Douglas E. Hirt

Toughness decrease of PLA-PHBHHx blend films upon surface-confined photopolymerization

The present research investigates the effect of photoinduced grafting reaction on the bulk properties of melt processed poly(L-lactic acid) (PLA)-poly[(3-hydroxybutyrate)-co-(3-hydroxyhexanoate)] (PHBHHx) blend films. PLA-PHBHHx blend films, comprising 10 wt % PHBHHx showed a remarkable toughness improvement. From dynamic mechanical analysis of melt processed PLA-PHBHHx blend films, the blend appears to be noncompatible. Unfortunately, PLA-PHBHHx blend films underwent rapid physical aging as characterized using differential scanning calorimetry, resulting in a significant toughness loss. Physically aged films regained the original toughness on annealing at 60 degrees C for 30 min. Annealed PLA-PHBHHx blend films also underwent physical aging leading to a significant toughness loss. Hydrophilic monomers like acrylic acid and acrylamide were successfully photopolymerized from the film surface using a sequential, two-step photografting approach. The resultant films were characterized using water contact angle goniometry, ATR-FTIR spectroscopy, and mechanical testing. PLA-PHBHHx blend films lost their toughness significantly on surface modification and this was assigned to UV-assisted solvent induced crystallization as characterized using wide-angle X-ray diffraction analyses.

Micropatterning of Covalently Attached Biotin on Poly(lactic acid) Film Surfaces

A two-step approach was used to micropattern covalently attached biotin on the surface of poly(lactic acid) (PLA) film. Poly(acrylic acid) (PAA) was micropatterned on PLA using photolithography in step 1, followed by carbodiimide wet chemistry to covalently attach biotin to acid groups in step 2. The PAA micropatterning reaction progression was monitored using attenuated total reflectance-Fourier transform infrared (ATR-FT-IR) spectroscopy, water contact angle goniometry, and atomic force microscopy (AFM). The PAA-biotin conjugation reaction characterization using XPS confirmed the carbodiimide mediated amidation reaction. The resultant PLA film was then immersed into a solution of fluorescence-conjugated streptavidin and examined under fluorescence microscopy to reveal various micropatterns.

Evaluating Bulk-to-Surface Partitioning of Erucamide in LLDPE Films Using FT-IR Microspectroscopy

The objective of this research is to experimentally characterize the spatial distribution of an additive across the thickness of a single-layer polymer film. Concentration-distribution data are then used to quantify the amount of additive that diffuses from the bulk of the film to the film surfaces as a function of time. These results are important because a films surface property, such as coefficient of friction, depends on the additive surface concentration. The concentration profiles of an erucamide slip agent in linear low-density polyethylene (LLDPE) films were measured with Fourier transform infrared microspectroscopy. This paper describes in detail the procedures used to microtome specimens and map the concentration profiles for the erucamide-LLDPE system. Data show that the additive concentration profile is uniform across the thickness of the film immediately after it has been formed. After aging at 60 °C for 4.5 h (not yet to equilibrium), approximately 40% of the additive accumulates at the film surfaces.

Characterization of Erucamide Profiles in Multilayer Linear Low-Density Polyethylene and Propylene-Ethylene Copolymer Films Using Synchrotron-Based FT-IR Microspectroscopy

The diffusion of erucamide in single layer polymer films has been monitored previously using FT-IR microspectroscopy [Appl. Spectrosc., 53, 11 (1999)]. This research extends that work to multilayer films. In particular, erucamide migration is characterized in press-laminated bilayer and coextruded trilayer linear low-density polyethylene (LLDPE) films and also coextruded bilayer films of LLDPE and a propylene-ethylene copolymer (PEC). Results in bilayers and trilayers demonstrate that the erucamide prefers to migrate to a film surface rather than into an adjacent layer, even in the presence of steep concentration gradients at layer–layer boundaries. The same behavior was observed for bilayers of LLDPE and PEC where it was anticipated that erucamide may diffuse into the less dense PEC layer. Attenuated total reflectance FT-IR was also used to confirm that little or no erucamide diffused through an additive-deficient layer to reach a film–air interface in a bilayer structure. However, results clearly showed erucamide migration from a core layer through additive-deficient skin layers to reach the surfaces of a trilayer film.

Improving the Wettability of Deep-Groove Polypropylene Fibers by Photografting

This paper presented photografting as a surface modification method to provide permanent wettability improvement to deep-groove polypropylene (PP) fibers. We also evaluated their wettability by testing the dynamic contact angle (DCA) on single fibers and characterized the wicking performance of fiber bundles when polyacrylamide (PAAm) and polyacrylic acid (PAA) were grafted onto the fibers. In this study, the increase in monomer concentration was found more effective than longer UV exposure time in creating higher graft density on deep-groove PP fibers. Acrylic acid (AA) monomers penetrated into the fiber and polymerized inside, but acrylamide (AAm) did not. Fiber dimension changed slightly upon grafting of PAAm, and enlarged significantly after grafting with PAA. DCA results show that the advancing water contact angle on single fibers decreased from 100 to 55° by grafting of PAAm and PAA, and spontaneous wicking of water was observed after surface modification. The wicking amount of the vertically placed fiber bundles showed a linear relationship to the square root of time at early wicking times.

Using Synchrotron-Based FT-IR Microspectroscopy to Study Erucamide Migration in 50-μm-thick Bilayer Linear Low-Density Polyethylene and Polyolefin Plastomer Films

The diffusion of additives in thick (∼500 μm) single layer and multilayer films has been characterized using FT-IR microspectroscopy.1,2 The objective of this research was to investigate additive migration and concentration profiles in coextruded multilayer films of industrially relevant thicknesses. In particular, the investigation focused on the migration of an erucamide slip agent in 50-μm-thick coextruded bilayer films of linear low-density polyethylene (LLDPE) and a polyolefin plastomer (POP). Erucamide concentration profiles were successfully mapped using synchrotron-based FT-IR microspectroscopy. The synchrotron radiation helped to achieve a higher spatial resolution for the thin films. Meticulous sample preparation was needed to map the thin film samples. Results with FT-IR microspectroscopy showed that the additive-concentration profiles were relatively uniform across the multilayer-film thickness irrespective of the intended initial additive distribution. For example, a bilayer planned for 1 wt % erucamide in an LLDPE layer and no erucamide in a POP layer showed significant additive migration into the POP layer at the extrusion rates used. FT-IR microspectroscopy results also showed that more erucamide migrated to the surface of a POP layer than an LLDPE layer. Attenuated total reflectance (ATR) FT-IR spectroscopy was used to confirm the time-dependent increase of erucamide surface concentration and that the increase was more pronounced at the surface of the POP layers.

Determining Mechanical Properties of Yarns and Two-Ply Cords from Single-Filament Data Part I: Model Development and Predictions

The objective of this research is to construct a computer model that can predict the properties of flat yams, twisted yams, and twisted cords from single-filament data. In this model, a modulus versus strain curve is obtained by taking the derivative of the average stress-strain curve from single-filament tensile tests. The distribution of elongation to break is then fit to a Gaussian curve and a relationship is derived between filament elongation and bundle elongation in a twisted structure. Using the principle of conserva tion of energy, the forces from the surviving filaments at a specific strain are summed to yield the resulting force on a ply, which is then used to calculate the tensile force on the cord. The model also predicts elongation to break, tenacity at break, and initial modulus of yams and cords.

Simulating the microbond technique with macrodroplets

Abstract In this study, the microbond technique has been simulated by the use of macrodroplets. These larger scale specimens consisted of cone-shaped epoxy droplets of length 6 mm, on 1 mm diameter steel wire. The specimens were formed reproducibly in a mold to provide 30 ° and 45 ° contact angles between fiber and resin. The model geometry was used to examine the effects of contact angle, loading position, and loading type (point versus axisymmetric loading) on the debonding strength. The results indicated that a higher debonding strength was achieved at the higher contact angle and at loading positions farther from the tip of the cone-shaped drop. When the load was applied near the tip of the drop, which is typical in microbond experiments, there was no statistical difference in debonding strength for point loading and axisymmetric loading. Finally, with the macrodroplets, it was possible to visually observe a three-stage debonding process.

Characterization of Erucamide Profiles in LLDPE Films: Depth-Profiling Attempts Using FTIR Photoacoustic Spectroscopy and Raman Microspectroscopy

This research focuses on mapping the concentration profile of erucamide in LLDPE film. Attenuated Total Reflectance (ATR) FTIR and FTIR microspectroscopy (FTIR-mS) have both been used previously to map concentration profiles in polymer films. However, ATR-FTIR spectroscopy is restricted to the near-surface region of a film while FTIR-mS works well in the film bulk but has deficiencies near film surfaces. Two other techniques, Raman microspectroscopy (R-mS) and FTIR photoacoustic spectroscopy (FTIR-PAS), reportedly work well for depth-profiling in polymers with micron or submicron resolution. Experiments were conducted with R-mS and FTIR-PAS to attempt to quantify the spatial distribution of erucamide in LLDPE film. The amide I carbonyl peak was identified from neat erucamide powder for both R-mS and FTIR-PAS. That peak was not observed with R-mS for film containing erucamide, even for films with a relatively high erucamide loading (1 wt.%). However, FTIR-PAS could detect statistically significant differences in erucamide concentration as a function of penetration depth, indicating that FTIR-PAS may be used as an effective depth-profiling tool for the erucamide-LLDPE system.

Determining Mechanical Properties of Yarns and Two-Ply Cords from Single-Filament Data Part II: Comparing Model and Experimental Results for PET

Part I provided a detailed description of a model developed to predict the mechanical properties of yarns and cords from single-filament properties. The objective in Part II is to assess the accuracy of the model by comparing predicted results with experimental data. Multifilament PET yams were obtained from various manufacturing facilities. For all but one case, the bundles were formed into twisted yams and two-ply cords using laboratory- scale equipment. The model shows good agreement with experimental force-elongation data, although there is some deviation at higher twist levels. This discrepancy is likely due to slight non-uniformities present in the laboratory-produced yarns and cords. A cord with a high level of twist and uniformity produced at a manufacturing site demonstrates excellent agreement between model and experimental results. As an example of its predictive capabilities, the model calculates the elongation to break and tenacity at break within 5% of the experimental value for the vast majority of twisted yarns and cords studied.