-carbon-chain polyamide elastomer material is a segmented copolymer formed by alternately using long-carbon-chain polyamide as a hard segment and polyether as a soft segment. The preparation method of the long-carbon-chain polyamide elastomer modified atmosphere preservative film can adopt one of extrusion blow molding or two-way stretching. The film preparation method provided by the invention does not need a solvent, and the preparation process is simple and environment-friendly. The modified atmosphere preservative film disclosed by the invention has good modified atmosphere performance, controllable and adjustable CO2 permeability, CO2 / O2 separability and water vapor permeability, also has an ethylene gas removal function and good mechanical properties and thermal stability, and can meet the fresh-keeping requirements of fruits and vegetables with different respiratory action intensities.

Description

Technical Field

[0001] The invention belongs to the field of food packaging, and in particular relates to a high-efficiency long-carbon-chain polyamide elastomer modified atmosphere fresh-keeping film and a preparation method and application thereof. Background Art

[0002] Due to the short shelf life of perishable products such as fruits and vegetables, about one-third of food is lost and wasted worldwide each year. The decay of fresh fruits and vegetables is a very complex process, including dehydration, respiratory metabolism, microbial growth and aging. Existing methods for extending the shelf life of food mainly include adding preservatives, waxing, irradiation, refrigeration, heat treatment and controlled atmosphere storage. However, excessive use of preservatives may lead to bioaccumulation of toxic substances; waxing can reduce the transpiration of fruits and vegetables, but chemicals will inevitably remain on the surface of food; heating and irradiation can reduce the reproduction of microorganisms, but the ripening and decay of food is inevitable; refrigeration can extend the shelf life of fresh fruits and vegetables, but salting out and frostbite are prone to occur during refrigeration, and the cost is high; and controlled atmosphere requires large equipment and places with a constant gas supply. Therefore, there is an urgent need to develop a sustainable, simple, universal and low-cost preservation technology.

[0003] After harvest, fruits and vegetables continue to breathe, and their corruption is closely related to the atmosphere (CO2 / O2 / H2O) inside the packaging material. Under respiratory control, fruits and vegetables with different respiratory metabolisms require different gas components. Since fruits and vegetables release ethylene gas (CH2=CH2, C2H4) with a ripening effect during the ripening process, it is not conducive to preservation to a certain extent. Breathable films with high CO2 / O2 selectivity and appropriate H2O permeability and C2H4 permeability can maintain an ideal atmosphere with low O2 concentration and high CO2 concentration, thereby inhibiting the physiological metabolism of plants and inhibiting the reproduction of bacteria. Therefore, the development of modified atmosphere packaging films with highly controllable permeability and biosafety has become a research hotspot in the current food packaging field.

[0004] At present, the most commonly used spontaneous modified atmosphere packaging films are polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC) films, which are widely available and low in cost, but have poor air permeability. Due to the large differences in respiration intensity between different fruits and vegetables, the requirements for CO2 and O2 in the packaging film are also different. For fresh fruits and vegetables with high respiration intensity or sensitive to CO2, conventional PE, PP and PVC can no longer meet the needs, and the air permeability and CO2 / O2 separation of packaging film materials must be improved. In order to solve the existing problems, researchers currently choose to introduce microporous structures or highly permeable silicon windows into conventional cling films to improve air permeability, and prepare multilayer films to achieve antibacterial and antioxidant functions.

[0005] CN101992564A introduces a method of embedding a silicon window on a polyethylene fresh-keeping bag body by hot pressing and bonding. In addition to being able to adjust the concentration ratio of CO2 and O2 inside and outside the bag body, the fresh-keeping bag prepared by the invention also contains antiseptic chemicals in the bag body itself, which can effectively reduce microorganisms on the surface of fruits and vegetables during storage and extend the shelf life. However, the silicon window area is small, and the improvement of air permeability is limited; and the bonding part is prone to aging, which is not conducive to the long-term use of the fresh-keeping film.

[0006] CN107177089A introduces a method for preparing microporous cling film by adding nano calcium carbonate using polyethylene and polystyrene as substrates. The invention uses nonionic surfactants and titanate coupling agents to increase the compatibility between the substrate and the inorganic filler. The microporous cling film obtained by extrusion blow molding-stretching has good softness and high strength. However, the introduction of micron-scale microporous structure will reduce the selectivity of CO2 / O2.

[0007] CN106589427A introduces a polyvinylidene fluoride (PVDF) asymmetric gas composition regulating membrane. The invention uses PVDF as raw material and N,N-dimethylformamide (DMF) as solvent. The casting liquid is cast on a flat plate to form a membrane. After drying to a certain degree, it is immersed in non-solvent deionized water. The non-solvent induced phase separation method is used to prepare a PVDF gas-controlled packaging film with uneven pore sizes. The obtained cling film has nano-scale micropores that can inhibit the respiration of fresh green peppers. However, the introduction of the microporous structure will cause the mechanical properties to decrease, and the preparation process involves high-boiling point solvents, which is not environmentally friendly.

[0008] CN106674576A introduces a method for preparing a breathable double-layer fruit and vegetable cling film, which uses a laser to punch holes in polyethylene, polypropylene, polylactic acid, and polyhydroxyalkanoate resins to form an outer film, and then the base resin is blended with antibacterial agents and antioxidant functional components through a twin-screw machine to form a coating liquid, and the inner film of the functional components and the outer film punched by the laser are compounded through a coating process to form a breathable fruit and vegetable cling film. However, the dense coating layer is thick, and this double-layer structure design of the fresh-keeping bag will reduce the air permeability, resulting in the inability to discharge moisture in time.

[0009] Long-chain polyamide elastomer (LCPAE) is a multi-block copolymer composed of long-chain polyamide (LCPA) hard segments and polyether soft segments. The crystalline hard segments serve as physical crosslinking points to give the material mechanical strength and thermal stability, while the soft segment polyether has a lower glass transition temperature to give the material a certain degree of flexibility. By adjusting the composition of the soft and hard segments, a series of LCPAE with different hardness can be obtained, which are widely used in the fields of sporting goods, fabric coatings, medical devices, and gas separation. However, there are no patents or reports on the application of LCPAE-based materials in spontaneous atmosphere preservation.

[0010] In view of the above reasons, the present invention is proposed. Summary of the invention

[0011] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a high-efficiency long-chain polyamide elastomer modified atmosphere fresh-keeping film and its preparation method and application. The long-chain polyamide elastomer modified atmosphere fresh-keeping film is prepared by a melt film forming method using an LCPAE-based material as a resin, and has good spontaneous atmosphere-modifying performance, controllable and adjustable CO2 permeability, CO2 / O2 separation and water vapor permeability, and also has an ethylene gas removal function and good mechanical properties and thermal stability, and can meet the needs of different fruit and vegetable preservation.

[0012] In order to solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0013] The invention provides a high-efficiency long-chain polyamide elastomer modified atmosphere fresh-keeping film, which is prepared by using raw materials including long-chain polyamide elastomer materials. The long-chain polyamide elastomer is a block copolymer formed by polycondensation of a crystalline long-chain polyamide hard segment and a polyether soft segment.

[0014] The composition and structure of the soft segment and hard segment in the long-chain polyamide elastomer can be regulated, thereby optimizing the CO2 permeation performance and CO2 / O2 separation performance of the long-chain polyamide elastomer film material.

[0015] Further, according to certain embodiments, the crystalline long carbon chain polyamide hard segment is selected from at least one of PA1012, PA1212, PA612, PA610, PA810, PA1214, PA1313, PA1416, PA11, and PA12;

[0016] Preferably, the polyamide hard segment is PA1012.

[0017] Further, according to certain embodiments, the crystalline long carbon chain polyamide hard segment and the polyether soft segment are connected by an ester bond or an amide bond, and the polyether soft segment is selected from one or more of polyoxyethylene ether, polyoxypropylene ether or polytetramethylene oxide ether; preferably, the polyether soft segment is polytetramethylene oxide ether.

[0018] The hydrogen bond interaction between adjacent molecular chains of the long carbon chain polyamide hard segment can serve as a physical cross-linking point to give the material mechanical strength and thermal stability. The soft segment polyether has a low glass transition temperature to give the material a certain flexibility. The gas-controlled fresh-keeping film prepared by melt film forming method using long carbon chain polyamide elastomer as raw material has the advantages of high mechanical strength and strong tensile strength. Based on the dipole-quadrupole interaction between the ether oxygen group (dipole) and CO2 (quadrupole moment) in the polyether soft segment, and the special affinity for ethylene (CH2=CH2, double bond) produced by the respiration of fruits and vegetables, the membrane material based on LCPAE has high CO2 permeability, high CO2 / light gas separation and C2H4 removal ability.

[0019] In addition, the performance of the membrane material can be further optimized by adding second components such as nanofillers and other polymers and regulating the free volume and the chemical reaction with CO2 and ethylene gas.

[0020] Further, according to certain embodiments, the long carbon chain polyamide elastomer material is one or more of a long carbon chain polyamide elastomer, a long carbon chain polyamide elastomer alloy or a long carbon chain polyamide elastomer nanocomposite material.

[0021] According to certain embodiments, the long carbon chain polyamide elastomer alloy material of the present invention contains 5-25wt% of oligomers or polymers based on the total mass of the raw materials, wherein the oligomers or polymers include polymers or copolymers containing polyether groups;

[0022] Preferably, the oligomer or polymer is selected from at least one of polyethylene glycol, polyurethane, polybutylene terephthalate-based block copolymer, chitosan, polyvinylidene fluoride, poly(4-methyl-1-pentene), polydimethylsiloxane, polysulfone, polyimide, and polylactic acid.

[0023] According to certain embodiments, the long carbon chain polyamide elastomer nanocomposite material of the present invention contains 0.1-5wt% of nanofiller in the total mass of the raw materials, and the nanofiller is at least one of nano calcium carbonate, nano silicon dioxide, talc and montmorillonite.

[0024] The introduction of the second component in long carbon chain polyamide elastomer alloys and nanocomposites can, on the one hand, regulate the free volume of the LCPAE matrix membrane by constructing nanochannels or changing the activity of chain segments; on the other hand, it can promote the dissolution and diffusion of CO2 and C2H4 through carriers that have affinity or reversible chemical reactions with CO2 and C2H4, while regulating the permeation rate of water vapor.

[0025] According to certain embodiments, the high-efficiency long-chain polyamide elastomer modified atmosphere cling film is a single-layer or multi-layer composite film, and the thickness of the high-efficiency long-chain polyamide modified atmosphere cling film is 10-200 μm, preferably, the thickness of the modified atmosphere cling film is 10-80 μm.

[0026] According to certain embodiments, the modified atmosphere cling film has a CO2 permeability of ≥1 Barrer at 35°C, an ideal CO2 / O2 separation factor of ≥2, and a water vapor transmission rate of ≥200 g / (m 2 ·24h), ethylene gas permeability coefficient ≥ 0.2Barrer;

[0027] Preferably, the CO2 permeability coefficient of the LCPAE modified atmosphere cling film is ≥50 Barrer, the ideal CO2 / O2 separation coefficient is ≥5, and the water vapor transmission rate is ≥300 g / (m 2 ·24h), ethylene gas permeability coefficient ≥0.4Barrer.

[0028] Another important object of the present invention is to provide a method for preparing the above-mentioned high-efficiency long-chain polyamide elastomer modified atmosphere fresh-keeping film, which is a melt film forming method, including one or more of film blowing and biaxial stretching.

[0029] As a solution, the film blowing method comprises the following steps:

[0030] (1) placing pellets in a vacuum oven to remove water and dry, wherein the pellets include a long carbon chain polyamide elastomer material;

[0031] (2) mixing the pellets prepared in step (1) with a processing aid and performing extrusion blow molding to form a film;

[0032] (3) The film blown out in step (2) is pulled and rolled up, and cooled and shaped to obtain a thin film.

[0033] According to certain embodiments, the processing aid includes at least one of a chain extender, an antioxidant, a lubricant, a photocatalytic antibacterial agent and an opening agent; preferably, the processing aid is an antioxidant, a photocatalytic antibacterial agent and an opening agent.

[0034] According to certain embodiments, the antioxidant of the present invention is selected from one or more of hindered phenol antioxidants, hindered amine antioxidants, phosphite antioxidants or sulfur antioxidants;

[0035] The photocatalytic antibacterial agent includes one of nano titanium dioxide or nano zinc oxide;

[0036] The opening agent is selected from one or more of diatomaceous earth, talc, silicon dioxide, erucamide or oleamide.

[0037] Preferably, in step (2), the pellets and the processing aid are first plasticized and extruded by a twin-screw extruder, and then a sheet film is formed through a die. The temperature of the barrel zone 1, barrel zone 2, mold zone 1, and mold zone 2 of the extruder is controlled at 180-250°C, the screw speed is 10-100rpm, and the obtained tubular film is inflated into a film by compressed air under the melt flow state, and the diameter of the film bubble is controlled to be 50-2000mm.

[0038] More preferably, in step (3), the traction speed of the traction machine is 1-100 rpm, and the winding speed of the winding machine is 1-100 rpm.

[0039] As another solution, the biaxial stretching method comprises the following steps:

[0040] The pellets of the long carbon chain polyamide elastomer material are plasticized and extruded by a twin-screw extruder, and then a sheet film blank is formed through a die. The temperatures of the barrel zone 1, barrel zone 2, mold zone 1 and mold zone 2 of the extruder are 180-250°C, and the screw speed is 10-100rpm. The obtained sheet film blank is cast in a sheet shape on the roller surface of a steadily rotating cooling roller in a melt flow state, and then enters a longitudinal stretching area after being cooled and shaped by the cooling roller. The stretching temperature is 60-150°C, and then biaxial stretching is carried out at this temperature at a stretching rate of 10-300m / min, and a stretching ratio of 1-8 to obtain the film.

[0041] More preferably, the stretching temperature is 90-130° C., and the stretching ratio is 2.5-6.5.

[0042] The present invention also relates to the use of a long carbon chain polyamide elastomer in the preparation of a modified atmosphere fresh-keeping film, wherein the long carbon chain polyamide elastomer is a block copolymer formed by polycondensation of a crystalline long carbon chain polyamide hard segment and a polyether soft segment;

[0043] Preferably, the modified atmosphere cling film is used to preserve food;

[0044] Preferably, the modified atmosphere fresh-keeping film is used to preserve fresh fruits and vegetables, dairy products such as cheese, and meat products.

[0045] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0046] 1. The present invention provides a high-efficiency long-chain polyamide elastomer modified atmosphere cling film, which is processed from raw materials including long-chain polyamide elastomer materials. The elastomer is prepared by condensation polymerization of a crystalline long-chain polyamide hard segment and a polyether soft segment. The composition and structure of the elastomer soft segment and hard segment can be regulated, thereby achieving the regulation of CO2 permeability and CO2 / O2 separation performance of the long-chain polyamide elastomer film material.

[0047] 2. The present invention provides a high-efficiency long-chain polyamide elastomer modified atmosphere cling film, which is prepared by polycondensing a long-chain polyamide hard segment with a polyether soft segment to obtain a new long-chain polyamide elastomer having high mechanical strength and elongation at break, and then preparing the modified atmosphere cling film.

[0048] There is a dipole-quadrupole interaction between the ether oxygen groups in the polyether soft segment and CO2, and has good affinity with the double bonds of C2H4. Therefore, the film based on the long carbon chain polyamide elastomer has good gas conditioning properties and can also remove C2H4 produced by the respiration of fruits and vegetables to extend the shelf life.

[0049] 3. The present invention provides a high-efficiency long-chain polyamide elastomer modified atmosphere fresh-keeping film. By adopting long-chain polyamide elastomer alloys and nano-composite materials as raw materials, other polymers, oligomers or nano-fillers and other second components can also be introduced to make the free volume of the long-chain polyamide elastomer matrix film and the chemical interaction with CO2 and ethylene gases adjustable and controllable, thereby optimizing the gas permeation-separation performance of the membrane material and improving the fresh-keeping effect.

[0050] 4. The present invention provides a method for preparing a high-efficiency long-chain polyamide elastomer modified atmosphere cling film. The melt film-forming method adopted does not require a solvent, and the preparation process is simple and environmentally friendly. In addition, it does not require a large amount of additive components, which is more environmentally friendly and scientific.

[0051] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the drawings described below are only some embodiments. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the accompanying drawings:

[0053] Figure 1 The figure shows the preservation effect of the modified atmosphere cling film and open packaging of Example 3 of the present invention and Comparative Examples 1 and 2 on cherry tomatoes;

[0054] Figure 2 The diagram shows the preservation effect of the modified atmosphere cling film and open packaging of Example 3 of the present invention and Comparative Examples 1 and 2 on strawberries;

[0055] Figure 3 The graphs are weight variation over time of the modified atmosphere cling film of Example 3 of the present invention and Comparative Examples 1 and 2 and the process of open packaging strawberries.

[0056] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0058] The following examples 1-3 use a film blowing method to prepare films:

[0059] Example 1

[0060] In this embodiment, the specific steps of preparing the long carbon chain polyamide elastomer modified atmosphere fresh-keeping film (A1) are as follows:

[0061] A long carbon chain polyamide elastomer A with an intrinsic viscosity of 157.3 dL / kg, a Shore hardness of 40D, PA1012 as a hard segment, and polytetramethylene ether glycol-1000 as a soft segment was selected, with a tensile strength of 29.6±2.3 MPa and an elongation at break of 1250±130%.

[0062] (1) drying pellets of the long carbon chain polyamide elastomer A in a vacuum oven;

[0063] (2) The dried pellets, 0.5% antioxidant 1098, 1% photocatalytic antibacterial agent nano titanium dioxide, and 0.5% opening agent silicon dioxide are mixed evenly and plasticized and extruded through a twin-screw extruder. The hard segment melting point of the long carbon chain polyamide elastomer A is 173°C. The film is then formed into a tubular film through a die. The temperatures of the extruder barrel zone 1, barrel zone 2, mold zone 1, and mold zone 2 are 200°C, 220°C, 240°C, and 240°C, respectively. The screw speed is 10rpm. The obtained tubular film is blown into a film by compressed air under melt flow conditions, and the diameter of the film bubble is controlled to be 300mm.

[0064] (3) The film blown out in step (2) is pulled and rolled up, the pulling speed of the pulling machine is 50 rpm, and the winding speed of the winding machine is 50 rpm. After cooling and shaping, a LCPAE film (A1) with a thickness of 60 μm is obtained.

[0065] Example 2

[0066] In this embodiment, the specific steps of preparing the long carbon chain polyamide elastomer modified atmosphere fresh-keeping film (B1) are as follows:

[0067] A long carbon chain polyamide elastomer B was selected with an intrinsic viscosity of 188.0 dL / kg, a Shore hardness of 29D, PA1012 as the hard segment, and polytetramethylene ether glycol-2000 as the soft segment. The molecular weight of the hard segment prepolymer was the same as that of the elastomer A in Example 1, the tensile strength was 32.7±2.6 MPa, and the elongation at break was 2520±150%.

[0068] (1) drying pellets of the long carbon chain polyamide elastomer B in a vacuum oven;

[0069] (2) The dried pellets, 0.5% antioxidant 1098, 1% photocatalytic antibacterial agent nano titanium dioxide, and 0.5% opening agent silicon dioxide are mixed evenly and plasticized and extruded through a twin-screw extruder. The hard segment melting point of the long carbon chain polyamide elastomer B is 182°C. The film is then formed into a tubular film through a die. The temperatures of the extruder barrel zone 1, barrel zone 2, mold zone 1, and mold zone 2 are 210°C, 225°C, 255°C, and 255°C, respectively. The screw speed is 10rpm. The obtained tubular film is blown into a film by compressed air under melt flow conditions, and the diameter of the film bubble is controlled to be 300mm.

[0070] (3) The film blown out in step (2) is pulled and rolled up, the pulling speed of the pulling machine is 50 rpm, and the winding speed of the winding machine is 50 rpm. After cooling and shaping, an LCPAE film (B1) with a thickness of 63 μm is obtained.

[0071] Example 3

[0072] In this embodiment, the specific steps of preparing the long carbon chain polyamide elastomer modified atmosphere fresh-keeping film (C1) are as follows:

[0073] A long carbon chain polyamide elastomer C with an intrinsic viscosity of 190.5 dL / kg, a Shore hardness of 23D, PA1012 as a hard segment, and polytetramethylene ether glycol-3000 as a soft segment was selected. The molecular weight of the hard segment prepolymer was the same as that of the elastomers A and B in Examples 1 and 2, the tensile strength was 27.6±2.0 MPa, and the elongation at break was 2800±180%.

[0074] (1) drying pellets of the long carbon chain polyamide elastomer C in a vacuum oven;

[0075] (2) The dried pellets, 0.5% antioxidant 1098, 1% photocatalytic antibacterial agent nano titanium dioxide, and 0.5% opening agent silicon dioxide are mixed evenly and plasticized and extruded through a twin-screw extruder. The hard segment melting point of the long carbon chain polyamide elastomer C is 178°C. The film is then formed into a tubular film through a die. The temperatures of the extruder barrel zone 1, barrel zone 2, mold zone 1, and mold zone 2 are 210°C, 220°C, 250°C, and 250°C, respectively. The screw speed is 10rpm. The obtained tubular film is blown into a film by compressed air under melt flow conditions, and the diameter of the film bubble is controlled to be 300mm.

[0076] (3) The film blown out in step (2) is pulled and rolled up, the pulling speed of the pulling machine is 50 rpm, and the winding speed of the winding machine is 50 rpm. After cooling and shaping, an LCPAE film (C1) with a thickness of 62 μm is obtained.

[0077] The following Examples 4-6 use a biaxial stretching method to prepare films.

[0078] Example 4

[0079] The difference from Example 1 is that the pellets and the processing aid (the same as in Example 1) are plasticized and extruded by a twin-screw extruder, and then a sheet film is formed through a die. The temperatures of the extruder barrel zone 1, barrel zone 2, mold zone 1, and mold zone 2 are 200°C, 220°C, 240°C, and 240°C, respectively, and the screw speed is 10rpm. The obtained sheet film is cast in a sheet shape onto the roller surface of a steadily rotating cooling roller under the melt flow state. After cooling and shaping on the cooling roller, the film enters the longitudinal stretching equipment. The stretching temperature is 90°C, and then biaxial stretching is carried out at this temperature at a stretching rate of 120m / min. The stretching ratio is 3.5×3.5, and a LCPAE film (A2) with a thickness of 70μm is obtained.

[0080] Example 5

[0081] The difference from Example 2 is that the pellets and the processing aid (the same as in Example 2) are plasticized and extruded by a twin-screw extruder, and then a sheet film is formed through a die. The temperatures of the extruder barrel zone 1, barrel zone 2, mold zone 1, and mold zone 2 are 210°C, 225°C, 255°C, and 255°C, respectively, and the screw speed is 10rpm. The obtained sheet film is cast in a sheet shape onto the roller surface of a steadily rotating cooling roller under melt flow state. After cooling and shaping on the cooling roller, the film enters the longitudinal stretching equipment. The stretching temperature is 90°C, and then biaxial stretching is carried out at this temperature at a stretching rate of 100m / min. The stretching ratio is 3.5×3.5, and a LCPAE film (B2) with a thickness of 75μm is obtained.

[0082] Example 6

[0083] The difference from Example 3 is that the pellets and the processing aid (the same as in Example 3) are plasticized and extruded by a twin-screw extruder, and then a sheet film is formed through a die. The temperatures of the extruder barrel zone 1, barrel zone 2, mold zone 1, and mold zone 2 are 210°C, 220°C, 250°C, and 250°C, respectively, and the screw speed is 10rpm. The obtained sheet film is cast in a sheet shape onto the roller surface of a steadily rotating cooling roller under the melt flow state. After cooling and shaping on the cooling roller, the film enters the longitudinal stretching equipment. The stretching temperature is 90°C, and then biaxial stretching is carried out at this temperature at a stretching rate of 90m / min. The stretching ratio is 3.5×3.5, and a LCPAE film (C2) with a thickness of 73μm is obtained.

[0084] The following are Examples 7-18. The operating steps refer to Example 3 or Example 6, and the specific process parameters are shown in Table 1 and Table 2.

[0085] Table 1 Film blowing process parameters of Examples 7-12

[0086]

[0087]

[0088] Table 2 Biaxially stretched film forming process parameters of Examples 13-18

[0089]

[0090] The following Examples 19-22 are mixed matrix membranes prepared by adding a second component to a long carbon chain polyamide elastomer.

[0091] Embodiment 19

[0092] The difference between this embodiment and embodiment 3 is that the long-chain polyamide elastomer raw material used in this embodiment is an alloy of long-chain polyamide elastomer C / polyethylene glycol-350, wherein the addition amount of polyethylene glycol-350 is 5wt%, and the thickness of the film obtained by the method of embodiment 3 is 58μm.

[0093] Embodiment 20

[0094] The difference between this embodiment and Embodiment 19 is that the long-chain polyamide elastomer raw material used in this embodiment is an alloy of long-chain polyamide elastomer C / polyethylene glycol-350, wherein the addition amount of polyethylene glycol-350 is 20wt%, and the thickness of the film obtained by the method of Embodiment 3 is 55μm.

[0095] Embodiment 21

[0096] The difference between this embodiment and embodiment 3 is that the long carbon chain polyamide elastomer raw material used in this embodiment is a nanocomposite of long carbon chain polyamide elastomer C / nano-silicon dioxide, wherein the addition amount of nano-silicon dioxide is 1wt%, and the thickness of the film obtained by the method of embodiment 3 is 65μm.

[0097] Embodiment 22

[0098] The difference between this embodiment and Embodiment 21 is that the long carbon chain polyamide elastomer raw material used in this embodiment is a nanocomposite of long carbon chain polyamide elastomer C / amino-modified nano-silica, wherein the addition amount of amino-modified nano-silica is 1wt%, and the thickness of the film obtained by the method of Embodiment 3 is 68μm.

[0099] Comparative Example 1

[0100] In this comparative example, the specific steps of preparing polyethylene (PE) modified atmosphere cling film are as follows:

[0101] (1) Drying the PE pellets in a vacuum oven;

[0102] (2) The dried pellets, 0.5% antioxidant 1098, 1% photocatalytic antibacterial agent nano titanium dioxide, and 0.5% opening agent silicon dioxide are mixed evenly and plasticized and extruded through a twin-screw extruder. The melting point of PE is 126°C. The tubular film blanks are then formed through a die. The temperatures of the extruder barrel zone 1, barrel zone 2, mold zone 1, and mold zone 2 are 160°C, 170°C, 180°C, and 180°C, respectively. The screw speed is 10rpm. The obtained tubular film blanks are inflated into films by compressed air under melt flow conditions, and the diameter of the film bubbles is controlled to be 300mm.

[0103] (3) The film blown out in step (2) is pulled and rolled up, the pulling speed of the pulling machine is 50 rpm, and the winding speed of the winding machine is 50 rpm. After cooling and shaping, a PE film with a thickness of 57 μm is obtained.

[0104] Comparative Example 2

[0105] In this comparative example, the specific steps of preparing PA1012 modified atmosphere cling film are as follows:

[0106] (1) Drying PA1012 pellets in a vacuum oven;

[0107] (2) The dried pellets, 0.5% antioxidant 1098, 1% photocatalytic antibacterial agent nano titanium dioxide, and 0.5% opening agent silicon dioxide are mixed evenly and plasticized and extruded through a twin-screw extruder. The melting point of PA1012 is 190°C. The tubular film blanks are then formed through a die. The temperatures of the extruder barrel zone 1, barrel zone 2, mold zone 1, and mold zone 2 are 220°C, 230°C, 240°C, and 240°C, respectively. The screw speed is 10rpm. The obtained tubular film blanks are inflated into films by compressed air under melt flow conditions, and the diameter of the film bubbles is controlled to be 300mm.

[0108] (3) The film blown out in step (2) is pulled and rolled up, the pulling speed of the pulling machine is 50 rpm, and the winding speed of the winding machine is 50 rpm. After cooling and shaping, a PA1012 film with a thickness of 59 μm is obtained.

[0109] Test Example 1 Gas Permeability Test of Films Based on Long Carbon Chain Polyamide Elastomer

[0110] The CO2 permeability coefficient, O2 permeability coefficient and C2H4 permeability coefficient of the LCPAE-based film of the present invention were measured according to the method of GB / T 1038-2000, and the test temperature and pressure were 35°C and 1 Barrer, respectively. The water vapor transmission rate (WVTP) of the LCPAE-based film was measured at 23°C and RH=50% according to the method of ASTM E96B. The specific values ​​are shown in Table 3.

[0111] Table 3 Gas permeability properties of LCPAE-based films

[0112]

[0113]

[0114] By comparing the CO2 permeability, CO2 / O2 separation, ethylene gas permeability and water vapor permeability of Examples 1-6, it can be found that when the molecular weight of the hard segment is fixed, the larger the molecular weight of the soft segment, the higher the gas permeability and selectivity; similarly, by comparing Examples 3, 19-20, it can be learned that the introduction of polyethylene glycol containing a high ether oxygen group density is conducive to further promoting the permeation of CO2 and the separation of CO2 / O2. According to the performance parameters of Examples 7-12 and 13-18, it can be concluded that by adjusting the parameters of the membrane control process, a series of films with different thicknesses and structures can be obtained. When the thickness is less than 50μm, the permeability of the material increases with the decrease in thickness. From the performance parameters of Examples 3, 21-22, it can be learned that the introduction of silica can promote the separation of CO2 / O2, and due to the reversible reaction of amino groups with CO2, amino-decorated silica can further enhance the permeability-selectivity of the membrane material.

[0115] Based on the above results, the film prepared in the embodiment of the present invention has high CO2 permeability, CO2 / O2 separation and water vapor permeability, and also has a certain ethylene gas permeability; and by changing the copolymer composition, process parameters and the second component, the permeation-separation performance can be controlled and adjusted, which is expected to meet the preservation needs of fruits and vegetables with different respiratory metabolism.

[0116] Test Example 2: Test on the preservation effect of modified atmosphere plastic wrap on fresh cherry tomatoes and strawberries

[0117] Fresh strawberries and cherry tomatoes with different respiration intensities were placed in polypropylene bottles, and the films in Example 3 (LCPAE) and Comparative Example 1 (PE) and Comparative Example 2 (PA1012) were sealed on the mouths of the polypropylene bottles containing fruits with paraffin wax, and an open container was used as a control. The polypropylene bottles were placed in a room temperature environment for observation and weighed at regular intervals. Figure 1-3 .

[0118] from Figure 1 It can be seen that the cherry tomatoes packaged with LCPAE are still bright in color and full in size after 7 days, while the cherry tomatoes packaged with PE and PA1012 have white mold at the root and water droplets hanging on the bottle wall, and the surface of the cherry tomatoes in the open container is wrinkled.

[0119] from Figure 2 It can be seen that the strawberries in the open container lose water seriously due to their strong respiration. Compared with PE and PA1012 films, the water vapor generated by the respiration of strawberries in the polypropylene bottle packaged by LCPAE film can be removed in time, which will not cause the surface of the strawberries to rot.

[0120] Figure 3 The figure shows the change in the overall weight of the above materials during the packaging of strawberries. It can be seen that compared with open containers, LCPAE film can inhibit the respiration of strawberries, so the weight loss is small; compared with PE and PA1012 films, because LCPAE has a higher WVTP, the moisture generated by respiration can be removed in time. Therefore, although the weight has decreased to a certain extent, it can inhibit the reproduction of bacteria to a certain extent and will not cause the strawberries to rot, thereby extending the shelf life of strawberries. The weight loss is caused by the timely discharge of moisture generated by respiration. For spontaneous atmosphere-controlled cling film, it needs to discharge moisture and carbon dioxide in the package, which is not conducive to the reproduction of bacteria and microorganisms, so as to achieve the preservation effect.

[0121] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment, it is not used to limit the present invention. Any technician familiar with this patent can make some changes or modify the technical contents suggested above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the solution of the present invention.

Claims

1. A high-efficiency long-carbon-chain polyamide elastomer modified atmosphere fresh-keeping film, characterized in that: The invention is prepared by using raw materials including long carbon chain polyamide elastomer material. The long carbon chain polyamide elastomer is a block copolymer formed by polycondensation of a crystalline long carbon chain polyamide hard segment and a polyether soft segment.

2. The high-efficiency long carbon chain polyamide elastomer modified atmosphere fresh-keeping film according to claim 1, characterized in that: The crystalline long carbon chain polyamide hard segment is selected from at least one of PA1012, PA1212, PA612, PA610, PA810, PA1214, PA1313, PA1416, PA11, and PA12; Preferably, the polyamide hard segment is PA1012.

3. The high-efficiency long carbon chain polyamide elastomer modified atmosphere fresh-keeping film according to claim 1, characterized in that: The crystalline long carbon chain polyamide hard segment is connected to the polyether soft segment by an ester bond or an amide bond, and the polyether soft segment is selected from one or more of polyoxyethylene ether, polyoxypropylene ether and polytetramethylene oxide ether; Preferably, the polyether soft segment is polytetramethylene oxide.

4. The high-efficiency long carbon chain polyamide elastomer modified atmosphere fresh-keeping film according to claim 1, characterized in that: The long carbon chain polyamide elastomer material is selected from one or more of a long carbon chain polyamide elastomer, a long carbon chain polyamide elastomer alloy or a long carbon chain polyamide elastomer nanocomposite material; Preferably, the long carbon chain polyamide elastomer alloy material contains 5-25wt% of oligomers or polymers based on the total mass of the raw materials, and the oligomers or polymers include polymers or copolymers containing polyether groups; preferably, the oligomers or polymers are selected from at least one of polyethylene glycol, polyurethane, polybutylene terephthalate-based block copolymers, chitosan, polyvinylidene fluoride, poly(4-methyl-1-pentene), polydimethylsiloxane, polysulfone, polyimide, and polylactic acid; Preferably, the long carbon chain polyamide elastomer nanocomposite material contains 0.1-5 wt% of nanofiller based on the total mass of the raw materials, and the nanofiller is selected from at least one of nano calcium carbonate, nano silicon dioxide, talc and montmorillonite.

5. The high-efficiency long carbon chain polyamide elastomer modified atmosphere fresh-keeping film according to any one of claims 1 to 4, characterized in that: The high-efficiency long-carbon-chain polyamide elastomer modified atmosphere cling film is a single-layer or multi-layer composite film, and the thickness of the high-efficiency long-carbon-chain polyamide modified atmosphere cling film is 10-200 μm, preferably, the thickness of the modified atmosphere cling film is 10-80 μm.

6. The high-efficiency long carbon chain polyamide elastomer modified atmosphere fresh-keeping film according to any one of claims 1 to 4, characterized in that: The CO2 permeability coefficient of the modified atmosphere fresh-keeping film is ≥1 Barrer, the ideal CO2 / O2 is ≥2, and the water vapor transmission rate is ≥200g / (m 2 ·24h), ethylene gas permeability coefficient ≥ 0.2Barrer; Preferably, CO2 permeability coefficient ≥ 50 Barrer, ideal CO2 / O2 ≥ 5, water vapor transmission rate ≥ 300g / (m 2 ·24h), ethylene gas permeability coefficient ≥0.4Barrer.

7. A method for preparing a high-efficiency long-chain polyamide elastomer modified atmosphere fresh-keeping film according to any one of claims 1 to 6, characterized in that: The method is a melt film forming method, including at least one of a film blowing method and a biaxial stretching method.

8. The preparation method according to claim 7, characterized in that: The film blowing method comprises the following steps: (1) drying pellets of long carbon chain polyamide elastomer material; (2) mixing the pellets prepared in step (1) with a processing aid and performing extrusion blow molding to form a film; (3) pulling and winding the film blown out in step (2), and cooling and shaping the film to obtain a thin film; Preferably, the processing aid is selected from at least one of a chain extender, an antioxidant, a lubricant, a photocatalytic antibacterial agent and an opening agent; preferably, the processing aid is an antioxidant, a photocatalytic antibacterial agent and an opening agent; Preferably, in step (2), the pellets are first melted and plasticized and extruded by a twin-screw extruder, and then formed into a tubular film blank through a die. The temperatures of the barrel zone 1, barrel zone 2, mold zone 1, and mold zone 2 of the extruder are controlled at 180-250° C., the screw speed is 10-100 rpm, and the obtained tubular film blank is inflated by compressed air in a melt flow state, and the diameter of the film bubble is controlled to be 50-2000 mm. Preferably, in step (3), the traction speed of the traction machine is 1-100 rpm, and the winding speed of the winding machine is 1-100 rpm.

9. The preparation method according to claim 7, characterized in that: The biaxial stretching method comprises the following steps: The pellets of the long carbon chain polyamide elastomer material and the processing aid are plasticized and extruded by a twin-screw extruder, and then a sheet film blank is formed through a die. The temperature of the barrel zone 1, barrel zone 2, mold zone 1, and mold zone 2 of the extruder is 180-250° C., and the screw speed is 10-100 rpm. The obtained sheet film blank is cast in a sheet shape on the roller surface of a steadily rotating cooling roller in a melt flow state, and then cooled and shaped by the cooling roller and then enters the longitudinal stretching area. The stretching temperature is 60-150° C., and then biaxial stretching is performed at this temperature at a stretching rate of 10-300 m / min, and the stretching ratio is 1-8 to obtain the film; Preferably, the isothermal temperature is 90-130° C., and the stretching ratio is 2.5-6.

5.

10. Use of a long carbon chain polyamide elastomer in preparing a modified atmosphere cling film, characterized in that: The long carbon chain polyamide elastomer is a block copolymer formed by polycondensation of a crystalline long carbon chain polyamide hard segment and a polyether soft segment; Preferably, the modified atmosphere cling film is used to preserve food; Preferably, the modified atmosphere fresh-keeping film is used to preserve fresh fruits and vegetables, dairy products, and meat products.

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