The Analytical Services Lab is part of NCSU Wilson College of Textile Engineering, Chemistry and Science Department (TECS).
The lab functions not only as a resource for graduate students to obtain data for their MS thesis or PhD dissertation work, but is also utilized for teaching and service.
- Outside lab services are mostly in the fields of textile & polymer manufacturing
- Testing, client interaction and communication is conducted by the ‘on staff’ Laboratory Manager.
- Client communication is maintained throughout the testing process to minimize unnecessary expenses and maximize the utility of the information generated.
- Collaboration with a diverse clientele of internal (incl. other NCSU Colleges) as well as external industry sponsors. We make every effort to accommodate testing requests in a timely manner and pricing is competitive to other commercial testing labs.
- For liability reasons we do not train or permit non-NCSU users on the instrumentation
- Limited wet chemistry techniques, like fiber burn outs or solvent Soxhlet extractions, are available,.
- Prices are typically quoted per project based on its complexity, instrument use and time involvement.
- A legal contract called a Fabrication and Testing Services Order Form “SOF” is set up by the University for industry clients to be signed prior to any testing work performed.
- Government affiliates and federally funded companies are eligible for the internal pricing structure.
- The lab does not participate in ‘reverse engineering’ or litigation cases.
Thermal Analysis Instrumentation
Differential Scanning Calorimetry (DSC)
DSC measures the amount of thermal energy absorbed or released by a substrate as a function of temperature or time known as “heat flow”. The TA Discovery DSC 250 with RCS cooler (enables cooling to -90oC) is a heat flux instrument with an autosampler.
- Melting Points (TM) ,
- Crystallization temperatures (TC)
- % crystallinity
- Glass Transition Temperatures (TG)
- Isothermal holds for kinetics evaluations.
- Samples can be liquids or solids, including pellets, powders and films
- Small sample size of 5-10mg
- Operating range is -900 C to 4500C
- Heating rates of up to 50oC per minute
- Units are measured as heat flow (mW) and temperature (oC)
- Must contain crystalline material or be capable of forming crystals during the heating process, resulting in an endothermic melting peak
- Grinding sample materials should only be done if it will not change their properties.
- Performance of active wear featuring phase change properties
- Variation in dyeability of synthetics can sometimes be traced to differences in crystallinity and crystal size, influenced by its thermal history
- Does not work for elastomers (ex. Spandex) that decompose rather than melt.
- Encapsulated samples are run against an empty reference pan of the same pan type.
- A purge gas is used to create an inert atmosphere around the sample and reference hotplates. Nitrogen, as the most commonly used purge gas, allows a controlled heating/cooling rate of up to 50oC/min between program and sample temperature. Noble gases such as Helium or Argon with higher thermal conductivity can also be used, but impact the rate and temperature range that can be achieved.
- Typical scan rate is 10oC /min.
- Effect of scan rate on sensitivity and resolution: A) Sensitivity: the faster the scan rate the greater the sensitivity. This typically applies if Tg’s are analyzed as they show a stronger transition when run at faster heating rates. The reason for this is that DSC measures the flow of energy and during a fast scan the energy flow increases over a shorter period of time. B) Resolution: Due to thermal gradients across a sample, the faster the scan rate the lower the resolution. Thermal gradients can be reduced by reducing sample size and improving sample contact with the pan.
Thermogravimetric Analysis (TGA)
TGA quantitatively measures weight loss (% or mg) of a sample due to decomposition loss of solvent/water as a factor of temperature or time. The TA Discovery TGA 550 with a standard furnace enables a heating profile from 25 to 950oC with typical heating rates of 10, 20 or 30oC per minute.
- Decomposition profile of liquids or solids
- Quantitative determination of
- number of constituents
- evaporation of volatiles
- water of hydration
- Isothermal degradation studies of substrates
- preliminary analysis to identify decomposition temperature profiles prior to DSC evaluation
- Typical sample size of 5 – 20 mg
- Samples are solids or liquids
- Graph displays temperature (oC) versus weight (mg or %)
- Available purge gases are N2 and Air.
- Samples can be liquid, solid, films or in powder form.
- Samples should free of static charge.
- Samples must not form corrosive gases (e.g. HCl or HF) upon decomposition
- Sample must not be toxic or carcinogenic
- Sample should not contain any metal salts or ions
- Carbon nanotube analysis
- Quality control of polymeric raw material for fiber extrusion
- The purge gas atmosphere during decomposition plays an important role, as it will impact the decomposition profile. Typically decompositions in N2 form higher thermally stable compounds and decompose at higher temperatures than in air, which is an oxidizing gas.
- Thermograms are evaluated by applying a first derivative to the raw data, which displays the rate of mass change and allows to select onset, starting and ending temperatures for weight percentage calculations.
- Mass changes occur based on various factors. A sample can actually increase in mass due to adsorption of the purge gas.
Agilent Cary 300 & Agilent Cary 5000 UV-Vis-NIR spectrophotometers
UV-Vis instruments are most commonly used to identify the wavelength of maximum light absorbance (lambda max). Colored solutions typically absorb in the visible region (Vis), whereas colorless chemical containing a suitable chromophore may absorb in the UV region.
- Lambda max (wavelength of peak absorbance)
- Determination of unknown dye concentrations
- Absorbance (Abs) or % Transmittance (%T) of solutions over a selected wavelength range
- Abs, %T and % reflectance (%R) of solid samples
- Dual beam instruments
- Integrating sphere modules for solid sample analysis
- Near Infrared integrating sphere (Cary 5000)
- Fabric protection software converts plots to numerical UPF value
- Agilent Cary 300 operating wavelength range 190-800 nm
- Agilent Cary 5000 operating wavelength range 175-3300nm
- Films must be thin enough to transmit light
- Solutions may need to be diluted to measure 1.5 or less absorbance units for the calibration curve to be linear
- Quantitative evaluation of dye solutions
- Ultraviolet Protection Factors (UPF) determinations of textile substrates for apparel and outdoor fabrics
- Evaluation of Near Infrared (NIR) absorbing dyes
- Analyses of dyes for solar cells, medical applications and renewable energy
- Measurement of thin polymer films
Spectroscopy is the interaction of electromagnetic radiation with matter. In the UV-Vis range electronic transitions take place. When a photon hits a molecule and is absorbed, the molecule undergoes a transition to a higher energy state. Molecules that exhibit double bonds exhibit the best UV absorbance.
In an organic dye molecule, the part of the molecule responsible for its color is called the chromophore.
Typically colored solutions absorb in the Vis range (360-700nm), non-colored solutions in the UV region (190-350nm). It is a common misperception that the lambda max for a compound is the color it appears. The actual color we see is called the ‘complimentary’ color, the sum of wavelengths/colors that were not absorbed by the sample.
- According to Beer’s Law, absorbance (A) is directly proportional to the concentration, assuming all other variables are constant.
- Deuterium lamps are used to produce the UV radiation, Tungsten lamps for Vis light.
- Quantification of dye in a solution requires accurate standards to obtain a calibration curve.
Fourier Transform Infrared (FTIR) Spectrometer
FTIR is used to qualitatively identify unknowns based on the functional groups that make up a molecule. The lab presently has two Thermo Fisher FTIR models, iS10 and iS50. The iS50 includes an interchangeable Raman module.
- Identification of substrates, including fibers, powders, films and liquids
- Contaminant analysis
- Finish analysis following a solvent extraction, or on a sample of a liquid finish or softener
- SpectaTM software enables constituent identification of up to four compounds in an unknown sample
- Extensive spectral libraries
- iS50 with built-in diamond Attenuated Total Reflectance (ATR) crystal and Raman module with 1064 nm NIR laser
- iS10 with OMNI ATR sampler with Germanium (Ge) crystal
- Sample to be analyzed must be free of solvents, including water
- The molecule must be IR active. All organic compounds and polymers are IR active
- FTIR has limited application for inorganic samples like salts or soil samples.
- Qualitative finish analysis
- Identification of fiber blends
- Bicomponent fiber analysis
- Analysis of rubber or polymer coatings
- Spectra are displayed as Absorbance (Abs) or % Transmittance (%T) v. wavenumber
- The FTIR x-axis scale is expressed in wavenumbers rather than nm (as in NIR) to indicate scanning from higher to lower energy, as 4000 -400 cm-1 when looking at a spectrum.
- The most common infrared regions used for analyses are the wavelength region just above the Vis region, extending from 800-2500nm. This is the longer wavelength, lower frequency region.
- Infrared (IR) is a form of heat radiation. When IR radiation is absorbed it causes the chemical bonds in the material to change vibrational energy levels.
- IR is also called ‘vibrational spectroscopy’. It is subdivided into Near Infrared (NIR) 800-2500nm, Mid Infrared (MIR / FTIR) 2500-25,000nm (4000-400 cm-1) and Far Infrared (FAR) greater than 25,000nm. FAR is typically not a very useful wavelength region as the crystal materials used for FTIR start to absorb in that wavelength region.
- FTIR is a technique that directs a light beam consisting of many frequencies of MIR light at once at a sample, measuring how much of that light intensity is absorbed by the sample, thereby providing information about the chemical structure of the molecule.
- For a molecule to absorb IR, the vibrations within a molecule must cause a net change in the dipole moment of the molecule. If there is a match in frequency of the radiation and the natural vibration of the molecular bond between 2 or more atoms, absorption occurs, which in turn increases the amplitude of the vibration displayed as a peak in the spectrum.
- Ge and Diamond are two common crystal materials used for ATR measurements. Attenuated Total Reflectance (ATR) allows for versatile sampling techniques with no sample preparation required
- Because they have different refractive indices (RI), each crystal material will result in differences in the IR depth of penetration (DOP) into the sample. Ge has a 0.5um, diamond a 2.4um DOP. In the case of a bicomponent fiber (sheath and core consisting of different polymers), peaks may be missing if the DOP is not sufficient using a Ge ATR.
- The available Raman module can selectively provide information on the ‘backbone’ structure of both organic and inorganic samples. The NIR laser will incinerate and decompose dark samples due to complete absorption of the heat energy generated by the NIR laser.
- Molecules such as O2 or N2, do not have a change in dipole moment and are not IR active. N2 gas is often used as a purge gas for the bench compartment to reduce CO2 and moisture peaks in a spectrum.
- As a rule, stronger bonds and smaller atomic mass functional groups exhibit stretching peaks at higher frequencies. Stretching vibrations typically occur above 1500 cm-1, bending vibration below 1500-400 cm-1‑.
- The depth of penetration of the IR light into the sample decreases using ATR as the wavenumber goes up. That means low wavenumber light penetrates farther into the sample than higher wavenumber light. A correction factor must be applied to the ATR measurement to make that spectrum equivalent in intensities to a %T / Abs spectrum of the same sample.
High Performance Liquid Chromatography (HPLC)
The Waters HPLC uses Size Exclusion Chromatography (SEC), a widely used technique for analyzing polymer samples to determine relative molecular weights and molecular weight distributions.
- Number average MW (M̄n), Weight average MW (M̄w), and Peak average MW (M̄p)
- Molecular weight distribution of polymers (polydispersity)
- Waters Alliance HPLC with 2695 pump system
- 2414 RI detector
- Empower 3 software
- THF & aqueous column
- Polymers must be soluble in THF or aqueous solutions (typically 0.1M NaNO3)
- Environmentally induced degradation of polymers
- Degradation of biomedical textiles
- SEC has become the most widely used technique for analyzing polymer samples to determine their relative molecular weights and weight distributions. (Polymers are large molecules composed of many repeating monomer units joined together.) It is nearly impossible to make polymers with all the same chain lengths.
- SEC is typically performed on molecules larger than 2000 Daltons in molecular weight. It is a technique that separates the different sizes of polymer chains in a sample and measure their relative abundance.
- The separation relies solely on the size of the polymer molecules in solution and is done under isocratic conditions, meaning the mobile phase concentration remains the same throughout the analysis.
- Once the polymer is dissolved in the solvent, the initially long chains of monomers that were linked together will ‘coil up’ on themselves to form a coil formation which resembles a ball of string. They now behave like tiny spheres with the sphere size dependent on the molecular weight. Higher molecular weights coil up to form larger spheres than lower molecular weight chains. This phenomenon makes them interact differently with the gel- like stationary phase in a column and leads to separation by size. Big spheres elute first as they do not penetrate as far into the pores of the stationary phase, while smaller molecules penetrate deeper into the stationary phase and elute later. Rule of thumb is BOCOF (Big Ones Come Out First)
- A polymer sample will contain a distribution of molecules of different chain lengths which in turn has a great impact on its physical properties, e.g., elasticity, brittleness, strength, elongation, flow & compression, flexibility to mention some.
- Standards with known molecular weights for THF SEC are made from polystyrene and from PEO/PEG for SEC in aqueous mobile phases.
Goniometer FDS Corp. Dataphysics OCA System
The goniometer measures the contact angle (θ)of water or other liquid a solid substrate. Angles are measured in degrees, which give an indication of the hydrophobic or hydrophilic surface properties of the substrate. Contact angle is one of the common ways to measure the wettability of a surface and is a quantitative measure of the wetting of a solid by a liquid. The instrument of choice to measure contact angles and dynamic contact angles is an optical tensiometer. A force tensiometers can also be used. … If contact angle is greater than 90°, the surface is said to be non-wetting with that liquid. Wetting refers to the study of how a liquid deposited on a solid (or liquid) substrate spreads, or the ability of liquids to form boundary surfaces with solid states. Contact angle is related both to surface tension and to thermodynamic equilibrium between phases. it is analyzed to measure the wettability of surfaces. Considering a droplet deposited on a horizontal surface, contact angle is defined as the angle formed by the liquid-gas interface with respect to the solid. Usually, surfaces showing contact angle with water higher than 90 are considered hydrophobic and for contact angle lower than 90 degrees hydrophilic. Thanks to the evaluation of surface tension and contact angle it is possible to:
- Fully automated dispensing, camera and data collection system
- Drop size as low as 3 µl
- Static sample stage
- Samples should be at least 1” diameter for multiple measurements
- Samples should not be contaminated by improper handling (exposing sample surface to natural skin oils)
- Samples should have relatively even surface for successful measurements
- Samples should be stable to the environment
- Characterization of hydrophobicity of knitted, woven or non-woven textiles
- Characterization of film surfaces
- The angle between the droplet and solid surface indicates the wettability of the surface based on the measured angle between the droplet and the substrate
- Water is typically used as the solvent, but other solvents may be used, depending on the application
- Dedicated syringes are used to dispense each liquid
Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray Spectroscopy (EDS)
Hitachi TM-4000 PlusXL with Oxford AZtecOne EDS
The Hitachi TM-4000 PlusXL is a high resolution desktop SEM, which uses a thermionic electron emission gun to scan a sample surface, resulting in high resolution images.
- Qualitative elemental analysis and chemical characterization
- Topographical analysis
- High resolution images
- Aztec EDS software included TruMap module to correct element overlap
- Detectors for secondary electrons (SE), backscatter electrons (BSE), cathodoluminescence (CL)
- 70mm traverse motorized rotating stage with 90 degree motorized tilt
- Samples should be dry
- Non-conductive samples can be sputter-coated with a conductive layer to improve imaging
- Most samples analyzed without destructive sample preparation
- No color information
- Typical samples are solid objects, often opaque
- Inorganic contaminant analysis
- Detection of flame retardants based on presence of specific elements
- High resolution images of fibers, including cross-sections
- Medical textiles
- Wearable technology
- Based on the idea that accelerated electrons in a vacuum behave similarly to light – travelling in linear direction.
- Electric and magnetic fields replace glass lenses and mirrors as used in optical microscopy.
- Wavelength is a major factor in resolution – the shorter the wavelength of an energy source, the greater the resolving power.
- Electrons have a wavelength of about 100,000 times smaller than light.
- Secondary electron (SE) detectors provide topographical information; Back-scattered electrons (BSE) provide information on composition.
- Cathodoluminescence provides optical properties of nanostructures; Images can combine more than one type of detector information
- Samples must be conductive; non-conductive materials can be sputter-coated with a fine layer of a conductive material to improve observation with SEM
NCSU, Wilson College of Textiles
1020 Main Campus Dr.
Centennial Campus R 2126
Raleigh, NC 27606
Research Assistant & Lab Manager
NC State, Wilson College of Textiles
1020 Main Campus Dr.
Raleigh, NC 27606
Responsible for Lab:
Dr. Jeffrey Joines