Engineered polylactide (PLA)–polyamide (PA) blends for durable applications: 1. PLA with high crystallization ability to tune up the properties of PLA/PA12 blends

Figures & data

Table 1. Products evaluated as nucleating agents (NAs) for PLA.

Code	Product	Supplier	Short description
NA1	Ecopromote	Nissan Chemical Industries, Ltd.	Phenylphosphonic acid zinc salt (PPA-Zn) of 2-3 µm as granulometry; Onset of thermal degradation >500 °C.
NA2	Sodium benzoate	Brenntag	Sodium salt of benzoic acid, nucleating agent (additive) especially used in polypropylene, polyesters (PET).
NA3	Bruggollen P252	Brüggemann Chemical	Synergistic mixture of various nucleating and lubricating products (proprietary composition). Crystallization accelerator for thermoplastic polyesters (allows PET recrystallization at about 197 °C (DSC)).
NA4	Talc JetFine® 3C A	Imerys Talc	Mg3Si4O10(OH)2, high aspect ratio, it improves the nucleation in crystalline polymers. Median diameter – d50 = 3.9 µm; Surface area (BET) = 14.5 m^2/g.
NA5	Talc Crys-Talc 7C	Imerys Talc	Mg3Si4O10(OH)2, micro-lamellar talc for polymer reinforcement and nucleation (PA, PLA, etc.). Granulometry by sedimentation (d50) = 1.9 µm; Surface area (BET) = 16.9 m^2/g.

Table 2. Codes of PLA(NA)/PA12 samples and their composition.

Code of sample	PLA(NA), wt.%	PA12, wt.%	Compatibilizer, wt.%
PLA(NA)	100	0	–
PLA80-PA20	80	20	–
PLA60-PA40	60	40	–
PLA40-PA60	40	60	–
PLA50-PA50^a	50	50	–
PLA20-PA80	20	80	–
PA12	0	100	–
PLA60-PA40/2J	58.8	39.2	2
PLA60-PA40/2XB	58.8	39.2	2

^aThe PLA50-PA50 sample was realized and characterized only by SEM to have more information about the evolution of morphology of PLA–PA blends.

Figure 1. Comparative DSC traces of starting neat PLA and of PLA-NA1-5 samples recorded (a) during cooling and (b) second heating (rate of 10 °C/min).

Table 3. Comparative DSC data on starting PLA and PLA-NA1-5 samples obtained during non-isothermal crystallization from the molten state (cooling by 10 °C/min) and following the succeeding heating scan.

Sample	DSC cooling by 10 °C/min			Second DSC heating scan, 10 °C/min
	Tc, °C	ΔHc, J/g	χc, %	Tg, °C	Tcc, °C	ΔHcc, J/g	Tm, °C	ΔHm, J/g	χf, %
Neat PLA (AR)	–	–	–	63	–	–	167	1.9	2.0
PLA-1% NA1	124	37.9	40.7	62	–	–	166	39.1	42.0
PLA-1% NA2	–	–	–	60	111	27.0	157; 164	38.3	12.2
PLA-1% NA3	100	21.5	23.1	62	97	3.0	167	33.4	32.7
PLA-1% NA4	107	25.5	27.4	63	–	–	163; 168	27.2	29.2
PLA-1% NA5	105	27.8	29.9	64	–	–	163; 168	32.7	35.2

Abbreviations: DSC cooling: crystallization temperature (T_c), enthalpy of crystallization (ΔH_c) and corresponding degree of crystallinity (χ_c,): Second DSC heating: glass transition temperature (T_g), cold crystallization temperature (T_cc), enthalpy of cold crystallization (ΔH_cc), melting temperature (T_m), enthalpy of fusion (ΔH_m), final degree of crystallinity (χ_f).

Figure 2. Comparative DSC curves of starting PLA and PLA(NA) displayed during cooling and second heating scan at rate of 10 °C/min and quantification of the main information.

Figure 3. DSC traces obtained during crystallization of PLA(NA) under isothermal conditions for determination of half crystallization time (t_1/2). In the inset of figure: isothermal crystallization of starting neat PLA at 110 °C assessing for a very long t_1/2.

Figure 4. Comparative DSC curves of (a, b) PLA(NA) and (c) neat PLA after IM at different temperatures of the mould and distinct residence time.

Table 4. Degree of crystallinity (%) of neat PLA and PLA(NA) following the processing by injection moulding at different mould temperatures.

Sample	Residence time, min ↓	Degree of crystallinity, % (at the temperature of the mould given hereunder)
		30–40 °C	80 °C	100 °C	120 °C
PLA(NA)	1	13.1	15.2	38.2	46.3
	2	15.9	27.4	40.2	46.7
Neat PLA	2	8.0	9.1	10.2	15.1

Figure 5. (a–f) SEM micrographs of cryofractured surfaces of PLA(NA), PA12, and PLA(NA)/PA samples.

Figure 6. (a–d) SEM micrographs of PLA(NA)/PA12 samples previously “etched” in chloroform.

Figure 7. (a, b) SEM micrographs of previously “etched” PLA50-PA50 samples to illustrate the inversion of the phase (PLA pass into PA as matrix).

Figure 8. Scheme to illustrate the morphology evolution by increasing the amounts of PA12 in PLA(NA)/PA blends.

Figure 9. TG (a) and D-TG curves (b) of PLA(NA), PA12, and PLA/PA blends (under air, 20 °C/min).

Table 5. Thermal parameters of PLA(NA), PA12 and PLA(NA)/PA blends as determined by TGA.

Sample code	T5%, °C	Weight loss up to 400 °C, %	Td1, °C (PLA)	Td2, °C (PA)
PLA(NA)	337	98	370	–
PLA80-PA20	341	81	367	442
PLA60-PA40	342	65	365	467
PLA40-PA60	344	47	364	466
PLA20-PA80	348	29	362	472
PA12	393	6	–	463

Figure 10. DSC traces recorded (a) during cooling and (b) second heating (10 °C/min) of PLA(NA), PA12 and their blends.

Table 6. Quantification of DSC data following the characterization of PLA(NA), PA12 and their blends.

Sample	DSC cooling, 10 °C/min						Second DSC heating, 10 °C/min
	Tc, °C (PLA)	ΔHc, J/g (PLA)^a	χ, % (PLA)	Tc (PA)	ΔHc, J/g (PA)^a	χ, % (PA)	Tg (PLA) °C	Tm, °C (PLA)	Tm, °C (PA)
PLA(NA)	125	33.9	36.5	–	–	–	62	166	–
PLA80-PA20	124	32.0	34.4	157	52.0	24.9	63	166	172; 177
PLA60-PA40	123	32.2	34.6	156	53.2	25.5	63	166	173; 178
PLA40-PA60	124	29.5	31.7	156	53.8	25.7	62	165	172; 177
PLA20-PA80	117	NA	NA	156	55.4	26.5	62	164	171; 177
PA12	–	–	–	153	51.3	24.5	NA	–	170; 178

^aValues normalized to the amounts of PLA or PA from samples.

Figure 11. DSC traces recorded during cooling (a) and second heating (b) of PLA60–PA40 blends with/without compatibilizers.

Figure 12. SEM images of PLA(NA)/PA12 60/40 wt.% with and without compatibilizers: (a, c, e) “non-etched” samples and (b, d, f) “etched” samples* in chloroform.

Table 7. Comparative mechanical properties^a of PLA(NA), PA12, and PLA(NA)/PA (50/50%.vol) blends with/without 2% Joncryl.

Sample	Max. tensile strength, MPa	Nominal strain at break, %	Young’s modulus, MPa	Izod impact resistance, kJ/m^2
PLA(NA)	61 ± 1	3.6 ± 0,8	2380 ± 60	2.6 ± 0.3
PLA(NA)/PA 50/50	45 ± 1	6.5 ± 1,2	2000 ± 60	2.5 ± 0.1
PLA(NA)/PA-2%J	52 ± 2	175 ± 22	1930 ± 40	4.4 ± 0.2
PA12	46 ± 2	183 ± 14	1390 ± 80	3.7 ± 0.2

^aSpecimens cutted from plates made by compression moulding. Tensile properties: ASTM D638, v = 1 mm/min, specimens type V; Izod – (notched) impact resistance: ASTM D256 (Method A, 3.46 m/s impact speed, 0.668 kg hammer).

Figure 13. Tensile strength–strain curves obtained following the mechanical characterization of PLA(NA), PA12, and PLA(NA)/PA (50/50 % vol.) blends with/without 2% Joncryl.