Preparation and weather resistance of modified nanocellulose aerogel/polylactic acid composites by china national petroleum and natural gas pipeline group

1.1 Main Raw Materials

NC: The raw material is cotton, sulfonated nanocellulose solution, with a solid content of 4.0%, diameter of 4-10 nm, length of 100-500 nm, pH of 4.0, Shenzhen Qihong Technology Co., Ltd.

GA: Solid content 50%, analytical pure, Damao Chemical Reagent Factory, Tianjing City.

PLA: average molecular weightM_wThe amount is 80,000, Shanghai Macklin Biochemical Co., Ltd.

Dichloromethane (DCM): Analytical grade, Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd.

1.2 Main Instruments and Equipment

Fourier Transform Infrared Spectrometer (FTIR): Tensor 27, Bruker Corporation, Germany;

X-ray Diffractometer (XRD): D8 Advanced, Bruker Corporation, Germany;

Analytical Balance: AL104, Mettler-Toledo Company;

Vacuum Drying Oven: DZF-100, Zhengzhou Great Wall Scientific Industrial and Trade Co., Ltd.

Freeze Dryer: ZLGJ-30, Ningbo Xinzhi Biotechnology Co., Ltd.

Universal Material Mechanics Tester: TST-C1007A, Taisite Instruments (Fujian) Co., Ltd.

SEM: S-4800, Hitachi, Japan;

Aging Chamber: BHO-401A, Shanghai Yiheng Experimental Instrument Co., Ltd.

1.3 Sample Preparation

Figure 1 shows the sample preparation flow chart. As illustrated in Figure 1, NC and GA are mixed in different proportions: 10 g NC + 0 mL GA, 10 g NC + 0.01 mL GA, 10 g NC + 0.02 mL GA, 10 g NC + 0.03 mL GA, and 10 g NC + 0.04 mL GA. The samples are respectively labeled as GA/NC-1, GA/NC-2, GA/NC-3, GA/NC-4, and GA/NC-5. The components are uniformly mixed through mechanical stirring to form a homogeneous translucent gel-like substance. The mixture is placed in a low-temperature environment, reacting at 4°C for 24 hours, and then transferred to -20°C for deep freezing. Finally, the gel is subjected to freeze-drying in a freeze dryer. The optimal amount of GA is determined to be 0.02 mL (GA/NC-3).

Dissolve pretreated PLA in DCM solution at different ratios, namely 1.5 g PLA + 7.5 mL CH.₂Cl₂1.5 g PLA + 15 mL CH₂Cl₂The GA/NC-3 was compounded with PLA-1 and PLA-2 solutions, respectively, via the solution impregnation method, and labeled as GA-NC/PLA-1 and GA-NC/PLA-2. They were then placed on a polytetrafluoroethylene plate for drying treatment to obtain the final product, GA-NC/PLA composite material.

1.4 Testing and Characterization

1.4.1 FTIR Test

The FTIR instrument was used to test GA/NC aerogel and GA-NC/PLA composite materials, analyzing the changes in infrared characteristic peaks before and after crosslinking modification. Before testing, the samples were placed in a vacuum drying oven at 55°C to remove moisture and then thoroughly ground. Subsequently, they were pressed into pellets using a tablet press set at a pressure of 1.5 TONS for 1.5 minutes. The testing range was 4,000 to 500 cm.^-1The resolution is 4 cm.^-1。

1.4.2 SEM Test

Using SEM to observe the microstructure of GA-NC/PLA composites, study the structural changes of samples before and after crosslinking modification, and analyze the pore structure and interface bonding state of the material.

1.4.3 XRD Test

The crystal structure of GA-NC/PLA composites was analyzed using XRD to study the changes in crystallinity before and after crosslinking modification. The X-ray source was CuKα, and the parameters of the diffractometer were adjusted with a scanning speed of 5°/min and a scanning range of 10° to 60°.

1.4.4 Aging Test

To study the aging resistance of composite materials, samples were placed in an aging test chamber for accelerated aging experiments. The temperature was set at 45 ℃ to observe the morphological changes of the composite materials after aging, with an aging time of 72 hours.

1.4.5 Mechanical Performance Testing

To characterize the mechanical properties of composite materials using a universal testing machine, the compression resilience performance was tested. The compression and recovery rates were set at 5 mm/min, with a temperature of 25°C, for 100 cycles to obtain the stress-strain cyclic curves. The test was conducted in accordance with GB/T 7759.1-2015.

2 Results and Discussion

2.1 Structural and Performance Characterization of GA-NC Aerogels

To investigate the crosslinking modification effect of GA on NC, the chemical structure of GA/NC aerogel and GA-NC/PLA composites was characterized using an FTIR instrument to analyze the variation patterns of characteristic functional groups. As shown in Figure 2, NC has a typical O—H stretching vibration peak (3,339 cm.^-1) C—H stretching vibration peak (2,897 cm⁻¹)^-1) and the C—O—C stretching vibration peak (1,080~1,180 cm)^-¹)^[12]From Figure 2, it can be seen that after the NC is modified by GA, the intensity of the O-H stretching vibration peak gradually decreases with the increase in GA concentration. This indicates that GA successfully reacts with NC, and some of the hydroxyl groups are replaced by acetal bonds.^[13]With the increase in GA concentration, GA forms acetal bonds (C—O—C), resulting in NC forming a more rigid three-dimensional network structure.^[14]The C—H vibration is restricted, leading to cross-linking of NC on the GA surface, which enhances the chemical stability and structural rigidity of the three-dimensional GA/NC aerogel.^[15]。

2.2 Structure and Performance Characterization of GA-NC/PLA Composites