Subsequent Injection Moulding Research Articles

Assessment of the tribological performance of glass fibre reinforced polyamide 6 under harsh abrasive environments

High-performance thermoplastics exhibit significant potential to substitute metals in various applications, primarily due to their remarkable tribological, thermal and mechanical characteristics. Nevertheless, their characteristics require further refinement. This research aims to assess and compare the influence of distinct material types on the tribological characteristics of Polyamide 6 composites, as well as their reliance on the PV factor, which is the result of the velocity and pressure product.In the current research, the friction and wear performances of polyamide 6 (PA6) reinforced with glass fibres were examined in adverse PV factors till materials failed. Twin screw extrusion and subsequent injection moulding procedures were utilised to process the materials. The tribo-performance of the materials was assessed in ambient conditions using a pin-on-disc abrasive configuration. The morphological analysis of the abraded surfaces was conducted through field emission scanning electron microscopy (FESEM), and the plausible wear mechanisms contributing to wear are explained. Furthermore, the materials were thoroughly characterised for their tribological, mechanical and physical behaviours.The wear behaviour depended mainly on operating parameters and composition. PA6 proved to be beneficial till moderate PV conditions but not for harsh operating environments as compared to PA6 reinforced with 25% by volume of glass fibres (PA625GF). PA625GF showed PVlimit value of 1.04 MPa m/s which was decisively superior to PA6 (0.78 MPa m/s). Additionally, under a load of 50 N, PA625GF could sustain a higher speed of 800 rpm as compared to PA6 (600 rpm). The results showed that under all testing conditions glass fibres can minimise the coefficient of friction. Under low PV settings, the specific wear rate of PA625GF was remarkably reduced owing to the presence of glass fibres, reflecting superior anti-wear properties. Notably, the wear resistance of PA6 was considerably improved by glass fibres, particularly under high PV conditions, resulting in a PVlimit of 1.04 MPa m/s. The enhancement in PVlimit was attributed to the protective function of the fibres on the matrix and their superior mechanical properties. PA625GF proved to be tribo-potential materials in abrasive wear mode under extreme conditions in terms of low specific wear rate (8.484 ×10−3 mm3/N.m) and PVsafe value (0.78 MPa*m/s). This study is expected to pave the way for the development of novel self-lubrication composite materials for harsh service environments.

P22 Fabrication methodologies for antimicrobial polypropylene surfaces with leachable and non-leachable antimicrobial agents

Abstract Objectives Develop a methodology for the fabrication of antimicrobial polypropylene (PP) surfaces with (i) leachable copper (II) chloride dihydrate (CuCl2·2H2O) and (ii) non-leachable magnesium hydroxide (Mg (OH)2) biocides. Methods and results Two methodologies are used to develop antimicrobial PP surfaces. One method involves melt blending and subsequent injection moulding, where the biocide additives were compounded with PP and subsequently injection moulded. The other method involves the thermal embossing of antimicrobial agents on the surface of a PP substrate. The obtained biocide-bearing PP surfaces were evaluated against Escherichia coli K-12 MG1655 for 0, 4 and 24 h to evaluate their antimicrobial properties. The injection-moulded PP bearing 5% CuCl2·2H2O showed a 6-log reduction of E. coli K-12 MG1655 after 24 h, while only 1 log reduction was observed for PP bearing 5% Mg (OH)2. The thermally embossed PP surfaces bearing CuCl2·2H2O and Mg (OH)2 particles (at a concentration of 10 mg/mL) showed 3 log and 4 log reduction, respectively, against E. coli K-12 MG1655 after 24 h. Conclusions The results clearly demonstrate that CuCl2·2H2O conferred antimicrobial properties to PP surfaces that were prepared by both injection moulding and thermal embossing approaches owing to the presence of leachable copper ions. In contrast, the non-leachable Mg (OH)2 imparted antimicrobial properties only to the surface prepared via the thermal embossing technique. Significance and impact Plastics with leachable biocides are effective antimicrobial surfaces, but their toxicity is a major concern. This study provides a fabrication methodology for non-leachable PP-based antimicrobial surfaces that are potentially safer. In addition, this strategy can be extended to many other plastic substrates.

Low-Temperature Fibre Direct Compounding of Cellulose Fibres into PA6.

This study reports on the development of a novel polymer processing approach that combines low-temperature (LT) processing and fibre direct compounding (FDC) to reduce the thermal stress on thermosensitive components that occurs during compounding and subsequent injection moulding (IM). Composites based on polyamide 6 (PA6) and cellulose fibres (CeF) were prepared using an LT-FDC process and in parallel with a conventional approach using a twin-screw extruder and IM. The morphological, optical, thermal, and mechanical properties of the prepared samples were investigated using optical microscopy (OM), differential scanning calorimetry (DSC), colorimetry, dynamic mechanical analysis (DMA) and tensile tests. Composites prepared using LT-FDC exhibited worse fibre dispersion but lower fibre degradation. In comparison to neat PA6, the LT-FDC composites had increased tensile modulus (Et) and storage modulus (E′) at 120 °C by up to 32% and 50%, respectively, while the tensile strength (σm) decreased by 20%.

Development of High Temperature Resistant Stereocomplex PLA for Injection Moulding.

In this study, the production of stereocomplex PLA formulations (sc-PLA) by compounding and subsequent injection moulding at different mould temperatures was investigated. Several selective nucleating agents were identified and compounded with different poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) ratios on a co-rotating twin screw extruder. The effect of nucleating agents (NA) on the crystallisation behaviour of the compound was systematically investigated by DSC analysis. The crystallisation behaviour of NA-21 (aluminium complex of a phosphoric ester), also in combination with talc, under cooling rates of up to 70 K/min was analysed. The wide-angle X-ray diffraction (WAXD) results showed a complete stereocomplex (sc) crystal formation on all specimens containing NA-21 even at the highest cooling rates. The thermo-mechanical testing of sc-PLA shows a Young’s modulus of approx. 3 GPa, yield stress of 30–40 MPa, elongation of 1%, and a heat deflection temperature (HDT-B) up to 180 °C. Processing sc-PLA exclusively via the processing route of compounding and injection moulding will open new areas of application for PLA at higher temperatures.

A study on the effect of nano-ZnO on hygroscopic characteristics of PP/Wood flour composites

ABSTRACT Polypropylene/wood flour composites having different nano-ZnO content were fabricated using melt compounding and subsequent injection moulding. The long-term water absorption and thickness swelling of the composites were studied for a range of water immersion times. It was found that the moisture absorption and dimensional stability of the specimens progressively decreased with an increasing nano-ZnO loading. The lowest water diffusion coefficient and swelling rate parameter were observed in the specimens produced with 4 phc nano-ZnO. The mechanism of water transport processes the specimens was proved to follow the kinetics of Fickian diffusion theory. Morphological findings revealed that the void content in the composite decreased by adding nano-ZnO. The hydrophobicity of the specimens reinforced with nano-ZnO improved by creating a tortuous path as a result of its characteristic barrier property. In comparison with the contact angle of untreated samples (71°), adding 4 phc of nano-ZnO increased the contact angle by 34% (95°).

A trade-off study toward highly thermally conductive and mechanically robust thermoplastic composites by injection moulding

In order to achieve high thermal conductivity (TC) for graphene-reinforced thermoplastic polymer composites, many efforts have been made to reduce the interfacial thermal resistance. However, good mechanical properties may be conflicting with thermal properties due to the poor interaction bonding between matrix and fillers. In this work, graphene sheets (GSs) filled thermoplastic polypropylene (PP) composite are prepared by three different moulding methods: i) melt extrusion with subsequent injection moulding, ii) single injection moulding and iii) hot-pressing. The relationship among processing methods, microstructures and properties are systematically demonstrated in detail. It is found that single injection moulding can be used to realize a random distribution of the filler with modest size to keep good mechanical properties, and an acceptable conductive network in the matrix to improve the thermal transfer ability of the composites. As a result, high TC of 2.07 Wm−1K−1 and tensile strength of 24 MPa are simultaneously achieved for 20 wt% GSs/PP composite, realizing a tradeoff between thermal and mechanical properties. Finite element simulation is also conducted to perceive the dependence of the thermal properties on the size and distribution of GSs filler. We think that this work provides an instructive route to design thermoplastic composites with overall consideration of thermal and mechanical properties and allows a considerable step to its industrial application.

Functionalization of Partially Bio-Based Poly(Ethylene Terephthalate) by Blending with Fully Bio-Based Poly(Amide) 10,10 and a Glycidyl Methacrylate-Based Compatibilizer.

This work shows the potential of binary blends composed of partially bio-based poly(ethyelene terephthalate) (bioPET) and fully bio-based poly(amide) 10,10 (bioPA1010). These blends are manufactured by extrusion and subsequent injection moulding and characterized in terms of mechanical, thermal and thermomechanical properties. To overcome or minimize the immiscibility, a glycidyl methacrylate copolymer, namely poly(styrene-ran-glycidyl methacrylate) (PS-GMA; Xibond™ 920) was used. The addition of 30 wt % bioPA provides increased renewable content up to 50 wt %, but the most interesting aspect is that bioPA contributes to improved toughness and other ductile properties such as elongation at yield. The morphology study revealed a typical immiscible droplet-like structure and the effectiveness of the PS-GMA copolymer was assessed by field emission scanning electron microcopy (FESEM) with a clear decrease in the droplet size due to compatibilization. It is possible to conclude that bioPA1010 can positively contribute to reduce the intrinsic stiffness of bioPET and, in addition, it increases the renewable content of the developed materials.

Additive manufacturing of metal components – process-material interaction in different process chains

In this paper we describe metal additive manufacturing (AM) processes in general, and laser bed fusion processes in particular. The process characteristics are described, and the various modelling approaches demonstrated. The open AM architecture developed at DTU Mechanical Engineering is introduced, as well as an alternative process chain based on AM and subsequent injection moulding.

Melt-viscosity and mechanical behaviour of polypropylene (PP)/wood flour composites: Effect of pulverization of wood flour with and without water

Abstract This study analyses the effect of pulverization of wood flour with and without water to the melt-viscosity and mechanical behaviour of polypropylene (PP)/wood flour (WF) composites. The composites were processed in an extruder and subsequent injection moulding. The effects of initial wood flour particle size, type of trees (namely cypress and European scots pine trees) as well as plate gap (200 μm and 350 μm) in pulverization were also evaluated in terms of melt-viscosity, tensile properties, Izod impact strength and fatigue behaviour of the prepared composites. PP/WF composites with pulverised wood flour with water exhibited higher melt-viscosity than that of nonpulverized and pulverized wood flour without water reinforced PP composites. Tensile strength values of composites were slightly affected by the pulverization of wood flour and the enhancement of tensile strength values were depended on the type of initial WF. From Izod impact test results of composites, it was found that the composites reinforced with pulverized wood flour with water displayed higher values of impact energy compared with the composites of pulverized WF without water. Depending on the type of initial WF particle, the positive effect of pulverization of wood flour with water to the fatigue life of the composites was also observed.

Monitoring of fibre dimensions after a novel wood-plastic compounding approach

Fibre length and width development were monitored for a novel procedure of combined wood chip defibration and wood-polymer compounding as well as further process steps for the production of wood fibre-based composites by applying an image analysis-based particle size measuring technique. While fibre dimension was maintained at a common level after refiner compounding, pelletizing was found to reduce both fibre length and width to about 50% of its initial dimension after refiner compounding. Subsequent injection moulding led to an additional fibre length reduction.

Injection-Moulding Compounding of PP Polymer Nanocomposites

The objective of this study is a comparison of different compounding techniques and their influence on Young’s modulus. Both conventional processing of polymer nanocomposites and processing in the unique Injection Moulding Compounder (PNC-IMC) were evaluated. Additionally, the effects of nanofillers on the thermal conductivity of polymer nanocomposites were investigated at various pressures. In comparison to conventional compounding process, in which the compound must be pelletized and fed into the injection moulding machine for the second plasticizing process, injection-moulding compounding combines these two processing steps. The material compounding and the subsequent injection moulding are done directly with only one plasticizing process, with the use of a heated melt line and a melt accumulator. In this study, both of these techniques were used for the production of polymer nanocomposites. This paper shows the different effects of processing techniques, screw speed, counter-pressure and different extruder length on Young’s modulus and demonstrates that, for the improvements, a compromise between shear energy input and residence time is essential. The increase of thermal conductivity by using nanofillers in comparison to the virgin polypropylene is shown. The investigated increase in thermal conductivity should be extremely appealing for the industry in terms of cycle time reduction in the injection moulding process. These first results give an excellent overview of both the possibilities and the limitations of the innovative concept of the PNC-IMC. Further studies on the detailed understanding of the exfoliation and intercalation of layered silicates in polymer melt will be done.

A method for estimating the fibre length in fibre‐PLA composites

Wood pulp fibres are an important component of environmentally sound and renewable fibre-reinforced composite materials. The high aspect ratio of pulp fibres is an essential property with respect to the mechanical properties a given composite material can achieve. The length of pulp fibres is affected by composite processing operations. This thus emphasizes the importance of assessing the pulp fibre length and how this may be affected by a given process for manufacturing composites. In this work a new method for measuring the length distribution of fibres and fibre fragments has been developed. The method is based on; (i) dissolving the composites, (ii) preparing the fibres for image acquisition and (iii) image analysis of the resulting fibre structures. The image analysis part is relatively simple to implement and is based on images acquired with a desktop scanner and a new ImageJ plugin. The quantification of fibre length has demonstrated the fibre shortening effect because of an extrusion process and subsequent injection moulding. Fibres with original lengths of >1 mm where shortened to fibre fragments with length of <200 μm. The shortening seems to be affected by the number of times the fibres have passed through the extruder, the amount of chain extender and the fraction of fibres in the polymer matrix.

Hybrid composites of jute and man-made cellulose fibers with polypropylene by injection moulding

A number of hybrid composites was made with jute, mercerised jute, and high tenacity man-made cellulose tyre cord yarn Cordenka of dissimilar ratios by a pultrusion process and subsequent injection moulding. Composites of jute, mercerised jute, and Cordenka were also made in order to compare the properties. The matrix material was a polypropylene/ethylene block copolymer (PP), and a maleic acid anhydride grafted PP (MAPP) was used as a coupling agent. The overall fiber contain was 25%. Mechanical properties such as tensile and bending strength, tensile and bending modulus, Charpy impact strength, and heat distortion temperature (HDT) were determined. High strength (>70 MPa) and excellent impact properties (>80 kJ/m 2) were achieved with pure Cordenka reinforcement. Partial substitution of jute instead of Cordenka leads to enhance stiffness properties of the composite as well as increased heat distortion temperature (HDT) values above 105 °C for all the tested compositions (25%, 50%, 75%, and 100% jute) and for an overall fiber load of 25%. On the other hand, impact strength decreases with increasing jute fraction down to 22 kJ/m 2 for pure jute. A good property balance is achieved for a composite with 25 wt.% jute and 75 wt.% Cordenka, maintaining impact strength of 79 kJ/m 2. Mercerisation of the jute fibers gave moderate improvements in the composite properties. Very good fiber (both jute and Cordenka) matrix adhesion was observed by SEM.

Effect of reprocessing on the fatigue strength of a fibreglass reinforced polyamide

The mechanical recycling of short fibre reinforced thermoplastics by granulation and subsequent injection moulding allows for recovery of both post consumer waste and in-plant recycled material in many industrial sectors. Parts made of these materials are often subjected to cyclic loads and therefore need to be designed against fatigue. The fatigue behaviour of reprocessed glass fibre reinforced polyamide 6,6 has been studied, using standard injection moulded specimens containing different percentages of recycled material. The effect of reprocessing of clean materials is mainly represented by fibre shortening in the injection moulding process and consequent degradation of the load bearing capacity of material. The relationship between the fatigue strength and the fibre length distribution has been discussed.

Electron beam processing of nylon 6 and hydrogenated nitrile rubber (HNBR) blends: 1. Development of high strength heat‐ and oil‐resistant thermoplastic elastomers

AbstractThe effects of electron beam irradiation on the morphology, mechanical properties and heat and hot oil resistance of a thermoplastic elastomeric blend of 50/50 nylon 6 and HNBR rubber were investigated. The morphology of the blend was studied by scanning electron microscopy, with special reference to the effects of processing via injection moulding and the radiation dose. Irradiation of extruded pellets at low doses and subsequent injection moulding improved the blend morphology, thereby enhancing the mechanical properties. The tensile strength of the blend increased with radiation dose. The irradiated blends had excellent hot oil resistance and the tensile strength of the blends did not change much after ageing at 150 °C for 72 h. Incorporation of 10 phr SRF black to the blend greatly improved the tension set property. Copyright © 2005 Society of Chemical Industry

Fracture characteristics of short glass fibre/maleated styrene–ethylene–butylene–styrene/polypropylene hybrid composite

AbstractMaleated styrene–ethylene–butylene–styrene triblock copolymer (SEBS‐g‐MA)/polypropylene 20/80 and SEBS/PP 20/80 blends reinforced with 30 wt% short glass fibres (SGF) were prepared by extrusion and subsequent injection moulding. The impact strength and fracture toughness of the hybrid composites were measured with the instrumented Charpy drop‐weight impact test and essential work of fracture (EWF) method. Drop‐weight impact measurements showed that the SGF/SEBS/PP composite exhibits higher impact strength than the SGF/SEBS‐g‐MA/PP hybrid at low impact speeds. Fibre pull‐out was responsible for the improved impact energy of the SGF/SEBS/PP composite subject to low impact velocity. At high impact speeds, the impact energy of the SGF/SEBS‐g‐MA/PP hybrid was slightly higher than that of the SGF/SEBS/PP composite. This was attributed to localized plastic deformation occurring in the fibre–matrix interfacial region. However, the EWF method revealed that the toughness of the SGF/SEBS‐g‐MA/PP hybrid was lower than that of the SGF/SEBS/PP composite. The effect of maleic anhydride (MA) functional groups grafted to SEBS on the fracture behaviour of the SGF/SEBS/PP hybrid composite is discussed.© 2002 Society of Chemical Industry

Poly(Butylene Succinate) Composites Reinforced with Short Sisal Fibres

Poly(butylene succinate) composites reinforced with short sisal fibre were prepared by melt mixing and subsequent injection moulding. The influence of fibre length, fibre content and the surface treatment of the natural fibres on the mechanical properties of the composites were evaluated. Regarding fibre length, the tensile and flexural properties of the composites had maxima at a fibre length of about 5 mm. The flexural and tensile moduli of the composites increased with increasing fibre content. Although the tensile strength hardly changed, the flexural strength increased up to a fibre content of 10 wt%. The dynamic mechanical analysis of the composites showed that the storage moduli at above ca.-16°C (corresponding to the glass transition temperature of the matrix) increased with increasing fibre content.

Lignocellulosic Fibre Reinforced Caseinate Plastics

Caseinate plastics were reinforced with two lignocellulosic fibres, i.e. wood pulp fibre and flax bast fibre by means of kneading and subsequent injection moulding. The tensile modulus increased from 200 MPa for the unfilled plastic to 1200 MPa at 20 wt% fibre addition. Simultaneously, the tensile strength increased from 6 to 30 MPa going from 0 to 20 wt% fibre incorporation. These results indicate a good interaction between the fibres and the mainly hydrophilic caseinate matrix.

Polysulphone and poly(phenylene sulphide) blends: 2. Mechanical behaviour

This paper reports the mechanical behaviour of injection moulded blends of polysulphone (PSF) and poly(phenylene sulphide) (PPS). The blends prepared by melt-extrusion and subsequent injection moulding are phase separated. Depending on moulding conditions, thermal history, and composition, tensile behaviour ranged from brittle to ductile, with or without cold drawing. Cold drawing was observed in compositions as-moulded with up to 50% by weight PPS. Upon annealing for 2h at 160°C, ductile failure was maintained for blends containing up to 35% by weight PPS. All other compositions failed in brittle fashion. Flexural strength and modulus, before and after annealing, exhibited negative deviation from the rule of mixtures. All the blends were found to be notch sensitive.

In Situ Composites Based on Thermotropic and Flexible Polymers

ABSTRACTBlends of a thermotropic liquid crystalline polymer (TLCP) and a thermoplastic matrix were compounded. Upon subsequent injection moulding and spinning, the TLCP was deformed into fine fibrils in the matrix, giving in-situ reinforcement. Especially after spinning, the composite fibres contain fibrils with very high aspect ratio, and exhibit mechanical properties in accordance with simple composite models for modulus and strength.