Optimization Study of Fluffy Materials Flocking Drainage Pipes to Resist Blockage Based on MD Binding Energy

: Drainage pipe blockage resulting from crystals is one of the causes for cracking and leakage of tunnel lining. Therefore, effective prevention from drainage pipe blockage caused by crystals is crucial to ensure the safety and stability of lining structures during the operation of tunnel drainage system. Based on a large number of indoor model tests and numerical simulation analyses, binding energy between four materials and the calcium carbonate aqueous solution (“solid + liquid” system) and that between the four materials and the two typical growth crystals of calcium carbonate (“solid + solid” system) were studied. The research results indicated that: (1) The four materials all had an adsorption effect on the calcium carbonate aqueous solution system, and the PA6 had the greatest adsorption effect while the PP had the smallest adsorption effect; (2) There was spontaneous adsorption between the PVC or PA6 and the two typical growth crystals of calcium carbonate and no adsorption between the PP or SiC and the two typical growth crystals of calcium carbonate unless external energy was in place; (3) The PP and SiC can be used as the materials for drainage pipe ﬂocking, but it shall be ensured that the ﬂuffy material has a good geometrical property. The prevention technology for crystallization that causes drainage pipe blockage ﬁlls the gap in the research of drainage pipe blockage caused by crystals, which can reduce the maintenance cost for the operation of the tunnel drainage system and ensure safe and normal operation of the tunnel.


Introduction
With the operation of tunnel projects, tunnel defects gradually emerge, among which drainage pipe blockage caused by crystals is a major factor affecting the service life of a tunnel. Carbonates formed by the inter-reaction of various ions of groundwater calcify into crystals over time, and these crystals accumulate in drainage pipes and cause blockage ( Figure 1). Improper treatment of the crystals can affect the smooth operation of a tunnel drainage system and further lead to the cracking and leakage of the tunnel lining ( Figure 2). Even worse, it may affect traffic safety and cause imponderable losses.
There are two kinds of causes for the blockage of tunnel drainage pipes. One is the environmental factor [1][2][3]: the concentration of ions such as calcium and magnesium in groundwater, the concentration of carbon dioxide in the air, and pH value of groundwater; the other is the construction factor [2,4]: concrete composition ratio, the form of the drainage system, etc. At present, research on the prevention technology of drainage pipe blockage caused by crystals is at the initial stage. The attachment of calcium carbonate crystals can be reduced through hydrophobic treatment on concrete base surfaces and PVC pipe walls with protective coating [5,6]; generation of crystals can be effectively lowered by optimizing the concrete materials and the concrete composition ratio, reducing the contact between groundwater and concrete, preventing CO 2 from entering the tunnel the contact between groundwater and concrete, preventing CO2 from entering th drainage pipe, as well as adding appropriate fly ash to shotcrete [2,4]. Drainage p tals mainly include insoluble calcite crystals, and the PEG-b-PAA-b-PS, poly(ethy col)-block-poly(acrylic acid)-block-poly(styrene) can prevent the phase transiti vaterite to calcite [7]; in the presence of biopolymer, the relative content of va creases with the application of ultrasonic treatment [8]; ultrasonic treatment m gathered calcium carbonate crystals more fragile [9]; RS1600, a green corrosion i makes the crystal structure of calcium carbonate change from calcite to vaterite cleaning solvent of organic acid reagents of single molecule carboxylic acids wit centration of 2000 ppm and a dichromate index of 17.71% and that of polymeri boxylic acids can effectively remove the karst crystal of a drainage pipe system w suring environmental protection [11]. Through a large number of 1:1 indoor mo and numerical simulation analyses, Liu Shiyang, et al. [12][13][14][15][16] studied the feasib reliability of drainage pipe flocking for resisting blockage from a macro perspect some good flocking parameters were obtained. The real solution to the attachmen tals of drainage pipes depends on the micro binding energy between the crystals drainage pipe. The presence of Fe 2+ and Mg 2+ can inhibit the growth of CaCO3, greater the concentration of Fe 2+ or Mg 2+ is, the stronger the inhibitory effect [17] High voltage electric field can hinder the synthesis of calcium ions and carbonate reduce the binding action of calcium ions or carbonate ions with the calcite growt surface, and it also promotes the dissolution of scale [18].  From the above analysis, we can see that at present, many researches on the tion technology of drainage pipe blockage caused by crystals are at a macro le there are few researches at a micro level. Therefore, based on the above indoor mo and numerical simulation analyses, binding energy between the materials and was analyzed by the molecular dynamics software to find the best flocking mate drainage pipes to resist blockage, which can provide a theoretical basis for the me the contact between groundwater and concrete, preventing CO2 from entering th drainage pipe, as well as adding appropriate fly ash to shotcrete [2,4]. Drainage p tals mainly include insoluble calcite crystals, and the PEG-b-PAA-b-PS, poly(ethyl col)-block-poly(acrylic acid)-block-poly(styrene) can prevent the phase transiti vaterite to calcite [7]; in the presence of biopolymer, the relative content of vat creases with the application of ultrasonic treatment [8]; ultrasonic treatment m gathered calcium carbonate crystals more fragile [9]; RS1600, a green corrosion in makes the crystal structure of calcium carbonate change from calcite to vaterite cleaning solvent of organic acid reagents of single molecule carboxylic acids wit centration of 2000 ppm and a dichromate index of 17.71% and that of polymeri boxylic acids can effectively remove the karst crystal of a drainage pipe system w suring environmental protection [11]. Through a large number of 1:1 indoor mo and numerical simulation analyses, Liu Shiyang, et al. [12][13][14][15][16] studied the feasib reliability of drainage pipe flocking for resisting blockage from a macro perspect some good flocking parameters were obtained. The real solution to the attachmen tals of drainage pipes depends on the micro binding energy between the crystals drainage pipe. The presence of Fe 2+ and Mg 2+ can inhibit the growth of CaCO3, greater the concentration of Fe 2+ or Mg 2+ is, the stronger the inhibitory effect [17] High voltage electric field can hinder the synthesis of calcium ions and carbonate reduce the binding action of calcium ions or carbonate ions with the calcite growt surface, and it also promotes the dissolution of scale [18].  From the above analysis, we can see that at present, many researches on the tion technology of drainage pipe blockage caused by crystals are at a macro le there are few researches at a micro level. Therefore, based on the above indoor mo and numerical simulation analyses, binding energy between the materials and was analyzed by the molecular dynamics software to find the best flocking mate drainage pipes to resist blockage, which can provide a theoretical basis for the me From the above analysis, we can see that at present, many researches on the prevention technology of drainage pipe blockage caused by crystals are at a macro level, and there are few researches at a micro level. Therefore, based on the above indoor model tests and numerical simulation analyses, binding energy between the materials and crystals was analyzed by the molecular dynamics software to find the best flocking materials for drainage pipes to resist blockage, which can provide a theoretical basis for the mechanism of resisting blockage by drainage pipe flocking.

Molecular Dynamics Software
Molecular Dynamics (MD) simulation has a history of about 50 years, whose success depends on the selection of an appropriate force field and a correct calculation method. The widely used MD simulation is becoming more and more important with the rapid development of computers. There are some commercial molecular dynamics computing software designed for the MD simulation, represented by the Materials Studio software of Accelary, which is a molecular dynamics simulation software featuring powerful functions, easy usage and clear images.
MD simulation considers the system to be studied as a collection of a large number of interacting particles whose motions follow the classical equation of motion (Newtonian equation, Hamiltonian equation or Lagrangian equation). By analyzing the force of each particle, equations of motion of various particles that constitute the system were numerically solved directly to obtain theses particles' coordinates and momentum at every moment. Then, the microscopic state consisting of the coordinates and momentum was averaged against time to calculate the macroscopic properties such as multisystem pressures, energy and temperatures.

Model Building
From a micro level, different materials produce different binding energy with the groundwater solution system or the crystals' microscopic crystal surface. The stronger the binding energy is, the stronger the adsorption between the materials and the ions or the crystals' crystal surface in the solution will be. Thus, the anti-crystallization effect of fluffy materials was analyzed based on the intensity of binding energy. The characteristics of fluffy materials ( Figure 3) and drainage pipe materials are shown in Table 1 below. The "solid-solid" model and the "solid-liquid" model were constructed with the amorphous cell of Materials Studio 8.0. The "solid-solid" model mainly included the double-layer model of different materials and the crystal surface of calcium carbonate crystals, and the "solid-liquid" model mainly included the double-layer model of different materials and calcium carbonate aqueous solution.  According to the Inorganic Crystal Structure Database (ICSD), calcite belon R-3cH space group, with the spatial parameters of a = b = 4.983 Å, c = 17.078 Å, α = 90°, γ = 120° (Figure 4). The study in [19] shows that the growth faces of calcite −1 0) and (1 0 4) crystal surfaces. The former was positively charged, while the la not charged. To obtain the binding energy between the materials and the calcite  materials was analyzed based on the intensity of binding energy. The characteristics of fluffy materials ( Figure 3) and drainage pipe materials are shown in Table 1 below. The "solid-solid" model and the "solid-liquid" model were constructed with the amorphous cell of Materials Studio 8.0. The "solid-solid" model mainly included the double-layer model of different materials and the crystal surface of calcium carbonate crystals, and the "solid-liquid" model mainly included the double-layer model of different materials and calcium carbonate aqueous solution.  Figure 3) and drainage pipe materials are shown in Table 1 below. The "solid-solid" model and the "solid-liquid" model were constructed with the amorphous cell of Materials Studio 8.0. The "solid-solid" model mainly included the double-layer model of different materials and the crystal surface of calcium carbonate crystals, and the "solid-liquid" model mainly included the double-layer model of different materials and calcium carbonate aqueous solution. "solid-solid" model and the "solid-liquid" model were constructed with the amorphous cell of Materials Studio 8.0. The "solid-solid" model mainly included the double-layer model of different materials and the crystal surface of calcium carbonate crystals, and the "solid-liquid" model mainly included the double-layer model of different materials and calcium carbonate aqueous solution. "solid-solid" model and the "solid-liquid" model were constructed with the amorphous cell of Materials Studio 8.0. The "solid-solid" model mainly included the double-layer model of different materials and the crystal surface of calcium carbonate crystals, and the "solid-liquid" model mainly included the double-layer model of different materials and calcium carbonate aqueous solution.     According to the Inorganic Crystal Structure Database (ICSD), calcite belongs to the R-3cH space group, with the spatial parameters of a = b = 4.983 Å, c = 17.078 Å, α = 90°, β = 90°, γ = 120° ( Figure 4). The study in [19] shows that the growth faces of calcite were (1 −1 0) and (1 0 4) crystal surfaces. The former was positively charged, while the latter was not charged. To obtain the binding energy between the materials and the calcite crystals, the models between different materials and the (1 −1 0) and (1 0 4) crystal surfaces were built respectively in the "solid-solid" model. The "solid-liquid" model mainly included the double-layer model of different materials and calcium carbonate aqueous solution. Given the low solubility of calcium carbonate, the calcium carbonate aqueous solution was formed with 350 water molecules, 3Ca 2+ and 3CO3 2− (Figure 5)  According to the Inorganic Crystal Structure Database (ICSD), calcite belongs to the R-3cH space group, with the spatial parameters of a = b = 4.983 Å, c = 17.078 Å, α = 90°, β = 90°, γ = 120° (Figure 4). The study in [19] shows that the growth faces of calcite were (1 −1 0) and (1 0 4) crystal surfaces. The former was positively charged, while the latter was not charged. To obtain the binding energy between the materials and the calcite crystals, the models between different materials and the (1 −1 0) and (1 0 4) crystal surfaces were built respectively in the "solid-solid" model. The "solid-liquid" model mainly included the double-layer model of different materials and calcium carbonate aqueous solution. Given the low solubility of calcium carbonate, the calcium carbonate aqueous solution was formed with 350 water molecules, 3Ca 2+ and 3CO3 2− (Figure 5), and the solution volume was 21.74 × 21.74 × 19.34 Å 3 .
According to the Inorganic Crystal Structure Database (ICSD), calcite belongs to the R-3cH space group, with the spatial parameters of a = b = 4.983 Å, c = 17.078 Å, α = 90 • , β = 90 • , γ = 120 • (Figure 4). The study in [19] shows that the growth faces of calcite were (1 −1 0) and (1 0 4) crystal surfaces. The former was positively charged, while the latter was not charged. To obtain the binding energy between the materials and the calcite crystals, the models between different materials and the (1 −1 0) and (1 0 4) crystal surfaces were built respectively in the "solid-solid" model. The "solid-liquid" model mainly included the double-layer model of different materials and calcium carbonate aqueous solution. Given the low solubility of calcium carbonate, the calcium carbonate aqueous solution was formed with 350 water molecules, 3Ca 2+ and 3CO 3 2− (Figure 5), and the solution volume was 21.74 × 21.74 × 19.34 Å 3 .  According to the Inorganic Crystal Structure Database (ICSD), calcite belongs to the R-3cH space group, with the spatial parameters of a = b = 4.983 Å, c = 17.078 Å, α = 90°, β = 90°, γ = 120° (Figure 4). The study in [19] shows that the growth faces of calcite were (1 −1 0) and (1 0 4) crystal surfaces. The former was positively charged, while the latter was not charged. To obtain the binding energy between the materials and the calcite crystals, the models between different materials and the (1 −1 0) and (1 0 4) crystal surfaces were built respectively in the "solid-solid" model. The "solid-liquid" model mainly included the double-layer model of different materials and calcium carbonate aqueous solution. Given the low solubility of calcium carbonate, the calcium carbonate aqueous solution was formed with 350 water molecules, 3Ca 2+ and 3CO3 2− (Figure 5), and the solution volume was 21.74 × 21.74 × 19.34 Å 3 .
(a) (b) (c)    Figures 6 and 7, and the combination model of the materials and the calcium carbonate aqueous solution is shown in Figure 8.  Figures 6 and 7, and the combination model of the materials and the calcium carbonate aqueous solution is shown in Figure 8.

Parameter Setting
The MD simulation was performed by the Forcite module in Materials Studio. First, the positions were assigned, and all atomic coordinates of the material layer were fixed through the universal COMPASS force field of high precision. The NVT was adopted because the system pressure was not a key factor. The 100 ps MD simulation under the NVT and velocity scale was first conducted to allow the system to reach an equilibrium state. Then, the MD simulation was performed under the NVT and Andersen thermostatic heat bath, with a time step of 1 fs, a simulation time of 200 ps, the system track being recorded every 1000 steps, a simulation temperature of 298 K, and a cutoff radius of 12.5 Å.

System Equilibrium
The equilibrium of the system was determined by the temperature and energy. The accuracy of the simulation was characterized by the ratio of energy convergence parameter (ΔEconverge), the total energy fluctuation value rms (Et), and the kinetic energy fluctuation value rms (Ek), as shown in Formulas (1) and (2) where E(0) and the E(i) were the initial total energy and the total energy when the iteration reached the ith step respectively, and Nnm was the times of simulation. When ΔEconverge ≤ 0.001, R ≤ 0.001, the calculation results were reliable. After calculation, the ΔEconverge and R of the simulation system at each temperature conformed to the above value range, indicating that the system reached equilibrium and the simulated calculation results were reliable.

Parameter Setting
The MD simulation was performed by the Forcite module in Materials Studio. First, the positions were assigned, and all atomic coordinates of the material layer were fixed through the universal COMPASS force field of high precision. The NVT was adopted because the system pressure was not a key factor. The 100 ps MD simulation under the NVT and velocity scale was first conducted to allow the system to reach an equilibrium state. Then, the MD simulation was performed under the NVT and Andersen thermostatic heat bath, with a time step of 1 fs, a simulation time of 200 ps, the system track being recorded every 1000 steps, a simulation temperature of 298 K, and a cutoff radius of 12.5 Å.

System Equilibrium
The equilibrium of the system was determined by the temperature and energy. The accuracy of the simulation was characterized by the ratio of energy convergence parameter (ΔEconverge), the total energy fluctuation value rms (Et), and the kinetic energy fluctuation value rms (Ek), as shown in Formulas (1) and (2) where E(0) and the E(i) were the initial total energy and the total energy when the iteration reached the ith step respectively, and Nnm was the times of simulation. When ΔEconverge ≤ 0.001, R ≤ 0.001, the calculation results were reliable. After calculation, the ΔEconverge and R of the simulation system at each temperature conformed to the above value range, indicating that the system reached equilibrium and the simulated calculation results were reliable.

Parameter Setting
The MD simulation was performed by the Forcite module in Materials Studio. First, the positions were assigned, and all atomic coordinates of the material layer were fixed through the universal COMPASS force field of high precision. The NVT was adopted because the system pressure was not a key factor. The 100 ps MD simulation under the NVT and velocity scale was first conducted to allow the system to reach an equilibrium state. Then, the MD simulation was performed under the NVT and Andersen thermostatic heat bath, with a time step of 1 fs, a simulation time of 200 ps, the system track being recorded every 1000 steps, a simulation temperature of 298 K, and a cutoff radius of 12.5 Å.

System Equilibrium
The equilibrium of the system was determined by the temperature and energy. The accuracy of the simulation was characterized by the ratio of energy convergence parameter (∆E converge ), the total energy fluctuation value rms (E t ), and the kinetic energy fluctuation value rms (E k ), as shown in Formulas (1) and (2) where E(0) and the E(i) were the initial total energy and the total energy when the iteration reached the ith step respectively, and N nm was the times of simulation. When ∆E converge ≤ 0.001, R ≤ 0.001, the calculation results were reliable. After calculation, the ∆E converge and R of the simulation system at each temperature conformed to the above value range, indicating that the system reached equilibrium and the simulated calculation results were reliable. Figure 9 shows the energy output curve of the equilibrium process, and Figure 10 shows the temperature output curve of the equilibrium process. From Figure 9, we can see that the potential energy, kinetic energy, non-bond energy and total energy flattened over time, indicating that the various energy of the system reached the equilibrium. From Figure 10, we can see that the temperature fluctuated 10% around 298 K, indicating that the temperature of the system also reached the equilibrium.
FOR PEER REVIEW 7 of 10 (2) Figure 9 shows the energy output curve of the equilibrium process, and Figure 10 shows the temperature output curve of the equilibrium process. From Figure 9, we can see that the potential energy, kinetic energy, non-bond energy and total energy flattened over time, indicating that the various energy of the system reached the equilibrium. From Figure 10, we can see that the temperature fluctuated 10% around 298 K, indicating that the temperature of the system also reached the equilibrium.

Binding Energy Analysis
Interaction between the materials and the crystallized ion solution (two typical growth crystal surfaces of calcium carbonate) was simulated by the molecular dynamics software. If the interaction was very strong, the crystallized ion aqueous solution (two typical growth crystal surfaces of calcium carbonate) would easily attach to the material layer, which meant that the contact area between the pipe wall and the fluffy material was prone to crystallization.
When using the double-layer model for simulation, the data of the fully balanced double-layer structure was collected at an appropriate temperature and a proper ensemble to obtain a series of equilibrium configurations. Then each possible equilibrium configuration was treated as follows: (1) Restore the lower fixed atoms to allow them to move (2) Figure 9 shows the energy output curve of the equilibrium process, and Figure 10 shows the temperature output curve of the equilibrium process. From Figure 9, we can see that the potential energy, kinetic energy, non-bond energy and total energy flattened over time, indicating that the various energy of the system reached the equilibrium. From Figure 10, we can see that the temperature fluctuated 10% around 298 K, indicating that the temperature of the system also reached the equilibrium.

Binding Energy Analysis
Interaction between the materials and the crystallized ion solution (two typical growth crystal surfaces of calcium carbonate) was simulated by the molecular dynamics software. If the interaction was very strong, the crystallized ion aqueous solution (two typical growth crystal surfaces of calcium carbonate) would easily attach to the material layer, which meant that the contact area between the pipe wall and the fluffy material was prone to crystallization.
When using the double-layer model for simulation, the data of the fully balanced double-layer structure was collected at an appropriate temperature and a proper ensemble to obtain a series of equilibrium configurations. Then each possible equilibrium configuration was treated as follows: (1) Restore the lower fixed atoms to allow them to move freely, copy three backups, and calculate the total energy (Etotal) of the system with backup

Binding Energy Analysis
Interaction between the materials and the crystallized ion solution (two typical growth crystal surfaces of calcium carbonate) was simulated by the molecular dynamics software. If the interaction was very strong, the crystallized ion aqueous solution (two typical growth crystal surfaces of calcium carbonate) would easily attach to the material layer, which meant that the contact area between the pipe wall and the fluffy material was prone to crystallization.
When using the double-layer model for simulation, the data of the fully balanced double-layer structure was collected at an appropriate temperature and a proper ensemble to obtain a series of equilibrium configurations. Then each possible equilibrium configura-tion was treated as follows: (1) Restore the lower fixed atoms to allow them to move freely, copy three backups, and calculate the total energy (E total ) of the system with backup 1; (2) Keep the lower layer of the backup 2 only, delete the upper layer, and calculate the energy (E lower ) of the lower layer; (3) Keep the upper layer of the backup 3 only, delete the lower layer, calculate the energy (E upper ) of the upper layer, and finally calculate the interaction energy by Formula (3). To calculate the adsorption energy of each material layer, let the interaction energy of the system be ∆E, and the binding energy (E binding ) be the opposite number of the interaction energy ∆E (Formula (4)). The details are as follows: where E total was the total energy of the system, E lower was the single-point energy of the material layer, E upper was the single-point energy of the crystallized ion aqueous solution system (two typical growth crystal surfaces of calcium carbonate) after interaction. Through simulation calculation, the energy value of the system after the interaction between the "solid + solid" model and the "solid + liquid" model is shown in Table 2, and the changing trend of the binding energy with the materials is shown in Figures 11 and 12.  Figure 11. The "solid-liquid" binding energy.   Through the above analysis, given the binding energy betw and the crystallized ion aqueous solution, we can select the PP w as the materials for drainage pipes; given the binding energy betw and the two typical growth crystals of calcium carbonate, we can s the materials for drainage pipes. From the analysis of MD simula lated that SiC had the best anti-crystallization effect in drainage p the result of the actual indoor macroscopic test [15] was contrar property of the fluffy material ( Figure 3) played a major role in effect of drainage pipes flocking. Therefore, for better anti-crysta and SiC can be used as the materials for flocking drainage pipes, shall have a good geometrical property (smooth surface and stra direction) so as to maximize the anti-crystallization effect of the dr

Conclusions
In this paper, the binding energies of PA6, PVC, SiC, PP and ca ous solution and calcium carbonate were studied by molecular dy ulation method. The interaction energy was negative, suggesting that the adsorption of the crystallized ion aqueous solution (two typical growth crystal surfaces of calcium carbonate) on each material surface was a spontaneous process, and a relatively stable system could be formed [20]. As it can be seen from Table 2 and Figure 8, the interaction energy between the four materials and the calcium carbonate aqueous solution was all negative in the "solid + liquid" model, and the binding energy was all positive, indicating that all the four materials had an adsorption effect on the calcium carbonate aqueous solution, and the PA6 had the greatest adsorption effect while the PP had the smallest adsorption effect, with the former being about 2.5 times of the latter. As it can be seen from Table 2 and Figure 9, the interaction energy between the materials of PVC or PA6 and the two typical growth crystals of calcium carbonate was all negative, and the binding energy was all positive, indicating that there was spontaneous adsorption between PVC or PA6 and the two typical growth crystals of calcium carbonate, and the binding energy between either of the two materials and (1 −1 0) crystal surface was greater than that between (1 0 4) crystal surface; the interaction energy between the materials of PP or SiC and the two typical growth crystals of calcium carbonate was all positive, and the binding energy was all negative, indicating that the adsorption between the PP or SiC and the two typical growth crystals of calcium carbonate was impossible unless there was external energy, and the adsorption of (1 0 4) crystal surface was greater than that of (1 −1 0) crystal surface.
Through the above analysis, given the binding energy between the four materials and the crystallized ion aqueous solution, we can select the PP with low binding energy as the materials for drainage pipes; given the binding energy between the four materials and the two typical growth crystals of calcium carbonate, we can select the PP and SiC as the materials for drainage pipes. From the analysis of MD simulation results, we speculated that SiC had the best anti-crystallization effect in drainage pipe flocking, however, the result of the actual indoor macroscopic test [15] was contrary. Thus, the geometric property of the fluffy material ( Figure 3) played a major role in the anti-crystallization effect of drainage pipes flocking. Therefore, for better anti-crystallization effect, the PP and SiC can be used as the materials for flocking drainage pipes, but the fluffy material shall have a good geometrical property (smooth surface and straight in the lengthwise direction) so as to maximize the anti-crystallization effect of the drainage pipe flocking.

Conclusions
In this paper, the binding energies of PA6, PVC, SiC, PP and calcium carbonate aqueous solution and calcium carbonate were studied by molecular dynamics numerical simulation method.
(1) PA6, PVC, SiC and PP all have adsorption effect on calcium carbonate solution, and the order of binding energy is PA6 > PVC > SiC > PP.
(2) The results show that PVC, PA6 and CaCO 3 can spontaneously adsorb on each other, while PP and SiC can only adsorb on each other with the help of external energy. The energy absorbed by (1 0 4) crystal face is greater than that absorbed by (1 −1 0) crystal face. (3) The follow-up research can start from the energy of the solution system and the crystal itself and find the technology to make the energy of the system or crystal in a low state, so that the crystal and the pipe are not combined. (4) From the point of view of anti-crystallization effect, while considering the binding energy between materials, it is also necessary to ensure the excellent geometric characteristics of pile (smooth surface and straight length direction), so as to maximize the anti-crystallization effect of flocking drainage pipe. In addition to the binding energy, the molecular weight and production process of polymer should also be considered in the follow-up study.