Engineered Porosity in Microcrystalline Diamond-Reinforced PLLA Composites - Effects of Particle Concentration on Thermal and Structural Properties

At a Glance

Metadata	Details
Publication Date	2025-10-04
Journal	Materials
Authors	Mateusz Ficek, Franciszek Skiba, Marcin Gnyba, Gabriel Strugała, Dominika Ferneza
Institutions	Wrocław University of Science and Technology, AGH University of Krakow
Analysis	Full AI Review Included

Executive Summary

This research successfully synthesized and characterized microcrystalline diamond (MDP)-reinforced Poly(L-lactic acid) (PLLA) composite foams, demonstrating precise control over structural and thermal properties for advanced biodegradable applications.

Engineered Porosity: Systematic control of hierarchical porosity was achieved, ranging from 11.4% to 32.8% by varying MDP concentration (5 to 75 wt%) and particle size (0.125 µm and 1.00 µm).
Structural Transition: X-ray microtomography confirmed a fundamental shift in pore architecture: increasing diamond content transitions the structure from large-volume interconnected pores (characteristic of neat PLLA) to numerous small-volume closed pores.
Physical Integration: Spectroscopic analysis (FTIR and Raman, 1332 cm^-1 diamond peak) confirmed purely physical interactions between the PLLA matrix and the MDP filler, with no evidence of chemical bonding.
Thermal Modification: Diamond incorporation reduced the PLLA melting temperature (T_m) from 180-181 °C down to 172 °C (at 75 wt% MDP125), and decreased the melting enthalpy (ΔH_m) from ~46 J/g to ~14.5 J/g, indicating modified crystallization behavior.
Reduced Stability: Thermogravimetric analysis (TGA) showed reduced thermal stability of the PLLA matrix due to the exceptional thermal conductivity of the diamond filler, which accelerates polymer degradation.
Value Proposition: The resulting composites provide a quantitative framework for designing lightweight, biodegradable materials with tunable porosity and enhanced thermal conductivity, suitable for high-value engineering applications.

Technical Specifications

Parameter	Value	Unit	Context
Matrix Material	Poly(L-lactide) (PLLA)	N/A	Density: 1.25 g/cm³
Diamond Filler Type	Microcrystalline Diamond (MDP)	N/A	HPHT synthesis, unmodified
MDP Median Size (D50)	0.125 / 1.00	µm	Two particle sizes tested (MDP125 / MDP1000)
Diamond Concentration Range	5 to 75	wt%	Range tested in PLLA matrix
Total Porosity Range	11.4 to 32.8	%	Controllable range achieved across all samples
Porosity (75 wt% MDP125)	11.4	%	Lowest recorded porosity
Porosity (Neat PLLA Reference)	24.4 or 32.8	%	Varies based on reference batch
Diamond Lattice Vibration	1332	cm^-1	Characteristic peak confirmed by Raman spectroscopy
PLLA Melting Temperature (T_m) (Initial)	180 to 181	°C	Observed at low MDP content (5-15 wt%)
PLLA Melting Temperature (T_m) (Reduced)	172	°C	Observed at 75 wt% MDP125 loading
Enthalpy of Melting (ΔH_m) Reduction	46 to 14.5	J/g	Decrease from neat PLLA to 75 wt% MDP125
X-ray Microtomography Resolution	19.64	µm	Voxel resolution for 3D structural analysis
TGA Pyrolysis Residue (900 °C)	~25	%	For 75 wt% diamond samples (matches PLLA content)

Key Methodologies

The composite foams were fabricated using the Thermally Induced Phase Separation (TIPS) method followed by freeze-drying (lyophilization).

Solution Preparation: A 2.5 wt% solution of PLLA (Resomer L210s) was prepared in 1,4-dioxane solvent, stirred for 24 h at 60 °C (500 rpm).
Filler Incorporation: HPHT microcrystalline diamond particles (0.125 µm or 1.00 µm) were added to the PLLA solution to achieve weight ratios ranging from 5 wt% to 75 wt% diamond content.
Casting and Freezing: The resulting suspensions were cast into 24-well plates (1 mL per well) and frozen for 24 h at -20 °C.
Lyophilization: Samples underwent freeze-drying for 24 h at a temperature of -50 °C and a pressure of ~20 Pa to yield porous foam composites.
Structural Analysis (µCT): X-ray Computed Microtomography (GE phoenix v|tome|xs) was used for 3D reconstruction and porosity quantification, applying a threshold-based algorithm on a cylindrical Region of Interest (ROI).
Morphological Analysis (SEM): Scanning Electron Microscopy (JEOL JSM-7800F) was used to examine cross-sections and observe particle dispersion and pore structure evolution.
Spectroscopic Confirmation: ATR-FTIR and Raman spectroscopy confirmed the absence of chemical interaction and validated the presence of diamond (characteristic peak at 1332 cm^-1).
Thermal Characterization: Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) were performed under a nitrogen atmosphere to determine melting behavior, crystallization kinetics, and thermal degradation profiles.

Commercial Applications

The unique combination of biodegradability, engineered porosity, and enhanced thermal properties makes these PLLA/MDP composites highly relevant for specialized, high-value markets.

Tissue Engineering Scaffolds: The controllable hierarchical porosity (11.4% to 32.8%) is ideal for designing scaffolds that require specific pore sizes and connectivity patterns to support cell proliferation and vascularization in bone or soft tissue regeneration.
Advanced Thermal Management: The high thermal conductivity of diamond, integrated into a lightweight, porous PLLA structure, is valuable for thermal dissipation in temporary electronic components or biomedical devices where biodegradable materials are mandated.
Specialized Filtration Media: The ability to transition pore morphology from interconnected networks to closed, small-volume pores allows for the design of specialized filters requiring precise control over fluid dynamics and separation efficiency.
Biodegradable Composites: Serving as a platform for next-generation sustainable materials requiring enhanced mechanical strength and thermal stability compared to pristine PLLA, particularly for temporary structural supports or packaging.

View Original Abstract

This research explores microcrystalline diamond particles in poly(L-lactic acid) matrices to create structured porous composites for advanced biodegradable materials. While nanodiamond-polymer composites are well-documented, microcrystalline diamond particles remain unexplored for controlling hierarchical porosity in systems required by tissue engineering, thermal management, and filtration industries. We investigate diamond-polymer composites with concentrations from 5 to 75 wt% using freeze-drying methodology, employing two particle sizes: 0.125 μm and 1.00 μm diameter particles. Systematic porosity control ranges from 11.4% to 32.8%, with smaller particles demonstrating reduction from 27.3% at 5 wt% to 11.4% at 75 wt% loading. Characterization through infrared spectroscopy, X-ray computed microtomography, and Raman analysis confirms purely physical diamond-polymer interactions without chemical bonding, validated by characteristic diamond lattice vibrations at 1332 cm−1. Thermal analysis reveals modified crystallization behavior with decreased melting temperatures from 180 to 181 °C to 172 °C. The investigation demonstrates a controllable transition from large-volume interconnected pores to numerous small-volume closed pores with increasing diamond content. These composites provide a quantitative framework for designing hierarchical structures applicable to tissue engineering scaffolds, thermal management systems, and specialized filtration technologies requiring biodegradable materials with engineered porosity and enhanced thermal conductivity.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma18194606

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