Waterproof material as well as preparation method and application thereof

Abstract

The invention provides a waterproof material as well as a preparation method and application thereof, and belongs to the field of tunnels. The invention provides a waterproof material, which is prepared from the following raw materials in parts by mass: 20 to 40 parts of linear low density polyethylene; 40 to 50 parts of polypropylene; 10-20 parts of a thermoplastic polyester elastomer; 10 to 15 parts of polyolefin elastomer; 15 to 25 parts of medium density polyethylene; and 2-5 parts of an antioxidant. The temperature resistance of the waterproof material is improved by adjusting the components and dosage of the raw materials in the waterproof material.

Description

Technical Field

[0001] The present invention relates to the field of tunnels, and particularly to a waterproof material, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of civil engineering at home and abroad, high geothermal tunnels have gradually become a new research hotspot in the fields of underground engineering and geotechnical engineering.

[0003] Different from ordinary geothermal tunnels, high geothermal tunnels bring many problems, such as harsh construction environment, damaged personnel health, low efficiency of mechanical equipment, cracking of lining concrete, serious deterioration of construction materials, etc. The research on high geothermal tunnels mainly focuses on the application aspect, while the product development aspect is relatively scarce. Conventional waterproof materials are mostly PE waterproof boards, EVA waterproof boards, and drainage boards. The critical temperature of deterioration of this waterproof material is about 30°C, which is not suitable for high geothermal tunnels. Therefore, it is urgent to improve the temperature resistance of waterproof materials. Summary of the Invention

[0004] The present invention provides a waterproof material, a preparation method thereof, and an application thereof. The waterproof material provided by the present invention has excellent temperature resistance.

[0005] The present invention provides a waterproof material, which includes the following raw materials by mass fraction:

[0006]

[0007] Preferably, at 190°C and a load of 2.16 kg, the melt index of the linear low-density polyethylene is 1.5 - 2.0 g / 10 min.

[0008] Preferably, at 190°C and a load of 2.16 kg, the melt index of the polypropylene is 2.0 - 3.0 g / 10 min.

[0009] Preferably, the Shore hardness of the thermoplastic polyester elastomer is 50 - 60D;

[0010] At 190°C and a load of 2.16 kg, the melt index of the thermoplastic polyester elastomer is 7.5 ± 0.2 g / 10 min.

[0011] Preferably, at 190°C and a load of 2.16 kg, the melt index of the polyolefin elastomer is 1.0 ± 0.2 g / 10 min;

[0012] The density of the polyolefin elastomer is 0.905 ± 0.1 g / cm 3 .

[0013] Preferably, at 190 °C and a load of 2.16 kg, the melt index of the medium-density polyethylene is 1.0 ± 0.2 g / 10 min;

[0014] The density of the medium-density polyethylene is 0.935 ± 0.1 g / cm 3 .

[0015] Preferably, the antioxidant includes one or more of antioxidant 1010, antioxidant 1076, distearyl thiodipropionate, antioxidant 2246, and antioxidant 264.

[0016] The present invention also provides a method for preparing the waterproof material described in the above technical solution, including the following steps:

[0017] Melt and blend the raw materials of the waterproof material and then extrude.

[0018] Preferably, the melt blending includes:

[0019] Perform a first melt blending on polypropylene, thermoplastic polyester elastomer, and part of the antioxidant to obtain a first blend;

[0020] Perform a second melt blending on linear low-density polyethylene, polyolefin elastomer, medium-density polyethylene, and the remaining antioxidant to obtain a second blend;

[0021] Perform a third melt blending on the first blend and the second blend.

[0022] The present invention also provides the application of the waterproof material described in the above technical solution or the waterproof material prepared by the above technical solution preparation method in a tunnel.

[0023] The present invention improves the temperature resistance of the waterproof material by adjusting the components and dosages of the raw materials in the waterproof material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a process flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention provides a waterproof material, which includes the following raw materials in parts by mass:

[0026]

[0027] By mass parts, the raw materials of the waterproof material provided by the present invention include 20-40 parts of linear low density polyethylene. In specific embodiments of the present invention, the mass parts of the linear low density polyethylene can be 20 parts, 25 parts, 30 parts, 35 parts or 40 parts; the melt index of the linear low density polyethylene is preferably 1.5-2.0 g / 10 min; the model of the linear low density polyethylene is preferably Daqing Petrochemical 9047.

[0028] By mass parts, the raw materials of the waterproof material provided by the present invention include 40-50 parts of polypropylene. In specific embodiments of the present invention, the mass parts of the polypropylene can be 40 parts, 42 parts, 44 parts, 46 parts, 48 parts or 50 parts; the melt index of the polypropylene is preferably 2.0-3.0 g / 10 min; the model of the polypropylene is preferably Yangzi Petrochemical k8003.

[0029] By mass parts, the raw materials of the waterproof material provided by the present invention include 10-20 parts of thermoplastic polyester elastomer. In specific embodiments of the present invention, the mass parts of the thermoplastic polyester elastomer can be 10 parts, 12 parts, 14 parts, 16 parts, 18 parts or 20 parts; the Shore hardness of the thermoplastic polyester elastomer is preferably 50-60D. In specific embodiments of the present invention, the Shore hardness can be 50D, 52D, 54D, 55D, 58D or 60D; at 190 °C and a load of 2.16 kg, the melt index is preferably 7.5±0.2 g / 10 min; the model of the thermoplastic polyester elastomer is preferably DuPont 5556 in the United States; the thermoplastic polyester elastomer is a block copolymer containing polyester hard segments and polyether soft segments. Among them, the polyether soft segments and the uncrystallized polyester form an amorphous phase, and the polyester hard segments are partially crystallized to form crystalline microdomains, which act as physical crosslinking points, making the linear structure of the material a network structure and improving the mechanical properties of the system. In addition, the thermoplastic polyester elastomer has the characteristics of high strength, excellent flexibility and excellent heat resistance, especially outstanding heat resistance, and can still maintain good mechanical properties when used at a maximum of 120 °C.

[0030] By mass parts, the raw materials of the waterproof material provided by the present invention include 10-15 parts of polyolefin elastomer. In specific embodiments of the present invention, the mass parts of the polyolefin elastomer can be 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts; at 190 °C and a load of 2.16 kg, the melt index of the polyolefin elastomer is preferably 1.0±0.2 g / 10 min, and the density is preferably 0.905±0.1 g / cm 3; The type of the polyolefin elastomer is preferably Dow 8540 of the United States; the polyolefin elastomer is a thermoplastic elastomer obtained by in-situ polymerization of ethylene and octene using a metallocene catalyst, having a very narrow molecular weight distribution, endowing it with excellent heat resistance and fluidity. There are no unsaturated double bonds in its structure, and it has excellent aging resistance.

[0031] By mass, the raw materials of the waterproof material provided by the present invention include 15-25 parts of medium-density polyethylene. In specific embodiments of the present invention, the mass parts of the medium-density polyethylene can be 15 parts, 16 parts, 17 parts, 18 parts, 19 parts or 20 parts; at 190 °C and a load of 2.16 kg, the melt index of the medium-density polyethylene is preferably 1.0 ± 0.2 g / 10 min, and the density is preferably 0.935 ± 0.1 g / cm 3 ; The type of the medium-density polyethylene is preferably Lotte P2460 of South Korea; the medium-density polyethylene uses octene as a monomer and forms a special spatial molecular structure through copolymerization, having better thermal properties than low-density polyethylene.

[0032] By mass, the raw materials of the waterproof material of the present invention include 2-5 parts of antioxidant. In specific embodiments of the present invention, the mass parts of the antioxidant can be 2 parts, 3 parts, 4 parts or 5 parts; the antioxidant preferably includes one or more of antioxidant 1010, antioxidant 1076, distearyl thiodipropionate, antioxidant 2246 and antioxidant 264.

[0033] The present invention also provides a preparation method of the waterproof material described in the above technical solution, including the following steps:

[0034] Melt and blend the raw materials of the waterproof material and then extrude.

[0035] In the present invention, the melt blending preferably includes:

[0036] Perform the first melt blending on polypropylene, thermoplastic polyester elastomer and part of the antioxidant to obtain a first blend;

[0037] Perform the second melt blending on linear low-density polyethylene, polyolefin elastomer, medium-density polyethylene and the remaining antioxidant to obtain a second blend;

[0038] Co-extrude the first blend and the second blend.

[0039] In the present invention, polypropylene, thermoplastic polyester elastomer and part of the antioxidant are subjected to the first melt blending to obtain a first blend. During the melt blending, the crystalline part of the polyester hard segment of the thermoplastic polyester elastomer can physically crosslink polypropylene, thereby improving the overall mechanical properties.

[0040] In the present invention, the partial antioxidant is preferably 40-66.7% of the total antioxidant. In specific embodiments of the present invention, the partial antioxidant can be 40%, 45%, 50%, 55%, 60%, 65% or 66.7% of the total antioxidant.

[0041] In the present invention, the time of the first melt blending is preferably 10-15 min. In specific embodiments of the present invention, the time of the first melt blending can be 10 min, 11 min, 12 min, 13 min, 14 min or 15 min.

[0042] In the present invention, the first melt blending is preferably carried out in a screw extruder; the metering pump frequency of the screw extruder is preferably 15-20 Hz. In specific embodiments of the present invention, the metering pump frequency can be 15 Hz, 16 Hz, 17 Hz, 18 Hz, 19 Hz or 20 Hz; the length-diameter ratio of the screw in the screw extruder is preferably 30; the temperature of the feeding section of the screw extruder is preferably 210-225 °C, the temperature of the compression section is preferably 225-235 °C, the temperature of the homogenization section is preferably 235-245 °C, the temperature of the screen changer is preferably 234-240 °C, and the temperature of the gear pump is preferably 230-234 °C. In specific embodiments of the present invention, the temperature of the feeding section of the screw extruder can be 210 °C, 215 °C, 220 °C or 225 °C, the temperature of the compression section can be 225 °C, 228 °C, 230 °C, 232 °C or 235 °C, the temperature of the homogenization section can be 235 °C, 238 °C, 240 °C or 245 °C, the temperature of the screen changer can be 234 °C, 235 °C, 236 °C, 238 °C or 240 °C, and the temperature of the gear pump can be 230 °C, 231 °C, 232 °C, 233 °C or 234 °C.

[0043] In the present invention, linear low-density polyethylene, polyolefin elastomer, medium-density polyethylene and the remaining antioxidant are subjected to a second melt blending to obtain a second blend. During the melt blending, the linear low-density polyethylene molecules can be embedded in the special spatial structure of the medium-density polyethylene to form a stable encapsulation structure, thereby improving the temperature resistance of the system.

[0044] In the present invention, the time of the second melt blending is preferably 10-15 min. In specific embodiments of the present invention, the time of the second melt blending can be 10 min, 11 min, 12 min, 13 min, 14 min or 15 min.

[0045] In the present invention, the second melt blending is preferably carried out in a screw extruder; the metering pump frequency of the screw extruder is preferably 15 - 20 Hz. In specific embodiments of the present invention, the metering pump frequency can be 15 Hz, 16 Hz, 17 Hz, 18 Hz, 19 Hz or 20 Hz; the length-diameter ratio of the screw in the screw extruder is preferably 30; the temperature of the feeding section of the screw extruder is preferably 180 - 190 °C, the temperature of the compression section is preferably 193 - 200 °C, the temperature of the homogenization section is preferably 203 - 210 °C, the temperature of the screen changer is preferably 200 - 207 °C, and the temperature of the gear pump is preferably 195 - 200 °C. In specific embodiments of the present invention, the temperature of the feeding section of the screw extruder can be 180 °C, 182 °C, 184 °C, 186 °C, 188 °C or 190 °C, the temperature of the compression section can be 193 °C, 195 °C, 197 °C, 199 °C or 200 °C, the temperature of the homogenization section can be 203 °C, 205 °C, 207 °C, 209 °C or 210 °C, the temperature of the screen changer can be 200 °C, 203 °C, 205 °C or 207 °C, and the temperature of the gear pump can be 195 °C, 196 °C, 197 °C, 198 °C, 199 °C or 200 °C.

[0046] After obtaining the first blend and the second blend, the present invention performs a third melt blending on the first blend and the second blend.

[0047] In the present invention, the third melt blending is preferably carried out successively in a distributor and a runner. In the present invention, the temperature of the distributor is preferably 225 - 230 °C. In specific embodiments of the present invention, the temperature of the distributor can be 225 °C, 226 °C, 227 °C, 228 °C, 229 °C or 230 °C; the temperature of the runner is preferably 193 - 198 °C. In specific embodiments of the present invention, the temperature of the runner can be 193 °C, 194 °C, 195 °C, 196 °C, 197 °C or 198 °C.

[0048] In the present invention, the blend obtained from the third melt blending enters the die used for extrusion under the action of the screws used in the first melt blending and the second melt blending.

[0049] In the present invention, the temperature of the extrusion die used for extrusion is preferably 195 - 205 °C. In specific embodiments of the present invention, the temperature of the extrusion die can be 195 °C, 197 °C, 200 °C, 203 °C or 205 °C.

[0050] In the present invention, the temperature of the cooling roll used for cooling is preferably 45 - 55 °C. In specific embodiments of the present invention, the temperature of the cooling roll can be 45 °C, 48 °C, 50 °C, 52 °C or 55 °C.

[0051] The present invention also provides the application of the waterproof material described in the above technical solution or the waterproof material prepared by the preparation method described in the above technical solution in a tunnel.

[0052] Figure 1 The process flow chart of the embodiment of the present invention is as follows: The materials in bin 1 and bin 2 are respectively melt-blended through screw 1 and screw 2 and then extruded through an extrusion die and cooled and shaped.

[0053] The following is a detailed description of the waterproof material provided by the present invention, its preparation method and application in conjunction with embodiments, but they cannot be construed as limiting the protection scope of the present invention.

[0054] Linear low density polyethylene, Daqing Petrochemical 9047;

[0055] Polypropylene, Yangzi Petrochemical k8003;

[0056] Thermoplastic polyester elastomer, DuPont USA 5556;

[0057] Polyolefin elastomer, Dow USA 8540;

[0058] Medium density polyethylene, Lotte Korea P2460;

[0059] Antioxidant, antioxidant 1010.

[0060] Example 1

[0061]

[0062] Among them, the material in bin 1 is;

[0063] Polypropylene 50 parts by weight;

[0064] Thermoplastic polyester elastomer 20 parts by weight;

[0065] Antioxidant 1 part by weight;

[0066] The material in bin 2 is:

[0067]

[0068] The stirring time of the materials in the two bins is 10 min. The length-diameter ratio of the two screws is 30. The temperature of screw 1 is set as follows: feeding section 225 °C, compression section 235 °C, homogenization section 245 °C, screen changer 240 °C, gear pump 234 °C; the temperature of screw 2 is set as follows: feeding section 190 °C, compression section 200 °C, homogenization section 210 °C, screen changer 207 °C, gear pump 200 °C. The metering pumps of screw 1 and screw 2 are set the same, which is 20 Hz.

[0069] After the materials in silos 1 and 2 are mixed, they enter the extrusion die through a distributor (230°C) and a runner (198°C) for extrusion.

[0070] The temperature of the extrusion die is set at 205°C. The temperature of the cooling roll is 55°C.

[0071] Example 2

[0072]

[0073] Among them, the materials in silo 1 are:

[0074] 40 parts by weight of polypropylene;

[0075] 15 parts by weight of thermoplastic polyester elastomer;

[0076] 2 parts by weight of antioxidant;

[0077] The materials in silo 2 are:

[0078]

[0079] The stirring time of the materials in both silos is 12 min. The length-diameter ratio of the two screws is 30. The temperature of screw 1 is set as follows: feeding section 210°C, compression section 225°C, homogenizing section 235°C, screen changer 234°C, gear pump 230 - 234°C; the temperature of screw 2 is set as follows: feeding section 180°C, compression section 193°C, homogenizing section 203°C, screen changer 200°C, gear pump 195°C. The metering pumps of screw 1 and screw 2 are set the same, at 15 HZ. The temperature of the extrusion die is set at 195°C. The temperature of the cooling roll is 45°C.

[0080] After the materials in silos 1 and 2 are mixed, they enter the extrusion die through a distributor (225°C) and a runner (193°C) for extrusion.

[0081] Example 3

[0082]

[0083] Among them, the materials in silo 1 are:

[0084] 45 parts by weight of polypropylene;

[0085] 10 parts by weight of thermoplastic polyester elastomer;

[0086] 2 parts by weight of antioxidant;

[0087] The materials in silo 2 are:

[0088]

[0089] The stirring time of the materials in the two bins is 13 min. The length-diameter ratio of the two screws is 30. The temperature settings of screw one are: 215 °C for the feeding section, 230 °C for the compression section, 240 °C for the homogenization section, 237 °C for the screen changer, and 232 °C for the gear pump; the temperature settings of screw two are: 185 °C for the feeding section, 195 °C for the compression section, 207 °C for the homogenization section, 204 °C for the screen changer, and 198 °C for the gear pump. The metering pumps of screw one and screw two are set the same, at 17 HZ. The temperature of the extrusion die is set at 200 °C. The temperature of the cooling roller is 50 °C.

[0090] After the materials in bins one and two are mixed, they enter the extrusion die through the distributor (227 °C) and the runner (195 °C) for extrusion.

[0091] Example 4

[0092]

[0093] Among them, the materials in bin one are:

[0094] 45 parts by weight of polypropylene;

[0095] 10 parts by weight of thermoplastic polyester elastomer;

[0096] 2 parts by weight of antioxidant;

[0097] The materials in bin two are:

[0098]

[0099] The stirring time of the materials in the two bins is 12 min. The length-diameter ratio of the two screws is 30. The temperature settings of screw one are: 218 °C for the feeding section, 232 °C for the compression section, 242 °C for the homogenization section, 238 °C for the screen changer, and 232 °C for the gear pump; the temperature settings of screw two are: 187 °C for the feeding section, 197 °C for the compression section, 207 °C for the homogenization section, 205 °C for the screen changer, and 196 °C for the gear pump. The metering pumps of screw one and screw two are set the same, at 18 HZ. The temperature of the extrusion die is set at 202 °C. The temperature of the cooling roller is 52 °C.

[0100] After the materials in bins one and two are mixed, they enter the extrusion die through the distributor (228 °C) and the runner (197 °C) for extrusion.

[0101] Comparative Example 1

[0102] 75 parts by weight of linear low-density polyethylene;

[0103] 25 parts by weight of medium-density polyethylene;

[0104] 2 parts by weight of antioxidant;

[0105] Use the same screw extruder as in Example 1, and the length-diameter ratio of the two screws is 30. The process parameters are as set for Screw Two in Example 3. The two feed bins are both proportioned with linear low-density polyethylene: medium-density polyethylene: antioxidant = 75:25:2 and the raw material masses in the two feed bins are the same.

[0106] Comparative Example 2

[0107] 80 parts by weight of linear low-density polyethylene;

[0108] 20 parts by weight of polypropylene;

[0109] 2 parts by weight of antioxidant;

[0110] The process is the same as in Comparative Example 1. Only the material ratio is adjusted.

[0111] Comparative Example 3

[0112]

[0113]

[0114] The materials in Feed Bin One are:

[0115] 35 parts by weight of linear low-density polyethylene;

[0116] 28 parts by weight of thermoplastic polyester elastomer;

[0117] 2 parts by weight of antioxidant;

[0118] The materials in Feed Bin Two are:

[0119] 45 parts by weight of linear low-density polyethylene;

[0120] 20 parts by weight of polypropylene;

[0121] The process parameters are the same as in Example 4.

[0122] Comparative Example 4

[0123]

[0124] Among them, the materials in Feed Bin One are;

[0125] 30 parts by weight of polypropylene;

[0126] 5 parts by weight of thermoplastic polyester elastomer;

[0127] 1 part by weight of antioxidant;

[0128] The materials in Feed Bin Two are:

[0129]

[0130] The process parameters are the same as those in Example 1.

[0131] The thickness of the products in the above cases is 2.0 mm and the width is 4 m.

[0132] For the mechanical property test, samples were taken from Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3, and physical property tests were carried out. Among them, the tensile test was carried out according to the provisions of GB / T 18173.1-2012, and the tensile speed was (250±50) mm / min; the puncture strength test was carried out according to the provisions of 5.3.10 in TB / T 3360.1-2014, and a top needle with a length of 20 mm was used to pierce the sheet material. The top piercing speed was 100 mm / min, and the maximum pressure value was recorded during the process. The tear strength was carried out with a non-cut right-angle specimen according to GB / T 529, and the speed was (250±50) mm / min. Among them, the high-temperature tensile strength, puncture strength, and tear strength at 40 °C, 60 °C, and 70 °C were tested after preheating at the specified temperature for 1 h.

[0133] Table 1 Physical Property Test Results

[0134]

[0135]

[0136] It can be seen from the above table that the waterproof material for high geothermal temperature provided by the present invention has a longitudinal fracture tensile strength of more than 31.0 MPa at 23 °C, more than 22.7 MPa at 40 °C, more than 20.5 MPa at 60 °C, and more than 18.6 MPa at 70 °C; the transverse fracture tensile strength is more than 30.5 MPa at 23 °C, more than 25.0 MPa at 40 °C, more than 20.7 MPa at 60 °C, and more than 18.2 MPa at 70 °C; the longitudinal fracture elongation rate is more than 718% at 23 °C, more than 948% at 40 °C, more than 976% at 60 °C, and more than 1082% at 70 °C; the transverse fracture elongation rate is more than 818% at 23 °C, more than 996% at 40 °C, more than 1068% at 60 °C, and more than 1134% at 70 °C; the puncture strength is more than 664 N at 23 °C, more than 532 N at 40 °C, more than 358 N at 60 °C, and more than 308 N at 70 °C; the longitudinal tear strength is more than 141 kN / m at 23 °C, more than 114 kN / m at 40 °C, more than 102 kN / m at 60 °C, and more than 90 kN / m at 70 °C; the transverse tear strength is more than 132 kN / m at 23 °C, more than 114 kN / m at 40 °C, more than 92 kN / m at 60 °C, and more than 82 kN / m at 70 °C. It shows that the waterproof material provided by the present invention still maintains excellent mechanical properties at high temperatures and can be used for high geothermal tunnels.

[0137] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A waterproof material, characterized in that: In parts by mass, it includes the following raw materials:

2. The waterproof material according to claim 1, characterized in that: At 190° C. and a load of 2.16 kg, the linear low-density polyethylene has a melt index of 1.5 to 2.0 g / 10 min.

3. The waterproof material according to claim 1, characterized in that: At 190° C. and a load of 2.16 kg, the melt index of the polypropylene is 2.0-3.0 g / 10 min.

4. The waterproof material according to claim 1, characterized in that: The Shore hardness of the thermoplastic polyester elastomer is 50-60D; The thermoplastic polyester elastomer has a melt index of 7.5±0.2 g / 10 min at 190° C. and a load of 2.16 kg.

5. The waterproof material according to claim 1, characterized in that: The polyolefin elastomer has a melt index of 1.0±0.2 g / 10 min at 190° C. and a load of 2.16 kg; The density of the polyolefin elastomer is 0.905±0.1 g / cm 3 .

6. The waterproof material according to claim 1, characterized in that: At 190°C and a load of 2.16 kg, the melt index of the medium-density polyethylene is 1.0±0.2 g / 10 min; the density of the medium-density polyethylene is 0.935±0.1 g / cm 3 .

7. The waterproof material according to claim 1, characterized in that: The antioxidant includes one or more of antioxidant 1010 , antioxidant 1076 , distearyl thiodipropionate, antioxidant 2246 and antioxidant 264 .

8. The method for preparing the waterproof material according to any one of claims 1 to 7, characterized in that: The following steps are involved: The raw materials of the waterproof material are melt-blended and then extruded.

9. The preparation method according to claim 8, characterized in that: The melt blending comprises: The polypropylene, the thermoplastic polyester elastomer and a part of the antioxidant are first melt-blended to obtain a first blend; The linear low-density polyethylene, the polyolefin elastomer, the medium-density polyethylene and the remaining antioxidant are subjected to a second melt blending to obtain a second blend; The first blend and the second blend are subjected to a third melt blending.

10. Use of the waterproof material according to any one of claims 1 to 7 or the waterproof material prepared by the preparation method according to any one of claims 8 to 9 in tunnels.

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