Semicrystalline Thermoplastics Research Articles

A continuous phase-evolution model for cold and strain-induced crystallization in semi-crystalline polymers

The dynamic crystallization during extreme thermomechanical history under producing or service strongly influences the dimensional stability of the semi-crystalline thermoplastic polymers. To produce high-precision structural components, the proper thermomechanical history needs to be carefully designed to eliminate the crystallization-induced shrinkage. On the contrary, the rapidly developed four-dimensional (4D) printing technology tries to amplify the crystallization-induced shrinkage to directly produce the complex curvatures without supporting materials. However, the crystals formed at different deformation states might have different orientations, leading to an anisotropic residual deformation. Therefore, tracing of all crystals formed with different initial configurations is the key issue to ensure the geometric accuracy of both the high-precision and the deformable components. In this study, we developed a continuous phase-evolution model for both the cold and the strain-induced crystallization in semi-crystalline thermoplastics. The irreversible cold crystallization is analogized as the raindrop falling into the pool, and the reversible strain-induced crystallization is analogized as the nonequilibrium liquid-gas phase transformation. Using the continuous phase-evolution concept, the crystal growth is described by a series of continuously formed crystal phases sequentially added into the initial amorphous medium. Each newly formed crystal phase is in a stress-free state at the formation moment, and therefore the crystallization history coupled with the whole deformation history can be memorized. By introducing the oriented growth tensor representing the stress-free state of all formed crystals, the deformation-history dependent anisotropic crystallization and the corresponding residual deformation can be traced. The developed model is validated by comparing with the experimental data of the dynamic crystallization in amorphous poly l-lactide polymers under thermomechanical loading cycles. Finally, the predictive capability of the model is illustrated by several demonstrations, to show the influences of deformation-history dependent crystallization orientations and the corresponding anisotropic residual deformation.

Characterization of crystallization kinetics in Polyamide 6 with a focus on modeling the thermoforming process: experiments, modeling, simulations

Thermoforming of continuous fiber-reinforced plastics made of semi-crystalline thermoplastics has gained significant interest due to its potential for producing lightweight and high-strength components for various applications. Before thermoforming, a laminate is heated to a temperature beyond the melting point of the thermoplastic. During the subsequent forming process, the laminate is continuously cooled, which triggers non-isothermal crystallization in the semi-crystalline matrix material. In this context, the study of crystallization kinetics is crucial in identifying phase transition, analyzing exothermic latent heat during crystallization and determining inhomogeneous crystallinity distribution caused by uneven cooling in the laminate’s thickness direction. This contribution primarily deals with experimental investigations, modeling and finite element simulations for characterizing the crystallization kinetics in the matrix material, Polyamide 6 and investigating the aforementioned factors. To model the crystallization kinetics, an extended form of the Avrami model, known as the modified Nakamura–Ziabicki model, is adopted. The parameters for the modified Nakamura–Ziabicki model, which depend on the local cooling rates, are identified based on fitting the model to flash DSC (differential scanning calorimetry with high cooling rates) and standard DSC non-isothermal cooling experiments. Finally, the model is implemented into the commercial FE software COMSOL Multiphysics® and the crystallinity evolution in the laminate is simulated for the process-relevant die and laminate temperatures and laminate thicknesses.

Polyphenylene sulfide for high-rate composite manufacturing: Impacts of processing parameters on chain architecture, rheology, and crystallinity

High performance semi-crystalline thermoplastics necessitate high temperature processing to form useful structures, but the effects of repeated exposure to these extreme environments on key polymer properties are not well understood. This work investigates the influence of degradation-driven structural changes resulting from exposure to standard melt processing conditions in oxygen rich environments on the rheological properties, crystallization behavior, and crystal structure of polyphenylene sulfide (PPS). Melt processing temperatures (300°C, 320°C, and 340°C) and hold times (up to 60 min) are varied to probe the effects of thermal exposure on polymer properties. Extended melt-state exposure causes an increase in PPS melt viscosity due to the formation of complex branched/crosslinked structures where increasing temperature causes this process to occur more rapidly. Dynamic isothermal rheology of PPS displays a 70x increase in the complex viscosity at 10 rad/s after 60 minutes at 340°C. Frequency sweep rheological experiments reveal a notable deviation from linearity (terminal slope = 2) with slopes as low as 0.14 after thermal exposure. Stress recovery experiments indicate thermally processed PPS requires more time to relax stress under an applied strain. Imperfections along the polymer backbone in the form of branches/crosslinks decrease overall crystallinity and reduce lamellar thickness, with no changes to the unit cell structure. For semi-crystalline high performance thermoplastic matrix composites relying on high degrees of crystallinity to provide solvent resistance and strength, these results have serious implications for the need to tightly control melt processing steps and understand the final material state. Furthermore, viscoelastic properties of post-processed PPS polymers should be considered for recycling and reuse strategies.

A modified neo-Hookean model for semi-crystalline thermoplastics assessed by relaxation and zero-stress creep tests of recycled polypropylene and polyoxymethylene

The mechanical behavior of thermoplastics is strongly rate-dependent, and oftentimes it is difficult to find constitutive models that can accurately describe their behavior in the small to moderate strain regime. In this paper, a hyperelastic network model (modified neo-Hookean) and a set of experiments are presented. The testing consists of monotonic tensile loading as well as stress relaxation and zero stress creep. Two materials were tested, polyoxymethylene (POM) and recycled polypropylene (rPP), representing one more rigid and brittle and one softer and more ductile semi-crystalline polymer. The model contains two main novelties. The first novelty is that the stiffness is allowed to vary with the elastic deformation (in contrast to a standard neo-Hookean model). The second novelty is that the exponent governing viscous relaxation is allowed to vary with the viscous deformation. The basic features of the new model are illustrated, and the model was fitted to the experimental data. The model proved to be able to describe the experimental results well.

Radical-Mediated Ring-Opening Photopolymerization for Semicrystalline Thermoplastic Additive Manufacturing

Conventional approaches to stereolithographic additive manufacturing (SLA) employ liquid resin formulations based on multifunctional (meth)acrylates and epoxides that afford cross-linked polymeric networks upon polymerization. Nevertheless, the utilization of resins that yield semicrystalline thermoplastics provides facile access to physical and mechanical properties that are otherwise difficult to attain, such as high toughness and resistance to solvent swelling as well as additional postfabrication processing options that can be used to extend the life cycle of three-dimensional printed polymers. Here, we report the SLA-based additive manufacturing of semicrystalline thermoplastics utilizing the radical-mediated ring-opening photopolymerization of seven- and eight-membered cyclic allylic sulfides. Photopolymerization of resin formulations incorporating seven- and eight-membered cyclic allylic sulfides and crystallization of the resultant (co)polymers were examined using Fourier transform infrared spectroscopy, photorheology, and isothermal photo-differential scanning calorimetry. The formulated resins were found to polymerize and subsequently crystallize rapidly upon irradiation under ambient conditions. The mechanical properties of stereolithographically printed copolymers approached the bulk copolymer mechanical properties, demonstrating unusually strong interlayer adhesion atypical of layerwise, stereolithographic printing of semicrystalline polymers. Finally, high-quality, recyclable, semicrystalline thermoplastic parts were printed and melted down, demonstrating the potential for these semicrystalline materials to provide a path for improved sustainability of polymeric parts produced via SLA.

Co-drawing of technical and high-performance thermoplastics with glasses via the molten core method

Among the different fundamental aspects that govern the design and development of elongated multimaterial structures via the preform-to-fiber technique, material association methodologies hold a crucial role. They greatly impact the number, complexity and possible combinations of functions that can be integrated within single fibers, thus defining their applicability. In this work, a co-drawing strategy to produce monofilament microfibers from unique glass-polymer associations is investigated. In particular, the molten core-method (MCM) is applied to several amorphous and semi-crystalline thermoplastics for their integration within larger glass architectures. General conditions in which the MCM can be employed are established. It is demonstrated that the classical glass transition temperature compatibility requirements for glass-polymer associations can be overcome, and that other glass compositions than chalcogenides can be thermally stretched with thermoplastics, here oxide glasses are considered. Composite fibers with various geometries and compositional profiles are then presented to illustrate the versatility of the proposed methodology. Finally, investigations are focused on fibers produced from the association of poly ether ether ketone (PEEK) with tellurite and phosphate glasses. It is demonstrated that upon appropriate elongation conditions, the crystallization kinetics of PEEK can be controlled during the thermal stretching and crystallinities of the polymer as low as 9 mass. % are reached in the final fiber. It is believed such novel material associations as well as the ability to tailor material properties within fibers could inspire the development of a new class of hybrid elongated objects with unprecedented functionalities.

Influence of deposition rates on the mode I fracture toughness of in-situ consolidated thermoplastic composites

Innovations in recycling, automated and out-of-autoclave processes have renewed significant interests in carbon fibre - polyether ether ketone (CF/PEEK) thermoplastic composites. The crystallinity and, consequently, fracture toughness of semi-crystalline thermoplastics is affected by the cooling rates during processing. Extensive review of published data indicates that in-situ consolidation deposition rates affect PEEK crystallisation. This paper investigates the influence of automated fibre placement (AFP) deposition rates from 76 to 124 mm/s on the crystallinity and mode I fracture toughness of Cytec PEEK polymer matrix with carbon Fibre (AS4/APC2) laminates. The experimental results showed a decrease in crystallinity when the material deposition rate was increased. However, this did not translate into an improvement in fracture toughness. The preliminary study showed an increase in fracture toughness from 76 to 100 mm/s deposition rates. The 124 mm/s samples had the lowest fracture toughness despite having the lowest crystallinity. The crystallinity was not the only driving mechanism in improving the fracture toughness performance and good consolidation is an important factor as well.

Modelling of the melting point shift in semi-crystalline thermoplastics dependent on prior cooling rate and heating rate

The different local properties of plastic parts are highly dependent on local thermal histories. In DSC measurements a shift in peak melting temperature was detected in semi-crystalline thermoplastics (Polypropylene and Polyamide) dependent on the heating rate and prior treatment conditions of the samples. To investigate such phenomena, the shift in peak melting temperature depending on a prior cooling and subsequent heating for polyamide 6.6 and isotactic polypropylene is examined using Flash-DSC measurements. Due to crystallisation and heat conduction effects the temperature shows a dependence on the cooling and heating rate. From the observations, a model was developed that is able to predict the measured peak melting temperature as a function of the cooling and heating rate. A phenomenological model is developed uniting the effect of cooling rate prior and the melting rate in order to predict the main melting point. • Modelling the melting temperature of the welding of injection moulded parts. • Semi-crystalline polymers: isotactic polypropylene and polyamide 6.6. • Analysis of thermal effects of iPP and PA6.6 representing industrial polymers. • Correlation of both cooling history and heating rate on melting temperature. • Thermal analysis at high cooling and heating rates using the Flash-DSC 2+.

Low Temperature Powder Bed Fusion of Polymers by Means of Fractal Quasi-Simultaneous Exposure Strategies.

Powder Bed Fusion of Polymers (PBF-LB/P) is a layer-wise additive manufacturing process that predominantly relies on the quasi-isothermal processing of semi-crystalline polymers, inherently limiting the spectrum of polymers suitable for quasi-isothermal PBF. Within the present paper, a novel approach for extending the isothermal processing window towards significantly lower temperatures by applying the quasi-simultaneous laser-based exposure of fractal scan paths is proposed. The proposed approach is based on the temporal and spatial discretization of the melting and subsequent crystallization of semi-crystalline thermoplastics, hence allowing for the mesoscale compensation of crystallization shrinkage of distinct segments. Using thermographic monitoring, a homogenous temperature increase of discrete exposed sub-segments, limited thermal interference of distinct segments, and the resulting avoidance of curling and warping can be observed. Manufactured parts exhibit a dense and lamellar part morphology with a nano-scale semi-crystalline structure. The presented approach represents a novel methodology that allows for significantly reducing energy consumption, process preparation times and temperature-induced material aging in PBF-LB/P while representing the foundation for the processing of novel, thermo-sensitive material systems in PBF-LB/P.

Foundational Investigation on the Characterization of Porosity and Fiber Orientation Using XCT in Large-Scale Extrusion Additive Manufacturing.

The great potential of Extrusion Additive Manufacturing (EAM) for structural prototyping in the automotive industry is severely limited by the directional bias in the build direction. The layerwise fabrication leads to reduced mechanical properties at the layer-to-layer interface compared to the bulk of the strand. Especially for the often-used semi-crystalline thermoplastics, the mechanical properties strongly depend on the processing parameters, even more so if short fibers are used as fillers. Therefore, ideal processing windows in which the mechanical strength and modulus in the z-direction reach their maximum can be identified for these parameters, resulting in a reduced directional bias. The influence of the EAM processing parameters on mechanical strength has already been investigated, correlating strength with thermal conditions during printing. However, these considerations did not distinguish between the thermal effect on the polymer properties, the formation of voids and pores at the layer interface, and the resulting fiber orientation for different strand proportions. Therefore, in this study, the effect of different processing temperatures and layer heights on the pore size and distribution, as well as the fiber orientation in the different regions of the mesostructure was investigated using X-ray Computed Tomography (XCT).

Thermoplastic matrix material influences on the mechanical performance of additively manufactured carbon-fiber-reinforced plastic composites

Materials design and development continue to be more relevant as applications continue to rise for additively manufactured carbon-fiber-reinforced-plastic (CFRP) composites. Plastic matrixes bond and protect the fiber and help to transfer load through the composite to support intended applications. This makes it more necessary to understand the influences of thermoplastic matrixes on the mechanical performance of the composites fabricated through the additive manufacturing (AM) technique. This study investigated Acrylonitrile–Butadiene–Styrene (ABS) and Polyamide (PA) matrixes, which represent the bulk of the amorphous and semicrystalline engineering-grade thermoplastics matrixes, respectively, used in CFRP composite applications. Mechanical properties: tensile, compression, flexural, and thermal properties were examined, with the results showing the thermoplastic matrixes compositions and morphologies influences on the mechanical properties. The CF-PA was found to offer superior strength, ductility, and toughness because of their close-packed ordered lamellar matrix morphology, while the CF-ABS was found to offer superior modulus because of their loose morphology which more easily rearrange in reaction to stress upon elastic deformation. The mechanical properties results were reinforced by the fracture failure modes and the thermal analysis results which showed the CF-PA composite’s ability to withstand higher mechanical performance and temperatures before failure.

The 3-Phase Structure of Polyesters (PBT, PET) after Isothermal and Non-Isothermal Crystallization.

According to the 3-phase model, semi-crystalline thermoplastics consist of a mobile amorphous fraction (MAF), a rigid amorphous fraction (RAF), and a crystalline fraction (CF). For the two polyesters Polybutylene Terephthalate (PBT) and Polyethylene Terephthalate (PET), the composition of these phases was investigated using the largest possible variation in the isothermal and non-isothermal boundary conditions. This was performed by combining the conventional Differential Scanning Calorimetry (DSC) with the Fast Scanning Calorimetry (FSC). From the results it can be deduced that the structural composition of both polymers is characterised by a large fraction of the rigid amorphous phase. This is mainly formed either during the primary crystallization in the low temperature range or during the subsequent secondary crystallization that follows primary crystallization in the high temperature range. Depending on the thermal history, the fraction of the mobile amorphous phase of both polymers approaches a minimum, which does not appear to be undercut.

Sugar-Based Polymers with Stereochemistry-Dependent Degradability and Mechanical Properties.

Stereochemistry in polymers can be used as an effective tool to control the mechanical and physical properties of the resulting materials. Typically, though, in synthetic polymers, differences among polymer stereoisomers leads to incremental property variation, i.e., no changes to the baseline plastic or elastic behavior. Here we show that stereochemical differences in sugar-based monomers yield a family of nonsegmented, alternating polyurethanes that can be either strong amorphous thermoplastic elastomers with properties that exceed most cross-linked rubbers or robust, semicrystalline thermoplastics with properties comparable to commercial plastics. The stereochemical differences in the monomers direct distinct intra- and interchain supramolecular hydrogen-bonding interactions in the bulk materials to define their behavior. The chemical similarity among these isohexide-based polymers enables both statistical copolymerization and blending, which each afford independent control over degradability and mechanical properties. The modular molecular design of the polymers provides an opportunity to create a family of materials with divergent properties that possess inherently built degradability and outstanding mechanical performance.

Crystallization behavior under process conditions in Powder Bed Fusion of polymers

With respect to materials, the powder bed fusion process is largely accompanied by semi-crystalline thermoplastics, with polyamide 12 most predominately used. Not yet experimented is the influence of the newly applied powder - capable of up to 40 K lower temperatures than the building bed - on the melt pool, and its effect on crystallization. Crystallization-induced stresses directly after powder application leads to the break-off criterion curling or later warpage; furthermore, mechanical limitations are expected due to rapid crystallization. The influence of the applied powder and the repeated exposure of overlying layers on the crystallization kinetics is simulated by flash DSC measurements, demonstrating that the undercooling has a significant influence on crystallization time. However, if the exposure of the overlying layers, and therefore increased temperature is considered, an enhanced crystallization time is observed. These results contribute to the understanding of crystallization behavior in the process, and verify published heat simulation.

Development of material-adapted processing strategies for laser sintering of polyamide 12

Laser sintering of polymers (LS) is one of the most promising additive manufacturing technologies as it allows for the fabrication of complexly structured parts with high mechanical properties without requiring additional supporting structures. Semi-crystalline thermoplastics, which are preferably used in LS, need to be processed within a certain surface temperature range enabling the simultaneous presence of the material in both, the molten and solid state. In accordance with the most common processing models, these high temperatures are held throughout the entire building phase. In the state of the art, this leads to high cooling times and delayed component availability. In this paper, process-adapted methods, in-situ experiments and numerical simulations were carried out in order to prove that this drawback can be overcome by material-adapted processing strategies based on a deepened model understanding. These strategies base on the fact, that the crystallization and solidification of polyamide 12 is initiated a few layers below the powder bed surface at high temperature and quasi-isothermic processing conditions. Therefore, isothermal crystallization and consolidation behaviour is analyzed by process-adapted material characterization. The influence of temperature fields during laser processing was analyzed in dependence of part cross-section, layer number and fabrication parameters and correlated to the resulting part properties. Furthermore, the possibility to homogenize the parts thermal history by controlling the part cooling is highlighted by a simulational approach. The authors show that the material-dependent solidification behavior must be taken into account as a function of the geometry- and layer-dependent temperature fields and demonstrate a major influence on the material and component properties. From these findings, new processing strategies for the laser exposure process as well as for the temperature control of the build chamber in z-direction arise, which allow for the acceleration of the LS process and earlier availability of components with more uniform part properties.

Brønsted Acid Catalyzed Stereoselective Polymerization of Vinyl Ethers.

Isotactic poly(vinyl ether)s (PVEs) have recently been identified as a new class of semicrystalline thermoplastics with a valuable combination of mechanical and interfacial properties. Currently, methods to synthesize isotactic PVEs are limited to strong Lewis acids that require a high catalyst loading and limit the accessible scope of monomer substrates for polymerization. Here, we demonstrate the first Brønsted acid catalyzed stereoselective polymerization of vinyl ethers. A single-component imidodiphosphorimidate catalyst exhibits a sufficiently low pKa to initiate vinyl ether polymerization and acts as a chiral conjugate base to direct the stereochemistry of monomer addition to the oxocarbenium ion reactive chain end. This Brønsted acid catalyzed stereoselective polymerization enabled an expanded substrate scope compared to previous methods, the use of chain transfer agents to lower catalyst loading, and the capability to recycle the catalyst for multiple polymerizations.

Multiscale Modeling of Polyamide 6 Using Molecular Dynamics and Micromechanics

Polyamide 6 (PA6) is a semicrystalline thermoplastic used in many engineering applications due to its high strength, good chemical resistance, and excellent wear/abrasion resistance. The mechanical properties of PA6 are dependent on two forms of crystallinity (α/γ). Semicrystalline thermoplastics have a hierarchical microstructure spanning length scales, necessitating the use of a multiscale model. Molecular dynamics (MD) simulation with the reactive INTERFACE force field was used to predict the elastic moduli of amorphous PA6. Semicrystalline PA6 was modeled using a multiscale modeling approach originally developed for semicrystalline polyetheretherketone (PEEK). This approach was facilitated by the NASA Glenn Research Center’s micromechanics software MAC/GMC. The inputs to the multiscale model were the elastic moduli of amorphous PA6, as predicted via MD and calculated stiffness matrices from the literature of the PA6 α and γ crystal forms. The multiscale model output was Young’s modulus, shear modulus, and Poisson’s ratio as a function of α and γ crystallinity. The predicted values of Young’s modulus and shear modulus compared well with experiment. The multiscale model predictions showed that the mechanical properties of semicrystalline PA6 with α and γ crystal forms are similar from amorphous to 40% crystalline and diverge after this limit, with the γ PA6 predictions having higher Young’s and shear moduli and lower Poisson’s ratio. Overall, the good agreement with experiment validated the use of the multiscale model for semicrystalline PA6, proving that the multiscale model may be used for semicrystalline polymers beyond PEEK.

Sensing the melting transition of semicrystalline polymers via a novel fluorescence technique

The melting point (Tm) is an important parameter that dictates the physical properties and thereby applications of semicrystalline thermoplastics. Conventional melting transition characterization techniques, e.g., differential scanning calorimetry, ellipsometry, optical microscopy, and X-ray based methods, probe Tm by monitoring temperature (T)-dependent thermal properties, morphologies, and microstructures. Although these techniques have been well developed, they tend to have their own limitations, e.g., X-ray based techniques require X-ray beams and most previous techniques can only measure spatially averaged properties throughout a film cross section or an entire bulk sample. Here, we have developed a new, simple, and versatile fluorescence technique for probing the melting transitions of semicrystalline thermoplastics. With this approach, fluorescent probes are incorporated into a semicrystalline polymer, either by physical doping or covalent labeling, and their T-dependent fluorescence intensity data exhibit a stepwise decrease nearby Tm because of the reduced restriction of intramolecular motion when crystals start to melt. Interestingly, the first derivative of the obtained T-dependent fluorescence intensity data can reveal more details of the underlying melting transition, e.g., the onset and endset of the melting transition as well as the peak melting temperature. The melting point values determined by fluorescence agree well with those characterized by conventional differential scanning calorimetry, confirming the validity of our fluorescence technique for probing melting transitions. In addition, this fluorescence technique can be applied with various types of fluorescent probes (e.g., fluorophores exhibiting either aggregation-induced emission or aggregation-caused quenching effects) and generalized to many semicrystalline thermoplastics (e.g., poly(l-lactic acid), poly(caprolactone), and poly(ethylene oxide)), while maintaining excellent sensitivity to melting transitions. Overall, our fluorescence technique represents an easy and contact-free melting point characterization approach that may allow for novel location-specific Tm investigations within heterogeneous polymeric systems (e.g., multilayer films, blends, and composites). Such a novel fluorescence technique can expand the toolbox for Tm determination and potentially lead to unprecedented insights into the design principles for semicrystalline thermoplastics.

Study the effect of Crystallization Factors on the Mechanical Properties of Semi - Crystalline Polymers for Transport Applications

Polyether ether ketone and which combined with carbon fiber by 20% and 30% as reinforcement which purchased from a company Tangyin Sanyou Engineering Plastic Co. Itd/China. the degree of crystallization An significant role in semi-crystalline thermoplastics is played by (e.g. toughness, stiffness and solvent resistance). Primary aim of this work is to use density, DSC and FTIR to Research into the various induced degrees of crystallinity in PEEK composites Strengthened with carbon fiber (CF). In this research, three sheets were used: virgin poly ether ether ketone (PEEK), (PEEK+20 percent carbon fiber), and (PEEK+30 percent carbon fiber). the samples’ mechanical and thermal properties produced ones were examined and compared in this study. The density test findings displayed a rise in crystallinity levels by (35.9, 54.4, 88.2) respectively, But a decrease in the degree of crystallinity when examining by DSC. The mechanical properties such as Tensile strength, Young’s module and impact strength It showed an improvement in properties with an increase in the percentage of reinforcement with CF. In addition, FTIR for pure PEEK, (PEEK+ 20 percent CF) and (PEEK+30 percent CF) is found to induce minor shafting in peaks by adding 30 percent of carbon fibers and does not cause new peaks to appear and this suggests that there is no chemical reaction between the fibers and the PEEK matrix.

Establishment of a Rotary Print Head to Effect Residual Stresses and Interlayer Bonding in an FLM-Process

In fused layer modeling (FLM) manufacturing technology, there is an increased demand for semi-crystalline materials due to their favorable mechanical properties, such as high strength and toughness. The reasons for their limited use are process-related residual stresses and reduced interlayer bonding, resulting in component distortion, warping and poor strength. Addressing these problems, this paper presents the development and implementation of a rotary print head that enables local laser pre-deposition heating and forced air cooling in the 2.5-dimensional FLM process. Samples of polypropylene are fabricated to investigate the effects of the modified process on residual stresses and interlayer bonding. The investigations show that local laser pre-deposition heating can positively influence the interlayer bonding. In combination with a reduction of the extrusion temperature and additional cooling, it is possible to considerably reduce the residual stresses. The results of this research show that pre-deposition heating and forced air cooling significantly improve the processability of semi-crystalline thermoplastics in the FLM process.