Nylon (PA) 1010 is an engineering plastic independently developed in China, which has many excellent properties and is widely used. As a structural material, PA1010 has higher requirements for its strength, wear resistance, and other aspects. Talc, as a widely sourced inorganic silicate mineral material, has low water absorption, high rigidity, good chemical and thermal stability, is non-toxic, and is inexpensive and readily available, showing great potential for development in reinforced filler material applications. To improve the strength and modulus of PA1010, thereby expanding its application fields and reducing material costs, the author prepared PA1010/talc composites through melt blending based on surface modification of needle-like talc, exploring the effect of talc filling amount on the mechanical properties of the composites.

1 Experimental Section

1.1 Main Raw Materials

    PA1010: Melting point 205°C, Shanghai Zhenwei Co., Ltd.

    Talc: Length-to-diameter ratio less than 15:1, length about 20 um, Xinyu Southern Talc Industry Co., Ltd.; Silane coupling agent: KH-550, purity ≥ 99.0%, Nanjing Shuguang Chemical Group Co., Ltd.

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1.2 Main Instruments and Equipment

    High-speed mixer: SHR-5A type, Zhangjiagang Ruida Machinery Manufacturing Factory;

    Twin-screw extruder: KS-20 type, Kunshan Kexin Rubber and Plastic Machinery Co., Ltd.;

    Injection molding machine: HTF80-W type, Ningbo Haitian Co., Ltd.;

    Electronic mechanical performance testing machine: CMT-5104 type, Shenzhen Cheng Plastic Application New Three Thoughts Material Testing Co., Ltd.;

    Dynamic mechanical analysis (DMA) instrument: DMA242C type, Netzsch, Germany;

    Melt flow rate (MFR) instrument: ZR21452 type, Metis Industrial Systems (China) Co., Ltd.;

    Scanning electron microscope (SEM): JSM-6700F type, Jeol, Japan.

1.3 Sample Preparation

    (1) Surface modification of talc.

    Dissolve the silane coupling agent KH-550 in anhydrous ethanol at a volume ratio of 1:4, then dilute with acetone to a 1% solution. Weigh a certain amount of talc into a three-necked flask, pour the prepared treatment solution into the flask, seal it, shake it well, and mechanically stir at room temperature for 3 hours to fully impregnate the talc. Then, take out the talc and dry it in a vacuum oven at 80°C for 12 hours for later use.

    (2) Preparation of PA1010/talc composites.

    Mix a certain amount of PA1010 with the surface-modified talc in a high-speed mixer and stir at high speed until uniform, then dry in a vacuum oven at 80°C until constant weight. Then, extrude and pelletize using an extruder, with the temperature of each section set at 220, 225, 225, 225, 220, and 215°C, and the screw speed set at 170 r/min. The obtained pellets are dried in a vacuum oven at 80°C for 24 hours, and standard samples are prepared using an injection molding machine, with the temperature of each section set at 225, 230, 230, and 225°C, and the mold temperature at 80°C. The mass fractions of talc in the composite materials are set at 10%, 20%, 30%, 40%, 50%, 60%, and 70%.

1.4 Performance Testing and Characterization

    Tensile properties were tested according to GB/T 1040-1992, with a gauge length of 50 mm. The tensile speed was 10 mm/min, temperature 19°C, and relative humidity 31%;

    Bending properties were tested according to GB/T 9341-2000, with a span of 68 mm, testing speed of 2 mm/min, temperature 19°C, and relative humidity 31%.

    DMA testing: The sample is rectangular, with dimensions of 60.0 mm × 10.0 mm × 4.0 mm, testing frequency of 1 to 33 Hz, testing temperature of -170 to 180°C, and heating rate of 10°C/min;

    The standard sample was frozen in liquid nitrogen for about 1.5 hours and then fractured. After drying in an oven at 60°C for 6 hours, the fracture surface was gold-coated under vacuum and observed with SEM, with an acceleration voltage of 15 kV. MFR was tested according to GB/T 3682-2000, with testing conditions of 230°C and 2.16 kg.

2 Results and Discussion

2.1 MFR

    Table 1 shows the MFR of PA1010/talc composites with different talc filling amounts. As seen from Table 1, with the increase in talc filling amount, the MFR gradually decreases. Extrusion and injection molding experiments indicate that when the talc mass fraction is ≤70%, both pure PA1010 and the composite can be successfully molded at the same temperature and pressure, with smooth surfaces and no burrs. However, when the talc filling amount is further increased,

the extrusion becomes difficult, causing difficulties in screw rotation. Therefore, the maximum mass fraction of talc in the composites prepared by the author is 70%.

    2.2 Mechanical Properties

    Figures 1 and 2 show the effects of talc filling amount on the tensile and bending properties of PA1010/talc composites.

   Figure 2 shows the effect of talc filling amount on the bending properties of PA1010/talc composites.

    From Figures 1 and 2, it can be seen that the addition of wollastonite significantly improves the tensile and bending properties of PA1010. As the amount of wollastonite increases, the tensile elastic modulus, tensile strength, bending elastic modulus, and bending strength of the composite material gradually increase. When the mass fraction of wollastonite is 70%, the tensile elastic modulus and tensile strength of the composite material increase by 256% and 29% respectively compared to pure PA1010, while the bending elastic modulus and bending strength increase by 367% and 93% respectively. This indicates that wollastonite short fibers play a reinforcing role in the PA1010 matrix. Due to the high rigidity of wollastonite itself, it restricts the movement of macromolecular chains in the matrix resin and does not deform under external forces, thus improving the tensile and bending properties of the composite material. However, when the wollastonite content is high, the toughness of the composite material decreases significantly. When the mass fraction of wollastonite is 70%, the notched impact strength of the cantilever beam of the composite material is about half of that of the original PA1010, which may limit the application fields of the composite material. This is an issue that needs to be addressed in future research.

    Figure 3 shows the SEM images of different sections of the PA1010/wollastonite composite material (with a wollastonite mass fraction of 20%). From Figure 3, it can be seen that wollastonite exists in both short fiber and particle forms in PA1010, and both forms of wollastonite are evenly distributed in the PA1010 matrix. The rigid wollastonite short fibers and particles act as a bridge support, enhancing the strength of PA1010, allowing it to withstand higher bending and tensile stresses.

  Figure 3 SEM images of different sections of the PA1010/wollastonite composite material.

2.3 Dynamic Mechanical Properties

    Figure 4 shows the relationship curve between the dynamic storage modulus (E') of pure PA1010 and PA1010/wollastonite composite materials at 10 Hz and temperature. From Figure 4, it can be seen that the E' of both pure PA1010 and its composite materials gradually decreases with increasing temperature, with the fastest decrease occurring near the glass transition temperature (Tg) (approximately 70°C). The composite material is in a glassy state below Tg, where the macromolecular chain segments in the resin matrix are frozen, allowing only small motion units to move. At the same temperature, as the amount of wollastonite increases, the E' of the composite material generally increases.

    -200 -150 -100 -50 0 50 100 150 200

    Temperature / °C Wollastonite mass fraction: a-0%; b-10%; c-20%; d-30%; e-40%

    f-50%; g-60%; h-70%

    Figure 4 Relationship curve of E' of pure PA1010 and composite materials with temperature.

    Figure 5 shows the relationship curve between E' of the composite material at Tg and the amount of wollastonite filler. From Figure 5, it can be seen that the E' of the composite material increases with the increase of wollastonite filler. The E' of pure PA1010 at Tg is 0.93 GPa, while the E' of the composite material when the wollastonite mass fraction is 70% is 4.43 GPa, which is a 376% increase compared to pure PA1010, indicating that wollastonite has a good reinforcing effect on PA1010.

The addition of wollastonite significantly increases the rigidity of PA1010.

    Figure 5 Relationship curve of E' of the composite material at Tg and the amount of wollastonite filler.

3 Conclusion

    (1) PA1010/wollastonite composite materials were prepared by melt blending method, and SEM showed that wollastonite is uniformly dispersed in the PA1010 matrix.

    (2) As the amount of wollastonite filler increases, the MFR of the composite material gradually decreases, but extrusion and injection molding experiments show that when the wollastonite mass fraction is ≤70%, the composite material still has good molding processing performance.

    (3) The addition of wollastonite significantly improves the strength and rigidity of PA1010. Compared to pure PA1010, the tensile and bending properties of the composite material are greatly enhanced, with the maximum increases in tensile strength and tensile elastic modulus being 29% and 256% respectively, and the maximum increases in bending strength and bending elastic modulus being 93% and 367% respectively.

    (4) The dynamic storage modulus of the composite material increases significantly with the increase of wollastonite filler, and when the wollastonite mass fraction is 70%, the dynamic storage modulus at Tg increases by about 376% compared to pure PA1010.

    (5) The wollastonite-filled PA1010 composite material has good comprehensive performance, the material preparation method is simple and easy to operate, and the wollastonite filling amount can reach up to 70%, which can significantly reduce the cost of the composite material.