Synthesis of PVA⁃g⁃PDLA and its modification for PLLA/PVA blends

doi:10.19491/j.issn.1001-9278.2025.10.002

Abstract

Abstract:

Poly（L⁃lactic acid）（PLLA） has attracted significant attention due to its environmental friendliness， processability， and mechanical properties. However， its low toughness and melt strength greatly limit its use as a blown film material. To solve this problem， we synthesized a graft copolymer， poly（vinyl alcohol）（PVA）⁃g⁃poly（D⁃lactic acid）（PDLA）， via the reaction of PDLA with PVA. This copolymer was then blended with PLLA/PVA using both direct and masterbatch melt blending methods. The crystallization behavior， rheological properties， relaxation behavior， and impact properties of the resulting blends were further investigated. The results indicated that， compared to the direct method， the masterbatch method produced blends with more and smaller stereo⁃complex crystals. This enhanced the melt strength， improved the relaxation behavior （increasing the characteristic relaxation time at 180 °C）， and induced clear strain hardening in extensional rheology. Additionally， the masterbatch blends exhibited superior impact toughness， with an impact strength of 6.03 kJ/m². This value is 3.8 times and 2.5 times higher than that of pure PLLA and the direct⁃method blend， respectively.

Key words: poly（L?lactic acid）, poly（vinyl alcohol）, graft copolymer, melt strength, impact toughness

CLC Number:

TQ321

MENG He, JIANG Li, ZHANG Kai, YANG Mingbo. Synthesis of PVA⁃g⁃PDLA and its modification for PLLA/PVA blends[J]. China Plastics, 2025, 39(10): 6-11.

Figures/Tables 9

Fig.1. 1H⁃NMR spectra of PDLA， PVA⁃MA and PVA⁃g⁃PDLA

Fig.2. XRD and DSC curves of PLLA/PVA/PVA⁃g⁃PDLA prepared by different methods

样品

hlk 110 晶粒

尺寸/Å

hlk 300/030 晶粒

尺寸/Å

hlk 200 晶粒

尺寸/Å

Tab.1. Grain size of SC crystal of PLLA/PVA/ PVA⁃g⁃PDLA blends

样品	T_m⁃HC/℃	△H_m⁃HC/J·g^-1	T_m⁃SC/℃	△H_m⁃SC/J·g^-1
MB	172.31	33.62	215.18	2.30
Mbb⁃MB	170.30	35.27	210.29	2.57

Tab.2. DSC data of the PLLA/PVA/PVA⁃g⁃PDLA blends

Fig.3. Dynamic rheological properties of PLLA/PVA/PVA⁃g⁃PDLA blends

Fig.4. Relaxation time spectra of PLLA/PVA/PVA⁃g⁃PDLA blends at 180 ℃ and 200 ℃

Fig.5. Tensile rheological curve of the PLLA/PVA/PVA⁃g⁃PDLA blends

Fig.6. Notched impact strength of the pure PLLA and the PLLA/PVA/PVA⁃g⁃PDLA blends

Fig.7. Impact surface morphology of the PLLA/PVA/PVA⁃g⁃PDLA blends

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