CC BY
15YflK 54.057/8:542
Yan-Hua Cai*, D.A. Filimonov**, Yan-Hua Zhang*
SYNTHESIS OF A^-BIS(BENZOYL) DODECANEDIOIC ACID DIHYDRAZIDE AND EFFECT ON NUCLEATION AND MECHANICAL PROPERTIES OF POLY(L-LACTIC ACID)
(*School of Materials and Chemical Engineering, ChongQing University of Arts and Sciences, Yong-
Chuan,ChongQing, P.R. China, **Ivanovo State University of Chemistry and Technology, Ivanovo, Russia) e-mail: caiyh651@yahoo.com.cn, daf81@mail.ru
N,N'-Bis(benzoyl) dodecanedioic acid dihydrazide (NA) was synthesized by a advanced routes, and the structure of NA had been confirmed by FT-IR, 1H NMR. The influence of the NA to nucleation and mechanical properties of Poly(L-lactic acid)(PLLA) were investigated. Compared to the neat PLLA, with the addition of 0.8% NA, the crystallization temperature (To) increase from 105.88 °C to 125.07 °C and the crystallization enthalpy (AH<) increase from 1.379 J'g1 to 29.17 J'g1 at a cooling rate of 1 °C/min from melt. The low content of NA can increase the mechanical properties of PLLA. Upon addition of 0.5%NA, comparing with the neat PLLA, the tensile strength modulus and elongations at break increase from 74.4 MPa, 3592.8 MPa and 2.72% to 85.3 Mpa, 4266.2 Mpa and 2.98%, respectively. And the impact strength possesses a maximum value for the critical NA loading 1%.
Key words: Benzoyl hydrazine, Dodecanedioic Acid, Poly(L-lactic acid), Nucleation
INTRODUCTION
Poly(L-lactic acid)(PLLA) is a semicrystal-line polymer with numerous desirable properties: lower energy consumption, biopolymer and non-toxic to the environment [1], Thus, it is widely used in biomedical applications [2], packaging materials [3-5] to automotive interior [6]. However, PLLA still has some disadvantages, such as slow crystallization rate, low crystalline degree and poor heat resistance. For all applications, it is of major importance to improve the crystallization characteristics of PLLA, which strongly affect its application. Thus, it is necessary to improve crystallization of PLLA to broaden its application.
In recent years, amide and its derivatives as important organic compounds had been widely used in synthesis of intermediates [7] and materials chemistry [8], drugs release [9], polymers [10,11], etc, and obtained a lot of progress. For example, Anna Pachu-ta-Stec et al. [12] reported that new N-substi-tuted amides of 3-(3-ethylthio- 1,2,4-triazol-5-yl) propenoic acid were designed and prepared by the condensation reaction of exo-S-ethyl-7-oxabicyclo-[2.2.1]-hept-5-ene-2,3-dicarbonyl isothiosemica- rbazide with primary amines. And some synthesized compounds were found to be evidently effective in vitro against lung cell line. The distinctly marked antiproliferative effect of some compounds in breast carcinoma cells in vitro was ascertained. There existed some literature [10] which reported amide could improved the crystallization of PLLA, Thus, in this paper, we synthesis N, N-
Bis(benzoyl) dode-canedioic acid dihydrazide as a nucleating agent to improve the crystallization of PLLA. At the same time, with the presence of NA, the mechanical properties of PLLA with different NA content were investigated.
EXPERIMENT
Materials. The materials used in this study were of analytical grade (AR) grade. Thionyl dichlo-ride, N, N-dimethylacetamide and Pyridine were procured from Mianyang Rongshen Chemical Reagents Company (Sichuan Province, China). Benzoyl hydra-zine and dodecanedioic acid were procured from Beijing Chemical Reagents Company (Beijing, China) and Chengdu Kelong Chemical Reagents Company respectively (Sichuan Province, China); Poly(L-lactic acid) was purchased from Nature Works LLC, USA.
Synthesis procedure of N, N'-Bis(benzoyl) dodecanedioic acid dihydrazide(NA). N,N-Bis-(benzoyl) tridecanedioic acid dihydrazide was prepared as shown in Scheme-1: dodecanedioic acid, thionyl dichloride of 50 mL in the presence of N,N-dimethylacetamide as catalyst was mixed, and the mixture was heated up to 80 °C, and held at 80 °C for 10 h with stirring. After cooling to room temperature and evaporation of thionyl dichloride in vacuum, the residue was dodecanedioyl dichloride.
Benzoic hydrazide and N,N-dimethylacet-amide of 50 mL were mixed, and the mixture was purged under nitrogen atmosphere. dodecanedioyl dichloride was added slowly onto the mixture, followed by adding pyridine of 0.057 mol, and the mix-
ture was heated up to 70 °C, and held at 70 °C for period of time with stirring. Reaction mixture was poured onto water of 300 mL and stirred, followed by filtrating. Obtained crude product was washed four times by water of each 300 mL at room temperature, and then washed by methanol of 300 mL at 50 °C to eliminate raw materials and by-products, the resulting product was dried in a vacuum at 65 °C. IR (KBr) u: 3215, 2924.3, 2847, 1644.2, 1603.7, 1573.9, 1535.9, 1461.8, 1416.9, 1159.7, 1075, 996.4, 949.7, 860.2, 781.6, 683.6, 619.8, 547.7, 520.3, 474.7 cm-1; !H NMR (DMSO, 500 MHz) S : ppm ; 10.29 (s, 1H, NH), 9.84 (s, 1H, NH), 7.47~7.88 (m, 5H, Ar), 2.16~2.19 (t, 2H, CH2), 1.54~1.57 (t, 2H, CH2), 1.21~1.28 (d, 2H, CH2).
DSC Q2000 instrument to heat at the heating rate of 10 °C/min. At last, the equilibrium melting temperatures of pure PLLA and PLLA/NA samples are obtained by using the Hoffman-Weeks plots.
For the mechanical properties, Dumbbell-shaped tensile test specimens with effective dimensions of 25mm*6mm* 1.0 mm were prepared by pneumatic-controlled impact shaping machine. Normal tensile tests were conducted on a D&G DX-10000 electronic tensile tester at the speed of 50 mm/min at room temperature. The tensile strength, elastic modulus and elongations at break were obtained by averaging over five specimens.
RESULTS AND DISCUSSION
Nucleating effect of NA. As to industrial applications of PLLA, It is very impor-2HClf+2S02j tant to investigate non-isothermal crystallization from melt. Fig. 1 shows the DSC curves of non-isothermal crystallization from melt at a cooling rate of 1 °C /min, and the thermal properties such as the crystallization temperature (To) and the crystallization enthalpy(A#c) obtained from DSC analysis are read in Table.
Scheme 1. Synthesis of N, W-bis(benzoyl) tridecanedioic acid dihydrazide
Preparation of PLLA/NA sample. PLLA and NA were dried over night at 60°C under vacuum respectively to remove residual water. Blending of PLLA and NA was performed on a counter-rotating mixer with a rotation speed of 32 rpm for 5 min, then at 64 rpm for 5 min. The processing temperature was set at 180°C but it increased to 185°C upon mixing. Products were hot pressed at 180 °C under 20 MPa for 3 min to prepare sheets. The sheets were then cooled down by being compressed at room temperature under 20 MPa for 10 min.
Characterization. The non-isothermal crystallization behavior of PLLA was measured by DSC Q2000 (TA Instrumrnts-Waters LLC, USA). The PLLA and PLLA/NA samples were first heated to 190 °C at a rate of 100 °C/min and held at the same temperature for 5 min, then were cooled at a cooling rate of 1 °C/min from melt. Finally, the samples were scanned again to 190 °C at 10 °C/min. The equilibrium melting temperature ( t) was measured as following: the sample was heated to 190 °C in heat table and maintained at that temperature for 5 min. Then the sample was quenched from melt to the crystallization temperature Tc (100, 105, 110, 115, 120 °C), held at that temperature for at least 60 min to ensure complete crystallization. At last, the sample was moved to
60
80
140
100 120 Temperature, °C
Fig. 1. DSC of PLLA and PLLA/NA crystallized from melt at a cooling rate of 1 °C/min
As seen in Fig. 1, upon cooling rate of 1 °C /min, the crystallization peak of PLLA can almost not be detected, which shows that the crystallization of neat PLLA is very slow. With addition of NA, crystallization peak appears in the DSC cooling curve. Compared to the neat PLLA, NA addition leads to the shift of crystallization peak to higher temperature indicating the increase of crystallization temperature, On the other hand, crystallization peak for PLLA containing NA becomes much sharper in the cooling process, this result shows that NA can serve as a nucleating agent for the crystallization, and increase the overall
crystallization rate of PLLA [13]. Degree of supercooling (ATmc) could be expressed as the nucleating effect on crystallization. Usually, the smaller the ATmc is, the greater nucleating effect on PLLA crystallization is. Upon cooling at 1 °C /min, as seen in Table, with increasing NA content, ATmc be
comes smaller, upon the addition of 0.8% NA, the ATmc is smallest, which indicates the best effect of crystallization at 0.8% NA. Compared to the neat PLLA, with the addition of 0.8% NA, the crystallization temperature(T0) increase from 105.88 °C to 125.07 °C and the crystallization enthalpy(A#c) increase from 1.379 J-g-1 to 29.17 J-g-1 at a cooling rate of 1 °C/min from melt.
Table. DSC date of PLLA/NA crystallized from melt at a cooling rate of 1 °C/min
Sample To/°C T /°C 1 mo' ^ T о /°C m AT */°C Atfc/Lg1
PLLA 105.88 96.28 161.21 55.33 1.379
PLLA/0.5%NA(O) 125.02 115.94 160.44 35.42 27.61
PLLA/0.8%NA(O) 125.07 119.25 159.19 34.12 29.17
PLLA/ 1%NA(O) 124.67 118.75 159.46 35.79 28.82
PLLA/2%NA(O) 121.70 115.75 159.56 37.86 28.06
PLLA/3%NA(O) 119.50 110.62 160.28 40.78 28.69
Note: * ATmC= T ° - To, T o - equilibrium melting temperature
1 5 2 0 2.5 3 0 o.o 0.5 1.0 1.5 2.C
Content/ % Content/ %
Fig. 2. The mechanical properties of PLLA with different NA contents. a) Tensile strength, b) Tensile modulus, c) Elongation at break,
d) Impact strength
Mechanical Properties. The mechanical properties of polymeric materials can be improved in different degrees if filler is dispersed in polymer. The tensile strength, tensile modulus, elongation at break and impact strength of PLLA with different NA contents are presented in Fig. 2(a-d), respectively. The
figures show that NA can improve the mecha-nical properties of PLLA in a certain extent. And low content of NA can increase the tensile strength, modulus and elongation at break of PLLA and possesses a maximum value for the critical NA loading 0.5%, Upon addition of 0.5%NA, comparing with the neat
PLLA, the tensile strength modulus and elongations at break increase from 74.4 MPa, 3592.8 MPa and 2.72% to 85.3 Mpa, 4266.2 Mpa and 2.98%, respectively. The enhancement of the tensile properties of PLLA/NA is due to the increasing of crystallization degree of PLLA with nucleating agent NA, on the other hand, low NA contents in PLLA existed a good dispersion and compatibility. When continuing to increase the NA contents, the tensile strength and modulus start to decrease, However, the tensile strength and modulus of PLLA/NA is larger than that of the neat PLLA when the content of NA is less than 3%. The elongations at break of PLLA/NA with more than 1% is inferior to that of the neat PLLA. At the same time, the impact strength of PLLA with different NA contents is presented in Fig. 2(d). From this figure the effect of adding NA can be seen clearly and directly. NA can improve the impact strength of PLLA when the content of NA is less than 2%, and the maximum value of impact strength of PLLA with 1% content is 13.2KJ/m [13].
CONCLUSION
In this paper, N, N'-Bis(benzoyl) dodecane-dioic acid dihydrazide was successfully synthesized from benzoyl hydrazine and dodecanedioyl dichloride which was deprived from dodecanedioic acid via acy-lation. The nucleating effect of NA for PLLA was evaluated by DSC. The result showed that NA as a kind of heterogeneous nucleation agent could significantly improve the crystallization of PLLA. Furthermore, the low content of NA can increase the mechanical properties of PLLA.
Acknowledgements. This work was supported by The Ministry of Science and Technology
of the People' Republic of China (project number 2007BAE42B00), ChongQing University of Arts and Sciences (project number Z2011CL11, 2012PYXM04) and Shanghai Leading Academic Discipline Project (project number s30107).
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