Properties of injection moulded blends of starch and modi?ed
biodegradable polyesters
Ramaswamy Mani,Mrinal Bhattacharya *
Department of Biosystems and Agricultural Engineering,University of Minnesota,1390Eckles Avenue,St.Paul,MN 55108-6005,USA
Received 23November 1999;received in revised form 28June 2000;accepted 27July 2000
Abstract
The properties of blends of starch and aliphatic biodegradable polyesters are presented in this paper.The aliphatic polyesters used include:poly e -caprolactone,polybutylene succinate and a butanediol±adipate±terephthalate copoly-mer.To improve the compatibility between the starch and the synthetic polyester,a compatibilizer containing an anhydride functional group incorporated on to the polyester backbone was used.The blends were melt compounded using a twin-screw extruder.The concentration of the starch in the blend was varied from 10%to 70%by weight.The amylopectin content of the starches varied from 30%to 99%.The addition of a small amount of compatibilizer in-creased the strength signi?cantly over the uncompatibilized blend.For the compatibilized blend,the tensile strength was invariant with starch content when compared to the original polyester,while it decreased with increase in starch content for the uncompatibilized blend.Blends displayed a sharp intake of water and those containing butanediol±adipate±terephthalate copolymer had a higher water absorption than those containing the other polyester.Each blend displayed two glass transition;one corresponding to the polyester and the other corresponding to starch.For com-patibilized blends,the glass transition temperature of starch in the blend is lower than that observed for the uncom-patibilized blend.For all polyester blends,those containing 99%amylopectin starch at 70%level had the lowest crystallinity which otherwise decreased with decreased amylopectin level in the starch.Blend morphology indicates that the starch phase become ?ner as the amylopectin in the blend increased.Also,a higher starch content led to greater melting of the starch granules and at 70%starch by weight,a cocontinuous phase between the starch and the synthetic polymer exists.ó2001Elsevier Science Ltd.All rights reserved.
Keywords:Starch;Aliphatic polyesters;Reactive blending;Processing;Properties
1.Introduction
In our earlier work [1±8],we have reported on the properties of blends of starch and polyole?ns contain-ing a small amount of compatibilizer.The compatibi-lizer selected was the corresponding synthetic polymer
with an anhydride functional https://www.doczj.com/doc/2711402745.html,patibilisation through the in situ formation of graft copolymers in polymer blends has become increasingly important and an attractive alternative to replace the method of adding block or graft copolymers separately.Results indicated that improved strength was observed over blends that contained no compatibilizers.In the present study we report on the properties of blends of starch and aliphatic polyesters.These compositions are expected to be fully biodegradable since the individual components are bio-degradable.
Several studies have been reported on the proper-ties of blends of biodegradable polyester and starch.Koenig and Huang [9]and Tokiwa and coworkers
[10]
*
Corresponding author.Tel.:+1-612-625-7733;fax:+1-612-624-3005.
E-mail address:bae@https://www.doczj.com/doc/2711402745.html, (M.Bhattacharya).
0014-3057/01/$-see front matter ó2001Elsevier Science Ltd.All rights reserved.PII:S 0014-3057(00)00155-5
evaluated the properties of starch/polycaprolactone (PCL)blends.PCL is a biodegradable polyester and thus the blends are fully biodegradable.A starch level of 25wt.%could be added without an appreciable decrease in properties.At higher levels,a50%decrease in tensile strength was observed.Since PCL has no functional groups to react to starch,a higher loading of the natural polymers was not possible.Yasin and coworkers[11] studied the degradation of various polysaccharide/poly-(hydroxybutyrate-co-valerate)(PHBV)blends.PHBV blended with polysaccharide had a higher rate of de-gradation than pure PHBV.Ramsay[12]blended wheat starch with PHBV and reported that,while the degra-dation accelerated with the addition of starch,the ten-sile strength was half of that for PHBV when25% starch was included.These studies[9±12]clearly indicate that physical blending between aliphatic polyesters and starch allows the usage of a modest level of starch ($25%).
Based on our earlier studies with blends of starch and anhydride functional polyole?ns,it was decided to modify the aliphatic polyesters by grafting a functional group on the polyester backbone.This grafted copoly-ester would act as a compatibilizer between the starch, which has an abundance of hydroxyl group,and the polyester.Even though most aliphatic polyesters are biodegradable by themselves,their cost is between5 and10times the cost of the polymers they are de-signed to replace.By adding starch the cost of the end product can be reduced provided a signi?cant amount of starch(b50wt.%)can be introduced into the product.
Nakamura and coworkers[13]reported on the preparation of polyesters with reactive groups in the main chain or side chain by organic two-phase interfa-cial polycondensation.Wilkie and coworkers[14]stud-ied the interaction between poly(ethylene terephthalate) and various vinyl monomers and reported that this in-teraction produces a physical blend rather than a graft polymer.We have grafted functional groups such as maleic anhydride(MA)and oxazoline to several poly-esters[15±17].Grafting of a functional group onto aliphatic and aromatic/aliphatic copolyesters was ac-complished by reactive extrusion in the presence of a free radical initiator using a twin-screw extruder.It was observed that time,temperature,monomer,and initiator concentrations a ect the graft content and the desired graft content with minimal degradation can be obtained by controlling these factors.
In this study,the physical and morphological prop-erties of starch and polyester are presented.A5%MA functionalized polyester was used as compatibilizer.The amount of starch was varied from10%to70%and blends with three di erent polyesters(poly e-caprolac-tone,polybutylene succinate and a butanediol±adipate±terephthalate copolymer)were evaluated.2.Experimental
2.1.Materials
PCL resins PCL787(MFI-4)and767(MFI-30), commercially available as TONE TM Polymer,were obtained from Union Carbide Chemicals and Plastics Division,Bound Brook,New Jersey.Eastar Bio Co-polyester14766TM,a butanediol,adipate and terephth-alate copolymer(MFI-20),was obtained from Eastman Chemical Company,Kingsport,Tennessee.Bionolle TM 1020,a polybutylene succinate copolymer(MFI-20), was obtained from Showa Highpolymer Co.Ltd.,To-kyo,Japan.The meltˉow indices were determined using ASTM test method D1238at190°C using a2.16kg load.These polyesters were incorporated with MA functional group using the procedure described else-where[17].The anhydride modi?ed polyesters are rep-resented for convenience as BMA,KMA,and PCLMA for Bionolle,Eastar,and PCL,respectively.Starches with di erent levels of amylopectin to amylose ratio (branched to linear)were https://www.doczj.com/doc/2711402745.html,mon corn starch (70%amylopectin and30%amylose),waxy corn starch (99%amylopectin),and two grades of high amylose corn starch containing50%and70%amylose(the rest being amylopectin)were blended with the polyester.
2.2.Blend preparation
The blends were prepared using a laboratory scale corotating twin-screw extruder(Rheomex TW-100, Haake Scienti?c Instruments,Paramus,New Jersey). The barrel length to diameter ratio was20:1and is di-vided into four zones.The temperature in each zone can be controlled and adjusted to desired levels.The tem-perature in the?rst four zones from the feed section during blend preparation was120°C,120°C,120°C,and 110°C,respectively,for PCL blends.For blends con-taining Eastar and Bionolle,the temperature pro?le was 120°C,130°C,130°C,and120°C.The screw speed used was60rpm which gave an approximate residence time of$40±45s.A mixture of maleated polyester(PCLMA or KMA or BMA),starch,and the required amount of respective unmodi?ed polymer were introduced to the extruder with a vibratory feeder and the resulting ex-trudate was chopped and ground to obtain samples for injection moulding.The starch was used as is and the moisture content ranged between10%and12%dry weight basis.The PCLMA used was PCL787,while the polyester in the blend was PCL767.The concentrations of starch and polyester were varied to obtain di erent compositions.At the end of the blending,the total moisture content dropped to4±5%dry weight basis.For comparison purposes both blends containing compati-bilizers(5%maleated polyester)and physical mixtures (no compatibilizers)were tested.
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2.3.Injection moulding
The extruded samples were injection moulded as is using a Boy50M injection-moulding machine.Test specimens for tensile testing were obtained according to the ASTM test method D-638.For Eastar and Bionolle blends,the melt temperature was150°C,mould tem-perature was45°C,injection pressure16MPa and a back pressure of4MPa.For blends containing PCL the melt and mould temperature was140°C and30°C re-spectively and the injection pressure was15MPa.The screw speed in all cases was100%.A SATEC Apex T1000tensile testing machine was used to obtain the mechanical properties of the blend.Tensile force was taken as the force at break of the specimen.Samples were conditioned at room temperature for48h before testing.A crosshead speed of3.0mm/min was used,and the values reported were the average of at least?ve specimens.
2.4.Water absorption of blends
The moulded samples were dried in a vacuum oven at 50°C until a constant weight was obtained.These sam-ples were immersed in water at room temperature.The samples were then removed at speci?c intervals,gently blotted with tissue paper to remove the excess water on the surface,and the weight recorded.This process was repeated at several time intervals.In order to ensure no leaching had occurred,samples were dried at the end of the test period and weighed and compared against the original sample weight.
2.5.Di erential scanning calorimetry
A Perkin Elmer di erential scanning calorimer(DSC
7)was used to determine the crystallinity of the polymer. The sample size was10±15mg with a heating rate of 10°C/min.
2.6.Dynamic mechanical analysis
The samples were compression moulded into rect-angular parallelepipeds of50?12?2mm3dimensions by pressing each sample at a constant force of10tons at 130°C for10min.A Rheometrics Mechanical Spec-trometer(RMS-800)was used to conduct the dynamic mechanical analysis(DMA)to evaluate properties such as loss modulus(G HH),storage modulus(G H),and loss tangent(tan d).The samples were subjected to sinusoidal strain in the torsion mode.The temperature sweep ex-periments were carried out with0.02%strain at a fre-quency of1.0rad/s.The temperature was increased at the rate of10°C/min.For starch/Bionolle and starch/ Eastar blends the tests were conducted at temperature betweenà70°C and110°C.For starch/PCL blends,the temperature ranged fromà90°C to55°C.
2.7.Wide-angle X-ray scattering
Wide-angle X-ray scattering(WAXS)patterns of the various samples were taken at room temperature using a SIEMENS D5005X-ray powder di ractometer with nickel-?ltered CuK a radiation(k 0X154nm).The ro-tating anode generator was operated at45kV and40 mA.The scanning regions of the di raction angle2h were5±35°with a step size of0.04and dwell of1.0, which covers all the signi?cant di raction peaks of starch and polyester crystallites.The degree of crystal-linity of samples was quantitatively estimated from the relative areas of crystalline and amorphous regions, which were computed by drawing a smooth curve.
2.8.Optical microscopy
The blend morphology was examined on injection moulded samples using an optical microscope.Thin sections($0.2l m)of the samples were obtained at à70°C after freezing under liquid nitrogen using Leica Cryomicrotome and transferred into optical micro-scope slides.The samples were obtained perpendicular (transverse)to the direction ofˉow.These thin sections were stained with iodine/potassium iodide solution be-fore obtaining images under the microscope at a mag-ni?cation of40?.The particle dimensions were read directly from the photographs.
3.Results and discussion
3.1.Physical properties
The tensile strength of starch/polyester samples are shown in Fig.1.As the starch content increased,the tensile strength of blends containing no compatibilizer decreased.These results are in agreement with that in the literature[9±12].The decrease is signi?cant even at a minimal starch level of10%where the tensile strength of the blend decreased by15±20%compared to the strength of the polyester.At higher concentrations(b50%)of starch the decrease is dramatic;the tensile strength de-creased by60%compared to the strength of the poly-ester.
When a small amount(5%)of maleated polyester is added to the blend,a dramatic increase in properties is observed(Fig.1).The properties of blends containing 70%starch are approximately similar to that of the synthetic polyester.There is a slight decrease in the tensile strength as the starch content is increased to30%, but the strength increases with further increase in starch content.For the hydroxyl group on starch to interact
R.Mani,M.Bhattacharya/European Polymer Journal37(2001)515±526517
with the anhydride group on the polyester,the starch must be in a molten form.In its native state starch exists in a granular form with granular size ranging from10to 30l m.Under extrusion conditions,with limited mois-ture content(`10%),melting of granules occur in the presence of high shear conditions in the extruder.At a 10%starch content,the viscosity of the blend is low enough that su cient stresses do not exist in the ex-truder,thereby leading to incomplete melting of the starch granules.As the starch content is increased,the stresses increase,thus,increasing the amount of melted starch granules.As the starch content increases to30%, the stresses increase,but is still not large enough in magnitude to destroy the granules[2,3].At concentra-tions in excess of50%starch by weight,the stresses ex-ceed a critical value for su cient melting of starch granules thus allowing for interaction[18].
The elongation of the blends are drastically reduced upon the addition of starch.Eastar has the highest elongation(800%),followed by PCL(650%),and Bi-onolle(300%).The elongation decreases sharply for all blends irrespective of polyester type as the starch con-tent increases beyond10%.At a10%starch level,the elongation of blends containing compatibilizer is lower than those without compatibilizers.At concentrations of 30%or higher,the elongation of compatibilized and uncompatibilized blends are similar and ranged between 10%and20%.Starch is a brittle material with a high modulus(b1GPa)and hence,its presence in the blends make these material more rigid.
The tensile strength as e ected by the amylose to amylopectin ratio is shown in Fig.2.Blends containing Bionolle and waxy starches(with higher amylopectin content)had the lowest strength of all the di erent starch type at the same starch content.These results show a trend similar to the one reported in our earlier paper with blends of starch and ethylene vinyl acetate [19].For blends containing PCL,the tensile strength is independent of the amylose to amylopectin ratio. Starch is composed of repeating1,4-a-D-glucopyranosyl units and is a mixture of amylose(linear structure)and amylopectin(branched structure)units.The molecular weights of amylose and amylopectin in the starches are normally in the order of several hundred thousand and several million,respectively.The highly branched structure of amylopectin degrades to a lower molecular weight component during processing[2]if the torque exceeds a critical value,thus,causing a reduction in strength.The torque during processing of these blends is a ected by the viscosity of the polyester matrix.Of the three polyesters,PCL has the lowest viscosity,and thus, the torque generated was not as high to cause signi?cant degradation of the starch macromolecules.The starch/ Bionolle blend,because of the higher viscosity of the polyester,and hence,higher torque,caused a signi?cant degradation of the amylopectin,leading to
lower Fig.2.E ect of amylose to amylopectin ratio on tensile strength of starch/polyester
blends.
strength.For blends containing Eastar polyester,the higher amylose starch gave lower strength.
3.2.Water absorption
The water absorption characteristics of the blends are shown in Fig.3.The equilibrium water absorption for blends as a function of starch content and type of polyester is summarized in Table1.As the starch con-tent increased,the time taken to reach the equilibrium water content decreased.For blends containing70% starch,there is a sharp uptake of water and the equi-librium absorption is reached in15days.This is in stark contrast to starch/polyole?ns blends[19]where the time required to achieve equilibrium absorption is much larger(around50days).Of the three polyesters used in this study,blends containing Eastar had the highest water absorption at all starch concentrations except at 10%by weight.The water uptake of blends containing Eastar was25%higher than blends containing Bionolle and PCL with the same amount of starch.This trend is similar to that observed for soy protein/polyester blends reported elsewhere[20].The Eastar polyester has the lowest crystallinity and this would account for the higher water absorption of these blends.In general,
PCL blends absorbed less water as compared to Bion-olle because of the higher crystallinity of PCL,except for blends containing waxy starch that absorbed the same amount of water.For blends containing10%by weight of starch,Bionolle absorbed the highest water. No signi?cant loss in weight was observed,indicating insigni?cant leaching during the experiments.
The equilibrium water uptake decreased with a de-crease in starch content,as expected.The hydroxyl group in starch can form a hydrogen bond with water and thus blends containing higher starch content ab-sorbed more water.Blends containing amylopectin had the highest water uptake irrespective of the polyester in the blend,while those containing high amylose had the lowest water uptake.This is partly due to the increased degradation of amylopectin molecules during processing and is also due to the branched structure that helps to retain more water.
3.3.Dynamic mechanical analysis
The glass transition temperature of starch depends on its moisture content as well as its amylose to amylo-pectin ratio[21].Fig.4illustrates the behaviour of storage modulus(G H)for starch/Bionolle blend.The temperature dependence of the G H of starch/Bionolle blends with high starch content(70%)in the blend showed(Fig.4)a slightly larger value,compared to a lower starch content(10%)in the blend.G H for the blend containing10%starch in the blends also had a slightly more rapid decrease at30°C.This could due to
the
Table1
Equilibrium moisture content M I and time to equilibrium for various starch/polyester blends
Blend composition Bionolle Eastar PCL
M I(%)t I(days)M I(%)t I(days)M I(%)t I(days) 70%Waxy starch21525.512206
70%Regular starch20525.5121612
70%Starch(50%amylose)19.5924201612
70%Starch(70%amylose)181222.5301612
50%Regular starch14141945930
30%Regular starch830850 5.540
10%Regular starch435250440
R.Mani,M.Bhattacharya/European Polymer Journal37(2001)515±526519
transition to equilibrium amorphous state,due to the low glass transition temperature of Bionolle ($à26°C).The DMA of starch/Bionolle,starch/Eastar and starch/PCL blends with di erent starch content and di erent amylose content in starch displayed two dis-tinct glass temperature transitions,indicating the phase separation between the blend components.The loss modulus (G HH )and the loss factor (tan d )behaviour for starch/Bionolle blends at di erent starch contents in the blend is illustrated in Fig.5.The ?rst transition due to Bionolle was between à40°C and 10°C with a peak maximum centered at à26°C;the second transition,corresponding to starch,was observed roughly between 40°C and 80°C.This observation is consistent with the studies on other starch/synthetic polymer blend systems [18,22±24].In these studies,blends of starch/ethylene±propylene copolymer,starch/ethylene±vinyl acetate,and starch/ethylene,showed two transitions;while a blend of starch/styrene maleic anhydride (SMA)showed a single
transition due to the close proximity of the T g s of the two polymers [18,22].However,the ternary blend of starch/SMA/EPMA showed three transitions,which corresponds to each of the three polymers.Qin et al.[25]and Chuang and Han [26]also observed the appearance of two glass transitions in the reactive blends.
The tan d peak positions for compatibilized and un-compatibilized 70%starch/Bionolle and starch/Eastar blends with di erent starch type are shown in Table 2.For the compatibilized starch/Bionolle blends,the sec-ond transition was observed at 65°C.This transition is due to starch in the blends.For blends containing lower levels of starch,the second transition is not signi?cant.In the uncompatibilized blends,the maximum value of the second transition peak occurred at approximately 74°C.This suggests that there is some blend miscibility in the compatibilized blends which facilitates the starch structural relaxation processes and enthalpy relaxation [27].The loss factor (tan d )of the starch/Eastar blends with di erent amylose to amylopectin ratios in starch is also shown in Table 2.In all cases,the ?rst
transition
Fig.5.Loss modulus and tan d versus temperature of starch/Bionolle blends at various starch content.
Table 2
Peak positions of tan d for starch/Bionolle and starch/Eastar blends Blend composition a
tan d peak position (°C)First transition Second transition Starch/Bionolle (compatibilized)à2665Starch/Bionolle (uncompatibilized)à2674Waxy starch/Eastar à3050Regular starch/Eastar à3053Amaizo 5/Eastar
à3058Amylomaize VII/Eastar
à30
58
a
Starch content
70%.
Fig.4.Storage modulus versus temperature of starch/Bionolle blends at various starch content.
520R.Mani,M.Bhattacharya /European Polymer Journal 37(2001)515±526
due to Eastar copolyester was betweenà40°C and à10°C with maximum peak centered atà30°C;in the second transition,corresponding to starch,the tan d peak maximum was observed between50°C and80°C.It can be seen that the maximum tan d value at the second transition peak moves to a slightly higher temperature (50±58°C)as the amylose content in the starch increases. This could be due to the presence of highly ordered structure as the amylose has linear structure.DMA for starch/PCL blends indicate that the?rst tan d transition peak,corresponding to PCL,was observed atà62°C which is the glass transition temperature of PCL.Due to the low melting temperature of PCL(60°C),we were unable to conduct the experiments for starch/PCL blends at a temperature greater than60°C.The glass transition temperatures of starch in these blends,at the moisture content and shear employed in this work,is relatively low compared to the starch/moisture systems studied by others[27±29]in a shearless environment. The lower glass transition values of starch could be due to the plasticizing e ect of synthetic polymer on starch and/or due to the formation of lower molecular weight products due to shearing action during extrusion[21].
Shogren[27]observed a transition between40°C and 50°C in an extruded starch system.The storage modulus (G H)of starch/Eastar blends with di erent amylose con-tents in the starch showed the G H is not a ected by the amylose to amylopectin ratio in the blends.
3.4.X-ray analysis
WAXS provides information about the short range order of the molecular constituents in polymer blends; types and levels of crystallinity can be determined by this technique.The X-ray di raction pattern of starches has been often used to classify the di erent types(e.g.A,B, C type)of native starches[30±32].The X-ray di racto-grams of pure starch samples of di ering amylose con-tent are presented in Fig.6.The corresponding X-ray di raction crystal pattern and crystallinity level calcu-lated from the ratio of di raction peak area and total di raction area are shown in Table3.The X-ray dif-fraction patterns of di erent starch types were compa-rable to the reported standard di raction patterns of di erent crystalline types[31,33].
Waxy maize starch(Amioca,A0)and regular starch show an X-ray scattering pattern that is typical A-type pattern[34,35],with strong reˉections at2h about15°and23°and an unresolved doublet at a2h of17°and18°(Fig.6).High amylose starches from Amaizo5(50% amylose)and Amylomaize VII(70%amylose)show a typical B-type pattern[35,36],with di raction peaks at 2h values of 5.7°,15°(broad),17.2°(strong),20°(broad),and a doublet at22±24°.As can be seen from Fig.6,with an increased amylose content(50%and 70%),the peaks at15°(2h)becomes weaker and broader,while the peaks at17°and18°(2h)merge to a large peak(17.2°).Similarly,the peak at22°decreases in intensity and splits into two peaks(doublet at22±24°). This is in agreement with those reported by Cheetham and Tao[37],where a transition of crystallinity patterns in maize starch granules from A to B-type via a C-type occurred at approximately40%amylose content.
The degree of crystallinity of samples were measured from the relative areas of crystalline and amorphous regions,which was computed by drawing a smooth curve [38].The crystallinities of pure starch with di erent amy-lose content is shown in Table3.It can be seen that the waxy starch(Amioca)which has no amylose has the highest crystallinity of40.46%,while high amylose starch (70%,Amylomaize VII)has the lowest crystallinity of 15.63%.Also,the degree of crystallinity is inversely proportional to the amylose content in the starch and it is commonly accepted that amylopectin,the high molecu-lar weight(108g/mol),highly branched constituent of the starch granule,is predominantly responsible for the crystalline structure of native starch[39].The degree of crystallinity of pure polyesters are also shown in Table3. The WAXS spectra of the pure polyesters(PCL,Bionolle and Eastar copolyester)indicate that the X-ray patterns of PCL showed distinct peaks at2h values of21.4°with a shoulder peak at22°and23.7°,while Bionolle showed peaks at19.6°and22.6°with a shoulder peak at22°(2h) and a small peak at29°.The Eastar copolyester showed unresolved broad multiple peaks at2h values of17.5°, 20.7°,23.2°and25°with the degree of crystallinity of 15.29%.The dergee of crystallinity of PCL and Bionolle polyesters are51.56%and41.45%,
respectively.
Fig.6.Wide-angle X-ray di raction pro?les of pure starch samples with di erent amylose contents.
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The calculated degree of crystallinity of various starch/polyester blends are shown in Table 4.Blends of 70%starch/polyester with di erent amylose content in starch showed the decrease in the degree of crystallinity as the amylose content increased,except for waxy starch/polyester blends.The degree of crystallinity of starch/Bionolle blends decreases from 39.82%to 31.45%as the amylose content increased,while in the case of starch/PCL and starch/Eastar copolyester blends it de-creases from 41.04%to 28.35%and from 12.56%to 4.26%,respectively.This to be expected,as the crystal-linity of pure starch has been attributed largely to the formation of double helices in amylopectin [31].Waxy maize starch (Amioca)/polyester blends showed less crystallinity than those corresponding blends containing regular starch.This could be due to the increased de-structurisation or gelatinisation of amylopectin,the high molecular weight,highly branched constituent of the starch granule,during the thermomechanical processing due to the higher torque experienced by blends.Blends of 70%starch/polyester with di erent amylose content in starch do not show any distinct crystalline phase for starch.The WAXS spectra of starch/Bionolle blends with di erent amylose content in the starch is shown in Fig.7.The X-ray patterns of these blends have distinct peaks at 2h values of 19.5°and 23.5°for starch/Bionolle blends (Fig.7)and 21.3°,21.9°and 23.6°for starch/PCL blends and unresolved multiple peaks at 17.5°,20.7°,
23.2°and 25°(2h )for starch/Eastar copolyester blends.These di raction peaks are at the same 2h values as were the pure polyesters.These results indicated that the starch crystalline phase has been destroyed partially or completely during the thermomechanical processing.However,the degree of crystallinity of starch/polyester blends with di erent starch contents (from 70%to 10%)increases as the starch content decreased in the blend (Table 4).
The WAXS spectra of starch/Bionolle blends with di erent starch contents indicate that the X-ray di rac-tion peaks of these starch/polyester blends with di erent starch contents appear at the same 2h values as those in pure polyesters.However,an increase in the crystalline phase intensity with decreased starch content in the
Table 4
Degree of crystallinity of various starch/polyester blends Starch content and type Degree of crystallinity (%)Bionolle PCL Eastar 70%Amioca
28.0235.149.6670%Regular starch 39.8241.0412.5670%Amaizo 5
30.5633.349.1670%Amylomaize VII 31.4528.35 4.2650%Regular starch 39.0249.3614.4630%Regular starch 45.3654.3619.8610%
Regular starch
54.27
61.23
24.22
Table 3
WAXS data of various starch and polyester samples Samples
Amylose content (%)Degree of crystallinity (%)Crystal pattern Pure starch Amioca (A0)
40.46A Regular starch (S)20±2526.55A Amaizo 5(A5)
5018.75B Amylomaize VII (A7)7015.63B Pure polyester Bionolle (B)±41.45±PCL
±51.56±Eastar (E)
±
15.29
±
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blend was observed.Blends of starch/PCL and starch/ Eastar copolyester also showed a similar behaviour.The increase in the crystallinity at a low level of starch content in the blend could be due to the minimal or negligible destruction of starch granular structure due to the low torque and hence,thermomechanical energy experienced during processing.Furthermore,there may be some nucleating e ect in the polyesters at the low level of starch content in the blend.
3.5.Di erential scanning calorimetry
Di erential scanning calorimetry was used to evalu-ate the thermal transitions(e.g.melting,enthalpy)of these starch/polyester blends.For pure polyesters,the melting endotherm occurred at62°C with enthalpy of 81.7J/g for PCL,117°C with enthalpy of75.1J/g for Bionolle,and111.7°C for Eastar copolyester with enthalpy of14.6J/g.The starch/PCL blends showed a major transition peak at57±62°C,which corresponds to melting of PCL crystalline components.It also shows a small endothermic peak at120±125°C,which could be due to the melting of low molecular weight starch granules.Starch/Bionolle blends showed a endothermic peak at approximately111±115°C with a small shoulder peak at approximately122°C,whereas,the starch/Eastar blends showed a small broad endotherm at around106±110°C due to the low crystallinity of Eastar copolyester. These results also indicate that the starch crystalline phase has been partially or completely destroyed during the thermomechanical processing.
3.6.Blend morphology
Analysis of the morphology of the blends has been performed by optical microscopy and Figs.8±10shows the microphotographs that reveal a granular arrange-ment of the starch within the polymer matrix.In its natural state,starch exists in a granular form and its size shape depends on the origin.Generally,native corn starch consists of spherical or ellipsoidical granules with size varying from5to25l m[27].Starch behaves like
a Fig.8.Optical micrograph of starch/Bionolle blends.(a)Amioca;(b)Regular starch;(c)Amaizo5;(d)Amylomaize VII.
R.Mani,M.Bhattacharya/European Polymer Journal37(2001)515±526523
thermoplastic material at high shear and high moisture (b 30%),while at a low moisture content of less than 10%,starch granules may melt when subjected to high shear and lead to some degradation and/or debranching.When the starch is blended with synthetic polymers in an extruder at a low moisture content,the resulting blends contain a mixture of molten polymer,molten starch and unmelted or partially melted starch granules.The properties of these blends depend on their mor-phology (phase structure)and the interfacial adhesion between starch and synthetic polymers.The extent of starch melting and degradation/debranching during thermomechanical processing depends on the moisture content,melt temperature,extruder screw speed and screw con?guration and a ects the ?nal properties of the blends.At the conditions employed in this study for melt blending of starch with synthetic polymers the starch granules do not undergo complete melting [22,40].Thus,we have a molten phase of starch and synthetic polymer in which starch granules are imbedded.Fig.8(a)±(d)shows the optical microphotographs,which reveal a granular arrangement of starch within the Bionolle matrix with di erent amylose to amylopectin ratios in the starch.It can be seen that the presence of discrete dark particles due to iodine stained starch indicates unmelted and homogeneously dispersed starch granules throughout the synthetic polymer matrix.The size of the starch granules in the blends was estimated to be about 10±20l m.This result is in agreement with other studies on blends of starch and synthetic polymers and indicates that some of the starch blended with thermoplastics maintains its granular shape despite the action of the shear forces during processing [22,41].
The starch phase became ?ner in the blend as the amylopectin content in starch increased.It can also seen that the starch granules are mostly melted and formed a cocontinuous phase with synthetic polymer matrix,
whereas in the uncompatibilized blend (Fig.9),the dis-tribution of starch granules are not homogeneously dispersed in the polymer matrix.In addition,these un-compatibilized blends showed poor mechanical proper-ties compared to those compatibilized blends as described earlier.These results con?rm that the mal-eated polyester acts as a compatibilizer and increases the interfacial adhesion between the blend components and thereby produces a ?ner and more uniform morphology,hence,resulting in signi?cantly improved mechanical properties.Fig.10(a)±(c)shows the microphotographs that reveal a granular arrangement of di erent starch contents (10%,30%and 50%)within the Bionolle ma-trix.It can be seen that the distributions of starch granules are not homogeneously dispersed in the poly-mer matrix at 30%starch content in the blend (Fig.10(b)).Whereas in the blends containing a higher starch content (50%and 70%)(Figs.10(c)and 8(b)),the starch granules are well dispersed throughout the synthetic polymer matrix and the granules of starch are mostly melted to form a cocontinuous phase.Also,the blends containing the starch content of 30%showed a lower tensile strength compared to those blends containing a higher starch content (50%and 70%).These results in-dicate that the dispersion of starch in its blends with other thermoplastics plays a crucial role in the eventual properties attainable by the blend.
4.Conclusions
Biodegradable blends of starch and aliphatic poly-ester give excellent properties when small amount of compatibilizers (anhydride functionalized polyesters)are added.The tensile strengths are comparable to that of the synthetic polyester,even at a starch level of 70%by weight.The elongation is drastically reduced as the percentage of starch is increased;this is particularly true of the compatibilized blend where at 10%starch content the elongation is reduced by 50%.The anhydride func-tionalized polyester reduces the size of the dispersed phase,thus enhancing the interaction between the two phases.
Water uptake is a ected by the type of starch,the type of polyester,and the starch content in the blend.Blends containing Eastar polyester had the highest water uptake while those containing PCL had the lowest in inverse proportion to the crystallinity of the polyester in the blend.The time required to reach the equilibrium water uptake is lower than with blends containing starch and polyole?n.The higher the percentage of amylopec-tin in the starch,the greater the equilibrium water up-take.The equilibrium water uptake decreased with decreased starch content in the blend while the time to reach equilibrium
increased.
Fig.9.Optical micrograph of uncompatibilized starch/Bionolle blend.
524R.Mani,M.Bhattacharya /European Polymer Journal 37(2001)515±526
DMA showed that the blends have two glass transi-tions,one for each polymer.For compatibilized blends,the temperature at which the second transition occurred in a starch/Bionolle blend at 70%starch content is lower than that of the uncompatibilized blend,indicating some compatibilisation.On the other hand,as the
amylose
Fig.10.Optical micrograph of starch/Bionolle blends with di erent starch content.(a)10%starch;(b)30%starch;(c)50%starch.
R.Mani,M.Bhattacharya /European Polymer Journal 37(2001)515±526525
content in the blend increased,the temperature at which the second transition occurred increased,indicating a highly ordered structure due to linear amylose molecules.
X-ray scattering indicated a decrease in the degree of crystallinity in the blends as the amylose content in-creased,except for waxy starch/polyester even though waxy starch had the highest crystallinity.This would indicate a greater disruption of starch granules during processing of blends containing waxy starch.The blends display peaks at the same2h values as do the pure polyester,indicating that the crystalline peaks in the starch have been destroyed during processing.
After?nal processing in an injection moulder,some starch granules still retain their shape resulting in blends containing a mixture of molten polymer,molten starch, and unmelted starch.The addition of compatibilizer enhances the interfacial adhesion between starch and synthetic polymers.The?ner starch phase that results with an increase of amylopectin in the blend is due to the higher torque experienced by blends containing waxy starch because of its higher viscosity.Also,as the starch content increased,the torque increased and led to greater melting of the starch granules.
Acknowledgements
The authors would like to acknowledge the?nancial support of the US Department of Energy(contract# DE-FG02-96ER12185).
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图表与口诀记忆when、as、while的区别 1.图表与口诀前知识 关键是比较主从句子的动词，看其动词的持续性。瞬间的理解成点，持续的理解成线。主从关系有：点（点点、点线），线线，线点。 点：为瞬间动词，准确地称为“终止性动词”，指动词具有某种内在界限的含义，一旦达到这个界限，该动作就完成了。如come（来），一旦“到来”，该动作就不再继续下去了。 瞬间动词：arrive, begin, borrow, become, buy, catch, come, die, find, go，give, graduate, join, kill, lose, leave, marry, realize… 线：为非瞬间动词，准确地称为叫“延续性动词”。包括动态动词静态动词。 动态动词：live, sit, stand, study, talk, work, write… 静态动词（状态动词）：情感、看法、愿望等。Be, belong, consist, exist, feel, hate, have, hope, love, want… 兼有瞬时和非瞬时的动词：feel，look，move，run，work，write…，需要根据不同的语境判断。 2. when、as、while的区别一览表 【表格说明】：第一个点或者线表示从句谓语动词的持续性特征，黑点表示从句所表示的动作持续短，为瞬间动词，线表示持续长，为非瞬间动词。1~7为主句与从句所表示的动作时间有重合，第8为主句与从句所表示的动作不是同时发生，而是有先后顺序。 线线重相并发生， 长线” 【主句谓语为非瞬间动词中的 动态动词】 【记忆：等线动， 相并发生，但： 【主句谓语为非瞬间动词中的 静态动词】 【记忆：等线动，
一、根据从句动作的持续性来区分 1.“主短从长”型：即主句是一个短暂性的动作，而从句是一个持续性动作，此时三者都可用。如： Jim hurt his arm while [when, as] he was playing tennis. 吉姆打网球时把手臂扭了。 As [When, While] she was waiting for the train, she became very impatient. 她在等火车时，变得很不耐烦。 注意：as用于引出一个持续性动词表示“在……期间”时，其谓语通常只能是那些含有动作和发展意味的动词，一般不能是那些不用于进行时态的动词(如be, seem, love, want, agree, see, know, have 等)，所以下面一句中的while不能换为as： A：I’m going to the post office. 我要去邮局。 B：While you are there, can you get me some stamps? 当你在邮局时，能帮我买几张邮票吗? 若主句与从句表示的是两个几乎同时发生的动作，含有类似汉语“刚要……就”“正要……却”的意思，英语一般要用as(也可用when)，且此时通常连用副词just。且此时，从句一般用进行时，主句用短暂性动词的一般时态。【注意与六区别】 I caught him just when [as] he was leaving the building. 他正要离开大楼的时候，我把他截住了。 Just as [when] the two men were leaving, a message arrived. 就在这两个人要离开的时候，突然有了消息。 2.“主长从长”型：即主句和从句为两个同时进行的动作或存在的状态，且强调主句动作或状态延续到从句所指的整个时间，此时通常要用while。如： I always listen to the radio while I’m driving. 我总是一边开车一边听收音机。 He didn’t ask me in; he kept me standing at the door while he read the me ssage. 他没有让我进去，他只顾看那张条子，让我站在门口等着。 但是，若主句和从句所表示的两个同时进行的动作含有“一边……一边”之意时，则习惯上要用as。如： He swung his arms as he walked. 他走路时摆动着手臂。 I couldn’t remember a story to tell the children, so I made one up as I went along. 我想不出有什么故事可给孩子讲了，只好现编现讲。 3.“主长从短”型：即主句是一个持续性动作，而从句是一个短暂性动作，此时可以用a s或when，但不能用while。如：
RF-BM-S01低功耗蓝牙 透传模块（BQB认证）数据手册（V1.50） 深圳市信驰达科技有限公司 2013-3-14
1.模块概述 为方便蓝牙4.0(BLE)应用技术在各个行业产品中的移植和使用，信驰达科技特别研发了BM-S01低功耗蓝牙透传模块，并通过了蓝牙技术联盟认证（BQB），详见：RF- RF-BM-S01 https://https://www.doczj.com/doc/2711402745.html,/tpg/EPL_Detail.cfm?ProductID=27655。客户的现有产品或者方案配合此透传模块，能方便地和iPhone5等移动设备(需支持蓝牙4.0)相互通讯。实现一些智能化控制和管理。 RF-BM-S01是一款采用美国德州仪器TI蓝牙4.0CC2540作为核心处理器的高性能、超低功耗（Bluetooth Low Energy）射频收发系统模块，它拥有目前行业内较小封装的尺寸（13.7x17.1x2.5mm）。该模块预装RF-star’s RF-BLE固件并符合BLE协议标准。 客户MCU通过串口与模块相连。模块启动后会自动广播，已打开特定APP的移动设备会对其进行扫描和对接，成功之后便可以通过通用串口和移动设备进行双向通信，用户可以通过数据通道和指令通道，进行数据交换或者对通讯参数的控制，数据具体含义由上层应用程序自行定义。移动设备可以通过APP对模块进行写操作，写入的数据将通过串口发送给客户的MCU。模块收到来自客户MCU串口的数据包后，将自动转发给移动设备。 2.接线示意图 *注：在老版本的资料中BRTS,BCTS被称为CCS,MCS 3.性能特点 1.使用方便快捷，无需任何蓝牙协议栈应用经验。 2.用户接口使用通用串口设计，双向读取，操作简单。 3.支持串口AT指令调整转发速率（动态功耗调整），模块命名。 4.串口数据包长度，可以是200byte以下(含200)的任意长度。 5.支持高速模式，最快可达4K/S，可稳定工作在2.5K-2.8K。
as when while 的区别和用法 as when while的用法 一、as的意思是“正当……时候”,它既可表示一个具体的时间点，也可以表示一段时间。as可表示主句和从句的动作同时发生或同时持续，即“点点重合”“线线重合”；又可表示一个动作发生在另一个动作的持续过程中，即“点线重合”， 但不能表示两个动作一前一后发生。如果主句和从句的谓语动词都表示持续性的动作，二者均可用进行时，也可以一个用进行时，一个用一般时或者都用一般时。 1、As I got on the bus，he got off. 我上车，他下车。（点点重合）两个动作都是非延续性的 2、He was writing as I was reading. 我看书时，他在写字。（线线重合）两个动作都是延续性的 3、The students were talking as the teacher came in. 老师进来时，学生们正在讲话。（点线重合）前一个动作是延续性的，而后一个动作时非延续性的 二、while的意思是“在……同时（at the same time that )”“在……期间(for as long as, during the time that）”。从while的本身词义来看，它只能表示一段时间，不能表示具体的时间点。在时间上可以是“线线重合”或“点线重合”，但不能表示“点点重合”。例如： 1、He was watching TV while she was cooking. 她做饭时，他在看电视。（线线重合） 2、He was waiting for me while I was working. 我工作的时候，他正等着我。（线线重合） 3、He asked me a question while I was speaking. 我在讲话时，他问了我一个问题。（点线重合）
产品规格书 PRODUCT SPECIFICATION 深圳云里物里科技股份有限公司 Version V4.1发布时间 2018-04-25 MODEL NO/DESCRIPTION 产品名称:蓝牙模块MS50SFA1C 产品型号:MS50SFA1C
版本说明
目录 版本说明 (2) 1.概述 (4) 2.应用领域 (5) 3.电气参数 (5) 4.模块尺寸图 (6) 5.引脚定义 (6) 6.模块配置 (7) 6.1透传模块出厂默认值 (7) 6.2蓝牙服务UUID (7) 6.3UUID描述 (7) 6.4工作模式 (7) 6.5模块应用示意图 (8) 7.透传数据【服务UUID：0xFFF0】(APP端) (8) 8参数设置说明 (8) 9.模块测试 (112) 10.支持的设备 (14) 11.PCB设计说明 (145) 12.注意事项 (15) 13.包装信息 (155) 14.质量保证 (166)
1.概述 MS50SFA1C串口模块采用nRF52810芯片,通过UART(串口)操作可以实现模块与手机之间数据传输。本模块从模块，具有命令控制可以修改模块的广播名称，修改广播间隔和连接间隔。使用该模块用户可以快速把数据以蓝牙方式进行传输。 正面反面 产品特征 远距离：10-60米（空旷环境） BLE协议栈深度优化，睡眠功耗1uA以下 传输速率最块可达7Kbps 支持串口指令配置 支持Android4.3+,7+ 无需MFi
2.应用领域 该模块主要用于短距离的数据无线传输领域。可以方便的和PC机的蓝牙设备相连，也可以与智能手机之间的数据互通。避免繁琐的线缆连接，能直接替代串口线。 ※健身器材设备，如跑步机，健身器等 ※医疗器械设备，如脉博测量计，心率计等 ※家用休闲设备，如遥控器，玩具等 ※办公用品设备，如打印机，扫描仪等 ※商业设备，如收银机，二维码扫描器等 ※手机外设配件，如手机防丢器等 ※汽车设备，如汽车维修仪等 ※其它人机交互设备 3.电气参数 参数测试值备注 工作电压 1.8-3.6V直流 工作频率2400-2483MHz可编程 频率误差+/-20KHz Null 发射功率-40~+4dBm可调整 接收灵敏度-96dBm Null 接收电流 4.6mA标准模式 发射电流 4.6mA发射功率为0dBm时 睡眠功耗1uA以下Null 遥控距离10-60米BER<0.1%,空旷 天线50ohm Null 模块尺寸16*12*2mm Null 存储大小192KB
When while as区别 一、根据从句动作的持续性来区分 1、“主短从长”型：即主句是一个短暂性动作，而从句是一个持续性动作，此时三者都可用。如： Jim hurt his arm while［when， as］ he was playing tennis. 吉姆打网球时把手臂扭伤了。 2、“主长从长”型：即主句和从句为两个同时进行的动作或存在的状态，且强调主句动作或状态延续到从句所指的整个时间，此时通常要用while。 I always listen to the radio while I’m driving. 我总是一边开车一边听收音机。 He didn’t ask me in; he kept me standing at the door while he read the message. 他没有让我进去，他只顾看那张条子，让我站在门口等着。 但是，若主句和从句所表示的两个同时进行的动作含有“一边……一边”之意时，则习惯上要用as。如： He swung his arms as he walked. 他走路时摆动着手臂。 3、“主长从短”型：即主句是一个持续性动作，而从句是一个短暂性动作，此时可以用as 或when，但不能用while。如： It was raining hard when [as] we arrived. 我们到达时正下着大雨。 二、根据主句与从句动作是否同时发生来区分 1、若主句与从句表示的是两个同时发生的短暂性动作，含有类似汉语“一……就”的意思，英语一般要用as (也可用when)。如： The ice cracked as [when] I stepped onto it. 我一踩冰就裂了。 2、若主句与从句表示的是两个几乎同时发生的短暂性动作，含有类似汉语“刚要……就”“正要……却”的意思，英语一般要用as(也可用when)，且此时通常连用副词just。如： I caught him just when [as] he was leaving the building. 他正要离开大楼的时候，我把他截住了。 三、根据是否具有伴随变化来区分 若要表示主句动作伴随从句动作同时发展变化，有类似汉语“随着”的意思，英语习惯上要用as，而不用when或while。如： The room grew colder as the fire burnt down. 随着炉火逐渐减弱，房间越来越冷。 注：若不是引导从句，而是引出一个短语，则用with，不用as。如： With winter coming on, it’s time to buy warm clothes. 随着冬天到来，该买暖和衣裳了。 四、根据从句动作的规律性来区分 若暗示一种规律性，表示“每当……的时候”，英语一般要用when。如： It’s cold when it snows. 下雪时天冷。 五、根据主从句动作的先后顺序来区分 若主句与从句所表示的动作不是同时发生，而是有先后顺序时，一般要用when。
浅谈BLE蓝牙透传模块的应用领域 无线蓝牙透传模块，顾名思义即数据透明传输，透明传输就是在数据传输过程中，发送方和接收方数据的长度和内容完全一致，不需对数据做任何处理，相当于一条数据线或者串口线。一般模块具有半成品的属性，是在芯片的基础上进行加工。换言之，蓝牙模块一般具有二次开发的特性。 云里物里研发的MS48SF2C是一款超低功耗蓝牙模块，通过UART(串口)操作可以实现模块与手机之间数据传输；具有命令控制可以修改模块的广播名称，修改广播间隔和连接间隔。使用该模块用户可以快速把数据以蓝牙方式进行传输；传输距离在10-60米。 应用领域： 一、机器人控制 一个工业机器人系统通常分为机构本体和控制系统两大部分。构成机器人控制系统的要素主要有计算机硬件系统及无线模块操作控制软件、输入/输出设备及装置、驱动器系统、传感器系统。 二、远程抄表 远程抄表系统主要是完成电度计量或信息采集、信息远传、后台软件处理和分析三部分任务。前后两部分技术已经成熟，抄表系统技术关键是解决信息远传——通讯问题。 三、门禁安全管理系统 门禁安全管理系统是新型现代化安全管理系统，它集微机自动识别技术和现代安全管理措施为一体，它涉及电子，机械，光学，计算机技术，通讯技术，生物技术等诸多新技术。它是解决重要部门出入口实现安全防范管理的有效措施。 四、工业数据采集 工业数据采集，是指从传感器和其它待测设备等模拟和数字被测单元中自动采集非电量或者电量信号,送到上位机中进行分析，处理。数据采集系统是结合基于计算机或者其他专用测试平台的测量软硬件产品来实现灵活的、用户自定义的测量系统。 五、无线遥控遥测 无线遥测系统是以计算机为基础的生产过程控制与调度自动化系统。它可以对现场的运行设备进行监视和控制，以实现数据采集、设备控制、测量、参数调节以及各类信号报警等各项功能。
When while as的区别和用法 when的用法 当主句使用持续性动词时. Dave was eating,when the doorbell rang.门铃响时,大卫在吃饭. 2.一个动作紧接着另一个动作发生. When the lights went out, I lit some candles.灯灭了,我赶紧点上一些蜡烛. 3.谈论生命中的某一阶段,或过去的某段时间. His mother called him Robbie when he was a baby. 在他很小时,他妈妈叫他Robbin. 4.指"每一次" When I turn on the TV, smoke comes out the back. 每当我打开电视,就有烟从后面冒出. while/as 的用法 从句多为进行时,而且为持续性动词. I'll look after the children while you are making dinner. 你做饭,我来照顾孩子. 注意事项: (1) “主短从长”型：主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用： He fell asleep when [while, as] he was reading. 他看书时睡着了。 Jim hurt his arm while［when，as］he was playing tennis. 吉姆打网球时把手臂扭伤了。 As［When，While］she was waiting for the train，she became very impatient. 她在等火车时，变得很不耐烦。 (2) “主长从长”型：若主、从句表示两个同时进行的持续性动作，且强调主句表示的动作延续到从句所指的整个时间，通常要用while： Don’t talk while you’re eating. 吃饭时不要说话。 I kept silent while he was writing. 在他写的时候，我默不做声。 但是，若主从句表示的两个同时进行的动作含有“一边…一边”之意思，通常用as：
when，while，as引导时间状语从句的区别 when，while，as显然都可以引导时间状语从句，但用法区别非常大。 一、when可以和延续性动词连用，也可以和短暂性动词连用；而while和as只能和延续性动词连用。 ①Why do you want a new job when youve got such a good one already？（get 为短暂性动词）你已经找到如此好的工作，为何还想再找新的？ ②Sorry，I was out when you called me．（call为短暂性动词）对不起，你打电话时我刚好外出了。 ③Strike while the iron is hot．（is为延续性动词，表示一种持续的状态）趁热打铁。 ④The students took notes as they listened．（listen为延续性动词）学生们边听课边做笔记。 二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生；while 和as从句的谓语动作必须是和主句谓语动作同时发生。 1．从句动作在主句动作前发生，只用when。 ①When he had finished his homework，he took a short rest．（finished先发生）当他完成作业后，他休息了一会儿。 ②When I got to the airport，the guests had left．（got to后发生）当我赶到飞机场时，客人们已经离开了。 2．从句动作和主句动作同时发生，且从句动作为延续性动词时，when，while，as都可使用。 ①When ／While ／As we were dancing，a stranger came in．（dance为延续性动词）当我们跳舞时，一位陌生人走了进来。 ②When ／While ／As she was making a phonecall，I was writing a letter．（make为延续性动词）当她在打电话时，我正在写信。 3．当主句、从句动作同时进行，从句动作的时间概念淡化，而主要表示主句动作发生的背景或条件时，只能用as。这时，as常表示“随着……”；“一边……，一边……”之意。 ①As the time went on，the weather got worse．（as表示“随着……”之意） ②The atmosphere gets thinner and thinner as the height increases．随着高度的增加，大气越来越稀薄。 ③As years go by，China is getting stronger and richer．随着时间一年一年过去，中国变得越来越富强了。 ④The little girls sang as they went．小姑娘们一边走，一边唱。 ⑤The sad mother sat on the roadside，shouting as she was crying．伤心的妈妈坐在路边，边哭边叫。 4．在将来时从句中，常用when，且从句须用一般时代替将来时。 ①You shall borrow the book when I have finished reading it．在我读完这本书后，你可以借阅。 ②When the manager comes here for a visit next week，Ill talk with him about this．下周，经理来这参观时，我会和他谈谈此事。 三、when用于表示“一……就……”的句型中（指过去的事情）。 sb．had hardly（＝scarcely）done sth．when．．．＝Hardly ／Scarcely had sb．done sth．when．．．
蓝牙透传模块选型8大要素 蓝牙作为一种近距离无线通信技术，是无线数据传输最成熟的解决方案，目前蓝牙透传模块已经得到广泛应用，如蓝牙彩灯控制方案、蓝牙医疗设备、蓝牙智能门锁等等。由于蓝牙技术已十分成熟且价格低廉，在物联网新兴领域已得到了充分重视，不过蓝牙透传模块在选型时也应考虑以下几点： 1、传输距离 蓝牙主要分两种功率级别，在蓝牙模块天线可视的情况下，CLASS1标准通信距离100米（当然稳定传输不丢包的传输距离在50米左右），CLASS2标准通信距离10米。实际厂家的蓝牙模块产品中，在天线可视的情况下可以稳定的传更远，如云里物里的蓝牙4.0模块MS49SF1实测稳定通信距离可达90米。 2、接口选择 蓝牙模块的接口分串行接口、数字IO口、模拟IO口、SPI编程口、USB接口及语音接口。一般数据传输时采用串行接口（TTL电平）。 3、传输内容 目前市场上的蓝牙模块数据传送与语音传输是不同型号的模块，采用的芯片不同，用户在选型时应特别注意。云里物里的蓝牙模块都是BLE蓝牙模块，即是数据传送模块，可支用户二次开发。 4、工作方式选择 蓝牙工作时一般分为主机和从机 5、蓝牙模块的控制能力 在工业环境中工作的蓝牙模块，尤其注重稳定性和可监控性，主机系统需要随时知道蓝牙模块的工作状态，好的蓝牙模块应该能够对外提供工作状态指示信号。 6、蓝牙模块传输速度选择 云里物里蓝牙4.0模块MS47SF1实测最高稳定不丢包，蓝牙4.2模块MS49SF2实测最高稳定不丢包传输速度为（下图，左为MS47SF1，右为MS49SF2）
7、供应商选择 选择蓝牙模块或是蓝牙方案，一般选择有研发、生产、销售和售后一体的供应商。很多比较便宜的蓝牙模块厂商，由于受限于资金、技术方面的水平，不能给客户提供完善的技术支持和售后服务。 云里物里专业致力于简化客户的产品应用设计，深耕BLE蓝牙透传模块领域，构建自有研发、测试、生产、销售和售后配套体系，可以很好的服务于终端客户！
蓝牙SPP串口透传模块JDY-31蓝牙模块使用手册
版本 版本日期说明V1.2 2018-09-21 发布版本
一、产品简介与应用 JDY-31蓝牙基于蓝牙3.0 SPP设计，这样可以支持Windows、Linux、android数据透传，工作频段2.4GHZ，调制方式GFSK，最大发射功率8db，最大发射距离30米，支持用户通过AT命令修改设备名、波特率等指令，方便快捷使用灵活。 二、产品应用 JDY-31为经典蓝牙协议、可以与支持蓝牙的电脑（台式、笔记本）、手机（android）通信。可应用于 ◆ Windows电脑蓝牙串口透传 ◆ Android蓝牙串口透传 ◆智能家居控制 ◆汽车ODB检测设备 ◆蓝牙玩具 ◆共享移动电源、共享体重称 ◆医疗仪器 三、模块参数详 型号JDY-31 工作频段 2.4GHZ 通信接口UART 工作电压 1.8-3.6V（建议3.3V） 工作温度-40℃ - 80℃ 天线内置PCB天线 传输距离30米 主从支持从机 模块尺寸19.6 * 14.94 *1.8 mm（长宽高） 蓝牙版本Bluetooth 3.0 SPP STM焊接温度<260℃ 未连接工作电流 4.7mA BLE连接后电流7.3mA 发射功率8db（最大） 接收灵敏度-97dbm SPP最大吞吐量16K bytes/s(android、windows)
JDY-31支持贴片与焊接排针 1、排针应用：排针规格为标准2.54间距排针，只需焊接模块上5个排针孔即可。 2、贴片应用：一般应用只需要连接VCC、GND、RXD、TXD 4个引脚，如需在连接 状态主动断开连接，在连接状态发送AT+DISC
When，While，As引导时间状语从句的区别 when，while，as显然都可以引导时间状语从句，但用法区别非常大。 一、when可以和延续性动词连用，也可以和短暂性动词连用；而while和as 只能和延续性动词连用。 ① Why do you want a new job when you’ve got such a good one already？（get为短暂性动词）你已经找到如此好的工作，为何还想再找新的？ ②Sorry，I was out when you called me．（call为短暂性动词）对不起，你打电话时我刚好外出了。 ③Strike while the iron is hot．（is为延续性动词，表示一种持续的状态）趁热打铁。 ④ The students took notes as they listened．（listen为延续性动词）学生们边听课边做笔记。 二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生；while 和as从句的谓语动作必须是和主句谓语动作同时发生。 1．从句动作在主句动作前发生，只用 when。 ①When he had finished his homework，he took a short rest．（finished 先发生）当他完成作业后，他休息了一会儿。 ②When I got to the airport，the guests had left．（got to后发生）当我赶到飞机场时，客人们已经离开了。 2．从句动作和主句动作同时发生，且从句动作为延续性动词时，when，while，as都可使用。 ①When ／While ／As we were dancing，a stranger came in．（dance为延续性动词）当我们跳舞时，一位陌生人走了进来。 ②When ／While ／As she was making a phone call，I was writing a letter．（make为延续性动词）当她在打电话时，我正在写信。 3．当主句、从句动作同时进行，从句动作的时间概念淡化，而主要表示主句动作发生的背景或条件时，只能用 as。这时，as常表示“随着……”；“一边……，一边……”之意。 ① As the time went on，the weather got worse．（as表示“随着……”之意） ② The atmosphere gets thinner and thinner as the height increases．随着高度的增加，大气越来越稀薄。 ③As years go by，China is getting stronger and richer．随着时间一年一年过去，中国变得越来越富强了。 ④The little girls sang as they went．小姑娘们一边走，一边唱。 ⑤The sad mother sat on the roadside，shouting as she was crying．伤心的妈妈坐在路边，边哭边叫。 4．在将来时从句中，常用when，且从句须用一般时代替将来时。 ①You shall borrow the book when I have finished reading it．在我读完这本书后，你可以借阅。 ②When the manager comes here for a visit next week，Ill talk with him about this．下周，经理来这参观时，我会和他谈谈此事。 三、when用于表示“一……就……”的句型中（指过去的事情）。
1、什么是蓝牙4.0，蓝牙4.0较之前版本蓝牙的区别。 蓝牙4.0 共3种工作模式，普通蓝牙模式，高速蓝牙模式和低速蓝牙模式，而以前的版本只支持普通蓝牙模式，其他模式不和普通蓝牙模式兼容； 2、蓝牙4.0 是BLE么？ 蓝牙4.0包含BLE, BLE是蓝牙4.0中的单模模式。 3、低功耗蓝牙和普通蓝牙有什么区别？ 最主要的区别是数据包有限制，因此功耗也更低。 4、目前是否所有手机都能支持低功耗蓝牙？ 不是，需要支持蓝牙4.0技术的手机，如苹果、三星、HTC等。 5、低功耗蓝牙4.0是否能够向下兼容之前版本的蓝牙，为什么？ 低功耗蓝牙不向下兼容，低功耗由于需要降低功耗，使用的通讯机制已经和普通蓝牙不同，所以无法通讯。 6、BLE蓝牙速率多少？ 物理层速率1M，实际转发速率是每次连接事件传20字节。 7、低功耗蓝牙模块的传输距离有多远？ 在0dB的情况下，标称100英尺，约60米。 8、BLE模块的传输速率是多大？能传的数据量有多大？ 转发速率最快4K/S,可稳定工作在2.8K/S。能传的数据量有多大，取决于你传多久。 9、BLE模块的抗干扰能力怎么样？穿墙能力如何？ 使用调频通讯方式，37个通讯频点，3个广播频点。可有效避免一些频点干扰。不建议穿墙使用，如果是空心木质墙体可以试试。 10、BLE模块是否为双工模块？ 是的，全双工。 11、BLE模块默认连接间隔是多少？可以调节吗？ V1.X是100ms,V2.0是20ms,V2.0可以调。 12、BEL模块串口数据包的大小可以是多少？ 200字节以内，包含200字节。 13、BLE模块的工作电流怎么计算的？标准的纽扣电池能用多久？ 持续的工作电流对时间积分，再求平均值。一秒一次连接，不计其它功耗，一年以上。 14.产品使用通过的BQB认证模块，还需要过其他蓝牙认证吗？ 只是要过产品的其他认证，比如FCC,CE，蓝牙部分无需再过认证。
When, while, as的区别和用法 版本一 (1) 若主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用： He fell asleep when [while, as] he was reading. 他看书时睡着了。 【注】as 用于引出一个持续性动词表示“在……期间”时，其谓语通常只能是那些含有动作(action)和发展(development) 意味的动词，一般不能是那些不用于进行时态的动词(如be, seem, love, want, agree, see, know, have 等)，所以下面一句中的while 不能换为as： A：I’m going to the post office. 我要去邮局。 B：While you’re there, can you get me some stamps? 当你在邮局时，能帮我买几张邮票吗? (2) 若主、从句表示两个同时进行的持续性动作，且强调主句表示的动作延续到从句所指的整个时间，通常要用while： Don’t talk while you’re eating. 吃饭时不要说话。 I kept silent while he was writing. 在他写的时候，我默不做声。 但是，若主从句表示的两个同时进行的动作含有“一边…一边”之意思，通常用as： She sang as she went along. 她边走边唱。 (3) 若从句是一个短暂性动作，主句是一个持续性动作，可用as / when 但不用while： It was raining hard when [as] we arrived. 我们到达时正下着大雨。 (4) 若主从句表示的是两个同时(或几乎同时)发生的短暂性动作，用as / when： I thought of it just when [as] you opened your mouth. 就在你要说的时候，我也想到了。 (5) 若要表示两个正在发展变化的情况，相当于汉语的“随着”，一般用as： Things are getting better and better as time goes on. 随着时间的推移，情况越来越好。 As it grew darker, it became colder. 天色越晚，天气越冷。 (6) 表示“每当…的时候”(暗示一种规律性)，一般要用when： It’s cold when it snows. 下雪时天冷。 He smiles when you praise him. 你夸奖他时他总是笑笑。 (7) 若主从句所表示的动作不是同时发生，而是有先后顺序时，一般要用when： I will go home when he comes back. 他回来时，我就回家去。 (8) when 可用作并列连词，表示“这时(突然)”；while 也可以用作并列连词，表示“而”、“却”(表示对比)；但as 则没有类似用法： We were about to start when it began to rain. 我们正要出发，这时天开始下雨了。 He likes coffee, while she likes tea. 他喜欢咖啡，而她却喜欢茶。 (9) as 和when 后均可直接跟一个名词，构成省略句，但while 一般不这样用： As [When] a boy, he lived in Japan. 他小时候在日本。
When while as 区别 一、根据从句动作的持续性来区分 1、“主短从长”型：即主句是一个短暂性动作，而从句是一个持续性动作，此时三者都可 用。如： Jim hurt his arm while ［ when， as］ he was playing tennis. 吉姆打网球时把手臂扭伤了。 2、“主长从长”型：即主句和从句为两个同时进行的动作或存在的状态， 状态延续到从句所指的整个时间，此时通常要用while 。 且强调主句动作或 I always listen to the radio while I ’ m driving. 我总是一边开车一边听收音机。 He didn ’ t ask me in; he kept me standing at the door while he read the message. 他没有让我进去，他只顾看那张条子，让我站在门口等着。 但是，若主句和从句所表示的两个同时进行的动作含有“一边,, 一边”之意时，则习惯上 要用 as。如： He swung his arms as he walked. 他走路时摆动着手臂。 3、“主长从短”型：即主句是一个持续性动作，而从句是一个短暂性动作，此时可以用as 或when，但不能用 while 。如： It was raining hard when [as] we arrived.我们到达时正下着大雨。 二、根据主句与从句动作是否同时发生来区分 1、若主句与从句表示的是两个同时发生的短暂性动作，含有类似汉语 “一英语一般要用 as (也可用 when)。如： ,, 就的”意思，The ice cracked as [when] I stepped onto it. 我一踩冰就裂了。 2、若主句与从句表示的是两个几乎同时发生的短暂性动作，含有类似汉语“刚要“正要 ,, 却”的意思，英语一般要用 as(也可用 when)，且此时通常连用副词 ,, just。如： 就” I caught him just when [as] he was leaving the building. 他正要离开大楼的时候，我把他截住 了。 三、根据是否具有伴随变化来区分 若要表示主句动作伴随从句动作同时发展变化，有类似汉语“随着”的意思，英语习惯上要 用as，而不用 when 或 while 。如： The room grew colder as the fire burnt down.随着炉火逐渐减弱，房间越来越冷。 注：若不是引导从句，而是引出一个短语，则用with ，不用 as。如： With winter coming on, it ’ s time to buy warm clothes. 随着冬天到来，该买暖和衣裳了。 四、根据从句动作的规律性来区分 若暗示一种规律性，表示“每当,, 的时候”，英语一般要用when 。如：It ’s cold when it snows. 下雪时天冷。 五、根据主从句动作的先后顺序来区分 若主句与从句所表示的动作不是同时发生，而是有先后顺序时，一般要用when 。
when/while/as区别用法详解 when, while, as都可作"当……的时候"解，但它们之间也有差别。 若主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用。 He fell asleep when/while/as he was reading. 他看书时睡着了。 when只表示一般的时间关系，它既可指时间的一点，也可指一段时间。用when时，从句的动作可与主句的动作同时发生，也可先于主句的动作，因此when用得最多。如： He was playing basketball when I saw him. 当我看见他的时候，他正在打篮球。 Don't forget to return this book for me, when you go to the library. 你去图书馆时，不要忘记替我还这本书。 while只能指一段时间，而不能指时间的一点。用while时，从句的动作或者与主句的动作同时发生，或者主句的动作是在从句的动作的进展过程中发生的。因此，从句中的谓语必须是表示延续性动作或状态的动词。这是while与when的主要差别。如： When we arrived in Beijing, it was raining. (arrive不是延续性的动词)我们到达北京时，天正在下雨。 Please do not trouble me while I am writing my homework. 我写作业时请不要打扰我。在用when和while连接的从句中，常省略与主句相同的主语和相应的be，而在as连接的从句中一般则不省略。如： He fell asleep while(he was)studying his grammar book.他在阅读语法书的时候睡着了。While in London,he studied music.他在伦敦的时候，研究音乐。 when 可用作并列连词，表示“这时(突然)”；while 也可以用作并列连词，表示“而”、“却”(表示对比)；但as 则没有类似用法： We were about to start when it began to rain. 我们正要出发，这时天开始下雨了。 He likes coffee, while she likes tea. 他喜欢咖啡，而她却喜欢茶。
when, while 和 as 引导时间状语从句的用法 这三个词的意思很简单，都有“当……时候”的意思。但学生经常会问三个词的区别在哪儿，特别是在做选择题的时候。别说是学生，就我个人而言，做这样的选择题要保证百分之百的 正确也是不可能的。现根据大量的实例和个人的思考，做一点小结，供大家参考。 一、when 的用法 如果只从现象来看，when 从句用的最多的是一般过去时，而主句的时态没有限制，根据具 体情况而定。 When he was a child he was always trying out new ideas. 他小时候就常常试验一些新的设想。 when she came into my room I was just reading a book. 她走进我房间时，我正在看书。 Were you writing when the teacher came in? 老师进来的时候，你在写信吗？ Sorry，I was out when you called me. 对不起，你打电话来的时候我出去了。 He was on the point of leaving when someone knocked at the door. 他正要走,这时有人敲门。 I thought of it just when you opened your mouth. 就在你要说话的时候,我也想到了。 I had hardly[scarcely] closed my eyes when someone knocked at the door. 我刚一闭上眼，就有人在敲门了。 根据以上的例句，我们可以总结出一点：when 从句的A事件，相当于另一个事件B发生的时间点。也就是说，when 从句的重点不在动作本身发生的状态，而只是把它作为一个时间 点，所以when 多数情况下用的是一般过去时，则不用正在进行时。因为如果用正在进行时，它表示的就是一段时间而不是一个时间点了。根据这一点，有的文章补充说：when 从句的动词大多是瞬时动词。这种说法也可以参照。 实际上，when 从句也可以有其它的时态，但几乎也不用进行时，因为它也只是作为一个时 间参照点。例如： When I got to the airport，the guests had left. 当我赶到飞机场时，客人们已经离开了。 When he had finished his homework，he took a short rest． 当他完成作业后，他休息了一会儿。 Why do you want a new job when you have got such a good one already？ 你已经找到如此好的工作，为何还想再找新的？ You shall borrow the book when I have finished reading it.