METHOD FOR PREDICTING PHYSICAL PROPERTIES OF POLYMERS

Abstract

The present invention relates to a method for predicting the physical properties of polymers. More specifically, the present invention relates to a method for predicting the processability of polymers using a molecular weight distribution curve.

Claims

1. A method for predicting physical properties of polymers comprising the steps of: measuring a molecular weight distribution curve of the polymer to be measured (herein, a log value of a molecular weight MW (log MW) is denoted by x-axis, and a molecular weight distribution to the log value (dwt/d log MW) is denoted by y-axis) using a gel permeation chromatography (GPC) at a temperature of 160 C.; dividing the section between 3.0 and 7.0 on the x-axis of the molecular weight distribution curve into four equal parts to obtain the integral value of the molecular weight distribution curve at each section; and predicting a die swell ratio value from the integral value.

2. The method for predicting the physical properties of polymers according to claim 1, comprising a step of calculating the predicted value of the die swell ratio according to the following Equation 1 using the integral value:
Die swell ratio, PV=(0.136)*A.sub.1+(0.1152)*A.sub.2+(0.1033)*A.sub.3+(0.181)*A.sub.4+13.97[Equation 1] in Equation 1 above, A.sub.1 is an integral value of a molecular weight distribution curve in the section where log MW is 3.0 to 4.0, A.sub.2 is an integral value of a molecular weight distribution curve in the section where log MW is 4.0 to 5.0, A.sub.3 is an integral value of a molecular weight distribution curve in the section where log MW is 5.0 to 6.0, A.sub.4 is an integral value of a molecular weight distribution curve in the section where log MW is 6.0 to 7.0, and the integral value of A.sub.1 to A.sub.4 means relative values when the integral value of the entire molecular weight distribution curve is 100.

3. The method for predicting the physical properties of polymers according to claim 1, wherein the polymer to be measured is a polyolefin.

4. The method for predicting the physical properties of polymers according to claim 3, wherein the polyolefin is a polymer or a copolymer obtained by polymerizing one or more monomers selected from the group consisting of ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and eicosene.

5. The method for predicting the physical properties of polymers according to claim 1, wherein the polyolefin has a weight average molecular weight of 100,000 to 1,000,000 g/mol.

6. The method for predicting the physical properties of polymers according to claim 1, wherein the polyolefin has a molecular weight distribution of 5 to 30.

7. The method for predicting the physical properties of polymers according to claim 1, wherein the polyolefin is used for a high-pressure pipe.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a molecular weight distribution curve (GPC curve) measured to predict the physical properties of polymers according to an embodiment of the present invention.

[0014] FIG. 2 is a graph showing the relationship between the calculated value and the actually measured value of the die swell ratio according to Equation 1.

[0015] FIG. 3 is a schematic view of an extrusion die for actually measuring the die swell ratio.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] In the present invention, the terms such as first, second, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from another.

[0017] Moreover, the terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Further, singular expressions a, an, and the used herein may include plural expressions unless the context clearly indicates otherwise. In addition, it should be understood that the meaning of the term comprising, including, having and the like is intended to specify the presence of stated features, numbers, steps, components or combinations thereof and does not exclude existence or addition of one or more other features, numbers, components or combinations thereof.

[0018] The invention can make various modifications and take various forms, and thus specific embodiments are illustrated and described in detail below. It should be understood, however, that the invention is not intended to be limited to any particular disclosure form, but includes all modifications, equivalents and alternatives falling within the spirit and scope of the invention.

[0019] Hereinafter, a method for predicting the physical properties of polymers according to specific embodiments of the invention will be described.

[0020] According to one embodiment of the present invention, there is provided a method for predicting physical properties of polymers comprising the steps of:

[0021] measuring a molecular weight distribution curve of the polymer to be measured (herein, a log value of a molecular weight MW (log MW) is denoted by x-axis, and a molecular weight distribution to the log value (dwt/d log MW) is denoted by y-axis) using a gel permeation chromatography (GPC) at a temperature of 160 C.;

[0022] dividing the section between 3.0 and 7.0 on the x-axis of the molecular weight distribution curve into four equal parts to obtain the integral value of the molecular weight distribution curve at each section; and

[0023] predicting a die swell ratio value from the integral value.

[0024] According to one embodiment of the present invention, the predicted value of the die swell ratio may be calculated according to the following Equation 1 using the above integral value:

Die swell ratio, PV=(0.136)*A.sub.1+(0.1152)*A.sub.2+(0.1033)*A.sub.3+(0.181)*A.sub.4+13.97[Equation 1]

[0025] in Equation 1 above,

[0026] A.sub.1 is an integral value of a molecular weight distribution curve in the section where log MW is 3.0 to 4.0, A.sub.2 is an integral value of a molecular weight distribution curve in the section where log MW is 4.0 to 5.0, A.sub.3 is an integral value of a molecular weight distribution curve in the section where log MW is 5.0 to 6.0, A.sub.4 is an integral value of a molecular weight distribution curve in the section where log MW is 6.0 to 7.0, and

[0027] the integral value of A.sub.1 to A.sub.4 means a relative value when the integral value of the entire molecular weight distribution curve is 100.

[0028] In the present invention, the polymer to be measured may be a polyolefin. Also, the polyolefin may be a polymer or a copolymer obtained by polymerizing one or more monomers selected from the group consisting of ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and eicosene.

[0029] The polyolefin is a resin obtained by polymerizing an olefin-based monomer such as ethylene in the presence of a catalyst such as metallocene, and is used in various fields due to excellent physical properties.

[0030] The physical properties of the polyolefin can be evaluated in several respects. For example, the weight average molecular weight, the number average molecular weight, the molecular weight distribution, the melt flow rate (MFR), the melt flow rate ratio (MFRR), the density, Full Notch Creep Test (FNCT) and the like can be measured and used comprehensively for evaluating the physical characteristics such as strength, processability and stability of polymers.

[0031] Among them, a polyolefin resin used in a pressure-resistant heating pipe, a large-diameter high-pressure pipe, or the like is required to have long-term stability under high pressure conditions. As a method of evaluating such processability, a method of measuring the die swell ratio can be mentioned.

[0032] FIG. 3 is a schematic view of an extrusion die for actually measuring the die swell ratio.

[0033] The die swell ratio can be calculated according to the following Equation 2 by cutting the resin of the middle portion of 20 to 40 cm with scissors and measuring its weight, when the resin coming out through an extrusion die (shown in FIG. 2) of an auto-blow molding m/c (Bloma Engineering, model: BM40DE 70) falls by 60 cm in the vertical direction.

Die Swell Ratio=Weight of Cut Resin (g)/Weight of Reference Resin (g)[Equation 2]

in Equation 2 above, the weight of the cut resin is a weight (unit: g) measured by cutting a resin (length: 20 cm) of the middle portion of 20 to 40 cm with scissors when the resin coming out through an extrusion die (outer diameter: 9 cm, inner diameter: 8.64 cm) falls by 60 cm in the vertical direction, and

[0034] the weight of the reference resin is a weight (unit: g) corresponding to the resin (length: 20 cm) when the extruded resin has no swell.

[0035] That is, referring to FIG. 3, with respect to the total length (L=60 cm) of resin coming out in the form of a pipe via an extrusion die having an outer diameter (R) of 9 cm and an inner diameter (R) of 8.64 cm, the resin (L=20 cm) of the middle portion of 20 to 40 cm is cut, its weight is measured, and the weight ratio of the reference resin is defined as a die swell ratio. In this case, the weight of the reference resin is a weight corresponding to a length of 20 cm in the resin when the extruded resin is uniformly extruded over the entire length without expansion phenomenon, that is, a weight corresponding to one-third of the total weight of the extruded resin.

[0036] However, the method of obtaining the die swell ratio according to the above method requires expensive measuring equipment which causes an increase in the development cost, and the measurement error is relatively large, which makes it difficult to evaluate and analyze the processability of polymers.

[0037] Thus, the present inventors have conduced continuous research about a method for evaluating the processability of polymer resins, and found that there is a certain correlation between the integral value for each section of the molecular weight distribution curve (GPC curve) of the polymer resin and the die swell ratio, thereby developing a method for predicting the die swell ratio from the molecular weight distribution curve with a high reliability. The present invention has been completed on the basis of such finding.

[0038] That is, it was confirmed that, through measurement of the molecular weight distribution of a polymer resin, particularly a polyolefin resin, the processability and dimensional stability could be predicted beforehand in products manufactured using the polymer resin.

[0039] In particular, the method for predicting the physical properties of polymers according to the present invention may be suitable for predicting the physical properties of the polyolefin resin used for the high-pressure pipe. For example, it can be usefully used for a method for predicting a die swell ratio of a polyolefin resin having a high molecular weight and high molecular weight distribution (PDI) in which the weight average molecular weight is 100,000 to 1,000,000 g/mol, or 100,000 to 800,000 g/mol, or 100,000 to 500,000 g/mol and the molecular weight distribution is 5 to 30, or 10 to 30, or 15 to 30.

[0040] Hereinafter, a method for predicting physical properties of polymers according to an embodiment of the present invention will be described with reference to the drawings.

[0041] FIG. 1 is a molecular weight distribution curve (GPC curve) measured to predict the physical properties of polymers according to an embodiment of the present invention.

[0042] First, the molecular weight distribution curve (GPC curve) is obtained for the polymer to be measured at 160 C. using a gel permeation chromatography (GPC). In this case, the log value of the molecular weight MW (log MW) is denoted by x-axis, and the molecular weight distribution to the log value (dwt/d log MW) is denoted by y-axis.

[0043] In the x-axis of the molecular weight distribution curve, that is, the log value of the molecular weight (log MW), the section between 3.0 and 7.0 is divided into four equal parts to obtain the integral values of molecular weight distribution curves in each section.

[0044] In the above molecular weight distribution curve, when the log MW includes a section deviating from 3.0 to 7.0, the deviating section is excluded, and only the section between 3.0 and 7.0 is divided into four equal parts to obtain the integral value.

[0045] Meanwhile, the method for predicting the physical properties of polymers according to the present invention may have a higher reliability when the sum of the integral values (A.sub.1+A.sub.2+A.sub.3+A.sub.4) in a section where log MW is 3.0 to 7.0 is close to 100 in the molecular weight distribution curve.

[0046] Referring to FIG. 1, the integral value A, of the molecular weight distribution curve in the section where log MW (x-axis) is 3.0 to 4.0 is obtained. Similarly, the integral value A.sub.2 of the molecular weight distribution curve in the section between 4.0 and 5.0, the integral value A.sub.3 of the molecular weight distribution curve in the section between 5.0 and 6.0, and the integrated value A.sub.4 of the molecular weight distribution curve in the section between 6.0 and 7.0 can be obtained from the GPC curve, respectively. In this case, the integral value of A, to A.sub.4 is used as a relative value when the integral value of the entire molecular weight distribution curve is 100.

[0047] The regression analysis was performed by comparing the relative values for each section (A.sub.1, A.sub.2, A.sub.3, A.sub.4) obtained from GPC curve as described above with respect to various polymer resins, especially polyolefin resins, with the die swell ratio, and as a result, the following relational equation was derived between the integral value for each section and the die swell ratio.

Die swell ratio, PV=(0.136)*A.sub.1+(0.1152)*A.sub.2+(0.1033)*A.sub.3+(0.181)*A.sub.4+13.97[Equation 1]

[0048] in Equation 1 above,

[0049] A.sub.1 is an integral value of a molecular weight distribution curve in the section where log MW is 3.0 to 4.0 and A.sub.2 is an integral value of a molecular weight distribution curve in the section where log MW is 4.0 to 5.0, A.sub.3 is an integral value of a molecular weight distribution curve in the section where log MW is 5.0 to 6.0, A.sub.4 is an integral value of a molecular weight distribution curve in the section where log MW is 6.0 to 7.0, and

[0050] the die swell ratio in Equation 1 is a physical property corresponding to the actual measurement value of the die swell ratio obtained by extruding an actual resin using an extrusion die and measuring the degree of expansion.

[0051] As a result of verifying the above Equation 1 for a large number of polyolefin resins prepared by various preparation methods, it was found that R.sup.2 is 0.8 or more, or 0.9 or more, which is highly reliable.

[0052] From the above relational equation, the die swell ratio from the GPC curve, which is relatively easy to measure, can be obtained with high reliability, and it is expected that the cost and time required for evaluating the processability can be greatly reduced. In particular, since the die swell ratio can be predicted only by the GPC curve without additional measurement procedure for a newly developed polymer resin, it is expected that it will contribute greatly to the research and development of a new resin.

[0053] Hereinafter, the present invention will be described in more detail by way of examples. However, these examples are presented for illustrative purposes only and the scope of the invention is not limited thereto in any way.

EXAMPLES

Examples 1 to 6

[0054] Ten types of polyethylene resins exhibiting various molecular weight distribution curves and having a density in the range of 0.930 to 0.950 g/cm.sup.3 were prepared by polymerizing ethylene according to the established method by a metallocene catalyst.

[0055] From the molecular weight distribution curve of each polyethylene, the die swell ratio of the polyethylene resin was calculated by the following Equation 1.

Die swell ratio, PV=(0.136)*A.sub.1+(0.1152)*A.sub.2+(0.1033)*A.sub.3+(0.181)*A.sub.4+13.97[Equation 1]

[0056] in Equation 1 above,

[0057] A.sub.1 is an integral value of a molecular weight distribution curve in the section where log MW is 3.0 to 4.0, A.sub.2 is an integral value of a molecular weight distribution curve in the section where log MW is 4.0 to 5.0, A.sub.3 is an integral value of a molecular weight distribution curve in the section where log MW is 5.0 to 6.0, A.sub.4 is an integral value of a molecular weight distribution curve in the section where log MW is 6.0 to 7.0, and the integral value of A.sub.1 to A.sub.4 means relative values when the integral value of the entire molecular weight distribution curve is 100.

[0058] In addition, the actually measured value of the die swell ratio according to Equation 2 and the predicted value of the die swell ratio according to Equation 1 are compared, and the results are shown in Table 1 below.

[0059] Further, the relationship between the calculated value and the actually measured value of the die swell ratio is shown in FIG. 2.

[0060] 1) Molecular weight distribution curve: Continuous molecular weight distribution was measured using a gel permeation chromatography-FTIR (GPC-FTIR) at a measurement temperature of 160 C., and a log value of the molecular weight MW (log MW) was denoted by x-axis, and the molecular weight distribution to the log MW (dwt/d log MW) was denoted by y-axis, to thereby draw a molecular weight distribution curve.

[0061] 2) Die Swell Ratio: The die swell ratio can be calculated according to the following Equation 2 by cutting the resin of the middle portion of 20 to 40 cm with scissors and measuring its weight, when the resin coming out through an extrusion die (shown in FIG. 2) of an auto-blow molding m/c (Bloma Engineering, model: BM40DE 70) falls by 60 cm in the vertical direction.

Die Swell Ratio=Weight of Cut Resin (g)/Weight of Reference Resin (g)[Equation 2]

[0062] in Equation 2, the weight of the cut resin is a weight (unit: g) measured by cutting a resin (length: 20 cm) of the middle portion of 20 to 40 cm with scissors when the resin coming out through an extrusion die (outer diameter: 9 cm, inner diameter: 8.64 cm) falls by 60 cm in the vertical direction, and

[0063] the weight of the reference resin is a weight (unit: g) corresponding to the resin (length: 20 cm) when the extruded resin has no swell.

TABLE-US-00001 TABLE 1 Weight average Equation 1 molecular Molecular Calculated Actually weight weight Integral value for each section of GPC curve value measured (g/mol) distribution A.sub.1 A.sub.2 A.sub.3 A.sub.4 (hr) value Example 1 327,770 25.3633 20.32166 46.56404 21.54408 9.325724 1.928617 1.95 Example 2 289,554 25.5294 24.33681 43.46446 22.11837 8.197844 1.884451 1.89 Example 3 318,468 27.2125 23.28312 41.87206 23.68627 8.969476 1.909568 1.92 Example 4 387,890 16.6455 8.937892 54.84982 22.18146 11.05058 2.144248 2.14 Example 5 336,559 16.4472 11.11483 57.50293 19.56069 9.555881 2.083812 2.00 Example 6 282,228 21.7701 16.84771 46.21066 25.3944 10.04293 1.914232 1.86 Example 7 352,109 10.7814 5.549175 58.08235 24.5495 9.882188 2.199586 2.19 Example 8 370,725 12.2554 6.387199 56.98076 24.17443 10.49551 2.140251 2.16 Example 9 359,399 11.5344 6.112806 55.78383 25.68316 10.35217 2.185548 2.19 Example 10 366,132 10.9130 5.516394 55.77089 25.85677 10.685 2.189975 2.16

[0064] As shown in Table 1 and FIG. 2, the die swell ratio (PV) value calculated according to Equation 1 of the present invention is a highly reliable predicted value with R.sup.2=0.9355 as compared with the actually measured die swell ratio value.