The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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Tensile Properties Modification of Ductile Polyoxymethylene/ Poly (Lactic Acid) Blend by Annealing Technique
This research aimed to improve tensile property of polyoxymethylene/poly (lactic acid) blend (POM/PLA) by annealing process. POM/PLA at ratio of 60/40 was injection molded to dumbell specimens. The blend was annealed at 80 C and 100 °C for 10-30 min. The effect of annealing on crystallinity, mechanical performance and fracture behavior was investigated. Crystallinity of PLA in the blend increased with increasing annealing times, which resulted in the increment of tensile strength and tensile modulus of POM/PLA blend. However, higher crystallinity of PLA in the blends after annealing yielded higher notch sensitivity and lower fracture toughness as compared to unannealed blend. The optimum condition of POM/PLA (60/40) was found at annealing temperature of 80 °C for 10 min, which obtained good in tensile strength and tensile modulus of the blend. It can be noted that notch sensitivity factor of neat polymer was improved in unannealed POM/PLA blend.
Polystyrene Foam Insulation: Implementation of Alternate Sustainable Flame Retardant
Sustainable solutions are being increasingly demanded in the construction product market place. Polystyrene insulation is an increasingly important component of green construction. The benefits of insulation in residential and commercial buildings include lower energy consumptions, improved thermal comfort, reductions in the first costs of the heating and cooling equipment and reductions in CO2 emissions from the burning of fossil fuels across the United States.
As with all foam insulations, polystyrene foam insulation is combustible and must comply with stringent building and fire codes, which have been in place since 1976. The basic requirement in codes is a flame spread index of 75 or less and a smoke developed index of 450 or less when tested in accordance with ASTM E84, in addition to separation of the foam insulation from building occupants through use of a thermal barrier, typically ½” gypsum board. Additional requirements are in place depending upon the particular application.
Like many other building products – from electrical wires to structural and decorative wood products to paint – foam insulation uses flame retardants to protect people and property from the hazards of fire. Flame retardants used in foam insulation meet current regulations and their history of safe use is supported by scientific research.1 Manufacturers are committed to product safety and the effectiveness of flame retardants, and support research and development efforts to continually advance and improve these materials.
A recent announcement by the Design for the Environment program of the U.S. EPA detailed a suitable polymeric flame retardant for use in polystyrene foam insulation. The chemistry is a brominated polymeric flame retardant to replace Hexabromocyclododecane (HBCD)2. HBCD has recently been listed as a persistent organic pollutant (POP) under the UNEP Stockholm convention and is on the Authorisation List (Annex XIV) under the European Union REACH (Regi
Flow of Molten Plastics: Puzzles and Problems
When high-molecular weight polyolefins and vinyl polymers are melted and formed into commercial products, the melts show themselves to be not just viscous liquids but complex fluids that exhibit a range of peculiar flow behaviors that cause problems for processors. Extrudate swell, shark skin, and wall slip are among the phenomena that complicate life for the plastics engineer. These arise from the elasticity of melts, their very high viscosities and the large normal stress differences generated in shear. Normal stress differences generate flow in a direction orthogonal to the principal flow and are the cause of the well-known rod-climbing or Weissenberg effect, which is shown in Fig. 1 in a polymer solution. It has also been observed in molten polymers.
Multicomponent Injection Molding of Thermoplastics and Liquid Silicone Rubber (LSR) – Either Cured by Heat or UV Light
For processing thermally curing liquid silicone rubber (LSR) as well as UV light curing LSR for multicomponent injection molding with thermoplastics in an comparable way a processing center was designed and set into operation.
For the production of the multicomponent specimens a modular tool was designed. In there a thermoplastic plate gets molded on the one side, then gets transferred automatically by a robot system and gets overmolded by the silicone on the other side. The complete silicone side of the tool is easily changeable from a heated cavity, which is more or less state of the art, to a transparent cavity, wherein the UV LSR gets cured by according LEDs.
In first studies tests have been carried out concerning the adhesion between several thermoplastic materials and different LSR types, cured by heat as well as by UV light. The adhesion has been tested according to VDI 2019.
The used injection molding technique makes an intermediate treatment like surface activation of the thermoplastic plate possible before it gets overmolded. Therefore exemplarily different surface treatments and their effects on the adhesion strength of the material composite were evaluated.
New Materials Bring New Testing Challenges
Polymers have been utilized in automotive applications for many years. However as OEM’s strive for affordable lightweight vehicles, suppliers are discovering what may have been acceptable yesterday is today’s opportunity for improvement. One such opportunity involves utilizing new materials to differentiate automotive interiors. Faced with the challenge of setting new trends, interior design engineers must also satisfy customer expectations that the materials used will withstand the rigors of everyday use. This paper reviews the recent development of piano-black; high-gloss components that eliminate the need for secondary processes such as painting, and how one OEM discovered during field tests their initial screening tests were inadequate. Scratch and mar testing solutions are discussed for a better understanding of how to compare and select the finishing option that offers the most durable outcome.
Thermal and Time-Dependent Rheological Stability Behavior of Polyacrylonitrile with Various Plasticizers
The feasibility of melt spinning polyacrylonitrile (PAN) with plasticizers has been investigated for decades but it is still not been commercialized yet. In this paper, the thermal and time-dependent rheological stability behavior of PAN with various plasticizers is reported. The thermal behavior experiments show that the plasticizers are able to sufficiently decrease the melt temperature of PAN which make the melt spinning process feasible. The timedependent rheological stability experiments show that PAN could hold its viscosity stable without significant degradation and crosslinking for a sufficient period of time below 180?.
Applied Rheology for Understanding Flow Instabilities in Polymer Processing
Due to the fact that polymer melts behaves as non- Newtonian viscoelastic fluids, their flow behavior is rather complex and leads to number of flow phenomena which have negative impact on their processing and final product properties [1-19]. The polymer melt elasticity, high shear viscosity, extensional viscosity and its tendency to slip at the solid surfaces causes the flow destabilization. Typical flow instabilities occurring during polymer melt flows are die drool [1-2, 11-12, 15-18], neck-in [3, 5, 7, 15, 17], film blowing instabilities [3, 5, 14, 15-17] and interfacial instabilities in coextrusion [4, 5, 6, 10, 15, 17]. In this work, it is demonstrated how the polymer melt rheology and modeling of polymer processing can be used to understand and minimize the above mentioned flow instabilities occuring in extrusion and coextrusion technologies.
Slow Crack Growth Fracture Resistance Parameter Evaluation for Parent and Joint HDPE Materials
Slow crack growth (SCG) under sustained loads (pressure and axial loads) is one of the limiting failure modes that affect the long term performance of High Density Polyethylene (HDPE) pressure piping identified for use in replacement of existing steel piping for Class II applications in nuclear power plants. Several different tests have shown  the much lower time to failure of joint HDPE material when compared to the parent HDPE material, indicative of the much lower SCG resistance of the joint HDPE material. Hence, the integrity of the HDPE pipe joints and the critical flaw size evaluation is an area of increased focus for the nuclear industry and regulators, and the plastic pipes industry. Towards this end, task and working groups have been formed within the ASME Boiler and Pressure Vessel Code Committee Sections XI, IX, and III to address the needs for the HDPE piping evaluations in nuclear safety related applications. This current study is a comparison of the resistance to the SCG exhibited by the parent and fusion HDPE materials in the SENT specimen testing. Analysis of the crack growth resistance parameter through crack-mouth-opening-displacement (CMOD), and crack-opening-angle (COA) revealed a marked difference between the parent and fusion HDPE material. The experimental analysis also revealed a similar crack growth in normalized time indicative of the same constraint in the experimental specimen, but differing fracture energy in the parent HDPE material versus the butt-fusion joint material. The findings are in line with the large difference observed in the time to failure between the parent and fusion HDPE materials from creep tests at constant load.
Microinjection Molding: Influence of Molding Parameters on the Electrical Conductivity of Polypropylene Filled with Multi-Walled Carbon Nanotubes
Polypropylene (PP) composite with 10 wt% multi-walled carbon nanotubes (CNT) was prepared by melt dilution and then subjected to microinjection molding (?IM) process. A mold with a three-step configuration along the flow direction was adopted. The influence of actual injection molding parameters on the electrical conductivity of the microparts was evaluated by design of experiments (DOE) method. The distribution of maximum shear rates within the microparts was simulated via Autodesk Moldflow Insight, and the distribution of CNT along the flow direction was examined by scanning electron microscopy (SEM). Results indicated that the distribution of overall maximum shear rates follows an order of thin section>middle section>thick section, in harmony with the state of dispersion of CNT within the micro-components.
Improving the Mechanical Properties and Flame Retardancy of Multilayered PP Foam/Films via the Introduction of Flame Retardants
In this work we improve the mechanical properbities and flame retardancy of polypropylene (PP) foam/films produced by continuous multi-layered co-extrusion.Two different types of PP were used and named as PP1 and PP2. The nitrogen/phosphorous based flame retardant (FR) particles play the dual role of nucleating agent and flame retardant. FR particles were used to fabricate PP-FR composites. To investigate the effect of FR on PP crystallization and rheology, DSC thermograms, small amplitude oscillatory shear (SAOS), transient extensional viscosity were measured on both PP1 and PP2 system. FR particles played role of a nucleating agent for both PP1 and PP2 system. PP2 system has a 4x higher zero shear viscosity than PP1, while PP1 system showed much stronger strain-hardening than PP2. PP1 foam/ PP2 film structures were fabricated with different FR content. Both neat PP1 foam/PP2 film and PP1 foam/PP2 film-20%FR have good 16 layered film/foam structures and well-defined ellipsoidal shape bubble cells. The compressive modulus of PP1 foam/ PP2 film samples is 5-6 times higher than that of PP1 foam samples. Compressive strain of PP1 foam/ PP2 film samples is 2-3 times higher than one of PP1 foam samples. PP1 foam/ PP2 films showed excellent flame retardancy.
Properties of Melt Blended Chitin Nanowhisker-Polypropylene Composites
Chitin is a well-known biopolymer that can be extracted from crustacean shells and inherently has good mechanical properties. This paper focuses on using chitin nanowhiskers as a filler to improve the properties of neat polypropylene. Melt blended chitin nanowhisker polypropylene composites with chitin nanowhisker loadings ranging from 2 to 10 wt% was used for analysis. A combination of thermal, barrier, and mechanical properties were examined using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), water vapor transmission test, and tensile test respectively. It was observed that the chitin nanowhisker helped improve thermal stability and crystallization. Additionally, an improvement of about 20% and 17% in elastic modulus and ultimate tensile strength respectively was observed at 5 wt% chitin nanowhisker loading. Lastly, a 258% improvement in water vapor resistance was displayed for the 2 wt% chitin nanowhisker loading. Results from the study showed that chitin nanowhisker is a suitable biodegradable filler material for polypropylene to strengthen its thermal, barrier, and mechanical properties.
Extensional Mixing Elements for Twin-Screw Extrusion: Effectiveness at Dispersive Mixing Operations in Composites
The extensional mixing element for twin-screw extrusion was applied to the melt mixing of two different polypropylene/carbon nanofiller systems and compared to a standard shear kneading block in an effort to improve the state of dispersive mixing of the operation. It was concluded that there was a qualitative and quantitative difference in microscale dispersion for both carbon nanotubes and graphene nanosheets when implementing the extensional mixing element, as evidenced by the optical microscopy images and subsequent image analysis. However, the composites exhibited minimal differences in rheological or electrical percolation, indicating that the reducing the initial agglomerate size is only a small part of effective composite production.
Improving the Barrier and Mechanical Properties of PET/Clay Nanocomposites
In this study, an investigation of oleic acid-modified clay versus plain clay with regard to the physical and barrier properties of PET/clay nanocomposites was performed. The contribution of the active and passive oxygen barrier approaches by modifying nanoclays with an unsaturated fatty acid (oleic acid) as an oxygen scavenger was studied. Montmorillonite (MMT) and Cloisite 30B nanoclays were modified by long-chain oleic acid and identified as ol-MMT and ol-30B, respectively. PET/clay nanocomposites were prepared with modified ol-MMT and modified ol-30B by using a twin screw extruder. XRD indicated that there was a significant improvement on the dispersion of nanoclays modified with long-chain oleic acid into the PET matrix, and an exfoliated structure was achieved. DSC data also revealed that crystallization behaviors of nanocomposites prepared with oleic acid modified clays are similar to that of extruded PET. Significant improvements in the mechanical and barrier properties of stretched PET/clay nanocomposites were achieved.
Use of Conductive AFM for Composites of PP Modified with Carbon Nanofillers
In this paper, composites of polypropylene (PP) with four different carbon based fillers are compared. These are single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), nanodiamonds (ND) and nanohorns (CNH). The geometry and properties of these filler and the effects on composites’ properties such as conductivity and morphology are correlated. Initial conductivity was measured by electrometer, then secondarily by atomic force microscope (AFM) in the conductivity mode. Morphology studies were performed using the AFM as well using the topography mode.
The results show that MWCNTs had the lowest electrical percolation threshold of about 1 wt%, followed by SWCNTs, whereas ND and CNH were not conductive up to 10 or 15 wt% loading. In conductive AFM conductive areas could be only found in composites with MWCNTs, here studied at 5 wt% loading. There was a singular instance of conductivity found composites with 5 wt% SWCNTs as well, but the MWCNT composite was the only sample with significant conductivity. The conductivity was correlated to the presence of the MWCNTs present on the surface through the analysis of morphological AFM scans.
A Process for Generating Composites of Acrylonitrile-Butadiene-Styrene Reinforced with a Thermotropic Liquid Crystalline Polymer for Use in Fused Filament Fabrication
In this paper, processing conditions were determined to blend Thermotropic Liquid Crystalline Polymers (TLCP’s) with acrylonitrile butadiene styrene (ABS) for use in Fused Filament Fabrication. Differences between the available TLCP’s based on rheology were also determined for generation of longer fibrils in the ABS matrix. Rheological tests on the matrix polymer (ABS) and TLCP’s of various melting points were carried out to find the temperature ranges where viscosity of the TLCP is lower than that of ABS, which leads to successful generation of longer fibrils when processed using a novel blending technology referred to as the dual extrusion system. All the TLCP’s tested viz. HX3000, HX6000 and HX8000, supplied by DuPont, are composed of various ratios of terephthalic acid, 4-hydroxybenzoic acid (HBA), hydroquinone, and hydroquinone derivatives. Only HX8000 had its complex viscosity below that of ABS in the stable temperature range of ABS. Moreover, only HX8000 had a long overlap of temperature with ABS for favorable conditions leading to longer fibril generation.
Impact of Elevated Temperatures on Surface Properties of Erucamide-Containing Polyethylene Films
Erucamide is a migratory slip agent added to polyethylene (PE) films to reduce their coefficient of friction (COF). While a low initial COF can be achieved with the addition of small amounts of erucamide to PE, COF increases as the films are exposed to elevated temperatures during transportation and storage. In order to understand the cause(s) of COF increase, a broad suite of complimentary analytical techniques were employed to study changes in (i) surface erucamide content, (ii) erucamide surface coverage, and (iii) film surface morphology caused by exposure to elevated temperatures. Significant reduction in surface erucamide content and lack of crystal stacking were observed in films heated at 60 and 75 °C, all of which correlate well with increase in COF. However, films heated at 45 °C did not show any measurable change in these properties, even though COF did increase.
Effect of different fiber tex feeding on mechanical properties of glass fiber reinforced RPET composite by DFFIM process
Two different linear densities of Glass fiber (GF) consisting 1200 and 2400 tex, which were reinforced recycled PET (RPET) composites fabricated by DFFIM process. The results indicated that processing ability of GF/RPET composites with 180-rpm injection screw speed on fiber loading content were in range of 16 wt.% to 55.7 wt.% It was found that the incorporation of glass fiber into RPET composites improved tensile properties, bending properties and impact properties. However the improving tendency on mechanical properties of GF/RPET composites was constant, when fiber loading content was over 40 wt.% for impact strength and 50 wt.% for tensile and bending strength, respectively. At high fiber loading content, 2400 tex of glass fiber exhibited in higher agglomeration of glass fiber especially in core layer when compared with 1200 tex of glass fiber. In addition the fiber length was decreased with the increasing of fiber loading content. The decreasing of fiber length, fiber distribution, effectiveness coefficient and poor fiber orientation resulted in the declination of mechanical properties.
Inversed Cooling Channel Design for Injection Moulds Based on Local Cooling Demand and Material Properties
Due to the high influence of the cooling phase in injection molding, the thermal mold design is a crucial element for high precision injection molded parts. Thus, a method for an automated cooling channel design phase o the local cooling demand of the part is introduced. A hybrid simulation chain is used to calculate this demand and derive cooling channels afterwards. Also an outlook how to influence and control the local cooling supply of the derived cooling channel system is given and implemented as an extension to the methodology. First results show a promising perspective to combine local cooling demand and supply for an improved and suitable thermal mould design.
Modeling of Dispersive Mixing in a Twin-Screw Extruder with Three Parameter Residence Stress Distribution
In twin-screw extrusion compounding processes, dispersive mixing has a significant effect on final properties. Due to the complex flows that develop in a twin-screw extruder, prediction of dispersive mixing is difficult. The Residence Stress Distribution (RSD) is an in-line, experimental method to quantify the stress in a melt that induces dispersion. The RSD method uses the percent break-up (%BU) of stress-sensitive micro-beads to quantify the stress history in a twin-screw melt at any set of operating conditions. Using the %BU information across an operating condition domain, a predictive equation is generated to estimate the stress level in a melt as a function of operating conditions. In the following paper, predictive equations are generated with the variables of screw speed, specific throughput, and barrel temperature. Results show that increases in screw speed and specific throughput increase the %BU, while increases in barrel temperature decrease the percent break-up. In addition, the effect of screw speed and specific throughput is lessened as the barrel temperature increases. These equations allow for prediction and control of a twin-screw compounding process with three separate operating conditions.
Trouble Shooting Hot Tip Induced Polycarbonate Splay
Splay is a primary source of fallout when injection molding parts using polycarbonate. Elimination of splay is a difficult proposition, but maintaining acceptable baseline fallout across production is crucial to keeping waste under control and shipment of defects to customer to a minimum. Overall splay was reduced from 1.8 to 0.9 percent on parts running in excess of 1.4 million annually. The analysis provided in this paper shows how the extent of splay waste was identified, root cause analysis conducted, corrective action implemented, and results verified for one source of polycarbonate splay in a production environment.
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