SPE Library

The single most important parameter in compounding polymer products is melt temperature. Melt temperature has a greater impact on product quality than any other parameter in the compounding process yet it is often overlooked in both its importance and with regard to the difficulty and necessity of proper measurement.

Melt temperature is a response variable that must be controlled within a specified range to produce the highest quality compound possible. Failure to accurately measure or maintain the proper melt temperature can lead to unexplained variability in process yields, finished product properties and customer acceptance.

This paper discusses the fundamental requirements of melt temperature measurement during compounding. Properly measuring and controlling this fundamental variable is critical to consistently producing high quality polymer compounds.

We discuss and report on the morphology and general properties of blends composed of poly(lactic acid) (PLA), poly(butylene adipate-co-terephthalate) (PBAT), and polypropylene (PP). It is shown that PLA can be evenly dispersed in the PP matrix. However, it appears as isolated not-anchored droplets with variable size distribution. It was also found that PLA is miscible at the interphase with the PBAT. It is followed that the PLA/PBAT phases appear as indivisible units when dispersed in the PP matrix. The morphology of the blend radically changes with the addition of a terpolymer based on ethylene and/or acrylic ester and glycidyl methacrylate as well as with the incorporation of maleic anhydride grafted PP (MA-g-PP). However, the PLA and PBAT phases remain as a unit even in presence of these additives. In general, the properties of the blends depend on the PLA or PLA-PBAT to PP ratio and their inability and/or ability to form a continuous phase.

A study on the flammability properties of different natural fiber reinforced polypropylene composites is done. A long term aging study by accelerated aging of the samples is performed to determine its effects on the flammability properties. These properties are determined through the limiting oxygen index (LOI) analysis and burn rate test of the samples. Results from both the LOI and burn rate tests showed an increase in the flammability of the composites as compared to the base resin, polypropylene (PP) resulting from the addition of the more flammable fibers. Under the experimental condition/ aging as studied, the flammability of the biocomposites studied by LOI remained mostly the same indicating that the composites retained their flame ignition properties. The burn rate test showed an increase in the burn rate of all the composites due to the increase in void which accelerated the heat transfer through the samples. The flammability resistance of soy meal-PP based composite was shown to be superior in comparison to other biomass filled-PP composites as studied in this work.

A rash of failures in PEX-AL-PEX piping in residential domestic hot water and hydronic heating systems in the United States and Canada led to an investigation into the nature and cause of the failures. Failures, which occurred after less than 10 years of service, were characterized by blistering and splitting of the exterior pipe wall, preceded by darkening and bulging of the outer PEX layer. Laboratory examination of field samples revealed brittle microcracking of the inner PEX layer and corrosion holes in the aluminum layer precipitating hydrostatic rupture of the outer PEX layer. Tests showed that the PEX material had low gel content (indicative of inadequate crosslinking), and early depletion of the antioxidant, thus lowering the resistance to oxidative degradation. This study shows the importance of proper formulation and testing of the antioxidant package for ensuring satisfactory performance of thermoplastic pipe for the intended design life.

Elastomers are wide-meshed cross-linked (vulcanized) polymers and recycling is difficult. Thermoplastic materials can be molten by exposing them to thermal energy and put into different shapes or mixed with other ingredients to form new compounds. Elastomers do not have a melting point, in order to put them into different shapes or mix them with other materials, first the cross-linking has to be broken and the elastomer plasticized again, in other words ?de-vulcanized?. Since this is much more difficult than just melting, in comparison to thermoplastics, elastomers, due to this difficulty, were mainly reduced in size and added as filler in other materials or burned for energy and not recycled into the original raw materials. However, until today there existed no continuous economical process that has been established in the industry.

The stress-relaxation behaviors of several PC-based materials are compared after being subjected to various levels of tensile strain for up to 48h. All resins tested showed decreases in stress over the course of the experiment, with most of the relaxation occurring within the first 6h. At 0.6% tensile strain, the PC-based materials we studied showed force decreases from 9-20% after 48h, much lower than what we observed for ABS or a copolyester. The consistency of our results for the PC resins studied suggests that stress-relaxation is not significant when comparing their ESCR behavior.

Porous materials and foams are widely used for sound absorption purposes in different sectors. To answer the needs for light weight compact noise insulation material with high sound absorption capability, the microstructure of porous membranes can be designed for optimum performance while occupying the same volume with the same weight. Such engineered structures are known as Functionally Graded Material (FGM). In the present study, novel functionally graded foam with superior sound absorption is introduced and compared to uniform foams of the same porosity. The designed graded membrane demonstrates 20% improved performance. Foams are fabricated from bio-based polymer (Polylactide (PLA)) and are environmentally friendly.

This paper details the development of compliant surfaces possessing a high coefficient of friction (COF) through the use of fibrous composites. The fibrous composites consist of a hard glass fiber phase reinforcing a compliant thermoplastic polyurethane matrix ? fabricated using twin-screw compounding and compression molding. Furthermore, the skin layer is mechanically removed to expose the glass fibers. The coefficient of friction of the composite on ice is 0.25 versus a coefficient of friction of 0.04 for molded polyurethane. Using mechanical alignment, the coefficient of friction can be as high as 0.32. The exposed glass fiber phase exhibits a ?micro-cleat? effect for fracturing the ice and providing the high friction force

Speed and flexibility have always been known to be a tradeoff for adhesives. Current cyanoacrylates, light cure acrylics, hot melt adhesives, two-component silicones and polyurethanes can provide either flexibility and/or relatively fast fixture speeds. In most cases, however, there exists a tradeoff with shear strengths, adhesive cost, ease of dispense, or ability to cure at all (i.e. bonding opaque substrates with a light cure acrylic). Henkel has developed two Loctite instant adhesives that offer high flexibility and fast fixture speed while maintaining high strength on a majority of substrates. Thorough testing of Loctite? 4902TM (product A) and Loctite? 4903TM (product B) has confirmed that these new formulations perform equally, if not better, in standard cyanoacrylate categories such as fixture speed, shear strength, and heat aging. Testing as also proven that while maintaining these desired performance parameters, the new formulations have also increased sealing reliability on common flexible substrates.

It is well established that the addition of solid particles that absorb light across ultra-violet (UV) wavelengths can improve the environmental durability of plastics. Thermoplastic polyester elastomers are sensitive to UV degradation in both exterior and interior applications. This paper describes an experimental evaluation of the improvement in UV performance of a polyester elastomer, Hytrel?, with the incorporation of a conventional chemical UV stabilizer along with different UV absorbing or scattering solid fillers. A rapid screening method is described that measures mechanical elongational properties as a function of UV exposure time. The results show that the particle type and size, the dispersion quality and melt compounding conditions affect UV durability.

Polyamide 6 composites reinforced with various cellulose nanocrystal (CNC) contents were prepared by in-situ polymerization technique. Melt rheological properties of these composites were studied in both linear and non-linear viscoelastic regimes. The results showed that incorporation of cellulose nanocrystals even at low loadings results increased storage and loss modulus, complex viscosity and development of elastic properties in the melt. The composites showed shear thinning behavior especially at higher CNC loadings. The low frequency linear viscoelastic region showed the onset of the formation of percolated network structures of CNCs within the polymer matrix. The structure break-up and recovery tests further confirmed the evolution of CNC agglomerates and development of elastic properties, as well as, high shear-rate dependency of the filled samples.

In this study, we experimented with using water solu?ble polyvinyl alcohol (PVOH) patterns to create internal geometries within injection molded parts. By overmolding sacrificial PVOH patterns with a ? shell, and subsequently dissolving the inserts, diverse internal features were fabricated with traditional injection mold?ing equipment. Metrological study perform?ed on the components has shown that precise control of the internal dimensions is possible over a wide range of processing temperatures and conditions. White light interferometry analysis conducted on the surfaces of the PVOH patterns and shell materials show that the process is capable of replicating microscale features and decora?tions onto the internal surface of the molded components. It is suggested that, in the modern global market, compa?nies differentiate on the basis of innovation and speed of development. This process can help develop and mass-manufacture complex parts with internal geometries and undercut features faster and more economically than the industrial alternatives.

Technologies that enable ionomers to be blended with polyamides in high loading for attaining synergistic effects of both components are explored. A new ionomer that contains reactive functional groups forms blends with nylon 6 of nanoscale morphology with particle size of 60-90 nm and almost monodispersed size distribution. Nanoscale morphology is observed in all blend compositions, which enables to make nylon 6 blends possessing properties similar to nylon 11 and nylon 12. Poor ZnCl2 salt resistance is known to be a deficiency for short chain polyamides, such as nylon 6 and nylon 66. Nylon 6 modified with Na/Zn ionomer at a loading of 35 wt. % or higher was found to exhibit excellent ZnCl2 stress cracking resistance. The discovery opens a new avenue to manage salts resistance for developing flexible polyamides based on lower cost polyamides.

The intent of this paper is to demonstrate the truly permanent nature of a new patent protected heat fusion process for the transfer of graphics to polyethylene, polypropylene and other olefin products. As stated in Wikipedia, ?Heat fusion (sometimes called heat welding or simply fusion) is a welding process used to join two different pieces of a thermoplastic. This process involves heating both pieces simultaneously and pressing them together. The two pieces then cool together and form a permanent bond. When done properly, the two pieces become indistinguishable from each other. Dissimilar plastics can result in improper bonding.?

This paper will:
Explain the difference between the new Polyfuze Graphic and other labeling processes such as In-Mold Labels (IML), Hot Stamp (Foil), Screen/Pad Printing and adhesive backed stickers.
Define the environmental significance of each of these decorating methods vs. heat fused graphics.

Colorant Solutions to Meet Global Packaging Regulations
Sharon Ehr, Technology Manager
Uniform Color Company


Today?s packaging regulations are confusing at best. Compliance with global food contact and cosmetic regulations has become standard practice rather than the exception.

Identifying the proper regulation for a specific application and geographic area can be challenging. Food and cosmetic packaging regulations can vary drastically from country to country. Often times regulations are ambiguous and in some cases conflict with each other.

Proper colorant and additive selection depends on defining the final application, how that package may be used and the product inside the package which may come in contact with the plastic part. Clear understanding of these parameters can provide end users assurance that the proper colorant package is used for the appropriate application while offering the broadest possible colorant palette.

Commercial simulation software employs mathematical models to simulate the plastics flow and to provide useful guidelines on the process set-up. One such model is the well applied Cross-WLF viscosity model. With seven material coefficients, the model is able to predict the viscosity as a function of temperature, shear rate, and pressure. However, to the best knowledge of the authors, there is no readily accessible methodology for determining these seven coefficients, which presents a challenge for users pursuing such information. In this work, we present a methodology on determining such coefficients using thermal and rheological data generated for a polylactic acid. The methodology presented is expected to be robust at least for amorphous plastics.

Due to the chemical activity of rubber compounds, storage temperature and -time of the material prior to processing do have a significant influence on the processability of rubber compounds in injection molding.
The aim of this work is to quantify storage-induced material changes in the laboratory as well as to evaluate how these changes affect the injection molding process. Furthermore, two key process indicators (KPIs) are presented which allow the evaluation of the material condition inline.
Therefore, a batch of a NBR model compound filled with carbon black was produced to be used for injection molding experiments in its fresh state as well as for repetitive experiments after a storage period of three months at cooled ambience. This is generally the maximum storage period for commercially processed rubbers.
Several process settings were varied systematically to identify the most important parameters regarding the processing stability of the compound. Simultaneously to the injection molding experiments, the material was characterized in the laboratory for its changes in rheological, thermodynamic and curing behavior in dependence on the storage time.
While a significant viscosity increase with storage time was observed, the incubation time of the rubber decreased which diminishes the possible processing window. The results of the injection molding experiments clearly show that the material changes observed in the laboratory can also be monitored in the injection molding process. With two KPIs based on machine signals, the inline evaluation of the material storage condition is possible and allows timely triggering of counteractions to ensure process stability as well as the estimation of expectable part quality.

The axisymmetric and flat sheet extrudate swell is studied with application in the optimization of a New Generation Fuel System (NGFS?) manufacturing process for the automotive industry. A series of extrudate swell measurements for HDPE melts are carried out using an optical micrometer attached to the capillary rheometer in order to study the effect of die geometrical characteristics, temperature (isothermal and non-isothermal) and gravity on extrudate dimensions. It is found that temperature plays a significant role in the extrudate swell when isothermal measurements are performed; i.e. temperature of exit is maintained equal to temperature in the die. As a single value cannot characterize the extrudate swell, the whole profile of the extrudate at the exit is determined and reported. The ultimate extrudate swell that corresponds to the swell when all stresses have been relaxed was also studied, and this can be significantly different from typical extrudate swell values measured at the die exit.

The polymer extrudate swell phenomenon is studied to understand the effects of parameters such as past deformation history, die design characteristics, viscoelastic characteristics and process conditions. Accurate prediction of extrudate swell is very crucial in applications such as blow molding, extrusion and fiber spinning. The integral K-BKZ and differential PTT constitutive models are used to simulate the extrudate swell phenomena of a high molecular weight HDPE in capillary extrusion, under various geometric and operating conditions. The simulated swell results were further compared with experimental observations. It was found that the K-BKZ model overpredicts and the PTT model slightly under-predicts the experimental measurements. An attempt has been made to explain the discrepancy between swell predications using K-BKZ and PTT models by studying various material rheological functions using these rheological models.

This paper presents innovative solutions concerning the utilization of engineering polymers in bioblends and biocomposites designated for automotive applications. The studied biomaterials have lower-cost, lower-weight, and at least same performance comparing with the current engineering thermoplastics used in automotive parts. Polyamide (PA6) and acrylonitrile-butadiene-styrene (ABS) were formulated using different types and concentrations of cellulosics, polylactic acid (PLA) as a bio-sourced polymer, and in a combination of cellulosics and PLA. These biomaterials were characterized in terms of morphology, mechanical properties, and heat deflection temperature. The extruded biocomposites, foamed in injection molding process, presented similar properties as the unfoamed and reference counterparts while being around 25-30% greener, lighter and less expensive.