Preparation and Properties of Graphene/Novel Degradable Plastics Hybrid Low Enthalpy of Phase Transition Materials

Graphene (GNs) were chosen to modify hybrid and novel degradable plastics PTLA/polymethyl methacrylate (PMMA). The low enthalpy of melting phase transformation (MEPT) materials (PTLA/PMMA)/GNs were prepared by adding the GNs at different mass fraction(1%, 2%, 3%, 4%) into PTLA/PMMA, and the properties of the hybrid phase change materials were characterized. The results indicated that the MEPT of PTLA/PMMA materials can be significantly reduced with the addition of GNs. The addition of 3% (mass) GNs made the MEPT of PTLA/PMMA material decreased by more than 50%. With the increase of GNs mass fraction, the MEPT hardly changed; Fourier transformed infrared (FT-IR) spectra showed that the interaction between GNs and PTLA/PMMA was physical; Scanning electron microscope (SEM) images showed that the components of GNs and PTLA/PMMA were mixed evenly without phase separation; The thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) cycle performance tests showed that the decomposition temperature of the (PTLA/PMMA)/GNs material was up to 280 °C, and the properties could remain stable during the circulation process. The addition of GNs could effectively reduce the MEPT of the (PTLA/PMMA)/GNs material, increase the heat transfer efficiency, and have good thermal reliability.


Introduction
PTLA is a new biodegradable polyester polymer material obtained by the copolymerization of lactic acid and propylene carbonate.Polymeric Methyl Methacrylate (PMMA) is an amorphous polymer, also known as organic glass due to its good light transmission performance, with a density of 1.14-1.20 g/cm 3 and a specific gravity of 1.19.It not only has a very high light transmittance (92%), but also has high mechanical strength, light weight, UV and outdoor aging resistance, excellent electrical performance and other characteristics [1,2].Unfortunately, PMMA is light, brittle and easy to crack in practical application.In view of these shortcomings, we choose the mixture of PTLA and PMMA with a mass ratio of 1:1 as a new degradable plastic, and further as a green cigarette cooling material that could conduct heat rapidly.
Since the discovery of fullerenes in 1985 and carbon nanotubes in 1991, the research on carbon materials has attracted great interest of researchers all over the world.GNs has attracted immense attention since it was successfully prepared for the first time in 2004 [3].GNs is regarded as the most promising material in the 21st century for its excellent mechanical, thermal, optical and electrical properties.It is worth mentioning that GNs is a two-dimensional planar carbon material similar to honeycomb.The carbon atoms are arranged in regular hexagonal lattice period, and the structure is very stable and has good flexibility, which is the most ideal two-dimensional nano material at present [4,5].Accordingly, GNs is widely used to improve the mechanical, electrical and thermal properties of polymers.In order to further improve the heat transfer rate of PTLA/PMMA materials, reduce the MEPT and enhance the stability, we added GNs of different mass for modification to explore tobacco cooling materials with better performance.

Materials
PTLA and were purchased from Anhui BBCA biochemical and futerro PLA Co., Ltd (Anhui, China).PMMA were obtained from Da Mao Chemical Reagents Factory (Tianjin, China).GNs and chloroform (CHCl 3 ) were purchased from Aladdin Technology Co., Ltd, Shanghai, and used directly as received without further purification.

Preparation of PTLA/PMMA Films and (PTLA/PMMA)/GnPs Films
Firstly, 12.0 g PTLA and 12 g PMMA were putted into a round bottom flask respectively, then added CHCl 3 reagent to fully cover the PTLA masterbatch, and simultaneously putted round bottom flask into a constant temperature oil bath at 40 ℃.After all the above five materials were dissolved in CHCl 3 , 10 ml of solution was taken from the round bottom flask, and then putted them into the glass bottle with a correct label, and then applied it on the glass plate cleaned with dilute hydrochloric acid and methanol in turn to form 10×10 cm uniform film shape, and finally, PTLA/PMMA films were formed through a vacuum drying way to remove organic solvents such as CHCl 3 .

Property Tests
The thermogravimetric analysis (TGA) analysis wsa determined by thermogravimetric analyzer (Netzsch sta449f3) in the 25 to 800 ℃ range with a heating rate of 10 ℃/min from under nitrogen atmosphere.Scanning electron microscopic (SEM) images were acquired on a field emission scanning electron microscopic (HITACHI SU-8010) with an operating voltage of 10 kV.Fourier transform infrared (FTIR) spectroscopy was collected on Nicolet IS10 FTIR infrared spectrometer in the 400-4000 cm −1 range.Phase change properties of mixed materials were determined by differential scanning calorimeter (NETZSCH STA 449 F3/F5) in the 0 to 120 ℃ range with a heating rate of 5 ℃/min from under nitrogen atmosphere.   1 shows the MEPT properties of the five composites films.It can be seen from the figure that PTLA/PMMA belongs to amorphous polymer material, Which has the highest MEPT of 23.77 J/g.It is obvious that the addition of GNs can significantly reduce the MEPT of the material.When the additive amount of GNs is 3%, the MEPT decreases by 50.48%.However, it is worth mentioning that when the added amount of GNs exceeds 2%, the MEPT of the material remains unchanged basically.Compared with pure PTLA/PMMA materials, the addition of GNs can effectively increase the heat transfer of the materials, so that the composite materials can achieve phase transition faster and consume less heat.This is an obvious advantage for the non-toxic and green cigarette cooling materials that need fast heat transfer and cooling.the thermal conductivity of the five materials can still remain stable without significant changes after five cycles.According to the comprehensive Td and thermal cycling stability curves, the addition of GNs does not change the thermal stability of the material, and meets the requirements for steadiness in the production and reuse of cigarette cooling materials.Figure 3 shows the FT-IR spectrum of PTLA/PMMA and 3% (mass) (PTLA/PMMA)/GNs.The main functional peaks in FT-IR spectrum were C-H vibration peak at 3000 cm -1 , -C=O vibration peak at 1720 cm -1 , C-H bending vibration absorption at 1450 cm -1 and C-O-C tensile vibration absorption peak at 1143 cm -1 [6].It is apparent that the peaks of 3% (mass) (PTLA/PMMA)/GNs all correspond to the characteristic absorption peaks of pure PTLA/PMMA, and there is no obvious new characteristic absorption peak.This indicates that the mixing of GNs and PTLA/PMMA belongs to physical action rather than chemical reaction between them.Figure 4 shows the surface topography of the five composites films.It can be seen that the surfaces of the five materials are uniform, and there are no obvious gullies and sharp protrusions on the film surface.Especially for the composite materials (b-e), the addition of GNs does not damage the film structure, and there is no phase separation phenomenon, which also has excellent film-forming performance.

Conclusions
In this research, PTLA/PMMA degradable plastic with a mass ratio of 1:1 was used as the research object, and low MEPT composites were prepared by adding different proportions of GNs.Subsequently, we studied the differences in MEPT, thermal stability, mode of action and surface micro morphology of PTLA/PMMA and GNs mixed under different proportions.The addition of GNs can significantly reduce the MEPT of PTLA/PMMA material.When the proportion of graphene exceeds 2%, the MEPT of this material decreases by 50%.This clearly shows that the phase transition can be achieved with less heat consumption in the production of thin film materials, which can quickly heat transfer to achieve the purpose of cooling, and also makes the processing process light and simple, and saves the cost of energy consumption.The Td and thermal cycle stability of the five materials were obtained by TGA and DSC tests.The Td can be maintained at about 280 ℃, and the thermal conductivity can still remain stable after five heat absorption and release cycles.This suggests that the five materials have good thermal stability and meet the requirements for steadiness in film production and practical application.By analyzing the FT-IR spectra, it can be determined that the mixing between GNs and PTLA/PMMA is a physical action without chemical reaction.Through SEM images, it can be clearly and intuitively reflected that the five composite materials have no phase separation phenomenon and possess excellent film-forming performance.This work provides some guidance for further research on green cigarette cooling materials with high heat transfer efficiency.

Figure 1 .
Figure 1.Enthalpy curves of melting phase transformation of five mixed materials..

Figure
Figure1shows the MEPT properties of the five composites films.It can be seen from the figure that PTLA/PMMA belongs to amorphous polymer material, Which has the highest MEPT of 23.77 J/g.It is obvious that the addition of GNs can significantly reduce the MEPT of the material.When the additive amount of GNs is 3%, the MEPT decreases by 50.48%.However, it is worth mentioning that when the added amount of GNs exceeds 2%, the MEPT of the material remains unchanged basically.Compared with pure PTLA/PMMA materials, the addition of GNs can effectively increase the heat transfer of the materials, so that the composite materials can achieve phase transition faster and consume less heat.This is an obvious advantage for the non-toxic and green cigarette cooling materials that need fast heat transfer and cooling.

Figure 2 .
Figure 2. a) Td of five composites, b)Thermal cycling stability of five composites..

Figure
Figure2ashows the decomposition temperature of the five composites films.It can be seen from the figure that the five materials all have a high decomposition temperature of 280 ℃.Figure2bshows the thermal cycling stability of the five composites films.It was vital to show that the DSC curves of the five materials at the stage of heat absorption and release are highly coincident from the figure, and Figure2ashows the decomposition temperature of the five composites films.It can be seen from the figure that the five materials all have a high decomposition temperature of 280 ℃.Figure2bshows the thermal cycling stability of the five composites films.It was vital to show that the DSC curves of the five materials at the stage of heat absorption and release are highly coincident from the figure, and

Figure 4 .
Figure 4. SEM images of five composites surface