Additive Manufacturing of PLA/Basalt Composites

Vocabulary terms and definitions related to the additive manufacturing, mechanical testing, and thermal analysis of PLA/basalt composites based on the provided lecture transcript.

Additive manufacturing

The process of building objects layer by layer from digital models; specifically used to 3D print PLA/basalt composite samples via the MEX/FDM technique.

Screw extruder

A machine (e.g., Noztek Xcalibur, single screw) that melts and pushes material through a die using a rotating screw to produce filaments at temperatures of $180–210^{\circ}C$.

Weight ratios of basalt filler

The proportion of basalt relative to total composite mass; tested at $0_{wt\%}$, $1_{wt\%}$, $3_{wt\%}$, and $5_{wt\%}$ to determine optimal reinforcement.

Fused deposition modeling (FDM) technique

Also called MEX, a 3D printing method using a BBC3040 printer at a $210^{\circ}C$ nozzle temperature and $50\,mm/s$ speed to deposit melted filament layer by layer.

Tensile strength

The maximum stress a material withstands when pulled apart; neat PLA achieved $53.11\,MPa$, while basalt addition caused a decrease, reaching $-33.45\%$ at $5_{wt\%}$.

Flexural strength

The stress a material resists when bent; neat PLA achieved $90.91\,MPa$, with improvements at $1_{wt\%}$ ($+0.6\%$) and $3_{wt\%}$ ($+2.73\%$) but a drop at $5_{wt\%}$ ($-19.61\%$).

Impact strength

The energy absorbed per unit area during sudden fracture; neat PLA measured $2.63\,kJ/m^2$, with PLA+3B showing the best composite performance ($+0.38\%$).

Tensile modulus

A measure of stiffness under pulling force; improved by $5.23\%$ at $1_{wt\%}$ and $11.01\%$ at $3_{wt\%}$ basalt addition due to stiff particles resisting deformation.

Flexural modulus

A measure of stiffness under bending; consistently improved with all filler ratios by $+16.02\%$, $+28.25\%$, and $+32.74\%$ for 1, 3, and $5_{wt\%}$ respectively.

Shore D hardness value

A numerical scale for rigid plastics using a 5 kg load; values increased with filler: 78.59 (neat PLA), 79.60 (1B), 81.15 (3B), and 83.26 (5B).

Thermogravimetric analysis (TGA)

A thermal test measuring weight loss from $30–600^{\circ}C$ at $10^{\circ}C/min$ under nitrogen to assess thermal stability and degradation behavior.

Thermal barrier

A property where basalt fillers resist heat transfer, shifting degradation onset to higher temperatures and reducing early weight loss in PLA.

Chain scission

The breaking of polymer backbone chains due to heat, hydrolysis, or stress; in neat PLA, it reduces molecular weight and accelerates degradation.

Glass transition temperature ($T_g$)

The temperature ($58–61^{\circ}C$ for these samples) where a polymer transitions from a rigid glassy state to a flexible rubbery state.

Viscoelastic properties

The combined elastic and viscous behavior measured via DMA, showing storage modulus, loss modulus, and damping factor across $30–130^{\circ}C$.

Dimensional stability

The ability to maintain shape under temperature/load; assessed via TMA, where PLA+1B kept CTE below $800\,ppm/^{\circ}C$ at $100^{\circ}C$.

Molecular weight

The mass of a polymer chain; PLA degradation begins when this falls below $10\,kDa$, allowing for microbial attack.

Isomeric ratio

The proportion of L- and D-lactic acid in PLA; influences degradation rate, crystallinity, and mechanical properties.

Surface morphology

Microscopic physical structure analyzed via SEM to observe filler distribution, voids, fracture behavior, and layer adhesion.

Anisotropic nature

Having different mechanical characteristics in different directions; a limitation in MEX 3D printing where interlayer bonds are weaker than in-plane bonds.

Porosity

Internal voids within a material; increases with basalt content up to $4.78\%$ at 5_{wt\%, negatively affecting mechanical properties.

Agglomeration effect

The clustering of filler particles into larger groups, creating stress concentration zones; observed especially at $5_{wt\%}$ loading.

Slicing software

Software like Ultimaker Cura that converts 3D CAD STL files into G-codes defining printing coordinates and thin horizontal layers.

ASTM D638-Type IV

The standard test method for tensile properties of plastics; specifies specimen geometry and a $3\,mm/min$ crosshead speed.

ASTM D790

The standard test method for flexural properties of plastics, performed at a $3\,mm/min$ crosshead speed.

ASTM D256

The standard test method for determining the impact resistance of plastics using a pendulum (e.g., Zwick/Roell hit5.5P).

Enthalpy ($\Delta H$)

Total heat content measured in DSC as cold crystallization enthalpy ($\Delta H_{cc}$) and melting enthalpy ($\Delta H_m$) to calculate crystallinity.

Crystallinity degree ($X_c$)

The percentage of crystalline regions; highest in neat PLA ($16.01\%$) and reduced by basalt (down to $1.20\%$ at $1_{wt\%}$).

ASTM E831-03

The standard test method for linear thermal expansion of solid materials used in TMA to measure CTE and dimensional stability.

Storage modulus

The component of the complex modulus representing elastic energy storage; composites surpass neat PLA above $T_g$ due to mechanical interlocking.

Damping factor (tan $\delta$)

The ratio of loss modulus to storage modulus; PLA+3B achieved the lowest value ($0.89$), indicating superior bonding.

Sintering process

The bonding of material layers through heat and pressure without full melting; reduced by basalt's low thermal conductivity.

Mechanical percolation threshold

The critical filler concentration for a continuous network; PLA+5B falls below this, explaining its decreased modulus.

Mechanical keying

A physical interlocking mechanism where rough filler surfaces grip the polymer matrix without chemical bonding.

Polymorph phases

Different crystalline structures ($α$ and $α'$) formed by PLA during cold crystallization between $117–121^{\circ}C$.

CTE values

Coefficient of Thermal Expansion; measures expansion in $ppm/^{\circ}C$. Rising sharply above $T_g$, exceeding $2000\,ppm/^{\circ}C$ in PLA+3B and PLA+5B.

Physical aging

A process where amorphous polymer chains rearrange toward a more stable state over time below $T_g$, seen as an endothermic peak in DSC.