Method for judging two-way tensile property of polyethylene raw material

Abstract

The invention provides a method for judging the two-way tensile property of a polyethylene raw material, the raw material is one or more linear low-density polyethylene, the raw material is subjected to a small-angle X-ray scattering experiment after being longitudinally stretched, if a detection signal is a shish-kebab crystal signal, the raw material has the two-way tensile property, otherwise, the raw material does not have the two-way tensile property. According to the method provided by the invention, whether the polyethylene raw material can be used for two-way stretching or not can be preliminarily and rapidly evaluated from the raw material end, subsequent tedious test steps are omitted, the efficiency is high, and the cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer film detection, and particularly relates to a method for judging the biaxial stretching performance of polyethylene raw materials. Background Art

[0002] With the popularization of the concept of "single-material recyclable", the development of biaxially oriented polyethylene (BOPE) films has received more and more extensive attention. BOPE films are polyethylene films obtained by longitudinally and transversely stretching polyethylene using the flat film method, and have very excellent optical and mechanical properties, and are used to replace blown and cast polyethylene films, biaxially oriented polypropylene (BOPP) films, biaxially oriented nylon (BOPA), and biaxially oriented polyethylene terephthalate (BOPET) films in the application of packaging films.

[0003] Due to the particularity of biaxial stretching, ordinary film-grade polyethylene resins are usually difficult to be processed by biaxial stretching. In recent years, companies such as Mitsui Chemicals and Dow Chemical have successively launched commercial special materials for BOPE films, making the industrialization of biaxially oriented polyethylene possible. However, to determine whether a linear low-density polyethylene (LLDPE) resin raw material can be biaxially stretched, actual production line verification is required, which has a long cycle and high cost. Moreover, there is no full understanding of what characteristics of LLDPE can be biaxially stretched.

[0004] In summary, there is an urgent need to provide a method that can quickly identify whether LLDPE can be biaxially stretched, which is used to preliminarily verify whether an LLDPE raw material is suitable for biaxial stretching. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for judging the biaxial stretching performance of polyethylene raw materials, and this method has the characteristics of being simple and convenient.

[0006] To achieve the above purpose, the present invention provides a method for judging the biaxial stretching performance of polyethylene raw materials. The raw materials are one or more linear low-density polyethylenes. After the raw materials are longitudinally stretched, a small-angle X-ray scattering experiment is carried out. If the detected signal is a shish-kebab crystal signal, it has biaxial stretching performance, otherwise it does not have biaxial stretching performance.

[0007] In the method for judging the biaxial stretching performance of polyethylene raw materials of the present invention, the raw materials are subjected to extrusion casting treatment before being longitudinally stretched.

[0008] In the method for judging the biaxial stretching performance of polyethylene raw materials of the present invention, the magnification of the longitudinal stretching is 3-6 times.

[0009] The method for judging the biaxial stretching performance of polyethylene raw materials according to the present invention, wherein the wavelength of the small-angle X-ray is 0.122 - 0.1226 nm -1 , and the distance from the sample to the detector is 4400 - 4600 mm.

[0010] The method for judging the biaxial stretching performance of polyethylene raw materials according to the present invention, wherein after the raw materials are detected by a differential scanning calorimeter, there are still two melting peaks on the DSC melting curve, and the temperature difference ΔT between the two melting peaks is ≥10 °C.

[0011] The method for judging the biaxial stretching performance of polyethylene raw materials according to the present invention, when the raw materials are detected by a differential scanning calorimeter, the raw materials are heated from 20 - 25 °C to 150 - 170 °C, isothermally maintained for 5 - 10 min to eliminate the thermal history, then cooled to 20 - 25 °C to complete crystallization, and then heated from 20 - 25 °C to 150 - 170 °C to obtain the DSC melting curve.

[0012] The method for judging the biaxial stretching performance of polyethylene raw materials according to the present invention, wherein the heating rate is 5 - 10 °C / min and the cooling rate is 5 - 10 °C / min.

[0013] The method for judging the biaxial stretching performance of polyethylene raw materials according to the present invention, wherein the model of the differential scanning calorimeter is DSCDQ2000 or DSC8500.

[0014] Advantages of the present invention:

[0015] The method provided by the present invention can preliminarily and quickly evaluate whether a polyethylene raw material can be used for biaxial stretching from the raw material end, saving the subsequent cumbersome test steps, with high efficiency and low cost. Description of the drawings

[0016] Figure 1 It is the SAXS signal of Example 1;

[0017] Figure 2 It is the SAXS signal of Comparative Example 1 Detailed implementation manners

[0018] The present invention will be specifically described below through examples. It is necessary to point out here that the following examples are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention according to the above content of the present invention.

[0019] Detection methods and equipment

[0020] The small-angle X-ray scattering (SAXS) experiment was carried out on the X-ray scattering device at beamline BL16B of the Shanghai Synchrotron Radiation Facility. The wavelength (λ) of the X-ray was 0.124 nm. The scattering signal was collected using a Pilatus 300K area detector. The detection plane consisted of 487×619 pixels, and the pixel size was 172×172 μm 2 , the distance from the sample to the detector was 4500 mm, and the exposure time was 10 ms. The X-ray scattering data was analyzed using the Fit2D software of the European Synchrotron Radiation Facility (ESRF). The influence of air and equipment on scattering was deducted for each group of data before analysis.

[0021] The differential scanning calorimeter model was DSC DQ2000.

[0022] Example 1

[0023] A LLDPE raw material composition was selected, which consisted of LLDPE with a branching degree of 1.7% and LLDPE with a branching degree of 0.8% in a mass ratio of 7:3.

[0024] The raw materials were subjected to extrusion casting and longitudinal stretching according to the following steps:

[0025] Step 1: The two LLDPEs were put into a twin-screw extruder, melted and blended, extruded into pellets, and dried to obtain a polyethylene raw material composition.

[0026] Step 2: The polyethylene raw material composition was put into an extruder and extruded into a cast film through a three-layer co-extrusion die head. The melting extrusion temperature was 180 °C, and the temperature of the casting roll was 20 °C;

[0027] Step 3: The cast film was longitudinally stretched 3 times at a longitudinal stretching temperature of 110 °C, and then a small-angle X-ray scattering experiment was carried out. The scattering signal is as Figure 1 shown, and it can be seen that there is a shish-kebab crystal signal.

[0028] DSC test on the raw materials:

[0029] 5 mg of the raw material was weighed and put into a crucible. It was heated from 25 °C to 160 °C at a heating rate of 10 °C / min, held for 5 min, then cooled to 25 °C at a rate of 10 °C / min to complete crystallization. Then it was heated from room temperature 25 °C to 160 °C at a heating rate of 10 °C / min, and the DSC curve was recorded. Two melting peaks were obtained. The melting temperature of the high-temperature peak was 124.3 °C, the melting temperature of the low-temperature peak was 112.1 °C, and the difference ΔT between the melting temperature of the high-temperature peak and the melting temperature of the low-temperature peak was 12.2 °C.

[0030] Biaxial stretching experiment of the raw materials:

[0031] Step 1: Put two kinds of LLDPE into a twin-screw extruder, and through melt blending, extrusion granulation, and drying, a polyethylene raw material composition is obtained.

[0032] Step 2: Put the polyethylene raw material composition into an extruder, and extrude it into a cast film through a three-layer co-extrusion die head. The melt extrusion temperature is 180 °C, and the temperature of the casting roll is 20 °C;

[0033] Step 3: Subject the cast film to longitudinal stretching, transverse stretching, and heat setting in sequence, and wind it up to obtain the biaxially oriented polyethylene film. The longitudinal stretching is 3 times, the transverse stretching is 5 times, the longitudinal stretching temperature is 110 - 125 °C, the transverse stretching temperature is 115 - 130 °C, and the heat setting temperature is 115 - 125 °C. It is found that the cast film can be biaxially stretched without film breakage within this temperature range, and finally the biaxially oriented polyethylene film is obtained.

[0034] Example 2

[0035] Select an LLDPE raw material composition, which is composed of LLDPE with a branching degree of 1.7% and LLDPE with a branching degree of 0.8% in a mass ratio of 7:3.

[0036] Extrude and cast the raw materials and conduct longitudinal stretching according to the following steps:

[0037] Step 1: Put two kinds of LLDPE into a twin-screw extruder, and through melt blending, extrusion granulation, and drying, a polyethylene raw material composition is obtained.

[0038] Step 2: Put the polyethylene raw material composition into an extruder, and extrude it into a cast film through a three-layer co-extrusion die head. The melt extrusion temperature is 240 °C, and the temperature of the casting roll is 40 °C;

[0039] Step 3: Longitudinally stretch the cast film 6 times, with the longitudinal stretching temperature being 125 °C, and then conduct a small-angle X-ray scattering experiment. Its scattering signal is Figure 1 similar and has a shish-kebab crystal signal.

[0040] Conduct DSC testing on the raw materials:

[0041] Weigh 5 mg of the raw material and put it into a crucible. Heat it up to 160 °C, keep it warm for 5 min, and then cool it down to room temperature at a rate of 10 °C / min to complete crystallization. Then heat it up from room temperature of 25 °C to 160 °C at a heating rate of 10 °C / min, record the DSC curve, and obtain two melting peaks. The melting temperature of the high-temperature peak is 120.1 °C, the melting temperature of the low-temperature peak is 107.2 °C, and the difference ΔT between the melting temperature of the high-temperature peak and the melting temperature of the low-temperature peak is 12.9 °C.

[0042] Biaxial stretching experiment of the raw materials:

[0043] Step 1: Put two kinds of LLDPE into a twin-screw extruder, and after melting and blending, extrusion granulation, and drying, a polyethylene raw material composition is obtained.

[0044] Step 2: Put the polyethylene raw material composition into an extruder, and extrude it into a cast film through a three-layer co-extrusion die head, where the melting extrusion temperature is 240 °C and the temperature of the casting roll is 40 °C;

[0045] Step 3: Subject the cast film to longitudinal stretching, transverse stretching, and heat setting in sequence, and wind it up to obtain the biaxially oriented polyethylene film, where the longitudinal stretching is 3 times, the transverse stretching is 5 times, the longitudinal stretching temperature is 110 - 125 °C, the transverse stretching temperature is 115 - 130 °C, and the heat setting temperature is 115 - 125 °C. It is found that the cast film can be biaxially stretched without film breakage within this temperature range, and finally the biaxially oriented polyethylene film is obtained.

[0046] Example 3

[0047] Select a kind of LLDPE raw material composition, which is composed of LLDPE with a branching degree of 1.7% and LLDPE with a branching degree of 0.8% in a mass ratio of 8:2.

[0048] Extrude and cast the raw materials according to the following steps and conduct longitudinal stretching:

[0049] Step 1: Put two kinds of LLDPE into a twin-screw extruder, and after melting and blending, extrusion granulation, and drying, a polyethylene raw material composition is obtained.

[0050] Step 2: Put the polyethylene raw material composition into an extruder, and extrude it into a cast film through a three-layer co-extrusion die head, where the melting extrusion temperature is 200 °C and the temperature of the casting roll is 30 °C;

[0051] Step 3: Longitudinally stretch the cast film 3 times, with the longitudinal stretching temperature being 120 °C, and then conduct a small-angle X-ray scattering experiment, and its scattering signal is Figure 1 similar, having a shish-kebab crystal signal.

[0052] Conduct DSC testing on the raw materials:

[0053] Weigh 5 mg of the raw materials and put them into a crucible. Heat them up to 160 °C, keep them warm for 5 min, and then cool them down to room temperature at a rate of 10 °C / min to complete crystallization. Then heat them up from room temperature of 25 °C to 160 °C at a heating rate of 10 °C / min, record the DSC curve, and there is only one melting peak at 120.0 °C.

[0054] Biaxial stretching experiment of the raw materials:

[0055] Step 1: Put two kinds of LLDPE into a twin-screw extruder, and obtain a polyethylene raw material composition through melt blending, extrusion granulation, and drying.

[0056] Step 2: Put the polyethylene raw material composition into an extruder, and extrude it into a cast film through a three-layer co-extrusion die head, where the melt extrusion temperature is 180 - 240 °C and the temperature of the casting roll is 20 - 40 °C;

[0057] Step 3: Subject the cast film to longitudinal stretching, transverse stretching, and heat setting in sequence, and wind it up to obtain the biaxially oriented polyethylene film, where the longitudinal stretching is 3 times, the transverse stretching is 5 times, the longitudinal stretching temperature is 110 - 120 °C, the transverse stretching temperature is 115 - 125 °C, and the heat setting temperature is 115 - 120 °C. It is found that within this temperature range, the cast film can be biaxially stretched without film breakage, and finally the biaxially oriented polyethylene film is obtained.

[0058] Comparative Example 1

[0059] Select an LLDPE raw material composition, which is composed of LLDPE with a branching degree of 1.7% and LLDPE with a branching degree of 0.8% in a mass ratio of 8:2.

[0060] Extrude and cast the raw materials and conduct longitudinal stretching according to the following steps:

[0061] Step 1: Put two kinds of LLDPE into a twin-screw extruder, and obtain a polyethylene raw material composition through melt blending, extrusion granulation, and drying.

[0062] Step 2: Put the polyethylene raw material composition into an extruder, and extrude it into a cast film through a three-layer co-extrusion die head, where the melt extrusion temperature is 180 °C and the temperature of the casting roll is 20 °C;

[0063] Step 3: Longitudinally stretch the cast film 3 times, with the longitudinal stretching temperature being 110 °C, and then conduct a small-angle X-ray scattering experiment. Its scattering signal is as Figure 2 shown, and it can be seen that there is no shish-kebab crystal signal.

[0064] Conduct DSC testing on the raw materials:

[0065] Weigh 5 mg of the raw material and put it into a crucible. Heat it up to 160 °C, keep it warm for 5 min, and then cool it down to room temperature at a rate of 10 °C / min to complete crystallization. Then, heat it up from room temperature of 25 °C to 160 °C at a heating rate of 10 °C / min, record the DSC curve, and obtain two melting peaks. The melting temperature of the high-temperature peak is 121.2 °C, the melting temperature of the low-temperature peak is 111.1 °C, and the difference ΔT between the melting temperature of the high-temperature peak and the melting temperature of the low-temperature peak is 10.1 °C.

[0066] Biaxial stretching experiment of the raw materials:

[0067] Step 1: Put two kinds of LLDPE into a twin-screw extruder, and obtain a polyethylene raw material composition through melt blending, extrusion granulation, and drying.

[0068] Step 2: Put the polyethylene raw material composition into an extruder, and extrude it into a cast film through a three-layer co-extrusion die head, where the melt extrusion temperature is 180°C and the temperature of the casting roll is 20°C;

[0069] Step 3: Subject the cast film to longitudinal stretching and transverse stretching in sequence. The cast film cannot be well biaxially stretched within the entire stretching temperature range in the longitudinal and transverse directions, and a biaxially stretched polyethylene film cannot be prepared.

[0070] Certainly, the present invention may also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for judging the biaxial stretching performance of polyethylene raw materials, characterized in that, the raw materials are one or more linear low-density polyethylenes. After the raw materials are longitudinally stretched, a small-angle X-ray scattering experiment is carried out. If the detected signal is a shish-kebab crystal signal, it has biaxial stretching performance; otherwise, it does not have biaxial stretching performance.

2. The method for judging the biaxial stretching performance of polyethylene raw materials according to claim 1, characterized in that, the raw materials are subjected to extrusion casting treatment before being longitudinally stretched.

3. The method for judging the biaxial stretching performance of polyethylene raw materials according to claim 1, characterized in that, the magnification of the longitudinal stretching is 3-6 times.

4. The method for judging the biaxial stretching performance of polyethylene raw materials according to claim 1, characterized in that, The wavelength of the small-angle X-ray is 0.122 - 0.1226 nm -1 , and the distance from the sample to the detector is 4400 - 4600 mm.

5. The method for judging the biaxial stretching performance of polyethylene raw materials according to claim 1, characterized in that, after the raw materials are detected by a differential scanning calorimeter, there are still two melting peaks on the DSC melting curve, and the temperature difference ΔT between the two melting peaks is ≥10 °C.

6. The method for judging the biaxial stretching performance of polyethylene raw materials according to claim 5, characterized in that, when the raw materials are detected by a differential scanning calorimeter, the raw materials are heated from 20-25 °C to 150-170 °C, isothermally held for 5-10 min to eliminate the thermal history, then cooled to 20-25 °C to complete crystallization, and then heated from 20-25 °C to 150-170 °C to obtain the DSC melting curve.

7. The method for judging the biaxial stretching performance of polyethylene raw materials according to claim 6, characterized in that, the heating rate is 5-10 °C / min, and the cooling rate is 5-10 °C / min.

8. The method for judging the biaxial stretching performance of polyethylene raw materials according to claim 6, characterized in that, the model of the differential scanning calorimeter is DSC DQ2000 or DSC8500.

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