SPE Library

Poly(lactic acid) or PLA is a commercial biopolymer made from lactic acid derived from sugar fermentation. “Greenbased” [1] PLA is desired as a biodegradable film, sheet and food packaging alternative to oil-based polymers. PLA has a Tm melting point range of 150-162°C [2]. Unfortunately, PLA has poor melt strength and impact strength. High melt strength and impact strength are important properties when manufacturing sheet, film, fibers and molded goods. In this paper we explored several ideas to improve the performance of PLA while maintaining its “green” characteristics. We found that an acrylic based core-shell polymer used at a low concentration significantly increased the Gardner impact strength of 15mil extruded sheet. Also, a high molecular weight acrylic copolymer used at low levels doubled the PLA melt strength. Lastly, reacting PLA with organic peroxides increased the shear modulus, molecular weight and melt strength based on rheometer, multi-angle light scattering and Rheotens analysis.

As companies search for strong, lightweight materials to incorporate into their product line, several are turning to fiber reinforced composites. While this material is lighter than traditional metals, its properties are dependent upon the manufacturing process and the orientation of the fibers within the part. For example, in a carbon fiber reinforced laminate the orientation of each ply directly affects the properties of the total stack and ultimately the final processed part. Employing a destructive testing method to determine material properties will render the part unsuitable for its intended application. Thus, a nondestructive testing method must be applied to determine the part’s material properties. The current study applies ultrasonic A-scan and C-scan techniques to characterize the final as-manufactured part. The as-manufactured part is not always the same as the as-designed part. Thus, a non-destructive testing technique that can validate manufacturing at the individual ply level is of critical importance. In this method, the C-scan measurements are analyzed using a custom Matlab program, and the results are displayed to the user in the form of a video. The video begins with an image of the top surface of the laminate, and each subsequent frame steps further into the thickness of the laminate. The uniqueness of this system lies in its ability to capture the carbon fiber tows within a given ply thus allowing the ply type and orientation to be determined for each lamina in the bulk laminate. While the initial results of this study are promising, surface features, which are a common artifact of the manufacturing process, have affected the analysis of the C-scan data. This study focuses on the effects of these surface features and discusses potential solutions.

In this work, blends of high-viscosity polyethylene dispersed in polystyrene (viscosity ratio > 4) were employed to study the effects of extensional flow mixing on morphology. Coarse blends, prepared in an internal mixer, were subjected to extensional flow by forcing them through converging flow dies, which resulted in decrease in the volume-average diameter of the drops. To inhibit coalescence, nanosilica was incorporated into the blend. This was found to decrease both the initial coarse blend dispersed phase size and the drop size after extensional flow. However, addition of nanosilica had only a small effect on blends subjected to extensional flow.

A new type of functions – a ratio of linear combination of dynamic moduli at different frequencies – and their bounding properties were studied. It was shown that these functions have an important feature, that is, if f represents a given ratio function for a Maxwell model whereas F represents the same function for a generalized Maxwell model, then f and F have exactly the same bounds. So the bounding properties of F can be known by analyzing simple function f only. The study showed that all four ratio functions proposed are bounded for a linear system, which means the dynamic moduli at different frequencies are not independent. Given any dynamic data, one can check the data by calculating the value of ratio function and comparing it with the bounds. If the value breaks the bounds and the violation cannot be attributed to normal experimental errors, then the data must be inconsistent. If the violation exists in the shifted data but not the original ones, then the shifted data might contain artificial errors. The method worked well as it was used to check the real G’, G” data reported in the literature.

The mold filling process of fiber reinforced parts manufactured by injection or compression molding plays a significant role on the quality of the finished product. For instance, during the injection molding process, the fountain flow dominates the mold filling stage, having a strong effect on fiber orientation at different locations within the molded part. In this work, the effect of fountain flow on fiber orientation is studied via simulation as well as experimentation. The fiber motion is simulated using a mechanistic approach where fibers are modeled as interconnected elements subjected to hydrodynamic and contact forces (fiber-fiber interactions). The simulation results show a good match with experiments performed in a device that allows visualization of the fountain flow region during injection molding.

A joint Natural Fiber Composite (NFC) research project [1] aims for an integrated mechanical/crash simulation of natural fiber reinforced plastics. This paper presents results from one of the NFC tasks, namely, an alternative way to find fiber orientation material parameters for commercial simulation software by using a mechanistic fiber motion model. During processing of fiber reinforced plastic parts, anisotropy is introduced due to fiber alignment caused by the deformation of the flowing polymer melt. Different models are available to model the development of fiber orientation during processing. These orientation models include material dependent parameters, which are obtained using cumbersome reengineering techniques. These techniques involve measuring the fiber orientation within the finished parts, and fitting the material dependent parameters until the model’s fiber orientation distributions match the actual fiber orientation. For glass fibers, the models and the parameters have been well investigated. However, data for modeling the orientation distribution development during processing natural fiber filled resins, is basically non-existent. Furthermore, actual measurements of fiber orientation distributions within natural fiber filled composites are challenging to obtain. In this work, an alternative method has been developed to find the fiber-fiber interaction coefficient Ci from the Folgar-Tucker model, by coupling the model with a mechanistic fiber model. In this technique, Ci is iteratively optimized until the fiber orientation distribution computed using the Folgar-Tucker model fits the fiber orientation fields predicted by the mechanistic model. With this virtual method, the costly measurement of actual fiber orientation fields within a finished part, and the subsequent re-engineering approach can be avoided. Furthermore, the mechanistic model can be used to determine any material dependent parameters needed for other fiber orientation predictive model

We studied the melt fracture and wall slip behaviors during the capillary extrusion of metallocene-catalyzed bimodal polyethylene resins. The bimodal resin comprising a higher content of low molecular weight component showed more wall slip and unusual melt fracture behavior. GPC measurement done on the surface section of the extruded pipe of the bimodal resin showed the wall had enriched low MW component relative to the bulk. The distinct separation of the two modes and the high content of small chains of the bimodal resin promote the flow-induced fractionation leading to the small chains being more concentrated near the die walls, which in turn result in significant wall slip and unusual melt fracture behaviors observed.

Proper processing of polymeric materials is often the key to achieving desirable properties, and good aesthetics in molded parts and extruded film or sheet. Proper drying of resin is particularly important for condensation polymers, which are often prone to molecular weight loss through hydrolysis. Tritan™ Copolyesters are transparent engineering thermoplastics used in medical, durable, and packaging applications. This paper discusses drying and processing conditions for Tritan Copolyesters, and its effects on mechanical properties, chemical resistance, and molded/extruded color.

The main objective of this research is to study the effects of matrix type and properties on the tensile properties and notch sensitivity of recycled jute mat reinforced polymeric matrix composites. A single recycled jute fiber mat was used as a natural fiber reinforcement system for three kinds of composites made from three types of resins. The three thermoset resins which were used as matrix for these composites are vinyl ester and two types of unsaturated polyester, low and high tensile strength resins. Three types of jute composites having the same fiber weight content were fabricated by the modified hand lay-up method with pre-impregnation stage in vacuum; we developed this method to solve the problem of the poor impregnation in the thick fiber mats using the normal hand lay-up method. This modification showed in this research as well as our previous research a better impregnation of resin throughout the jute mats and lower voids contents in the composites. Tensile tests have been performed on smooth specimens to evaluate the effect of matrix type and properties on the mechanical properties for the all considered composites. Also, tensile tests have been carried out on notched specimens with different center-hole diameters and having similarly geometrical diameter/width ratio to evaluate the notch sensitivity for each composite. All considered jute mat composites exhibited a higher tensile modulus than that of their neat resins. Although the higher tensile strength of the neat unsaturated polyester resin than that of the neat vinyl ester resin, the jute composites with vinyl ester matrix showed a higher tensile strength by 74% and 55% than that of both composites with unsaturated polyester matrix. In comparison with jute composites with high strength unsaturated polyester matrix, the jute composites with vinyl ester matrix showed a higher tensile modulus and strength by 13% and 55%, respectively. The two jute composites with unsaturated polyester matrix showed

Limitations in landfill capacity and the environmental impact of disposing of carpet waste in landfills have made recovering nylon from carpet waste an increasingly important enterprise. Since carpet compositions vary and can contain nylon-6 and/or nylon-6,6, along with variety of other materials, characterizing waste carpet composition and its thermal decomposition profile is essential for the recycling process. In this study, material recovered from carpet waste was analyzed by TG-FTIR, TG-MS, and TG-GC-MS. TG-GC-MS proved to be the most informative method of analysis because of its identification of organic decomposition productions characteristic of nylon-6 and nylon-6,6.

It is well known that the mechanical properties of isotropic polymers, such as tensile modulus and tensile strength, can be considerably improved by orientation of the molecular chains. This can be achieved by deforming the polymer in the solid state by die-drawing process It is also possible to orient a semi-crystalline polymer in two directions rather than one, resulting in polymer pipe, sheet or film with increased strength and toughness. Crystallite orientation has been studied in a series of HDPE pipes prepared via the die-drawing process. Combined results from small angle X-ray scattering and wide-angle diffraction reveal a change in the texture of the initially unoriented billets towards a uniplanar orientation with predominant orientation of the c*-axis (i.e. polymer chain axis) along the axial direction.

Magnesium hydroxide (MDH) is an inexpensive inorganic flame retardant agent that has been increasingly used to replace conventional halogen-containing flame retardants in polymers. In this work, the effects of combination of micro-sized MDH particles (mMDH) with different morphologies and nano-sized MDH particles (nMDH) on flame retardant and mechanical properties of random polypropylene copolymer /EVA blends were studied. The results demonstrated that the morphology of mMDH particles also plays an important role on flame retardant properties mechanisms of the polymer. Issues concerning with the initial endothermic decomposition stage of the mMDH particles are crucial in the final flame retardant property of the composites.

Molded in color weatherable Xenoy™ PBT-PC blends have been widely used in automotive, transportation, and leisure vehicles exteriors applications because these products offer a good balance of mechanical properties as well as weatherability. SABIC recently commercialized a Xenoy™ grade with improved property retention after heat and hydro ageing. While the initial impact strength of the new grade was similar to other existing weatherable Xenoy™ grades the property retention after heat and hydro ageing showed a significant improvement. Color retention under the SAE J1960 protocol of weathering was comparable to other existing grades in chromatic colors. Some of these blend properties shall be discussed in the paper.

Determining the acceptability of automotive interior has typically been accomplished through visual consensus and spectrophotometric analysis. As many have experienced in this all too subjective pursuit, not only can three or more separate sets of eyes discern three or more totally diverse variations in color acceptability, our benchmark instruments of choice can offer distinctly different opinions also. Diversity in devices, innumerable surface-variation characteristics of the sample and inherent human imperfection in the repeatability of the manual “reading” process are all contributing factors to spurious spectrophotometric results. We will discuss what instrumental options we have available in order to have our electronic results correlate with what we see.

A method based on ultrasonic technology to study the crystallization characteristics of injection molded parts has been proposed. A new method for calculating the ultrasonic velocity and attenuation is presented. The ultrasonic velocity and attenuation signals, together with differential scanning calorimetry (DSC) measurements, were used to characterize injection molded polylactic acid (PLA) speci-mens annealed at 80 °C for different periods of time. Experimental results show that the ultrasonic velocity and the ultrasonic attenuation increased with the degree of crystallinity in the annealed specimens. This suggests that the non-destructive ultrasonic technology could be an effective tool in characterizing or monitoring the crystallization of injection molded parts during or after injection molding.

Celanese has developed a new series of glass fiber reinforced polyoxymethylene (POM) co-polymers, - Hostaform® XGC (“Xtreme Glass Coupled”). Glass Fibers are commonly used to enhance stiffness and strength in thermoplastics. The adhesion between the fiber and the polymer matrix plays a predominant role governing the characteristics of the resulting reinforced plastics. Application of a specific coupling technology, together with the modification of the polymer backbone , leads to a unique mechanical property profile. The advantages of these products are a combination of improved strength and impact performance.

In this work, we have synthesized an amino acid conjugate of the triazole derivative 2-Amino-5-propyl [1,2,4] triazol [1,5-a] pyrimidin-7-(4H)-one (Triaz). The amino acid utilized is arginine due to its basic properties, thus rendering the final synthesized conjugate a positive charge. It is well known that cationic peptide conjugates show enhanced antimicrobial activity. Thus, we have examined the antimicrobial activity of the conjugate in the presence of the fungus Rhizopus. Further, fungal growth was monitored in a range of hydrophobic and hydrophilic environments by blending the conjugate with polymers such as polyethyleneglycol diacrylate (PEGDA), t-butyl acrylate (TBA) and diethylene glycol (DEG). Our results indicate that addition of PEGDA reduced antimicrobial growth, while DEG showed enhanced growth when Triaz was not conjugated with the amino acid. Thus the conjugate-polymer composites may have potent antimicrobial activity.

Open-cell thermoplastic based materials have elicited much interest in the field of sound absorption due to its recyclability and high capabilities in airborne dissipation. In this work, open-cell material with high density polyethylene (HDPE) is fabricated and used in the construction of multi-layer sound absorption systems for lower frequencies. The preliminary study results show that a combination of air gap with high open-cell material can significantly improve the low frequency absorption of open-cell materials. In the application of this concept, the requirement for thick materials to obtain the required sound absorption coefficient may be eliminated. This paper discusses two multi-layer sound absorption systems constructed with open-cell HDPE material and an air gap.

Defects in injection molded parts are undesirable with increasing part quality. The root cause for burn marks (dieseling) is the rapid compression of trapped air in the mold. An approach for estimating the air temperature in the cavity is presented that allows the prediction of burn marks. The approach uses screw position signals coming from the machine to estimate the temperature increase due to compression, the heat transfer to the mold and the heat transfer to the melt front. Effects of the injection rate, melt temperature and mold temperature were experimentally compared to analysis results. The estimation technique provided the correct trends for most effects. The analysis offers a potential opportunity to incorporate on-line determination of burn marks for quality control.

Solid and foam 1mm-thick polypropylene injection molded parts were produced using the advanced structural foam injection molding machine. Relatively uniform cell morphology was obtained when the polymer melt was injected with relatively high pressure and high flow rate. Foam samples with 75%, 4E8 cell/cc, and 10?m of void fraction, cell density, and cell size respectively were produced. The samples were perforated with 500?m, 400?m, 300?m, and 200?m in size considering a 1% perforation ratio for all the samples. Solid and foam micro perforated panels (MPPs) for sound insulation were developed. The foam MPPs showed 6% to 35% higher absorption coefficient than solid MPPs when a 6mm air-gap was considered.