Preparation of Carbon Fiber and Bamboo Fiber Reinforced Poly (butylene Adipate-co-terephthalate) Foams by Supercritical Carbon Dioxide Foaming

This research focused on developing PBAT/CF/BF carbon foams using scCO2 foaming technology to see data, how fiber synergy enhanced anti-shrinking properties will reduce density and improve compression resilience of foams. The PBAT carbon fiber, bamboo fiber compose the foam. Study provides an effective solution for the manufacture of degradable shrink-resistant, lightweight and high-stress polyester foam, which has application prospective in packaging, thermal insulation and other fields.

To begin place the PBAT, CF, and BF in an oven set at 80 degrees Celsius and incubate for eight hours. Using an electronic balance, weigh PBAT and CF proportionally to make a total of 200 grams. Pour the weighed PBAT and carbon fiber into a polyethylene bag.

Mix the contents thoroughly by shaking and kneading the bag for five minutes to achieve a uniform preliminary dispersion. Then turn on the power switch of the twin-screw extruder. Set the temperature of each heating zone on the extruder to 135, 145, 155, 165, and 160 degrees Celsius respectively.

Set the host screw rotation speed to five revolutions per minute and the feeder rotation speed to three revolutions per minute. Next, add pure PBAT pellets into the feed hopper of the extruder and operate the machine for 10 minutes to clean the screw. Switch the feedstock to the PBAT and 20 CF pre-mixed material and extrude continuously.

Then collect the extruded material from the outlet and crush it into granules using a powder granulator. Turn on the power switch of the flat vulcanizing machine. Then set the temperature of both the upper and lower plates to 165 degrees Celsius.

Measure 60 grams of the prepared granules according to the mold dimensions. Lay a polytetrafluoroethylene film over a flat gasket and immediately position the mold on top. Evenly distribute the weighed granules into the mold cavity.

Cover the mold with another polytetrafluoroethylene film and place a second flat gasket on top. Then place the assembled mold setup at the center of the heating plate of the flat vulcanizing machine. Initiate the mold closing process on the flat vulcanizing machine.

Apply a pressure of one megapascal and maintain the pressure for three minutes to expel trapped air and prevent bubble formation. Continue the mold closing operation. Increase the pressure to 10 megapascals and maintain this pressure for 10 minutes to ensure the material melts and fills the mold uniformly.

Then turn off the heating system. Activate the cooling mechanism on the vulcanizing machine and wait until the temperature drops below 40 degrees Celsius before depressurizing and removing the mold. Using a blade, cut the molded sheet into pieces.

Place the cut sample panels into the reaction vessel. Using a wrench, tighten the bolts of the reactor lid and close the reactor securely. Then close the exhaust valve of the reaction kettle to seal the system.

Now open the valve of the carbon dioxide cylinder. After that, open the intake valve of the booster pump. Then open the inlet valve of the reactor to inject carbon dioxide gas into the chamber.

After that, close the inlet valve of the reactor and allow the chamber to stabilize for three minutes. To discharge air from inside the chamber, open the exhaust valve of the reactor. Then turn on the power switches of both oil baths and set their temperatures to 165 degrees Celsius and 100 degrees Celsius respectively.

Place the reaction vessel containing the sample into the oil bath set at 165 degrees Celsius and incubate for 10 minutes. Open the inlet valve of the reactor to pressurize it with carbon dioxide. Set the pressure to 10 megapascals and maintain the temperature for 10 minutes.

Close the ventilation valve of the carbon dioxide cylinder, the intake valve of the booster pump, and the inlet valve of the reaction kettle. Then transfer the reaction vessel to the second oil bath set at 100 degrees Celsius and maintain both temperature and pressure for 60 minutes. Open the exhaust valve of the reactor and rapidly release the internal pressure within three seconds to obtain the foamed material.

Visual inspection confirmed clear differences in foam appearance and expansion with varying fiber content. The density of pure PBAT foam was found to be 0.19 grams per cubic centimeter with a foaming ratio of 6.23 and a stabilized shrinkage rate of 55.63%After incorporating different ratios of CF and BF, the foam density generally decreased, while the foaming ratio correspondingly increased. This indicates that the synergistic effect of CF and BF content can suppress foam shrinkage and enhance the dimensional stability of PBAT foams.

Scanning electron microscopy revealed that the PBAT and 20CF foam had the largest cell size followed by PBAT and 20BF, while foams with combined CF and BF showed intermediate sizes. The PBAT, CF, and BF foams exhibited the most uniform cell size distribution compared to CF only, or BF only formulations. The PBAT, 5CF, and 15BF foam achieved the highest cell density at 3.63 million cells per cubic centimeter.

The compressive strength was highest in PBAT, 15CF, and 5BF foam, reaching 0.26 megapascals. All composite foam samples exhibited consistent compressive resilience across the zero to 50%strain range. Future research may focus on exploring the long-term degradation behavior of compound foam in different environmental, and assessing the economic feasibility and environmental impact of composite foam production.